Objective: Evidence is needed to inform dietary strategies to promote a healthy weight and reduce cardiovascular risk. This study investigated the effect of increasing dietary protein on glucose metabolism under standardised conditions.

Methods: Ten healthy, lean (mean BMI 22.2 kg/m² (SD 2.2)) unrestrained consumers were studied over 3 five-day residential periods. They received diets providing 10%, 15%, or 25% protein (P), 30% fat and the remainder as carbohydrate in random order. Energy intake (EI) was ad libitum on days 1-3 and fixed at maintenance requirements on day 4. A continuous glucose monitor measured interstitial blood glucose concentrations on day 3 and day 4.

Results: During ad libitum eating mean interstitial glucose concentration and AUC were significantly lower (p <0.0001) during the 25%P diet (mean glucose 5.44 ± 0.2 mmol/l / AUC 7800 ± 337 mmol.min/l) than the 10%P (5.90 ± 0.2 mmol/l / 8470 ± 337 mmol.min/l) and 15%P diets (5.89 ± 0.2mmol/l / 8464 ± 347 mmol.min/l). Post-prandial maximum glucose concentrations were lower during the 25%P than the 10%P and 15%P diets. When EI was fixed, mean glucose concentration was significantly lower (p <0.0001) during the 25%P (5.31 ± 0.16mmol/l) diet than the 10%P (5.95 ± 0.16 mmol/l) and 15%P diets (5.66 ± 0.16 mmol/l) and lower during post-prandial periods after the 25%P diet.

Conclusions: Modest increases in dietary protein produce clinically significant reductions in glucose concentrations. This may be a useful dietary strategy to reduce cardiovascular risk, particularly for people with insulin resistance or diabetes.