Fuel Metabolism Following 3 Days on a Carbohydrate-Free Diet vs. 3 Days of Fasting in Men with Type 2 Diabetes: A Randomized Controlled Crossover Trial

Background: A 72-h fast results in a rapid decrease in circulating glucose to a lower level without a change in non-water body mass.Several metabolic adjustments are necessary.A nutrient-sufficient, carbohydrate (CHO)-free diet also has been reported to result in a decrease in glucose, and similar metabolic perturbations.However, direct comparisons are not available in subjects without, or with, type 2 diabetes (T2DM).Design: Using a crossover design, comparisons between a 72-h fast and ingestion of a CHO-free diet over 72 h were made in 7 male subjects with T2DM.Data also were compared to a baseline standard diet.Objective: We are interested in the effect of variations in the diet on human physiology and metabolism in subjects with and without T2DM.Recently we have used two different approaches to maximally eliminate carbohydrate from the diet: a carbohydrate-free (CHOfree) diet and fasting.Our overall objective has been to compare the results when the metabolic fuel being oxidized is largely fat, without a significant loss of lean body mass.Results: Fasting resulted in a greater and more rapid weight loss than a CHO-free diet.Resting metabolic rate and fuel mix being oxidized were similar.Glucose/glycogen utilization, based on CHO oxidation, was similar between the two, but much greater than reported in subjects without diabetes.Calculated protein metabolism rates were similar. Conclusions and Significance:In subjects with T2DM, metabolic adaptations to a CHO-free diet and a 72 h fast generally are similar.Both interventions result in a major decrease in circulating glucose concentration.Some, though not all, results are similar to those reported in subjects without diabetes.A decreased circulating glucose concentration and/or its rate of metabolism likely regulate these adaptations, which occur at a higher fasting glucose concentration in subjects with T2DM.The adaptation also spares hydrolysis of endogenous proteins.