Macronutrient content and quality, and risk of multimorbidity in the UK Biobank

Multimorbidity is a major determinant of lifespan in older adults. We aimed to examine the association between overall, healthy and unhealthy low-carbohydrate diets (LCD) and low-fat diets (LFD) with the incidence of multimorbidity.

112 710 individuals (40-70 years) from the UK Biobank were included. Food consumption was assessed using up to five 24-h dietary recalls. LCD and LFD scores were calculated based on macronutrient quality. We calculated three versions of each score-overall, healthy and unhealthy. Multimorbidity was defined as the coexistence of ≥2 of nine chronic diseases, including cancer, chronic obstructive pulmonary disease, dementia, Parkinson's disease, stroke, depression, osteoarthritis, diabetes, and coronary heart disease.

There were 8387 individuals with multimorbidity during a median follow-up of 10.7 years. Overall, LCD and LFD scores were not associated with higher multimorbidity risk. There was a higher multimorbidity risk for individuals in the highest quintile (Q5) of unhealthy LCD vs. lowest quintile (Q1) [fully adjusted hazard ratio (HR): 1.07, 95%CI: 1.01, 1.15, p-trend = 0.16] overall as well as among non-tobacco smokers [1.11 (1.00, 1.23), p-trend = 0.09]. The unhealthy LFD score was associated with multimorbidity overall [1.07 (1.00, 1.14), p-trend = 0.07] and never-smokers [1.12 (1.01, 1.24); p-trend = 0.01]. Healthy score results were less consistent. The plant protein component had an inverse association with incident multimorbidity risk, whereas the low-quality-fat and animal protein components were each associated with a higher risk of multimorbidity.

Diet scores defined only by the total amount of carbohydrates or fat were not associated with risk of multimorbidity. Unhealthy diet scores, including low-quality macronutrients and animal protein, were associated with increased risk of multimorbidity.