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Review Article
Dietary fats, teas, dairy, and nuts: potential functional foods forweight control?1–3 ABSTRACT
Although it is known that dietary restriction and increased Functional foods are similar to conventional foods in appearance, physical activity can lead to weight loss, such lifestyle changes but they have benefits that extend beyond their basic nutritional may be difficult to implement and maintain—thus, the high rate properties. For example, functional foods have been studied for the of recidivism among weight losers (3). Functional foods that prevention of osteoporosis, cancer, and cardiovascular disease. They effect energy metabolism and fat partitioning may be helpful have yet to be related to the prevention of obesity, although obesity adjuncts to a dietary approach to body weight control. The cur- is one of the major health problems today. The inclusion of foods or rent review examines current literature to identify potential func- the replacement of habitual foods with others that may enhance tional foods that may be useful in the prevention of weight gain energy expenditure (EE) or improve satiety may be a practical way or as adjuncts to weight-loss efforts. It is not within the scope of to maintain a stable body weight or assist in achieving weight loss; this review to examine overall diets or individual food compo- such foods may act as functional foods in body weight control. Some nents, such as vegetarian diets and fiber or protein, so that only foods that might be classified as functional foods for weight control foods that have been studied for their effects on body weight, EE, because of their effects on EE and appetite—including medium- or satiety (or all 3) are reviewed. Such potential functional foods chain triacylglycerols, diacylglycerols, tea, milk, and nuts—are re- that may be of interest include medium-chain triacylglycerols viewed here. Only human studies reporting EE, appetite, or body (MCTs), diacylglycerols, tea, milk, and nuts.
weight are discussed. When studies of whole food items are unavail-able, studies of nutraceuticals, the capsular equivalents of functionalfoods, are reviewed. To date, dietary fats seem to be most promising DIETARY FATS
and have been the most extensively studied for their effects on body Medium-chain triacylglycerols
weight control. However, the weight loss observed is small andshould be considered mostly as a measure to prevent weight gain.
MCTs are those triacylglycerols composed of fatty acids that Carefully conducted clinical studies are needed to firmly ascertain contain 6 –12 carbon atoms. These triacylglycerols differ from the effect of tea, milk, and nuts on body weight maintenance, to long-chain triacylglycerols (LCTs) not only in their chemical assess their potential to assist in weight-loss efforts, and to ascertain composition but also in the manner in which they are absorbed dose-response relations and mechanisms of action for the 4 food and transported from the gastrointestinal tract to organs. Both Am J Clin Nutr 2005;81:7–15.
MCTs and LCTs are digested to their respective medium- andlong-chain fatty acids (MCFAs and LCFAs, respectively) in the KEY WORDS
Medium-chain triacylglycerols, diacylglycer- gastrointestinal tract. Unlike LCFAs, which are repackaged as LCTs into chylomicrons for transport through the peripheralcirculation, MCFAs, because of their shorter chain lengths, donot require chylomicron formation for their absorption and trans-port (4, 5). As a result, MCFAs travel directly to the liver via the INTRODUCTION
portal circulation; therefore, they bypass peripheral tissues such Maintenance of a constant body weight requires a balance as adipose tissue, which makes them less susceptible to the ac- between energy intake (EI) and energy expenditure (EE), and tions of hormone-sensitive lipase and to deposition into adipose even a slight imbalance in this energy equilibrium can lead to tissue stores (Figure 1). In fact, MCFAs are mostly oxidized by
significant changes in body weight over time and may eventuallyresult in obesity (1). Obesity is one of the major health problems 1 From the Institute of Human Nutrition, College of Physicians and Sur- worldwide, and it is a risk factor for several chronic disorders, but geons, Columbia University, Obesity Research Center, St. Luke’s/Roosevelt there is no functional food for obesity, such as there is for car- diovascular disease (CVD) or cancer. In the Health Professionals Supported by a Canadian Institutes of Health Research Post-Doctoral Follow-up Study, mean weight change over a 10-y period was 1.8 3 Reprints not available. Address correspondence to M-P St-Onge, Depart- kg (2). Even small changes in energy balance may lead to such a ment of Nutrition Sciences, The University of Alabama at Birmingham, 1530 weight gain, which therefore may be prevented by slight modi- Third Avenue South, Birmingham, AL 35294. E-mail: [email protected].
fications in food intake, such as the inclusion of functional foods Accepted for publication July 6, 2004.
Am J Clin Nutr 2005;81:7–15. Printed in USA. 2005 American Society for Clinical Nutrition extrapolated in the same manner, equated to 263.3 kJ (63 kcal) atbaseline and 179.7 kJ (43 kcal) at the endpoint (11). Althoughbody weights did not change significantly in women, variationsin body weight in both men and women could be explained by thedifferences observed between EE with MCT consumption andthat with LCT consumption. Moreover, total adipose tissue, sub-cutaneous adipose tissue, and upper-body adipose tissue stores inmen decreased significantly with MCT consumption but not withLCT consumption (11).
Furthermore, data suggest that MCT consumption increases satiety more than does LCT consumption (10). In a subgroup ofmen, we tested the potential effect of MCT consumption on foodintake at a subsequent meal (12). After consuming the fixed-intake breakfast containing either MCTs or LCTs, men were FIGURE 1. Long- and medium-chain triacylglycerols are digested to
instructed to eat as much as they liked of a different, ad libitum their respective fatty acids in the gastrointestinal tract. Long-chain fatty acids lunch that did not contain the experimental fats. Although the (LCFAs) are packaged into chylomicrons for their transport to peripheral tissues, whereas medium-chain fatty acids (MCFAs) travel directly to the ҃ 5), there was a trend toward lower EI at liver via the portal circulation. As a result, LCFAs are mostly deposited into the lunch after the MCT-containing breakfast than at the lunch adipose tissue, whereas MCFAs are mostly oxidized to carbon dioxide in the after the LCT-containing breakfast. The slightly lower EI [Ҁ925 liver, and small amounts are elongated to LCFAs and incorporated into kJ (221 kcal)] was due to significantly lower fat intake (Ҁ12.4 g) at the lunch after the MCT-containing breakfast than at the lunchafter the LCT-containing breakfast (12).
the liver for use as a source of energy and thus have been reported These results add to the body of literature examining the ef- to behave more like glucose than like fats (5). The metabolic fects of MCT consumption on EE and further confirm the po- differences between MCTs and LCTs prompted researchers to tential of MCTs to act as dietary adjuncts for improved body examine their effects on EE and body composition. Several re- weight maintenance or even, possibly, weight loss. However, views discussed the physiologic processing of MCTs (4 – 6).
weight-loss studies are needed to confirm this latter role of Early studies examined the effects of MCTs on EE in humans MCTs. Found in the form of liquid oil extracted from coconut oil, (7–9). Those investigators mostly reported a greater thermogenic MCTs could easily be incorporated into the North American diet effect of MCTs than of LCTs, but their studies were of a short as a replacement for other LCT-rich vegetable oils. A study duration (10). As a result, although it was suggested that the examining the acceptability (ie, appeal to the consumer) of dif- consumption MCTs could lead to an energy imbalance that may ferent food items made with an MCT oil found that the drop assist in weight loss or in the prevention of obesity (7–9), those cookies, muffins, and quick loaf breads were acceptable, but the early studies did not provide evidence of the longer-term effects rolled cookies were not (13). In clinical studies in which one-half of MCTs on thermogenesis. Furthermore, the short-term nature of the total fat intake was from an MCT oil, it was found that of the studies precluded the possibility of examining body- incorporation of an MCT-rich oil into cakes and cookies pro- composition changes that would theoretically result from the duced acceptable products. Moreover, subjects had no com- plaints about the taste of the oil or of the mashed potatoes, pasta, In the School of Dietetics and Human Nutrition at McGill or desserts in which it was incorporated (M-P St-Onge, personal University, we recently used a 4-wk crossover feeding experi- observations, 1999 –2001). One must keep in mind, however, ment to compare the effects of MCT and LCT consumption on that baked goods are typically high in energy, and these foods EE and body composition in both men (11) and women (12). In should be consumed sparingly even if the replacement of LCTs both studies, subjects were fed controlled diets that were de- by MCTs contributes to the enhancement of EE and satiety. An signed to maintain body weight and that differed only in the type oil containing only MCT could be incorporated into foods as part of added dietary fat: MCTs or LCTs. Diets were fed for 4 wk and of a salad dressing, but it may not be appropriate for frying were separated by a 4-wk washout period. EE and body compo- because of its low smoke point. One possible way to circumvent sition, measured by magnetic resonance imaging, were assessed this problem would be to combine an MCT oil with other vege- at baseline and the endpoint of each experimental phase. As a table oils having higher smoke points, such as canola oil or result, we could determine whether the greater effects of MCTs safflower oil, which would then make the MCT oil more suitable than of LCTs on thermogenesis were maintained over a 4-wk period and whether any increase in EE with MCT consumption There are, however, some concerns regarding the effects of over that seen with LCT consumption would result in significant MCT consumption on plasma lipid concentrations (14). In fact, changes in body composition, regardless of the isoenergetic con- a recent study (15) found an intake of 70 g MCT oil/d for 21 d tent of the diets. We found that EE increased with the consump- increased total cholesterol, LDL-cholesterol, triacylglycerol, tion of MCTs more than it did with that of LCTs at baseline and and glucose concentrations by 11%, 12%, 22%, and 4%, respec- at the endpoint in men and women; however, the extent to which tively, relative to an equivalent intake of high-oleic sunflower oil.
thermogenesis was increased varied slightly. In women, differ- There is thus some concern regarding the cardiovascular effects ences in daily EE, extrapolated from 6.5 h of indirect calorimetry of MCTs. One possible way to prevent adverse cardiovascular measurements, equated to 167.2 kJ (40 kcal) from measurements effects would be to combine plant sterols, which have showed taken at baseline and to 209 kJ (50 kcal) from measurements benefits for cholesterol concentrations (16), with an MCT oil.
taken at the endpoint (12). In men, differences in daily EE, When this combination is consumed, total and LDL-cholesterol concentrations are lower than those observed after LCT con- in subjects who were supplementing their diets with diacylglycerol- containing foods than in those who were supplementing their dietswith triacylglycerol-containing foods (body weight change: Ҁ3.6% Diacylglycerols
and Ҁ2.5%, respectively). The percentage change in intraabdomi- Diacylglycerols have also been reported to increase thermo- nal adipose tissue did not differ significantly between the groups.
genesis more than triacylglycerols do and to have the potential to Although these previous studies did not examine the potential assist in weight loss (19) because of a mechanism of action mechanism leading to greater effects of diacylglyerols than of similar to that of MCTs. Diacylglycerols of the 1,3 conformation triacylglycerols on loss of fat mass, it seems likely that the effects are catabolized to 2 free fatty acids and a glycerol moiety, as op- could be due to greater EE, fat oxidation, or reductions in appetite posed to 2 free fatty acids and a 2-monoacylglycerol molecule, after with diacylglycerol than with triacylglycerol consumption rather hydrolysis of triacylglycerol. In the case of triacylglycerol, the than to differences in the energy contents of diacylglycerol and 2-monoacylglycerol molecule acts as a backbone for the reforma- triacylglycerol. Diacylglycerol and triacylglycerol have been tion of a triacylglycerol molecule for packaging into chylomicrons shown to have similar energy values [37 kJ/g (9 kcal/g)] (25). In (20). Because of the absence of 2-monoacylglycerol molecules, addition, a recent study showed that, when 12% of total daily EI diacylglycerols cannot be reformed for packaging into chylomi- was provided by diacylglycerol in foods, fat oxidation was crons, and thus the free fatty acid and glycerol molecules travel greater than that when EI was provided by triacylglycerol in as such in the circulation and are diverted to the liver, where they foods (23). EE did not differ significantly between the groups, are mostly oxidized (21). In fact, several enzymes involved in fatty but subjects reported being less hungry (area under the curve acid oxidation have been found to increase with diacylglycerol score: 281 and 472 mm · h, respectively) after diacylglycerol consumption for 14 d, whereas those involved in synthesis consumption than after triacylglycerol consumption. This study provides some information on the reasons for weight loss with Few studies (19, 23, 24) have compared the effects of diacyl- diacylglycerol consumption, but much remains to be established.
glyerols and of triacylglycerols on EE and body composition in Furthermore, the previous feeding experiments (19, 24) were humans. In the study by Nagao et al (19), 38 normal-weight men parallel-arm supplementation studies, and therefore the exact supplemented their diets with 10 g/d of either diacylglycerol or food intake of subjects could not be established with certainty, triacylglycerol. The experimental fats were provided in bread, which may have worked to confound the results obtained.
mayonnaise, and shortbread, which was for consumption at Diacylglycerols occur naturally in small concentrations in breakfast only. The remainder of the diet was self-selected, and several edible oils; the 9.5% concentration in cottonseed oil is subjects were not counseled to reduce EIs to promote weight loss.
among the highest (26). A diacylglycerol-rich cooking oil has The authors measured body composition by using single-slice been produced that contains Œ80% diacylglycerols and that computed tomography scanning and air-displacement plethys- looks and tastes like a conventional oil (26). Such an oil could mography. After 16 wk of supplementation, there was a signif- therefore be incorporated into foods or consumed as a salad icant decrease in body weight (Ҁ2.6 kg) in the diacylglycerol- dressing without imparting a distinct flavor to the food.
supplemented group, whereas the weight increase in the Studies examining the effect of changes in dietary fat type (11, triacylglycerol-supplemented group was 1.1 kg. The reductions 12, 19, 24) seem to indicate that this slight dietary modification in body mass index (BMI; in kg/m2), waist circumference, and may be beneficial for body weight control and weight loss. In visceral and subcutaneous adipose tissue at the level of the um- fact, the Japanese government has approved diacylglycerol as a bilicus were significantly greater with diacylglycerol than with food for specific health use to control postmeal blood lipids and triacylglycerol supplementation. The authors concluded that di- body fat (26). However, the magnitude of this effect is small acylglycerol supplementation suppresses body weight and re- when observed in a controlled setting, and therefore dietary fats gional fat deposition. However, in both groups, total fat con- may be most helpful in the prevention of weight gain when used sumption, including the test or control fat, did not meet the 50 g/d alone or in the enhancement of weight loss when incorporated in requirement and was assessed to be 43 g/d. This lack of compli- ance with the study protocol may have been partly responsible forthe changes observed in body composition. Furthermore, energyand fat intakes for each group were not provided.
BEVERAGES
A weight-loss study including overweight and obese men and women found that body weight and fat mass decreased to a greater extent in subjects consuming diacylglycerols than in Tea is the beverage with the greatest consumption worldwide those consuming triacylglycerols (24). All men and women in- (27). There are 3 categories of tea— black, green, and oolong— cluded in this randomized, parallel-arm experiment had a waist and the consumption of black tea accounts for 80% of total tea circumference Œ 90 cm (men) or Œ 87 cm (women). Subjects intake (27). Black tea leaves are fermented and contain mostly were asked to reduce their caloric intakes by 2090 –3344 kJ/d theaflavins and thearubigins as active components (27). Green (500 – 800 kcal/d) for a period of 24 wk, during which they tea is a nonoxidized, nonfermented tea, which contains polyphe- incorporated foods containing diacylglycerols or triacylglycer- nolic compounds such as epicatechin, epicatechin gallate, epi- ols. Foods provided 16 – 45 g/d of either diacylglyerols or tria- gallocatechin, and epigallocatechin gallate (EGCG), whereas cylglycerols, or 15% of the subjects’ energy requirements. Body oolong tea is partially oxidized and contains a considerable composition was assessed by whole-body dual-energy X-ray ab- amount of polyphenols (27). Tea polyphenols have been found to sorptiometry and single-slice computed tomography scanning at be powerful antioxidants that may reduce LDL oxidation and the the level of the L4 –L5 vertebrae. Both groups lost a significant formation of oxidized DNA metabolites, thus contributing to amount of body weight and fat mass, but the changes were greater Few studies have carefully examined the effects of tea con- in capsular or nonfood format (32). Healthy young men under- sumption on body weight or EE. In fact, only 2 studies have went three 24-h testing periods in a metabolic chamber to exam- examined the effect of tea consumption, as a beverage, on EE (29, ine whether 2 capsules of a green tea extract containing 50 mg 30). Rumpler et al (29) tested whether oolong tea increased EE or caffeine and 90 mg EGCG, taken 3 times/d, stimulated thermo- modulated substrate oxidation rates more than did control bev- genesis to a greater extent than did caffeine alone or placebo.
erages. Four different beverages were consumed 5 times/d for 3 d Twenty-four-hour EE with green tea extract treatment was each: full-strength oolong tea (3 g tea leaves in 300 mL water), greater than that with caffeine and placebo—9867 kJ (2360.5 half-strength oolong tea (1.5 g tea leaves in 300 mL water), water, kcal) and 9599 (2296.4 kcal) and 9538 kJ (2281.8 kcal), respec- and water ѿ caffeine (caffeine content equivalent to that of tively—which corresponds to an increase of 2.8% and 3.5% [268 full-strength tea). Each serving of full-strength oolong tea con- kJ (64.1 kcal) and 329 kJ (78.7 kcal), respectively] over the EE tained 48.7 mg EGCG and 53.7 mg caffeine, for a total intake of with caffeine and placebo, respectively. The 24-h respiratory 244 mg EGCG and 270 mg caffeine. Servings were consumed quotient with green tea extract treatment was lower than that with every 1.5 h from 0830 to 1430 as part of a controlled diet pro- caffeine and placebo— 0.852 compared with 0.873 and 0.881, viding 115% of energy requirements during the initial 2 d and respectively—which is indicative of greater fat oxidation with 100% of energy requirements on the 3rd day. Twenty-four-hour green tea extract treatment. It was concluded that oral adminis- EE with full-strength tea and water ѿ caffeine consumption was tration of a green tea extract stimulated thermogenesis and fat significantly greater than that with water alone. The increase in oxidation and, therefore, that green tea extract has the potential to EE with consumption of full-strength tea and for water ѿ caf- influence body weight and body composition. However, the feine was, respectively, 2.9% [281 kJ (67 kcal)] and 3.4% [331 kJ short-term nature of the study prevented the direct observation of (79 kcal)] greater than that for water. Fat oxidation increased by the effect of green tea extract intake on body composition.
12% relative to baseline for full-strength tea and by 8% for Dulloo et al (33) also confirmed the mechanism of action of the water ѿ caffeine. However, only the consumption of full- green tea extract in an in vitro experiment. This experiment strength tea resulted in significantly greater fat oxidation showed that the green tea extract significantly increased the rate (13.1%) than did the consumption of water. The authors con- of intrascapular brown adipose tissue oxygen uptake, but caf- cluded that oolong tea stimulated EE and fat oxidation in normal- feine alone did not. The authors concluded that the green tea weight males and could have some beneficial effects on a per- extract was a more effective potentiator of sympathetically me- son’s ability to maintain lower body fat. However, they also diated thermogenesis than was caffeine alone. In humans, this cautioned that weight maintenance would be facilitated only if green tea extract was also found to reduce body weight by 4.6% the effects of tea consumption on EE and fat oxidation were and waist circumference by 4.5% when 2 capsules were taken sustainable and if no dietary compensation occurred to offset the twice daily for 12 wk as part of a regular, self-selected diet (34).
Each capsule contained 375 mg catechins, including 270 mg Another recent study examined the effects of oolong tea and EGCG. However, this study did not include a control group or a green tea consumption on fasting EE (30). Eleven healthy report of the statistical procedures, and therefore clear conclu- normal-weight women were tested after drinking water and again sions cannot be drawn from these results.
after drinking oolong and green tea in random order. Oolong tea To date, no study has established the potential of tea as a was prepared by brewing 15 g tea leaves in 300 mL water, and functional food for weight maintenance. The only studies that each serving contained 77 mg caffeine and 81 mg EGCG. Green examined tea as a functional food found modest effects on EE and tea was prepared by dissolving 5 g powdered green tea in 300 mL were of very short duration (29, 30). Whether these slight in- water. Each serving of green tea contained 161 mg caffeine and creases in EE and fat oxidation persist over a long period remains 156 mg EGCG. EE was measured by using the Douglas bag to be established. Therefore, more research is necessary to as- method both at baseline and for 2 h after beverage consumption.
certain whether tea can be of assistance in better weight mainte- Resting EE was similar in the 2 groups before consumption of the nance or in weight-loss programs and whether its effects are more different beverages and remained low after water and green tea than those exerted by its caffeine content. Moreover, differences consumption but increased significantly after oolong tea con- between types of tea with respect to their effect on EE should be sumption. The cumulative increase in EE over resting EE after explored further. As yet, the quantity of tea that must be con- the consumption of oolong tea, green tea, and water was 110.7 sumed to obtain an effect on body weight has not been estab- (26.5 kcal), 49.5 (11.8 kcal), and 11.2 kJ (2.7 kcal), respectively, lished. A study in rats in which intraperitoneal injections of 100 over the 2-h measuring period. Respiratory quotients did not mg EGCG/kg body weight for 7 d resulted in losses in body differ between the 3 treatments. The authors concluded that, weight and fat mass found that plasma concentrations of EGCG because oolong tea had less caffeine and EGCG than did green after injection were 24, 2, 4, 1, and 1 ␮mol/L at 0.5, 1, 2, 5, and tea, the rise in EE must be due to the presence in oolong tea of 24 h, respectively (35). A concentration of 1 ␮mol/L would be more polymerized polyphenols than are found in green tea. How- similar to that in a 70-kg person 1 h after drinking 6 –12 200-mL ever, the measurement period in this study was very short, and it is not known whether the increased EE would extend over the fullpostprandial period—typically 6 –7 h— or whether increases would be observed on subsequent tea-drinking occasions.
Although a meta-analysis of calcium consumption and weight Another study that examined the effects of tea on thermogen- loss has not shown that calcium consumption is linked to greater esis (31) used tea as a nutraceutical rather than a functional food.
loss of body weight (36), there is increasing evidence that dairy Nutraceuticals are components that are isolated or purified from calcium may play a role in body weight regulation (37, 38).
a food or beverage, that have been shown to have health benefits Recently, Heaney (39) reported the effects of calcium consump- or reduce the risk of chronic disease, and that are usually found tion on body weight and the rate of body weight change in a longitudinal cohort of women. This study showed that predictedBMI decreased with an increased ratio of calcium to protein, sothat a ratio of 10 predicted a BMI of 22.5, whereas a ratio of 20predicted a BMI of 19.3. Calcium:protein of 9, corresponding toapproximately the 25th percentile of the currently recommendedintakes, predicted weight gain at midlife is 0.425 kg/y. The ob-served rate of weight gain was, however, 1 kg/y. If calcium:protein was 20, representative of the current recommendations,the predicted weight change would be Ҁ0.011 kg/y, and only3.7% of women would be predicted to gain 1 kg/y. The authorsuggested that the prevalence of obesity could be decreased by60 – 80% in women if their calcium intakes were at recom-mended amounts (39). These observations corroborate those ofothers (40, 41), who reported associations between calcium in-takes and body weight. From the third National Health and Nu-trition Examination Survey, it was found that the risk of obesitywas 85% lower in those in the highest quartile of calcium intakes,after adjustment for age, sex, race, and EIs, than in those in thelowest quartile (41). Similarly, in the Coronary Artery Risk De-velopment in Young Adults Study, dairy consumption was in- FIGURE 2. An increase in dietary calcium reduces 1,25-dihydroxyvitamin
D [1,25(OH )D] concentrations, resulting in down-regulation of calcium trans- versely associated with the prevalence of obesity (40), and Da- fer into adipose and pancreatic cells. Inside adipocytes, a reduction in intra- vies et al (42) reported that the odds ratio for overweight with cellular calcium leads to decreased fatty acid synthase (FAS) transcription calcium:protein below the median (Ȃ12 mg/g) was 2.25.
that results in a lowering of lipogenesis and increased lipolysis. In pancreatic Moreover, calcium intakes recently were reported to be neg- cells, reduced intracellular calcium concentrations decrease insulin output,which results in reduced lipogenesis and enhanced lipolysis in adipocytes. In atively associated with fat mass in the Quebec Family Study (43).
combination, these processes would help reduce fat deposition into and The authors of this study found that women who consumed 600 storage in adipose tissue. Adapted with permission from J Nutr 2003;133: mg calcium/d had greater body weight (82.3 kg compared with 69.8 and 65.0 kg for those consuming 600 –1000 mg and Œ1000 mg calcium/d, respectively), BMI (31.8 compared with 27.0 and25.0, respectively), percentage fat mass (37.3% compared with31.3% and 28.9%, respectively), absolute fat mass, waist cir- Cross-sectional studies (40, 41, 43) have thus found a relation cumference, and abdominal adipose tissue than did women who between milk or calcium consumption and body weight. Such consumed greater amounts of calcium, even after adjustments for cross-sectional studies, however, do not establish causal rela- EI, percentage of energy consumed as fat, dietary protein intake, tions, and, therefore, whether the relation between milk con- sumption and body weight is due to other characteristics of milk A potential mechanism of action of milk in the promotion of consumers is not known. For example, adults who do not eat fast weight loss has already been put forth (44). It is proposed that food drink more milk than do those who do eat fast food (50). In intracellular calcium plays a role in adipocyte metabolism and addition, milk may be replacing other, more energy-dense bev- that its concentrations are modulated by calcitrophic hormones.
erages in the diet. This, however, is debatable, because some find An increase in calcium intake in foods would down-regulate 1, lower milk intakes in those who consume more soft drinks (51) 25-dihydroxyvitamin D, which would result in a decrease in the and others find that soft drink intake is not associated with lower absorption of calcium into adipocytes and pancreatic islet cells calcium intakes in children and adolescents (52). Furthermore, (Figure 2). Within the adipocyte, intracellular calcium increases
results have been ambiguous in clinical studies: some showed no fatty acid synthase transcription and inhibits lipolysis. Within the effect of calcium (53, 54), and another showed a beneficial effect pancreas, intracellular calcium stimulates insulin release, which (55) on weight loss. One randomized clinical study recently further acts to inhibit lipolysis and stimulate fatty acid synthase examined the effects on bone turnover of protein-rich weight- transcription. Therefore, any reduction in intracellular calcium loss diets that are high in dairy protein and calcium and in mixed would lead to a reduction in lipogenesis and the stimulation of protein sources (53). Diets were not strictly controlled, but each lipolysis (44). This is supported by recent data showing that acute subject was given instructions on dietary requirements and was dietary calcium intake was correlated positively with 24-h fat provided with a digital kitchen scale and foods to cover 60% of oxidation and negatively with the 24-h respiratory quotient (45).
their total energy prescription. The entire study consisted of 2 However, in a controlled feeding experiment in which subjects phases, an energy-restriction phase of 12 wk and a subsequent were given diets containing 500 or 1400 mg dairy calcium/d in a energy-balance phase of 4 wk. The dairy protein diet contained crossover design for 7 d each, EE and substrate oxidation did not 2371 mg calcium, compared with 509 mg calcium for the mixed differ significantly between diets (46). However, other com- protein diet, and 62% of its total protein content was from dairy pounds within dairy products may act in concert with dietary products. Overall body weight loss was 10% during the energy- calcium to produce antiobesity effects. Such compounds that restriction phase, irrespective of dietary treatment. As planned, have been proposed are whey proteins (44), conjugated linoleic there was no weight loss during the energy-balance phase. Al- acid (47), and branched-chain amino acids (48). However, a though the primary endpoint of interest in this study was not recent study showed no effect of various conjugated linoleic acid weight loss per se, these results show that, as part of a weight-loss isomers on body weight loss over a period of 18 wk (49).
diet, high dairy protein and calcium consumption does not lead to greater weight loss than does a diet consisting of mixed protein calcium as part of a weight-loss program, but data for all of the subjects initially enrolled in the study were not reported (55).
Similarly, in a study examining the effects of calcium supple- Other clinical studies were post hoc analyses and were not spe- mentation in limiting bone loss during weight loss (54), there was cifically designed to test the hypothesis that calcium may play a no effect of calcium on body weight and fat mass loss. Obese role in body weight regulation (53, 54). More studies are there- postmenopausal and premenopausal women were randomly al- fore needed to draw definitive conclusions about the effects of located to a weight-loss diet with a 2100 kJ/d (500 kcal/d) energy calcium and dairy products on weight management. There is also deficit with or without 1000 mg elemental calcium/d for 25 wk.
some concern regarding a possible link between milk consump- Calcium supplements were provided as 2 pills to be taken at tion and prostate cancer. A recent meta-analysis found an odds breakfast and dinner. The control group received placebo pills.
ratio of 1.68 for prostate cancer in subjects with high milk con- Weight loss did not differ significantly between groups— 6.2 and sumption when examining 11 case-control studies (56). How- 7.0 kg for the placebo and the calcium supplement group, re- ever, other longitudinal studies have found either no association spectively. Accordingly, fat-mass loss also did not differ signif- (57) or a weak positive association (58) between higher milk icantly between placebo and calcium groups— 4.5 and 5.5 kg, consumption and prostate cancer (odds ratio: 1.34).
respectively. However, this study was not powered to detectchanges in body weight and fat mass between groups, and a posthoc power analysis showed that 500 subjects/group would have been necessary to detect a 0.8-kg difference in body weight, and Nuts vary widely in caloric content and fat composition and 265 subjects/group would have been required to detect a 1.0-kg have often been excluded from diets because of their high fat difference in fat mass between groups, with 80% power and 95% content (59). As a result, some concern existed with respect to the CIs. The authors thus proposed that the direction of change ob- potential effects on body weight of incorporating nuts in the diet.
served in this study suggests that, over longer periods and with an However, many of the supplementation studies that have exam- adequate number of subjects, calcium may have an effect on body ined the effects of nuts on lipid profiles have not found negative weight loss. Moreover, this study provided calcium in its ele- effects on body weight (60 – 68), but they did show that nuts— mental form, and it may be that calcium from dairy products has whether almonds (61, 65, 68, 69), walnuts (60, 67, 68), pecans a greater effect than does elemental calcium because of other (63), pistachios (66), or peanuts (62, 64)—improve plasma lipid components present in dairy foods. However, the results ob- profiles and can have a beneficial effect on CVD risk. Because tained by Bowen et al (53) suggest that this may not be the case.
very few studies have specifically examined the effects of nuts on A recent clinical trial aimed to ascertain whether dairy or body weight (70, 71), those studies that examined the effects of elemental calcium supplementation enhanced weight loss in nut consumption on plasma lipids and also reported body weight obese men and women (55). Subjects were examined after a 2-wk at baseline and endpoint (60 – 69) will be reviewed here. These lead-in period and were then randomly assigned to 1 of 3 groups: studies were not designed to produce weight loss.
group 1 consisted of control subjects who were restricting their Studies examining the effect of almonds on plasma cholesterol caloric intake by 2100 kJ/d (500 kcal/d) and consuming 0 –1 concentrations have also reported body weight changes during serving dairy products/d while taking a 400 –500 mg calcium the experimental and control feeding periods (61, 65, 69). In the supplement and a placebo pill (low-dairy group); group 2 re- study of Spiller et al (61), male and female subjects were exam- ceived the same dietary prescription as group 1, but the placebo ined after a 2-wk baseline period of no intervention and again pill was replaced by 800 mg calcium carbonate (high-calcium after 9 wk of supplementation with 100 g almonds/d [2424.4 kJ/d group); and group 3 had the same dietary prescription as group 1 (580 kcal/d)]; half of the almonds were whole blanched almonds, but consumed 3 servings dairy products/d (high-dairy group).
and the other half were ground almonds. Subjects were also Diets were followed for 24 wk. All subjects initially consumed provided with almond oil to replace other, normally used cooking 1 serving dairy products/d. Of the 41 subjects enrolled, 32 fats, and they were asked to eliminate margarine, butter, vege- completed the study; the data reported include completers only.
table oils, mayonnaise, most meats, shellfish, whole-fat dairy, At the end of the weight-loss period, subjects in the low-dairy, high-fat bakery products, potato chips, ice cream, avocado, and high-calcium, and high-dairy groups lost 6.4%, 8.6%, and 10.9% all other nuts from their diet. Total fat intake increased from 67 of body weight, respectively. Fat-mass loss followed the same to 90 g/d, and protein intake increased from 88 to 103 g/d, trend: the low-dairy, high-calcium, and high-dairy groups lost whereas carbohydrate intake decreased by 33 g/d. Although total 8.1%, 11.6%, and 14.1%, respectively, of total fat mass. Fat loss EI, assessed from 3-d food records at baseline and at weeks 4 and from the abdominal region represented 19% of the total fat loss 8 of the intervention period, increased by 338.6 kJ/d (81 kcal/d) in subjects in the low-dairy group and 50.1% and 66.2% for those over the study period, body weights did not change (74.9 kg at in the high-calcium and high-dairy groups, respectively. These baseline and 74.3 kg at week 9). On the basis of the difference in data show that calcium, particularly that from dairy products, can daily EIs, a theoretical weight gain of 0.66 kg would have been enhance weight loss in obese persons. However, only data from expected over the 9-wk period. Moreover, if the subjects had not those who completed the study were analyzed, and thus results partially compensated for the added calories provided by the may not represent all subjects. Furthermore, it is not known almonds, a weight gain of 10 kg would have been expected.
whether similar results would be obtained in persons who regu- More recently, Jenkins et al (65) studied 3 supplements in a larly consume larger amounts of dairy products.
randomized crossover design: control muffin, full-dose almond, A potential mechanism has been postulated to explain a pos- and half-dose muffin ѿ half-dose almond. The subjects, who sible role of calcium in body weight control, and yet it remains were hyperlipidemic men and women, consumed self-selected unclear whether there is a weight-loss effect of calcium. Only one National Cholesterol Education Program Step 2 diets and were clinical study was specifically conducted to examine the role of counseled to maintain a stable body weight. Depending on each subject’s energy requirements, full supplement doses pro- weights nor BMI changed during the supplementation period, vided 1200 (287 kcal/d), 1797.4 (430 kcal/d), and 2399.3 kJ/d despite an increase in EIs and fat intakes.
(574 kcal/d) for total energy requirements of 6688 (1600 kcal/d), In a study of pistachio nuts, men and women maintained their 6688 –10 032 (1600 –2400 kcal/d), and Œ10 032 kJ/d (Œ2400 regular diets for 3 wk and replaced 20% of their energy intakes kcal/d), respectively. Authors found a dose effect of almonds on with pistachio nuts for the subsequent 3 wk (66). As assessed by CVD risk factors but no change in body weights over the 1-mo food records, subjects consumed the same number of calories and supplementation periods. In this study, the lack of body weight macronutrients during the 2 phases. As expected, there was no change with all supplements may have been due to good com- significant change in body weight during the study, which pliance with counseled weight-management strategies and not showed good compliance with the dietary replacement protocol.
necessarily to a satiating effect of the almonds. Nevertheless, Although of short duration, this study shows that subjects can food records during the supplementation periods indicated an successfully substitute pistachio nuts for other foods in a regular, energy intake during the full-dose almond phase that was 560.1 free-living diet without increasing their body weights.
kJ/d (134 kcal/d) more than that during the full-dose muffin All of the above-mentioned studies except that of Lovejoy et phase. This greater caloric intake should theoretically have led to al (69) found no weight gain with nut consumption, despite a weight gain during the full-dose almond phase that was 0.5 kg increases in EIs. If we assume adequate reporting of EIs, this more than the gain during the full-dose muffin phase. Therefore, absence of body weight gain may have been due to some degree assuming consistent reporting of dietary intakes during all phases of malabsorption of energy in nuts or to an increase in EE with nut of this study, there may be some unabsorbable energy in almonds consumption. The absence of body weight gain with nut supple- that negated the energy imbalance caused by the greater intakes.
mentation led to studies that examined the effects of nut con- Another supplementation study, however, found slight but sumption on body weight and energy balance (70, 71).
significant body weight gains when men and premenopausal The study by Fraser et al (71) tested the effect of consuming women supplemented their diets with 100 g almonds/d for 4 wk 1338 kJ almonds/d (320 kcal/d) for 6 mo on body weight in men (69). This slight weight gain of 0.9 kg for men and 0.3 kg for and women ranging in age from 25 to 70 y and with a BMI 95thpercentile. The almond supplement provided 15% of daily en- women occurred despite recommendations to reduce EIs by an ergy requirements for each person, and no dietary advice or amount equivalent to that provided by the almonds: Ȃ2424.4 recipes were provided. Subjects could incorporate the nuts as they wished. There was a nonsignificant weight gain of 0.4 kg for One study examined the effect of walnut consumption on the group overall, but, when subjects were separated by sex, the plasma lipid concentrations in hypercholesterolemic men and men gained 0.65 kg (P  0.01), and the women gained only 0.11 women (60). Two different diets were tested in a randomized kg (P ҃ 0.79). When the sexes were studied together, only crossover design for 6 mo each. During both phases, subjects persons in the lowest and middle tertiles of BMI gained weight.
were instructed to consume a Mediterranean diet of prescribed The estimated compensation for total EI was 78.2%. This study energy content, which emphasized vegetable products and fish showed that incorporating nuts in a regular, free-living diet does and limited red meat and eggs. For the control phase, olive oil was not lead to weight gain; however, no concurrent group without advised for cooking, and nuts were not allowed. During the the almond supplement was studied during that same period. It is walnut phase, subjects consumed 41–56 g walnuts/d in partial therefore not known whether study participation had an influence replacement of the olive oil and other fatty foods in the control on compliance or whether it helped improve dietary compensa- diet. Despite a trend toward greater EIs during the walnut phase than during the control phase [x៮ Ȁ SD: 7624.3 Ȁ 744 kJ/d Another study examined the effects of peanut consumption on (1824 Ȁ 178 kcal/d) and 7402.8 Ȁ 635.4 kJ/d (1771 Ȁ 152 energy balance and the hedonic ratings for peanuts and other kcal/d), respectively; P ҃ 0.11], body weights remained the same snack foods (70). Normal-weight men and women were given during both phases (69.9 and 70.1 kg for walnut and control Ȃ89 g peanuts/d, which is equivalent to 2113 kJ/d (505 kcal/d), phases, respectively). The difference in EIs between diets theo- to consume as they wished for 8 wk (free-feeding phase); this retically should have led to a weight gain of 1.2 kg over the 6-mo phase was followed by a 3-wk phase during which the peanuts were added to the baseline diet (addition phase) and an 8-wk Another study examined the effect of walnut consumption on phase during which peanuts replaced fat in the diet (substitution plasma lipid concentrations by feeding a habitual diet and a phase). The phases of the study were separated by 4-wk washout low-fat, free-living diet (67). Men and postmenopausal women periods. During the free-feeding phase, mean energy compensa- consumed their habitual diets for 4 wk and then supplemented tion was 66%, and the observed weight gain was 1.0 kg, which is those diets with 48 g walnuts/d for 6 wk; they then followed a significantly lower than the theoretical, expected weight gain of low-fat (20% of energy) diet for 6 wk and, finally, a low-fat ѿ 3.6 kg. Weight gain (0.6 kg) was also significantly lower during walnut diet for 6 wk. The walnut dose provided 1570 kJ/d (375.6 the addition phase than predicted (1.4 kg), and there was no kcal/d). EIs during the walnut phases exceeded those during the change in body weight during the substitution phase. Resting EE walnut-free phases by 1651 kJ/d (395 kcal/d) for the habitual diet increased by 11% after 19 wk of regular peanut consumption, and 1514 kJ/d (362.2 kcal/d) for the low-fat diet. Regardless of even after adjustment for changes in body weight. These results the additional EIs during the walnut supplementation phases, show that nut consumption may have a small effect on EE, which body weights did not increase during the walnut phases.
may partly explain the lower-than-expected weight gain ob- Similar observations were made when subjects consumed served in the free-feeding and addition phases.
self-selected 8-wk diets with 68 g pecans/d or no nuts (63). Pecan Finally, results from nut supplementation studies do not imply supplementation provided an extra 1918.6 kJ/d (459 kcal/d) and that nut consumption can assist in weight loss, and there are no 44 g fat/d. As was observed with walnuts (67), neither body definitive data on their ability to assist in the maintenance of stable weight. Nevertheless, their satiating power may play a role 8. Scalfi L, Coltorti A, Contaldo F. Postprandial thermogenesis in lean and in weight maintenance. In addition, the Nurses’ Health Study obese subjects after meals supplemented with medium-chain and long-chain triglycerides. Am J Clin Nutr 1991;53:1130 –3.
(72) and the Seventh Day Adventist Study (73) found lower body 9. Seaton TB, Welle SL, Warenko MK, Campbell RG. Thermic effect of weights with increased nut consumption. However, these cross- medium-chain and long-chain triglycerides in man. Am J Clin Nutr sectional studies may also reflect a healthier lifestyle pattern associated with nut consumption. Weight-loss studies incorpo- 10. St-Onge M-P, Jones PJ. Physiological effects of medium-chain triglyc- rating nuts should be conducted to ascertain whether nuts may erides: potential agents in the prevention of obesity. J Nutr 2002;132:329 –32.
assist in weight loss. At present, available research allows us only 11. St-Onge M-P, Ross R, Parsons WD, Jones PJ. Medium-chain triglycer- to speculate that nuts may assist in controlling body weight, ides increase energy expenditure and decrease adiposity in overweight perhaps via increased satiety levels, increased resting EE, or 12. St-Onge M-P, Bourque C, Jones PJ, Ross R, Parsons WE. Medium- versus long-chain triglycerides for 27 days increases fat oxidation andenergy expenditure without resulting in changes in body composition inoverweight women. Int J Obes Relat Metab Disord 2003;27:95–102.
CONCLUSION
13. Bowman F. MCT cookies, cakes, and quick breads: quality and accept- The studies reviewed here show that some foods have the ability. J Am Dietet Assoc 1973;62:180 –5.
potential to enhance weight loss or prevent weight gain. The body 14. Hill JO, Peters JC, Swift LL, et al. Changes in blood lipids during six days of overfeeding with medium or long chain triglycerides. J Lipid Res of literature seems to provide more support for the replacement of dietary LCTs with dietary MCTs or diacylglycerols than for 15. Tholstrup T, Ehnholm C, Jauhiainen M, et al. Effects of medium-chain the inclusion of other potential functional foods as part of the diet.
fatty acids and oleic acid on blood lipids, lipoproteins, glucose, insulin, However, available data suggest that beverages such as tea and and lipid transfer protein activities. Am J Clin Nutr 2004;79:564 –9.
16. St-Onge M-P, Jones PJ. Phytosterols and human lipid metabolism: ef- milk may also be of value. Additional clinical studies are needed ficacy, safety, and novel foods. Lipids 2003;38:367–75.
to ascertain whether tea and milk consumption can help improve 17. St-Onge M-P, Lamarche B, Mauger JF, Jones PJ. Consumption of a body weight maintenance and perhaps also assist in weight loss.
functional oil rich in phytosterols and medium-chain triglyceride oil More research is also necessary to reach conclusions about the improves plasma lipid profiles in men. J Nutr 2003;133:1815–20.
effects of nut consumption on body weight, and weight-loss 18. Bourque C, St-Onge MP, Papamandjaris AA, Cohn JS, Jones PJ. Con- sumption of an oil composed of medium chain triacyglycerols, phyto- studies with a control group are necessary to determine with sterols, and N-3 fatty acids improves cardiovascular risk profile in over- greater accuracy the possible effects of all of the potential func- weight women. Metabolism 2003;52:771–7.
tional foods reviewed here. Such studies would, however, re- 19. Nagao T, Watanabe H, Goto N, et al. Dietary diacylglycerol suppresses quire a very large sample size because the effect size is expected accumulation of body fat compared to triacylglycerol in men in a double-blind controlled trial. J Nutr 2000;130:792–7.
20. Breckenridge WC, Kuksis A. Diaglycerol biosynthesis in everted sacs of As yet, no weight-loss claim can be made for any of the foods rat intestinal mucosa. Can J Biochem 1975;53:1170 – 83.
examined here. Nevertheless, the data do suggest that incorpo- 21. Murata M, Hara K, Ide T. Alteration by diacylglycerols of the transport rating some of these foods in a healthy and balanced diet could be and fatty acid composition of lymph chylomicrons in rats. Biosci Biotech beneficial for weight maintenance. Perhaps the individual effect 22. Murata M, Ide T, Hara K. Reciprocal responses to dietary diacylglycerol of each dietary component on weight control might be too small of hepatic enzymes of fatty acid synthesis and oxidation in the rat. Br J to result in meaningful body-composition changes, but, if the dietary components were combined, their effects could be sig- 23. Kamphuis MM, Mela DJ, Westerterp-Plantenga MS. Diacylglycerols nificant. It is nonetheless important that these measures be com- affect substrate oxidation and appetite in humans. Am J Clin Nutr 2003; bined with energy restriction and increased physical activity to 24. Maki KC, Davidson MH, Tsushima R, et al. Consumption of diacyl- glycerol oil as part of a reduced-energy diet enhances loss of body weightand fat in comparison with consumption of a triacylglycerol control oil.
The author has no personal or financial conflicts of interest with respect to 25. Taguchi H, Nagao T, Watanabe H, et al. Energy value and digestibility of dietary oil containing mainly 1,3-diacylglycerol are similar to those oftriacylglycerol. Lipids 2001;36:379 – 82.
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