Dietary Protein, FGF21 and Glucose Homeostasis

A three-arm protocol was performed. In protocol 1, participants ingested either a low-protein (LP) meal or a higher protein (HP) meal in a randomized order, separated by 72 h, followed by a 5-week low-protein, high-carbohydrate (LPHC) diet. In protocol 2 and 3, participants ingested either a LPHC diet or a low-protein, high-fat (LPHF) diet for 5 weeks followed by a higher protein diet (HPD) for another 5 weeks. All diets were eucaloric. Resting metabolic rate (RMR) was measured pre, during and post the protein-restricted interventions. A hyperinsulimic-euglycemic clamp was performed post the protein-restricted interventions and post the HPD interventions. A basal subcutaneous abdominal fat biopsy was obtained post the protein-restricted interventions and post the HPD interventions. In a run-in period over 14 days, the participant records the daily number of steps and physical activity, in order to determine their habitual activity level. During this period, a 4-day dietary record is performed, where all ingested food was weighed and recorded. During the experimental period the participant followed the supplied diet. All food consumed during the interventions was handed out to the subject at the institute. All food was packaged and weighed to 1 gram of accuracy. During the dietary intervention, a weekly test in the morning was performed, where the resting metabolic rate was measured and blood samples taken from the arm vein. At week 0, 5 and week 10 body composition was measured by dual energy x-ray absorptiometry scanning (DXA), and the fat biopsy was obtained . At all tests participants arrived fasting at the institute at 8:00 a.m. in the morning. The participant arrived by car or public transport.