Associations of lower-carbohydrate and lower-fat diets with mortality among people with prediabetes

Background Although low-carbohydrate and low-fat diets are beneficial in short-term metabolic improvement, the associations of these dietary patterns, particularly with different food sources and quality of macronutrients, with mortality remain unclear among people with prediabetes. Objectives We aimed to examine the associations of different types of lower-carbohydrate diets (LCDs) and lower-fat diets (LFDs) with mortality among individuals with prediabetes. Methods This study included 9793 adults with prediabetes from the NHANES 1999-2014. Mortality status was linked to National Death Index mortality data through 31 December, 2015. Overall, unhealthy, and healthy LCD and LFD scores were determined based on the percentages of energy from total and subtypes of carbohydrate, fat, and protein. Cox proportional hazards regression models were applied to calculate HRs and 95% CIs. Results Higher healthy LCD score was associated with favorable blood glucose, insulin, HOMA-IR, C-reactive protein (CRP), and blood lipids, whereas higher healthy LFD score was associated with lower blood glucose and CRP at baseline (all P-trend < 0.05). During 72,054 person-years of follow-up, 1352 deaths occurred. The multivariate-adjusted HRs (95% CIs) of all-cause mortality per 20-percentile increment in dietary scores were 0.88 (0.80, 0.96) for healthy LCD score (P = 0.003), 0.85 (0.78, 0.93) for healthy LFD score (P < 0.001), 1.09 (0.99, 1.21) for unhealthy LCD score (P = 0.08), and 1.11 (1.00, 1.22) for unhealthy LFD score (P = 0.05). Isocalorically replacing 3%-5% energy of low-quality carbohydrate or saturated fat with high-quality carbohydrate, plant-based protein, or unsaturated fat was associated with a 14%-37% reduced all-cause mortality. Conclusions Healthy LCD and LFD scores were significantly associated with lower all-cause mortality, whereas unhealthy LCD and LFD scores tended to be associated with higher all-cause mortality, among people with prediabetes.