Impact of low-fat and full-fat dairy foods on fasting lipid profile and blood pressure: exploratory endpoints of a randomized controlled trial

Abstract

Background: Dietary guidelines traditionally recommend low-fat dairy because dairy's high saturated fat content is thought to promote cardiovascular disease (CVD). However, emerging evidence indicates that dairy fat may not negatively impact CVD risk factors when consumed in foods with a complex matrix.

Objective: The aim was to compare the effects of diets limited in dairy or rich in either low-fat or full-fat dairy on CVD risk factors.

Methods: In this randomized controlled trial, 72 participants with metabolic syndrome completed a 4-wk run-in period, limiting their dairy intake to ≤3 servings/wk of nonfat milk. Participants were then randomly assigned to 1 of 3 diets, either continuing the limited-dairy diet or switching to a diet containing 3.3 servings/d of either low-fat or full-fat milk, yogurt, and cheese for 12 wk. Exploratory outcome measures included changes in the fasting lipid profile and blood pressure.

Results: In the per-protocol analysis (n = 66), there was no intervention effect on fasting serum total, LDL, and HDL cholesterol; triglycerides; free fatty acids; or cholesterol content in 38 isolated plasma lipoprotein fractions (P > 0.1 for all variables in repeated-measures ANOVA). There was also no intervention effect on diastolic blood pressure, but a significant intervention effect for systolic blood pressure (P = 0.048), with a trend for a decrease in the low-fat dairy diet (-1.6 ± 8.6 mm Hg) compared with the limited-dairy diet (+2.5 ± 8.2 mm Hg) in post hoc testing. Intent-to-treat results were consistent for all endpoints, with the exception that systolic blood pressure became nonsignificant (P = 0.08).

Conclusions: In men and women with metabolic syndrome, a diet rich in full-fat dairy had no effects on fasting lipid profile or blood pressure compared with diets limited in dairy or rich in low-fat dairy. Therefore, dairy fat, when consumed as part of complex whole foods, does not adversely impact these classic CVD risk factors. This trial was registered at clinicaltrials.gov as NCT02663544.

Keywords: blood pressure; cardiometabolic disease; cardiovascular disease risk; dairy; humans; metabolic syndrome; serum lipid profile.

© The Author(s) 2021. Published by Oxford University Press on behalf of the American Society for Nutrition.

Figures

FIGURE 1

Flow diagram of study recruitment and enrollment.

FIGURE 2

Changes in LDL cholesterol (A), HDL cholesterol (B), LDL flotation rate (C), free fatty acids (D), triglycerides (E), and total cholesterol (F) in the limited-dairy diet (n = 21), low-fat dairy diet (n = 24), and full-fat dairy diet (n = 21) (per-protocol analysis, n = 66). Outcome variables are represented as the change variable calculated as the value at follow-up minus the value at baseline. Boxes represent 25th–75th percentiles, and whiskers 5th and 95th percentiles, with outliers represented by a solid dot. The medians are represented by horizontal bars across the boxes and the means are represented by crosses. The P values for the time by diet interactions from the overall repeated-measures ANOVA, adjusted for baseline HDL cholesterol (with the exception of change in HDL cholesterol), are displayed at the top of each boxplot. Rf, relative position of the major LDL peak in the gradient.

FIGURE 3

Cholesterol content in 38 fractions in participants consuming the limited-dairy diet (n = 21) (A), the low-fat dairy diet (n = 24) (B), or the full-fat dairy diet (n = 21) (C). Upper panels show absolute concentrations from CRC visit #1 (baseline) and visit #2 (follow-up), based on the per-protocol cohort for lipid analyses (n = 66), and lower panels show changes in cholesterol content in each fraction during the interventions. Significant differences were assessed using a repeated-measures ANOVA, with a primary emphasis on the time by diet group interaction. No statistically significant differential changes between the intervention groups were observed for any of the 38 lipoprotein fractions. CRC 1: clinical research visit 1 (baseline); CRC 2: clinical research visit 2 (follow-up). CRC, clinical research center; IDL, intermediate-density lipoprotein.