1. Based on a combination of two prospective cohort studies evaluating long-term health outcomes and dietary composition, higher amount of plant-derived protein intake was associated with decreased mortality. Replacement of animal protein with plant protein also demonstrated decreased mortality.
2. Much of the aforementioned benefit was observed amongst people who had at least unhealthy lifestyle factor, which included smoking, heavy alcohol intake, overweight or obesity, and physical inactivity.
Evidence Rating Level: 2 (Good)
Study Rundown: The effect of diet composition on health outcomes is a major topic of interest. Short-term data have suggested that replacement of carbohydrate content with protein sources may have improvement in obesity, blood pressure, lipid profiles, and glycemic regulation. The source of protein – plant versus animal – may also play an important role. This study utilized two prospective cohorts consisting of health professional to evaluate the effect of diet composition on long-term health outcomes.
The study demonstrated that increased intake of animal protein had increased frequency of adverse health behaviors and comorbid conditions such as lower physical activity and obesity. After correcting for known confounders, diet rich in animal protein was associated with increased cardiovascular mortality. On the other hand, diet with increased plant-derived protein was associated with lower all-cause and cardiovascular mortality. Substitution of animal protein with plant protein was linked to reductions in all-cause mortality. Much of this benefit was amongst people who had at least unhealthy lifestyle factor, which included smoking, heavy alcohol intake, overweight or obesity, and physical inactivity. The major strengths of the study were the size of the cohorts and the long duration of follow-up. However, relying entirely on questionnaire data to determine diet composition likely introduced bias into the results
In-Depth [prospective cohort]: This study used data from two cohorts: the Nurses Health Study (NHS) and the Health Professionals Follow-up Study (HPFS). Data were collected from 1980 to 2012 with follow-up rates greater than 95% in both cohorts. Questionnaires on health status were obtained at baseline and every 2 years thereafter while dietary content was assessed by the Food Frequency Questionnaire (FFQ) every 4 years. Patients were excluded if they had cancer, diabetes mellitus, cardiovascular disease at baseline or failed to fill out the questionnaires.
In the final analysis, there were 131 342 participants over 3 540 791 person-years of follow-up. After adjusting for known confounders, there was no association between high animal protein intake (>18% total daily energy intake) and all-cause mortality (p = 0.33), but there was increased risk of cardiovascular mortality with hazard ratio (HR) per 10% increment of dietary content of 1.08 (95%CI 1.01-1.16, p = 0.04). Plant derived protein had lower associated mortality with HR per 3% increment of dietary content of 0.90 (95%CI, 0.86-0.95, p < 0.001) for all-cause mortality, and 0.88 (95%CI 0.80-0.97; p = 0.007) for cardiovascular mortality. Replacement of 3% of energy content from animal protein with plant protein was associated with lower all-cause mortality. Replacing processed red meat with plant protein had a HR of 0.66 (95%CI 0.59-0.75), while replacing unprocessed red meat had a HR of 0.88 (95%CI 0.84-0.92). Replacement of fish and poultry sources of protein had HR of 0.94.
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