The purpose of this study is to find out if full-fat dairy and low-fat dairy have similar effects on risk factors for heart disease and diabetes. During the study, participants will consume two types of dairy products: low-fat dairy (milk, yogurt, and cheese) and full-fat dairy (milk, yogurt, and cheese). Each type of dairy will be consumed for 6 weeks with a ≥4-week break between. Measures will be taken to evaluate blood cholesterol, blood sugar, body weight, inflammation, blood pressure, heart health and dietary intake at the beginning and end of each 6 week period.

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:

1. 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.
2. 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

Study protocol and SAP will be uploaded to clinicaltrials.gov prior to enrollment of the first participant