This study will evaluate the effects of whole vs. nonfat milk consumption on body composition, cardiometabolic disease risk factors, and dietary quality.

Background The optimal type of milk is a topic of much debate. Several recent observational studies indicate that consuming whole (full-fat), compared to reduced-fat milk, is associated with less weight gain and decreased cardiometabolic disease risk. The observed beneficial effect of consuming whole milk on body weight may be due to its greater satiety value, leading to consumption of fewer calories from other lower quality (e.g., sugary) foods. Mechanistic studies indicate that substitution of carbohydrate with certain saturated fatty acids in milk increases low-density lipoprotein cholesterol (LDL-C). However, this increase has been attributed to large, buoyant particles that are less atherogenic than small, dense particles; is accompanied by an increase in high-density lipoprotein cholesterol (HDL-C); and may not elevate overall risk compared to carbohydrate.

Specific Aims and Hypotheses

• To examine the effects of milk consumption on body composition (Aim #1) and cardiometabolic disease risk factors (Aim #2). Primary Hypothesis. Consuming whole milk will result in less weight gain compared to consuming nonfat milk. Secondary hypothesis. Consuming whole milk will decrease cardiometabolic disease risk compared to consuming nonfat milk.
• To explore the effects of milk consumption on dietary quality (Aim #3). Exploratory hypothesis. Consuming whole milk will improve overall dietary quality by displacing lower quality foods compared to consuming nonfat milk, particularly among children with low baseline dietary quality.
• (Ancillary Study) To evaluate the effects of milk consumption on risk and prevalence of dental caries.

Design Randomized Controlled Trial. Participants (N=200, aged 9 to 12 years, BMI≥75th percentile) will be randomly assigned for 1 year to receive: 1) Whole milk, 3 cups/d or 2) Nonfat milk, 3 cups/d. To promote adherence to the interventions, the investigators will rely on home delivery of milk using methods consistent with previous successful studies.

Study Outcomes The primary outcome is change in fat mass measured by air displacement plethysmography (BodPod) at 3 time points (baseline and 6 and 12 months). To evaluate cardiometabolic disease risk factors, the investigators will obtain a plasma MetaboProfile®(LabCorp) that includes lipoprotein particle sizes and subfraction concentrations, novel measures of insulin-resistant dyslipoproteinemia and inflammation, and a conventional lipid profile. The investigators will also measure blood pressure.

For the Ancillary Study, outcomes include salivary cariogenicity (pH, flow, and buffering capacity); caries prevalence; dietary quality (cariogenic potential); and serum 25-hydroxyvitamin D.

Inclusion Criteria:

• Aged 9 to 12 years
• BMI ≥75th percentile for sex and age
• Residence in the Greater Boston catchment area

Exclusion Criteria:

• Aversion to nonfat or whole milk
• Physician diagnosis of major medical illness, eating disorder, or milk allergy (lactose intolerance not exclusionary as lactase treated milk can be provided)
• Plans to move away from the Greater Boston catchment area during the study period
• Plans to be away from home for ≥5 weeks during the study period (e.g., extended summer vacation)
• Change in body weight exceeding 10% during prior year
• Recent adherence to a special diet
• Chronic use of any medication or dietary supplement that could affect study outcomes
• Another member of the family (first degree relative) or household participating in the study

We will share de-identified IPD on Open Science Framework.

The Study Protocol will be posted prior to enrollment of the first study participant. The IPD and Analytic Code for each peer reviewed manuscript from the study will be posted at the time of publication.

The data will be available to any interested party through Open Science Framework.