Medical nutrition therapy is a critical part of managing and preventing type 2 diabetes (T2D), explains Simin Liu, MD, ScD. “Much research, including our own, has been conducted on the role of carbohydrates in diabetes, but less is known about the role of dietary protein,” Dr. Liu says. “In recent years, intake of animal protein has been associated with an increased risk for T2D, but research on plant protein is scarce and findings were not consistent. Therefore, we conducted a comprehensive and systematic assessment of protein food sources in relation to T2D, focusing on the role of replacing animal proteins with plant proteins. We also examined the role of mediating biomarkers to help understand the mechanistic pathways by which sources of protein may affect diabetes risk.”

For a study published in Diabetes Care, Dr. Liu and colleagues conducted analyses in two large and high-quality prospective cohorts, the Women’s Health Initiative (WHI) of 108,681 postmenopausal women in the United States, and the UK Biobank of 34,616 adults in the UK, all free of diabetes at baseline. “We investigated the role of different animal and plant-based protein sources in the incidence of T2D in both cohorts, evaluated the links between substituting different sources of protein with the incidence of T2D in both cohorts, and lastly, examined which biomarkers may explain the association of substituting plant for animal protein,” Dr. Liu notes. “The protein sources we examined included red meat, processed meat, poultry, high omega-3 seafood, low omega-3 seafood, cheese, yogurt, milk, and eggs as the animal sources, and legumes, nuts, and whole grains as the plant sources.”

Replacing Animal Protein With Plant Protein Helped Reduce T2D

The study team found that animal proteins, particularly red meat, processed meat, poultry, and eggs, were linked with an increased risk for T2D, and that plant protein, particularly whole grains and nuts, were correlated with a decreased risk for T2D in both cohorts of women and men in the US and UK. The substitution analysis also showed that replacing animal protein sources with any type of plant protein source reduced T2D risk in both cohorts.

“Our findings are in line with previous research on protein sources and diabetes prevention, as well as with plant based dietary patterns frequently recommended by diabetes and cardiovascular disease clinical practice guidelines,” Dr. Liu says. “For endocrinologists with patients who consume high amounts of animal proteins, particularly red and processed meats, having them replace some of these animal proteins with plant proteins may be beneficial for those at risk for T2D.”

Red Meat Consumption Can Impact Inflammation

One of the key takeaways from this study, Dr. Liu points out, is that replacing 5% energy from animal protein with plant protein was linked with a decreased risk for T2D and that this relationship was mediated by inflammation biomarkers, particularly high-sensitivity C-reactive protein (Table). “This is supported by research on the gut microbiota and dietary factors, such as red meat or whole grain intake, which can impact inflammation and endothelial dysfunction and, therefore, the risk for cardiometabolic diseases,” he says. “We also found that the mediating effects of the biomarkers decreased after we adjusted for BMI. This is not surprising, as previous research has shown mediating and confounding roles of BMI and adiposity in relation to adipose tissue derived cytokines in metabolic diseases.”

More attention should be placed on dietary protein sources in the prevention of T2D, according to Dr. Liu. “We hope that physicians and endocrinologists will realize the benefits of replacing some animal protein sources with plant protein sources in diets of their patients who are at risk for developing T2D. In addition, as some endocrinologists may not have time to thoroughly review diet with their patients, they should consider referring them to a registered dietitian for nutritional counseling.”

Dr. Liu and colleagues would like to see data from additional large, high-quality, prospective studies of diverse populations, particularly in low- and middle-income countries where diabetes and obesity are in a pandemic state. “Since our findings also showed that replacing red and processed meat with plant protein sources yielded the most benefit, we need to explore further if replacing other animal protein sources (dairy and seafood) with plant protein sources would be useful, particularly in different populations,” Dr. Liu says.