A Greater Emphasis On Nuts To Replace Animal Proteins Reduces Inflammation
Calcium is an essential nutrient for ubiquitous physiologic processes. The skeleton serves as a reservoir to ensure calcium availability to support these critical processes. As such, adequate bone mineral accrual is important for sustaining these physiologic processes as well as for structural strength of the skeleton. Optimizing bone mineral accrual during the development of peak bone mass has implications for lifelong skeletal health and the prevention of osteoporosis later in life .
The committee that developed calcium intake recommendations considered skeletal health to be the only health outcome with sufficient evidence on which to base calcium intake recommendations for children . Bone accretion, as measured by dual-energy X-ray absorptiometry, and calcium balance studies guided the pediatric recommendations. On the basis of these considerations, the Recommended Dietary Allowance for children aged 4–8 y was set at 1000 mg/d and for children aged 9–18 y at 1300 mg/d.
A recent review of studies of lifestyle factors affecting the development of peak bone mass found excellent evidence for calcium intake in the form of calcium supplements . The evidence was not as strong in studies that used dairy intake due, in part, to the challenges of conducting well-designed randomized controlled dietary interventions. A further concern in dairy-based dietary interventions is whether the addition of several servings per day of dairy foods would result in increased weight gain. This is a serious concern in the context of current pediatric obesity rates. Some studies, mainly in adults and animal models, have suggested that higher calcium and/or dairy intakes can prevent excess weight gain or aid in weight loss. Two studies in the current issue of the Journal represent well-designed prospective randomized intervention studies that used dairy foods as the calcium source, followed children for 12–18 mo, and addressed these important issues.
In the study by Vogel et al. , healthy-weight and overweight girls and boys (n = 240), aged 8–15.9 y (61% black, 35% white, 4% other), whose baseline calcium intake was <800 mg/d were randomly assigned to receive 3 servings of dairy foods/d, containing 300 mg each, for 18 mo. Controls continued their usual diet. Over the course of the study, the intervention group consumed 1500 mg Ca/d and the control group consumed 1000 mg Ca/d, assessed by food-frequency questionnaire. With the exception of bone mineral content of the tibia (P = 0.02), there were no group differences in bone accretion, weight, or fat gain.
The study by Lappe et al. assessed the effects of dairy intake on weight gain and adiposity in adolescent girls (aged 13–14 y) with BMI values ranging from the 50th to 98th percentiles. They enrolled 274 girls (81% white, 12% black), whose baseline calcium intake was <600 mg/d and randomly assigned them to receive milk or yogurt products that provided ≥1200 mg Ca/d for 12 mo. Controls continued their usual diet. Over the course of the study the intervention group consumed 1518 mg Ca/d, and the control group consumed 752 mg Ca/d, assessed by three 24-h recalls. The study did not find differences between groups in changes over time in percentage body fat or weight gain, even though energy intake increased more in the intervention group (P < 0.05).
We learn from these studies that, for youth with low dietary calcium intakes, excess weight gain is not a safety concern when recommending increased dairy intake to meet calcium needs, even among those who are overweight or obese. Dairy products are nutrient dense; in addition to calcium, they are a good source of protein, phosphorus, and other minerals and some vitamins, so this is a sound recommendation. Increased dairy consumption was associated with increased energy intake in both studies by ∼200 kcal/d, without a corresponding difference in weight gain. Is this a consequence of errors in reporting dietary intake? A short-term feeding study in overweight adolescent girls and boys supplemented with calcium carbonate or dairy did not find changes in energy balance , but self-reported energy intake was 35% lower than total energy expenditure as measured by stable isotopes . Reporting bias in energy intake could also affect calcium intake estimates. The consistency of the studies in this issue with regard to the magnitude of the group difference in energy intake suggests a real effect. Whether this effect is a result of reporting bias that uniquely accompanies food supplementation cohorts or true differences in energy balance regulation over long periods requires further investigation. Interestingly, 2 intervention studies in younger children showed an inverse association between calcium intake and gains in fat mass . Given the high variability that accompanies gains in fat and weight in older children and adolescents, the 2 new studies in this issue may have been underpowered to detect small effects of dairy intake.
The absence of group differences in bone mineral accretion in the study by Vogel et al. also suggests that 2 servings of dairy/d are sufficient to support bone accretion in 8- to 16-y-olds. Are the calcium intake recommendations higher than they need to be? Gains in bone mass increase with advancing age and are highly variable, even among children of the same age and sexual maturity stage . Linear growth is also highly variable. Calcium requirements to support growth and bone accretion therefore may be episodic and highly variable, especially during the ages when rapid growth and bone accretion take place. The large age span of the participants in this study may have masked potential age-specific differences between groups in bone accrual. More detailed investigation is needed to reconcile these findings with the evidence from calcium balance and bone accretion studies that supports the recommended calcium intake for children and adolescents.
In sum, there is no evidence for concern with regard to the safety of increasing dairy intakes in children and adolescents with respect to weight gain. However, until further evidence surfaces, maintaining the currently recommended calcium intake to optimize peak bone mineral accrual during adolescence should remain an important public health campaign. Dairy supplementation studies focused on adolescents during periods of rapid bone accrual are needed to more fully assess the effects of dairy intake in this critical period.