Cardiometabolic Effects of Low-Fat and Full-Fat Dairy

The overarching goal of this clinical trial is to characterize and compare the effect of full-fat dairy to low-fat dairy on low density lipoprotein cholesterol (LDL-C) and other cardiometabolic disease (CMD) risk factors in healthy adults and those at risk for CMD. This goal will be achieved with the following objectives:

• Characterize the effect of full-fat dairy compared to low-fat dairy on LDL-C and other CMD risk factors in healthy adults and adults at risk for CMD after 6 weeks.
• Compare the effect of full-fat dairy to low-fat dairy in healthy adults vs. adults at risk for CMD after 6 weeks.

This clinical trial will test two hypotheses: 1) intake of 3 cup-equivalents/day of full-fat dairy (milk, yogurt & cheese) has equivalent effects on LDL-C and other CMD risk factors to 3 cup-equivalents/day of low-fat dairy (milk, yogurt & cheese) in adults with normal BMI and optimal/near optimal LDL-C, and in adults with overweight/obesity and elevated LDL-C after 6 weeks; 2) the effect of full-fat dairy on LDL-C and other CMD risk factors, compared to low-fat dairy, is equivalent in adults with normal BMI and optimal/near optimal LDL-C compared to adults with overweight/obesity and elevated LDL-C after 6 weeks. This trial is expected to demonstrate equivalent effects of full-fat and low-fat dairy on LDL-C and other CMD risk factors in both healthy and at-risk adults.

This is a randomized clinical trial with 2 groups of adults. Group 1 will include adults with normal BMI (18.5 -24.9 kg/m2) and optimal/near optimal LDL-C (≤ 129 mg/dL). Group 2 will include adults with overweight/obesity (25-39.9 kg/m2) and elevated LDL-C (130-190 mg/dL). Within each group, subjects will undergo two 6-week dietary conditions in random sequence order, separated by a 4-week washout: 1) 3 cup-equivalents/day of full-fat dairy; 2) 3 cup-equivalents/day of low-fat dairy. Outcomes will be assessed at the start and end of each period.

Inclusion criteria

• BMI 18.5 to 39.9 kg/m2
• LDL-C ≤190 mg/dL assessed by the Modified Sampson-NIH Equation
• Currently consume milk, yogurt, and/or cheese daily
• Willing to eat 3 servings of dairy (milk, yogurt, cheese) for two 6-week periods during the study

Exclusion criteria

• Hemoglobin <13.2 g/dL for men or < 11.7 g/dL for women at screening
• Fasting triglycerides >350 mg/dL at screening
• ≥10% change in body weight within the 6 months prior to enrollment
• Blood pressure >140/90 mmHg at screening
• Fasting glucose ≥126 mg/dL
• Type 1 or type 2 diabetes
• Takes any (prescription or over-the-counter) anti-hypertensive, lipid-lowering, glucose-lowering or anti-inflammatory drugs, or drugs that alter body weight
• Intake of supplements that affect the outcomes of interest (i.e., lipids, blood pressure, glucose, body weight, inflammation and microbiome) and are unwilling to cease during the study period.
• Unwilling to refrain from starting to take any supplements, vitamins, nutritional products, or health foods that are not prescribed by a doctor for the duration of the study
• History of liver, kidney, or autoimmune disease
• Prior cardiovascular event (e.g., stroke, heart attack)
• Current pregnancy or intention of pregnancy within the next 12 months
• Lactation within the prior 6 months
• Dairy allergy/intolerance/sensitivity/dislike
• Antibiotic use within the prior four weeks
• Oral steroid use within the prior four weeks
• Use of tobacco or nicotine-containing products within the past 6 months
• History of cancer at any site within the past 10 years (eligible if ≥10 years without recurrence) or non-melanoma skin cancer within the past 5 years (eligible if ≥5 years without recurrence)
• Participation in another clinical trial within 60 days of baseline
• Currently following a restricted or weight-loss diet
• Prior bariatric surgery
• Intake of >14 alcoholic drinks/week and/or not willing to avoid alcohol consumption for 48 hours prior to test visits
• Does not speak and/or understand English
• Unwilling to refrain from donating blood and/or plasma during the study
• Weight <110 lb
• Lactose intolerance or sensitivity
• Unwilling to contact study staff before enrolling in other health-related research and avoid participating in any research that may interfere with this study
• For individuals taking thyroid medication: abnormal thyroid stimulated hormone (TSH) concentration, or change in dose of thyroid medication within the last 6 months
• Principal Investigator discretion related to the potential participant's ability to adhere to the study requirements, including being able to come to attend visits