Protocol for a randomized cross-over study measuring the effect of reduced protein intake on autophagic flux in healthy adults

Autophagy is a cellular mechanism that degrades damaged or unwanted material from cells and is particularly important during ageing. Autophagy has been widely studied in pre-clinical models and is known to respond to nutrient availability and in particular amino acids. However, clinical data are limited. This protocol paper describes a randomized cross-over clinical study investigating the effect of a four-week long reduction of dietary protein intake on autophagic flux (autophagic degradative activity) measured via a blood test in healthy adults. Sixty-one healthy participants will be recruited. Study participants will be randomly assigned to one of two diets for four weeks, then cross over to the other diet with a four-week washout period between diets. The diets will be: 1) Average Protein Diet: a control comparator diet with a macronutrient profile of 20% of energy from protein, 35% from fat (<10% saturated) and 45% from carbohydrate, with >30 g of fiber/day; 2) Reduced Protein Diet: 10% protein, 35% fat (<10% saturated), 55% carbohydrate, >30 g of fiber/day. This diet will provide 0.7 g of protein per kg of body weight (the recommended minimum daily protein intake). The primary outcome will be the change in autophagic flux between each diet. This study aims to determine whether reducing dietary protein intake in healthy adults can increase autophagy in humans. If positive, it creates the possibility that nutritional strategies could be used to prevent or delay autophagy- related diseases such as Alzheimer disease or atherosclerosis.