Association of Low-Carbohydrate and Low-Fat Diets with Mortality among US Adults

Importance: It is crucial to incorporate quality and types of carbohydrate and fat when investigating the associations of low-fat and low-carbohydrate diets with mortality. Objective: To investigate the associations of low-carbohydrate and low-fat diets with total and cause-specific mortality among US adults. Design, Setting, and Participants: This prospective cohort study used data from the US National Health and Nutrition Examination Survey from 1999 to 2014 from 37 233 adults 20 years or older with 24-hour dietary recall data. Data were analyzed from July 5 to August 27, 2019. Exposures: Overall, unhealthy, and healthy low-carbohydrate-diet and low-fat-diet scores based on the percentage of energy as total and subtypes of carbohydrate, fat, and protein. Main Outcomes and Measures: All-cause mortality from baseline until December 31, 2015, linked to National Death Index mortality data. Results: A total of 37 233 US adults (mean [SD] age, 49.7 [18.3] years; 19 598 [52.6%] female) were included in the present analysis. During 297 768 person-years of follow-up, 4866 total deaths occurred. Overall low-carbohydrate-diet and low-fat-diet scores were not associated with total mortality. The multivariable-adjusted hazard ratios for total mortality per 20-percentile increase in dietary scores were 1.07 (95% CI, 1.02-1.11; P =.01 for trend) for unhealthy low-carbohydrate-diet score, 0.91 (95% CI, 0.87-0.95; P <.001 for trend) for healthy low-carbohydrate-diet score, 1.06 (95% CI, 1.01-1.12; P =.04 for trend) for unhealthy low-fat-diet score, and 0.89 (95% CI, 0.85-0.93; P <.001 for trend) for healthy low-fat-diet score. The associations remained similar in the stratification and sensitivity analyses. Conclusions and Relevance: In this study, overall low-carbohydrate-diet and low-fat-diet scores were not associated with total mortality. Unhealthy low-carbohydrate-diet and low-fat-diet scores were associated with higher total mortality, whereas healthy low-carbohydrate-diet and low-fat-diet scores were associated with lower total mortality. These findings suggest that the associations of low-carbohydrate and low-fat diets with mortality may depend on the quality and food sources of macronutrients.