Association of Low-Carbohydrate and Low-Fat Diets With Mortality Among US Adults

Abstract

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.

Figure 1.. Hazard Ratios (HRs) of Total Mortality per 20-Percentile Increase in Unhealthy Low-Carbohydrate-Diet and Low-Fat-Diet Scores by Subgroups

Results were adjusted for age (20-34, 35-49, 50-64, and ≥65 years), sex (male or female), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other), educational level (less than high school, high school graduate or General Educational Development, and some college or above), ratio of family income to poverty (<1.30, 1.30-3.49, or ≥3.5), family history of diabetes mellitus (yes or no), family history of heart disease (yes or no), history of diabetes (yes or no), history of heart disease (yes or no), history of cancer (yes or no), physical activity (0, 0.1-0.9, 1.0-3.4, 3.5-5.9, or ≥6 hours per week), alcohol consumption (0, 0.1-4.9, 5-14.9, 15-29.9, or ≥30 g/d), smoking status (never smoker, former smoker, current smoker [1-14, 15-24, or ≥25 cigarettes per day]), dietary cholesterol intake (quintiles), and body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) (<21, 21-24.9, 25-29.9, 30-35, and >35) except the corresponding subgroup variates.

Figure 2.. Hazard Ratios (HRs) of Total Mortality per 20-Percentile Increase in Healthy Low-Carbohydrate-Diet and Low-Fat-Diet Scores by Subgroups

Results were adjusted for age (20-34, 35-49, 50-64, and ≥65 years), sex (male or female), race/ethnicity (non-Hispanic white, non-Hispanic black, Hispanic, and other), educational level (less than high school, high school graduate or General Educational Development, and some college or above), ratio of family income to poverty (<1.30, 1.30-3.49, or ≥3.5), family history of diabetes mellitus (yes or no), family history of heart disease (yes or no), history of diabetes (yes or no), history of heart disease (yes or no), history of cancer (yes or no), physical activity (0, 0.1-0.9, 1.0-3.4, 3.5-5.9, or ≥6 hours per week), alcohol consumption (0, 0.1-4.9, 5-14.9, 15-29.9, or ≥30 g/d), smoking status (never smoker, former smoker, or current smoker [1-14, 15-24, or ≥25 cigarettes per day]), dietary cholesterol intake (quintiles), and body mass index (BMI; calculated as weight in kilograms divided by height in meters squared) (<21, 21-24.9, 25-29.9, 30-35, and >35) except the corresponding subgroup variate.