Using the protein leverage hypothesis to understand socioeconomic variation in obesity.

Objectives: The protein leverage hypothesis (PLH) predicts that protein appetite will stimulate excess energy intake, and consequently obesity, when the proportion of protein in the diet is low. Experimental studies support the PLH, but whether protein leverage can be used to understand socioeconomic (SES) variation in obesity is unknown. The objective of this study was to test two hypotheses from the PLH under non-experimental conditions. Consistent with the PLH, we expect that (1) absolute protein intake will be similar across populations, here defined as SES groups and, (2) the proportion of protein in the diet will be inversely associated with energy intake.

Methods: This was a cross-sectional study conducted in a random sample of 135 low-, middle-, and high-SES women in Costa Rica. Anthropometry was used to calculate body mass index (BMI). Twenty-four-hour dietary recalls were used to measure dietary intake.

Results: The prevalence of obesity varied between low- (38.8%), middle- (43.9%), and high- (17.8%) SES women. Absolute protein intake was similar across low- (58.5 g), middle- (59.4 g), and high- (65.6 g) SES women (p = 0.12). Protein intake as a proportion of total energy intake was inversely associated with total energy intake only among middle- (r = -0.37, p = 0.02) and high- (r = -0.36, p = 0.01) SES women.

Conclusions: Consistent with the PLH, absolute protein intake was similar across SES groups. The relationship between the proportion of protein in the diet and total energy intake should be studied further in the context of real world conditions that may influence protein leverage.