Abstract

Background: Ketogenic diets, diets high in fat and protein and low in carbohydrates, have been shown to be effective for weight loss. Recently, plant-based diets and protein sources have gained in popularity as they are thought to be a healthier alternative to animal-based protein sources. There is limited evidence as to whether protein source impacts ketogenic dietary outcomes.

Objective: The aim of this study is to investigate how plant- and animal-based protein supplementation impact weight loss, body composition, and substrate oxidation following a 12-week high-protein, hypocaloric, ketogenic diet in adults with obesity.

Methods: Adults with obesity were recruited and randomized (N= 35) to receive a 12-week high-protein ketogenic diet which included plant- or animal-based protein supplements. Body composition was assessed through dual energy x-ray absorptiometry (DEXA) and computed tomography (CT). Substrate oxidation was assessed via indirect calorimetry before and after the intervention.

Results: Both the plant-based and animal-based groups saw significant reductions in overall weight, fat mass, and fat-free mass (p<0.001 for all). The plant-based group saw a significant reduction in carbohydrate oxidation (p=0.037), a trend to suggest an increase in lipid oxidation (p=0.054), and a trend to suggest a decrease in respiratory exchange ratio (p=0.057). There were no differences in any body composition variables nor resting energy expenditure following the intervention for either group.

Conclusion: Our results indicate that regardless of protein source, people who followed a 12-week high-protein ketogenic diet saw significant loss of weight, fat mass, and fat-free mas. Following a 12-week plant-based high-protein ketogenic diet may lead to a reduction in carbohydrate oxidation and an increase in lipid oxidation, but this may be due to differences in baseline dietary composition and further research is needed to determine the validity of the proposed conclusion.