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Animal-based and plant-based protein-rich foods and cardiovascular health: a complex conundrum.

Dietary protein is integral to human health, but controversies swirl around the cardiovascular health effects of consuming animal-based compared with plant-based protein-rich foods. This important nutrition and health issue is complicated by whether the relative effects of animal-based compared with plant-based protein-rich foods are assessed within the context of self-chosen, Western-style eating patterns typically consumed in the United States or healthier eating patterns recommended by government and health policy organizations. Other complicating factors include epidemiologic design features [e.g., observational cohort studies compared with randomized controlled trials (RCTs)] and the types of protein-rich foods and food products consumed. The vast majority of Americans self-choose unhealthy Western-style eating patterns, which are inconsistent with 2015– 2020 Dietary Guidelines for Americans (DGA) recommendations and contain excess saturated fats (>10% of energy intake per day) and sodium. Red meats are often described as unhealthy foods due to their saturated fat and sodium contents. Importantly, red meats inconsistently contribute to greater saturated fat and sodium intakes, with wide variability among meat products, ranging from lean, unprocessed meat (e.g., trimmed pork tenderloin: 1 g saturated fat and 48 mg sodium per 3-oz portion) to fatty, processed meat products (e.g., pork sausage: 39 g saturated fat and 775 mg sodium per 3-oz portion). Regarding dietary protein, on average, US adults consume more protein from animal sources (46% of total protein intake) than from plant (30%) and dairy (16%) sources (1). Consuming protein predominantly from animal sources may be viewed favorably (e.g., greater nutrient density and protein quality) or unfavorably (e.g., higher saturated fat and sodium intakes). Pertinent to cardiovascular health, the 2015–2020 DGA states that “strong evidence from mostly prospective cohort studies . . . has shown that eating patterns that include lower intakes of [red] meats as well as processed [red] meats and processed poultry are associated with reduced risk of cardiovascular disease (CVD) in adults” (2). This statement does not distinguish between types of red meats, extent of processing, nonprotein components of foods, the alternative (control) food used for testing, or the overall health-promoting properties of the cohorts’ diets. All of these factors may affect associations between animal-based and plant-based protein-rich foods and CVD risk factors (3). The need for more research regarding the impact of consuming red meats on CVD is highlighted by meta-analysis results showing that higher unprocessed red meat intake did not predict coronary heart disease (RR per 100 g/d: 1.00; 95% CI: 0.81, 1.23), but higher processed meat intake did (RR per 50 g/d: 1.42; 95% CI: 1.07, 1.89) (4). From a compositional and nutritional perspective, all meats are not the same, and lumping them all together belies the complex conundrum between red meat intake and cardiovascular health. Whereas observational research predominantly informed 2015–2020 DGA recommendations to consume less red meat to reduce long-term outcomes such as CVD onset and mortality (2), results from randomized controlled feeding trials are well suited to investigate cause-and-effect relations among proteinrich food sources and CVD risk factors, which are easier to measure in the short term (3, 5). In the current issue of the Journal, Bergeron et al. (6) provide novel insights on the relative effects of consuming red meat, white meat, and nonmeat protein sources, each for 4 wk, on atherogenic lipoprotein measures, including lipoprotein particles. The predominant protein sources tested in this RCT were unprocessed, lean red meat; unprocessed, lean white (poultry) meat; and nonmeat sources (legumes, nuts, grains, and isoflavone-free soy products). These protein sources were tested when the diets contained either low saturated fat (7% of total energy) or high saturated fat (14% of total energy), with the saturated fat contents of the diets manipulated predominantly by using dairy products with different fat contents. Consuming the red and white meat diets, compared to the nonmeat diet, resulted in higher fasting-state concentrations of total cholesterol, LDL cholesterol, and non-HDL cholesterol, along with higher plasma apolipoproteins (apo) B and apoA1. The higher LDL cholesterol was associated with higher large LDL cholesterol particle size but no differences in small and medium LDL cholesterol particle sizes. The concentrations and sizes of these compounds were not different between the red and white meat diets. These results prompted Bergeron et al. (6) to conclude