Dietary protein and changes in markers of cardiometabolic health across 20 years of follow-up in middle-aged Americans

Authors: HRUBY, ADELA - Jean Mayer Human Nutrition Research Center On Aging At Tufts University; JACQUES, PAUL - Jean Mayer Human Nutrition Research Center On Aging At Tufts University

Submitted to: Public Health Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/20/2018
Publication Date: 8/17/2018
Citation: Hruby, A., Jacques, P.F. 2018. Dietary protein and changes in markers of cardiometabolic health across 20 years of follow-up in middle-aged Americans. Public Health Nutrition. 21(16):2998-3010. https://doi.org/10.1017/S1368980018001854.
DOI: https://doi.org/10.1017/S1368980018001854

Interpretive Summary: Results from shorter-term clinical research trials suggest that high protein diets may lower cardiometabolic risk by helping to promote fat loss and preserve lean body mass. The current research, however, has not examined other cardiometabolic risk factors in relation to protein intake. In addition, it is known that cardiometabolic health tends to deteriorate with age, and there is little long-term data on protein and cardiometabolic health. As a result, we aimed to examine habitual protein intake in participants of the Framingham Heart Study Offspring cohort and its relationship with changes in cardiometabolic risk factors across up to five time points in 20 years of follow-up. We used data from food frequency questionnaires to determine total protein intake. Cardiometabolic markers included systolic (SBP) and diastolic blood pressures (DBP), circulating lipids (total and HDL cholesterol, triglycerides), a measure of kidney function called estimated glomerular filtration rate (eGFR), fasting plasma glucose (FG), weight, and waist circumference (WC). Our results demonstrated that the highest (as opposed to the lowest) protein consumers had positive changes in SBP and eGFR over the study period. Interestingly, the highest protein consumers had unfavorable associations with changes in fasting glucose. There were no significant associations between protein intake and weight, WC, DBP, or lipids. Our findings are consistent with other published literature studying healthy adults, in particular studies that examined protein intake in terms of g/day. Studies expressing intake in units of g/kg body weight/d or percent of energy have yielded findings inconsistent with studies expressing intake in g/day. This work highlights the importance of pursuing further investigation around how body mass may affect results. Ultimately, it will be important to establish a consistent methodology for examining protein intake to ensure that work in the field can be synthesized across studies.

Technical Abstract: Dietary protein plays a role in counteracting age-related muscle loss. However, there are limited long-term data on protein intake and markers of cardiometabolic health, which tend to deteriorate with age. We investigated relationships between protein intake and changes in cardiometabolic risk factors in participants of the Framingham Heart Study Offspring. Food frequency questionnaire-derived total protein intake (g/d) and cardiometabolic markers were assessed up to five times across up to 20 years. Markers included systolic (SBP) and diastolic blood pressures (DBP), circulating lipids (total and HDL cholesterol, triglycerides), estimated glomerular filtration rate (eGFR), fasting plasma glucose (FG), weight, and waist circumference (WC). Mixed models accounting for repeated measures were used to estimate adjusted mean annualized changes in outcomes per quartile category of protein intake across 12,333 unique observations in 3,066 participants (baseline mean age: 54.0 (9.7) y, BMI: 27.4 (4.9) kg/m^2, 53.5% female). In fully adjusted models, there were statistically significant favorable associations with annualized changes in SBP (lowest vs. highest intake: 0.34 [0.06] vs. 0.04 [0.06] mmHg, P trend=0.001) and eGFR (-1.03 [0.06] vs. -0.87 [0.05] mL/min/1.73 m^2, P trend=0.046), and unfavorable associations with changes in FG (0.23 [0.08] vs. 0.49 [0.07] mg/dL, P trend=0.004). There were no significant associations between protein intake and weight, WC, DBP, or lipids. Our findings are consistent with much of the literature studying healthy adults, especially when studies used protein intake in g/d; studies expressing intake in units of g/kg body weight/d or percent of energy have yielded discrepant findings.