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Dairy Council Digest Archives
Weight Control: An Emerging Beneficial Role for Dairy
Dairy's Role in Weight Management: An Unfolding Story
In Vitro and Experimental Animal Studies.
In vitro and experimental animal studies demonstrate an anti-obesity effect of dairy foods. Moreover, these studies are beginning to provide a plausible mechanism, explained by dietary calcium, of how dairy product consumption may help regulate body fat (19).
Adipocyte (fat cell) intracellular calcium, which is influenced in part by calcitrophic (calcium regulatory) hormones, plays a key role in regulating fat metabolism and storage in adipocytes (19,22-25). Researchers have hypothesized that 1,25-dihydroxyvitamin D, induced by low dietary calcium, stimulates the influx of calcium in adipocytes. This increase in intracellular calcium in turn stimulates lipogenesis (fat formation) and inhibits lipolysis (fat breakdown), resulting in expansion of adipocyte fat stores (19,22). On the other hand, suppression of 1,25-dihydroxyvitamin D with high calcium diets is thought to reduce intracellular calcium in fat cells, thereby decreasing lipogenesis and increasing lipolysis, resulting in an anti- obesity effect (19,22). In vitro studies using cultures of human adipocytes have shown that 1,25-dihydroxyvitamin D increases intracellular calcium and inhibits lipolysis, resulting in increased adipocyte fat stores (24).
Several studies using transgenic mice as a model for human obesity support a beneficial effect of dairy foods, partly explained by calcium, on body weight (19,23). When these mice were fed a low calcium, high fat, high sucrose diet for six weeks, adipocyte lipogenesis increased, lipolysis decreased, and gain in body weight and adipose tissue accelerated (19). In contrast, the high calcium diet markedly inhibited lipogenesis, increased lipolysis, and suppressed fat accretion and weight gain (19). The source of dietary calcium influenced adiposity, with dairy exerting a significantly greater anti-obesity effect than calcium supplements (19).
An anti-obesity effect of dairy foods, partly explained by calcium, is demonstrated in laboratory animal studies.
Additional studies in mice indicate that dairy foods accelerate weight and fat loss during energy restriction – an effect partly explained by calcium (23,25). When mice were fed an energy restricted, low calcium diet for six weeks, body weight and fat pad mass were reduced with no change in intracellular calcium (23). In contrast, when a high calcium, energy restricted diet was fed, not only did intracellular calcium decrease, but reductions in body weight and fat pad mass were greater than in mice fed the energy restricted, low calcium regimen (23). High calcium diets therefore suppress adipocyte intracellular calcium and shift the partitioning of dietary energy from storage to expenditure (22). Importantly, nonfat dry milk in the diet was even more effective than a calcium supplement alone in inducing this shift (i.e., reducing body weight/adipose tissue mass) (23).
Another study in mice found that when yogurt was used to increase dietary calcium in an energy-restricted diet, weight and fat loss were greater than in mice fed supplemental calcium (25). These studies demonstrate that dairy foods maximize the anti-obesity effects (19,22-25). In addition to dietary calciums inhibition of 1,25-dihydroxyvitamin D, calcium may augment weight loss by decreasing metabolic efficiency. In mice fed high calcium diets, the efficiency of energy utilization was reduced (19,23).
Human Studies. Although not yet confirmed by human clinical trials, accumulating evidence from epidemiological studies supports a beneficial effect of calcium and dairy foods on body weight in various populations. When food consumption was assessed in preschool children between 24 and 60 months of age and related to their body composition at 70 months of age, higher calcium intakes and more servings/day of dairy products were associated with lower body fat (26). The findings led the researchers to recommend further study of the adverse effects of chronically low calcium intakes on preschoolers’ body composition (26). In a case-control study to identify predictors of obesity among prepubertal Puerto Rican children, low intake of dairy foods was one of several factors associated with obesity (27).
Findings in adults also suggest a beneficial association between dairy foods and body weight. In an analysis of data from NHANES III, dietary calcium intake was inversely associated with body fat in both women and men after controlling for energy intake (19). Risk of obesity was 84% lower in women who consumed the highest amount of dairy foods (3 1/2 servings/day) compared to those who consumed the lowest amount of dairy foods (1 serving/day) (19).
In a secondary analysis of a two-year prospective study of 54 normal weight women 18 to 31 years participating in an exercise intervention, dietary calcium, adjusted for energy, was a significant negative predictor of changes in body weight and body fat (28). Total calcium and dairy calcium were inversely associated with changes in body weight and body fat when women consumed lower energy intakes (less than 1876kcal/day), but not when higher energy intakes (>1876kcal/day) were consumed (28). This finding led the researchers to suggest that high calcium/dairy intakes may improve the effectiveness of energy restricted diets (28).
In a recent study of lactose maldigestion and calcium intake in premenopausal African American women, a low calcium intake was associated with higher body mass index (29). Lactose maldigestion, which is relatively common in African Americans, is low levels of the enzyme, lactase, needed to digest lactose or milk’s sugar. By following a few simple dietary strategies (e.g., consuming milk with a meal), lactose maldigesters can comfortably consume recommended intakes of milk and other dairy foods without developing symptoms (lactose intolerance). Unfortunately, many lactose maldigesters avoid or limit intake of dairy foods, thereby reducing their calcium intake and missing the health benefits provided by dairy foods.
Evidence that calcium is partly responsible for dairy’s beneficial effect on body weight is supported by recent analyses of data from calcium intervention studies designed with primary skeletal endpoints (30,31). Based on a preliminary analysis of data from 780 women involved in five clinical studies (i.e., four observational and one double-blind, placebo-controlled, randomized trial of calcium intake), researchers estimated that about 3% of the variability in body weight could be explained by differences in calcium intake (30).
Research in both children and adults links higher intakes of calcium and dairy foods with lower risk for overweight and obesity. Moreover, dairy rather than calcium alone is associated with the greatest effect.
In an extension to this analysis, data from six observational studies and three controlled trials, none of which were designed with weight as an outcome variable, were re-analyzed to evaluate the effect of dietary calcium on body weight and body fat (31). Higher calcium intakes, expressed as lower body fat and/or body weight, were consistently associated with reduced weight gain at midlife. In this re-analysis, differences in calcium intake were estimated to explain less than 10% of differences in body weight among individuals (31).
Dairy foods may improve the effectiveness of weight reduction diets (32,33). In a study of 17 obese women consuming either a severely energy-restricted, mixed food diet (330kcal/day) containing 33g protein or a diet consisting solely of milk (780kcal/day, 46g protein), there was no significant difference in weight loss for the two regimens (32). However, greater fat loss occurred on the milk diet (32). Findings of a randomized clinical trial indicate markedly greater weight loss in patients consuming a milk-based energy-reduced diet (800kcal/day) for 16 weeks than in those on a standard 800 kcal diet (33).
The above findings supporting a beneficial effect of dairy foods in weight management have stimulated interest in the scientific community, evidenced by the following research presented at scientific meetings (34,35). According to preliminary findings from a Canadian study, low dietary calcium intake (less than 600mg/day) was linked to increased body fat, particularly in women (34). In a 3-year, double-blind placebo controlled trial of calcium supplementation (1,500mg/day) in women aged 19 to 26 years, the calcium supplemented women accumulated body fat at one-half the rate of the placebo-treated control, although the group as a whole gained body weight (35).
A recent multi-center population-based prospective study found that overweight young adults aged 18 to 30 who consumed the most dairy foods such as milk, cheese, and yogurt had a lower risk of becoming obese and developing insulin resistance syndrome (IRS) over 10 years (36). IRS, also known as Syndrome X, describes a group of risk factors — obesity, abnormal blood glucose control, high blood pressure, and lipid abnormalities (i.e., low HDL cholesterol, high triglycerides) — all of which increase the risk of diabetes and heart disease. Overweight individuals typically consumed fewer dairy foods than their normal weight counterparts (36). However, the risk of developing IRS was 71% lower among overweight individuals who consumed dairy foods 35 times per week compared to those who consumed dairy products less than 10 times per week (36). These findings were independent of the type of dairy product and its fat content. No association was found between dairy food intake and IRS in normal weight people.
Although the mechanism by which dairy intake may protect against IRS is unknown, the researchers point to several previous studies linking dairy foods and dairy food components such as calcium, magnesium, and potassium to reduced risk of hypertension, coronary heart disease, stroke, and type 2 diabetes (36). In addition, the intracellular role of calcium and other components of dairy products in body weight regulation may be involved. The researchers suggest that the decrease in milk and dairy product consumption over the past few decades, accompanied by increased soda consumption and snacking among children and adolescents, may play an important role in the epidemics of obesity and type 2 diabetes (36).
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