Basciani S, Camajani E, Contini S, et al. - In this randomized pilot study, researchers contrasted the effectiveness, safety and impact of 45-day isocaloric very-low-calorie ketogenic diets (VLCKDs) incorporating whey, vegetable or animal protein on the microbiota in patients with obesity and insulin resistance to test the assumption that protein source may modulate the response to VLCKD interventions. Forty-eight obesity patients [19 males and 29 females, HOMA index ≥ 2.5, age 56.2 ± 6.1 years, BMI 35.9 ± 4.1 kg/m²] were randomly allocated to three 45-day isocaloric VLCKD regimens (≤ 800 kcal/day) containing whey, plant or animal protein. All patients had a decrease in body weight, BMI, blood pressure, waist circumference, HOMA index, insulin, and total and LDL cholesterol. Patients who consumed whey protein experienced a more pronounced muscle strength improvement. VLCKDs resulted in a significant weight loss and a marked improvement in metabolic parameters over a span in 45 days. Whey or vegetable protein-based VLCKDs have a safer profile and result in a healthier microbiota composition than animal protein compounds. Whey protein containing VLCKDs are more efficient at preserving muscle strength.