An intervention designed to change the availability of beverages in the home environment increased consumption of milk while almost completely eliminating consumption of SSBs in overweight and obese Chilean children. These changes in beverage consumption increased the accretion of lean mass but did not significantly affect fat mass. The increased lean mass was accompanied by greater linear growth for the boys, but not for the girls.
The American Academy of Pediatrics recommends that children consume 2 (aged ≤8 y) to 3 (aged 9 y and older) servings of milk or dairy products per day (31
), consistent with the Dietary Guidelines for Americans
, 2005 (32
). According to these guidelines, a single serving of milk is specified as 8 fluid ounces (1 cup), which is equal to ≈240 g and slightly greater than the 200-g portion that was considered a serving in the present study. Recommendations are calculated from idealized dietary patterns in which the nutrients provided in milk, with a particular focus on calcium, also are obtained from other foods such as dark green leafy vegetables and legumes. However, most children do not consume idealized diets, and some experts argue that recommendations for milk and dairy products should be increased by one serving (≈240 g) per day, because this food group provides a readily available and relatively low-cost source of essential nutrients (33
). At follow-up in the present study, children in the intervention group reported drinking >1100 g milk/d (ie, between 4 and 5 servings/d). Thus, study outcomes reflect the effects of consuming milk in excess of current recommendations. Nevertheless, calcium intake for all study participants at follow-up was less than the recommended upper limit of 2500 mg for children (34
Studies examining the time course of postprandial aminoacidemia and protein turnover after milk consumption provide a plausible physiologic basis for interpreting the greater accretion of lean mass in the intervention group than in the control group (22
). The 2 major protein fractions in milk are whey and casein (37
). Whey is digested rapidly and causes an abrupt and transient increase in aminoacidemia that stimulates whole-body protein synthesis (35
). In contrast, casein is digested more slowly and does not stimulate protein synthesis, but suppresses protein breakdown (35
). Postprandial metabolism after milk consumption may lead to increased accretion of lean mass over time because of the distinct and synergistic effects of whey and casein in promoting net anabolism.
Another potential mechanism may involve the direct adverse effects of SSBs on body composition. SSBs are among the greatest contributors to dietary glycemic load (mathematical product of dietary glycemic index and total carbohydrate) (38
) in children's diets. A high-glycemic-load meal has been shown to elicit reactive hypoglycemia and counterregulatory hormone secretion in the late postprandial period (40
). Counterregulatory hormones have proteolytic actions that may adversely affect lean body mass if persistently elevated (41
), as previously proposed (42
). Indeed, rodents fed a high-glycemic-index diet had significantly less lean tissue at the same mean body weight than did rodents fed a low-glycemic-index diet (44
With increased consumption of milk and decreased consumption of SSBs occurring concurrently, energy intake decreased in the intervention group. The significance of this finding, based on self-report of diet, is not readily apparent given that we observed no changes in body weight or BMI. Nevertheless, milk may be more satiating than SSBs because of its mixed macronutrient composition (45
), low glycemic load (46
), and other intrinsic properties, such as micronutrient profiles, that influence insulin signaling and glucose homeostasis (47
). An increase in satiety may lead to lower energy intakes over time.
Our data are consistent with previous randomized controlled trials conducted in developed countries, indicating no changes in fat mass with increased consumption of milk and dairy products (48
). In a study of 9- to 13-y-old girls, Chan et al (48
) reported no effect with supplementation of dairy products providing 1200 mg Ca/d (equivalent to ≈4 servings of milk/d) over 1 y. Likewise, Cadogan et al (49
) found no effect with provision of 568 mL/d (≈2.5 servings/d) of extra milk to 12-y-old girls for 18 mo, and Merrilees et al (50
) observed no effect with an increase in dairy foods to provide an extra 1000 mg Ca/d (equivalent to ≈3.3 servings of milk/d) to teenage girls over 2 y. In a 1-y study of young women, Gunther et al (51
) found no differences in fat mass between 3 study groups with daily consumption of milk or dairy products providing calcium in average amounts of 742, 1026, or 1131 mg (approximating 2.5, 3.4, and 3.8 servings of milk, respectively). Moreover, a secondary regression analysis of 6-mo of follow-up data from the latter study indicated that the estimated net beneficial effect on fat mass of relatively high (≈4 servings) compared with low (≈1.7 servings) daily intake of milk or dairy products is <2 kg over 18 mo (52
). Thus, associations between intake of milk or dairy products and body weight and composition reported in several (18
), although not all (53
), observational studies may be due to small but cumulative effects over time.
None of the randomized controlled trials cited above (48
) showed an increase in accretion of lean mass with increased consumption of milk or dairy products, as observed in the present study. Previous studies were conducted in developed, rather than in developing, countries. Moreover, discrepant findings may relate to differences in subject characteristics or details of the intervention. Previous studies focused on girls who were at various stages of puberty and not overweight (48
). In contrast, we enrolled boys and girls who were prepubertal and overweight or obese at baseline. Regarding interventions, some of the previous studies provided a variety of dairy products to subjects (48
), whereas we provided only milk given the focus of the present study on beverage consumption. The present study also was unique in that we aimed to not only increase the consumption of milk but also to decrease the consumption of SSBs. The dual focus of the intervention may have conferred added benefit.
Study strengths and limitations warrant comment. The strengths included a state-of-the-art method for assessing body composition, an environmental intervention that relied largely on beverage deliveries to the home, and a high retention rate. Families were receptive to opening their homes to the study nutritionist for delivery of the milk beverages, and only 6 of 50 children in the intervention group requested discontinuation of beverage delivery. Follow-up DXA assessments were completed in 3 of these 6 children, such that analyses could be conducted according to the intention-to-treat principle using data from 95% of the subjects who were randomly assigned to a study group. Moreover, on the basis of data derived from the FFQ, the intervention had the anticipated effect, ie, it significantly decreased the consumption of SSBs and increased the consumption of milk. Limitations of the study included a relatively small sample size and short intervention period. Reliance on self-report for dietary assessment was an additional limitation, as in all trials of free-living subjects. In addition, we recognize that concerns have been raised for the long-term adverse health effects of high levels of dairy consumption (55
)—an issue we were unable to address because of the study's short duration.
In conclusion, replacing the habitual consumption of SSBs with milk may have beneficial effects on lean body mass and growth in children. We did not observe a change in fat mass or percentage body fat, either because of the study's short duration or because replacement of one energy-containing beverage for another does not affect these endpoints. Larger studies are needed to evaluate the long-term effects of altering beverage consumption on body composition in children and to determine which beverages promote optimum growth and chronic disease risk reduction among pediatric populations in different regions of the world.