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Dairy Council Digest Archives
Dairy Foods' Role in Achieving a Healthy Weight
Achieving a Healthy Weight With Dairy Foods
Human Studies. As discussed in several reviews of the scientific literature, numerous, but not all, studies show that increasing dietary calcium reduces adiposity in obese adults without restricting calories and markedly accelerates weight and body fat loss secondary to caloric restriction. Further, some studies have found that dairy products exert significantly greater effects on body composition and weight loss than calcium alone (14,16-18).
One of the earliest indications that dairy products might affect body weight occurred in a trial examining the antihypertensive effect of calcium in obese African American men (22). Researchers observed that increasing calcium intake from ~400 to ~1,000mg/day by feeding two cups of yogurt/day for one year unexpectedly reduced body fat by nearly11 pounds (4.9kg) and lowered circulating insulin without an accompanying reduction in caloric intake (22). Subsequently other studies in African Americans showed that high calcium/dairy food intakes have a beneficial effect on body weight/body fat (23-25).
An analysis of data from NHANES III, 1988-1994, showed an inverse association between calcium intake and body fat, especially in women, after controlling for confounding factors (22). The relative risk of high body adiposity was greatest in women with the lowest calcium intake and progressively decreased with increased calcium and dairy food intake (22). In a secondary analysis of an exercise intervention trial involving 54 normal weight young adult women followed for two years, those with higher calcium intakes (1,200 to1,400mg/day) gained less body weight and body fat than those with calcium intakes <400mg/day (26). Consumption of total dietary calcium and dairy food sources of calcium had a negative effect on weight gain only at lower energy intakes (<1,876 calories), not at higher energy intakes (26).
More recently, a cross-sectional study of nearly 500 adults in phase two of the Quebec Family Study found that women who had a daily calcium intake of <600mg had significantly greater body weight, percentage of body fat, fat mass, body mass index, waist circumference and abdominal fat, after adjusting for confounding factors, than women who consumed more than 600 mg calcium/day (27). Although a trend for these associations was found in men, it was not significant after considering confounding factors. Most of the dietary calcium came from dairy products (27).
A beneficial effect of calcium, and particularly dairy products, on body weight/fat loss and prevention of weight gain has been shown in a wide age range of Caucasians and African Americans of both genders.
Further support for dairy foods’ beneficial role in weight management comes from a population-based prospective study, Coronary Artery Risk Development in Young Adults (CARDIA), in which 3,157 adults aged18-30 years were followed for 10 years (24). Among overweight young adults, increased intake of dairy foods was associated with reduced incidence of all components of insulin resistance syndrome, particularly obesity, after adjusting for confounding lifestyle and dietary factors. Insulin resistance is believed to be an underlying feature of the metabolic syndrome (i.e., abdominal obesity, high blood triglycerides, low HDL cholesterol, high blood pressure and high blood glucose levels), which affects as many as 22% of U.S. adults and increases their risk for developing diabetes and cardiovascular disease (28). The CARDIA study showed that risk of weight gain over the10 years was 67% lower in those who consumed the most dairy foods compared to those who consumed the least (24). Neither the type of dairy product nor its fat content affected the study results. Also, both African Americans and Caucasians benefited equally from the increased intake of dairy products (24).
Studies in children and adolescents also show an inverse association between calcium/dairy products and body fat (29-32). In a three year longitudinal study in which the diets and body composition of 53 preschool children were analyzed, children with higher intakes of calcium/dairy foods, expressed as calcium equivalents, had lower body fat at 70 months of age than children with lower calcium/dairy food intakes (30). A follow-up to this study shows that habitual higher intake of dietary calcium, of which milk and other dairy products were the major contributors, was related to lower body fat in 8-year-old children (32). The data from this study demonstrate that changes in dietary calcium over time explain 4.5% to 9.0% of the variability in body fat (32).
Secondary analyses of data from observational and controlled trials, in which calcium intake was the independent variable and either bone mass or blood pressure the original endpoint, reveal a consistent association between higher calcium intakes and lower body weight or weight gain (12,19,33). Based on these analyses, calcium intake is estimated to explain from 3% to10% of the total variation in adult body weight (19), which is remarkably consistent with the percentage range reported above for children (32). Increasing populationwide calcium intakes to currently recommended dietary intake levels (i.e.,1,200-1,300mg/day) is estimated to substantially reduce the prevalence of overweight and obesity (12,19).
The majority of epidemiological studies support a beneficial effect of calcium, and particularly dairy foods, in weight management. The failure of a few studies to support this association (34,35) may be explained by factors such as high baseline calcium intakes, lack of control of energy intakes, and/or a low prevalence of obesity (36).
In the first prospective clinical trial directly investigating the effects of calcium/dairy foods on body weight and body fat loss, 32 obese adults were maintained on balanced, reduced calorie diets (500kcal/day deficit) for 24 weeks and randomized to a control diet (0-1 serving dairy foods/day and 400 to 500mg calcium/day supplemented with a placebo), a high calcium diet (control diet supplemented with 800mg calcium/day), or a high dairy food diet (3-4 servings of lowfat dairy foods/day, total calcium intake of1,200–1,300mg/ day) (37). The control subjects lost 6% of their body weight, which was increased to 8% with the calcium supplements and 11% with the dairy food diet. A similar trend was observed for fat loss, with the greatest loss occurring in subjects on the high dairy food diet (37).
An unexpected finding was a marked change in the distribution of body fat loss. Fat loss from the abdominal region accounted for19% of total fat lost on the low calcium diet, 50% on the high calcium diet, and 66% on the high dairy food diet (37). This finding is of significance given that obesity in the trunk region is associated with greater health risks than an equal amount of fat deposited in the lower body (38,39). The researchers concluded that increasing dietary calcium not only accelerates weight and fat loss secondary to caloric restriction, but also has a more favorable effect on the distribution of fat loss (i.e., more fat is lost from the abdominal region) (37). Furthermore, intake of dairy products had a substantially greater effect on both fat loss and fat distribution compared to an equivalent amount of supplemental calcium (37). Using data from human studies, researchers recently estimated that increasing Americans’ intake of dairy foods to 3 to 4 servings/day would reduce the incidence of obesity by 5% in the first year and by 25% at 5 years, resulting in projected healthcare cost savings of $2.5 billion and $37.5 billion, respectively (40).
Research indicates a plausible mechanism whereby calcium intake influences energy metabolism and obesity risk. Studies are underway to identify additional dairy food components that contribute to this food’s greater beneficial effect on weight than calcium alone.
Experimental Animal Studies. Studies in transgenic mice overexpressing the agouti gene specifically in adipocytes (i.e., a model of human obesity) demonstrate a beneficial effect of calcium, and particularly dairy foods, on body weight/body fat (13,14,17,18, 22,41). Mice fed a high fat/high sucrose diet low in calcium for six weeks exhibited marked increases in adipocyte lipogenesis (fat formation), decreases in lipolysis (fat breakdown), and increases in body weight and body fat mass (22). However, high calcium diets reduced lipogenesis and stimulated lipolysis, resulting in reductions in body weight gain and body fat (22). Dairy food sources of calcium (nonfat dry milk) had significantly greater effects than calcium alone (22).
When transgenic mice were fed an energy-restricted diet, dietary calcium and, to a greater extent, calcium-rich dairy products (nonfat dry milk) increased lipolysis, decreased lipogenesis, and accelerated loss of body weight and fat (41).
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