Insulin resistance often goes hand in hand with weight gain and obesity. Losing weight can reduce or even correct insulin resistance, but the best diet for addressing insulin sensitivity is not clear.
There is some debate around the effect of protein on insulin resistance – both in terms of how much you eat and the source of protein included. This raises the question – can a high-protein diet improve insulin resistance, and does the source matter?
Background
Insulin resistance (IR) is a common complication of obesity. It is also a major risk factor for chronic diseases such as type 2 diabetes and cardiovascular disease. With IR, decreased sensitivity to insulin in tissues can affect absorption of glucose into tissues, particularly the skeletal muscles. This leads to elevated insulin levels.
The primary treatment of obesity is weight loss via restricting the dietary energy intake, as weight loss can improve insulin sensitivity. A common approach is to increase protein intake to increase satiety and preserve muscle mass during weight loss. However, some studies have found that a high protein diet can reduce insulin sensitivity.
It’s been suggested that the source of protein can influence insulin sensitivity. Research has found that a diet high in vegetable protein can improve insulin sensitivity, whereas a diet high in animal protein is associated with decreased insulin sensitivity and a higher risk of type 2 diabetes.
Researchers designed a study to explore the impact of diets with varying protein content and sources on insulin resistance in subjects with obesity.
The study
A one month randomised controlled trial took place. The participants were aged 18-60 years with a BMI between 30-60 and insulin resistance (Matsuda index<4.3 and HOMA-IR≥2.5).
Exclusion criteria included diabetes, hypertension, cardiovascular disease, liver disease, cancer, pregnancy, smoking, alcohol or substance abuse, weight loss of >3kg within the previous 3 months. Use of medications for many chronic health conditions was also grounds for exclusion.
80 participants were randomised into one of 4 groups:
- A normal protein diet (20%) with predominantly animal protein sources (Animal NP)
- A normal protein diet (20%) with predominantly vegetable protein sources (Vegetable NP)
- A high protein diet (25-30%) with predominantly animal protein sources (Animal HP)
- A high protein diet (25-30%) with predominantly vegetable protein sources (High NP)
All participants received a menu with a hypocaloric diet of 1800kcal/day. This included preparation instructions for 15 days, a recipe booklet and accompanying videos, and a weekly food pantry with 80% of food items on the menu. Compliance was monitored through phone calls, food logs and support via social media (Facebook groups and WhatsApp chats).
Baseline measurements of body weight, body composition, blood pressure, resting energy expenditure and biochemical parameters such as fasting serum blood glucose and insulin were recorded. These were repeated at the conclusion of the study.
The findings
All 4 groups saw a reduction in body weight, BMI and waist circumference.
There was improvement in Insulin sensitivity in all groups. However, there were greater improvements in the Animal HP group and Vegetable HP groups. The Animal HP group saw an improvement of 92.7% and the Vegetable HP group 60.4%.
The Animal and Vegetable HP groups also saw reductions in fat mass, triglycerides, CRP and leptin/adiponectin index and increases in skeletal muscle mass.
Conclusions
The researchers concluded that in people with obesity and IR, a high-protein hypocaloric diet can improve insulin sensitivity by 60-90% in one month. The source of protein and changes to weight did not affect this improvement.
Some limitations were noted. The use of HOMA-IR and Matsuda index are not the reference standard for insulin sensitivity. It was also not clear if the changes were due to the protein content of the diets or the distribution of the other macronutrients.
Future studies are needed to confirm the effect of amount and source of protein on insulin resistance in the greater population.
Reference
González-Salazar, L.E., Pichardo-Ontiveros, E., Palacios-González, B., Vigil-Martínez, A., Granados-Portillo, O., Guizar-Heredia, R., Flores-López, A., Medina-Vera, I., Heredia-G-Cantón, P.K., Hernández-Gómez, K.G. and Castelán-Licona, G., 2020. Effect of the intake of dietary protein on insulin resistance in subjects with obesity: a randomized controlled clinical trial. European Journal of Nutrition, pp.1-13.