"Studies that ignore the vastly heterogeneous nature of large food groups and simply assess plant protein versus animal protein will undoubtedly miss critical caveats underlying the unique relationships between different protein sources and type 2 diabetes risk."
People with type 2 diabetes know to avoid certain carbohydrates that raise blood sugar levels. Counting carbohydrates is as easy as checking the nutrition label on foods for grams of sugar. But carbohydrates are not the only nutrient that affects blood sugar levels. Despite being sugar-free, proteins can influence -- either positively or negatively -- insulin secretion and glucose production as well. However, nutrition labels offer little help when it comes to understanding the impact of proteins, because it is not the grams of protein that matter but the protein source.
In a new peer-reviewed paper, California Dairy Research Foundation Executive Director Gonca Pasin, Ph.D., and nutrition scientist Kevin B. Comerford, Ph.D., report that milk and other dairy foods are the only animal proteins to consistently show beneficial effects on glucose production and insulin secretion.
To understand why dairy has different effects than beef, pork, or poultry, the authors suggest looking beyond nutrition labels and into the food matrix. Although it sounds like something out of a sci-fi movie, the food matrix approach simply means considering the complexity of food rather than looking at one particular nutrient. And milk is a very complex food.
Compare a glass of milk with one ounce of beef; both come from a cow, and both provide about the same amount of protein. But once consumed, some major differences between these protein sources become apparent. A cut of beef comes from muscle tissue and is made up of structural proteins. In stark contrast, milk evolved to be a food source for developing offspring and contains proteins with immunological, hormonal, and nutritional functions. As a result, milk contains unique types of proteins that are more biologically active in the human body than those from animal tissue.
"Not all protein sources are created equal in their abilities to modulate insulin secretion and insulin sensitivity," explain the authors.
One protein group that appears to have a particularly strong influence on insulin production is whey. Perhaps best known for its role in promoting muscle growth, milk's unique whey protein has demonstrated effects on insulin secretion. Indeed, the same branched-chain amino acids from whey proteins that play a role in stimulating protein synthesis in muscle tissue also stimulate the pancreas to produce insulin.
In addition, whey proteins can positively influence insulin sensitivity. The authors report on a study that found milk consumption in subjects with type 2 diabetes resulted in a five-fold greater increase in insulin response than would be expected based on its glucose response. What could explain this discrepancy? One suggestion is that the amino acid chains from whey proteins interact with chemical and hormonal signals from fat cells. In type 2 diabetics, these signals prevent insulin from moving glucose from the bloodstream and into the cells. However, whey proteins may interfere with these signals, allowing the insulin to effectively do its job.
Despite having unique proteins, dairy is often lumped in with other animal proteins in long-term prospective cohort studies that investigate the association between diet and risk of developing type 2 diabetes. These studies find that compared to plant proteins, animal proteins are associated with a higher risk of developing type 2 diabetes, and thus recommend replacing animal proteins -- including dairy -- with plant proteins.
But as the authors explain, "Studies that ignore the vastly heterogeneous nature of large food groups and simply assess plant protein versus animal protein will undoubtedly miss critical caveats underlying the unique relationships between different protein sources and type 2 diabetes risk."
Indeed, when protein type is assessed individually, dairy proteins have the same lower risk association as plant proteins. The epidemiological evidence repeatedly finds that a higher intake of dairy foods, including milk, cheese, and yogurt, reduces the risk of developing type 2 diabetes.
Importantly, it is unlikely that whey protein is working alone. Calcium, magnesium, and even the presence of probiotics in fermented dairy products may add to or work synergistically with whey protein to positively influence blood glucose regulation. Hence, the emphasis on the food matrix approach--we consume food, not nutrients, which requires looking at all of the components to assess potential health benefits.
The authors believe that given the interaction between the ingredients in the foods we eat, and the way our bodies metabolize glucose and produce insulin, dietary choices can be highly effective in managing type 2 diabetes. But, they also warn that, "a person's age, activity level, body composition, hormone levels, genetics, gut microbiota, and lifestyle factors all play a huge role in how a person reacts to different foods and dietary patterns. Therefore, not all people will benefit the same from the same dietary intervention."
They also recommend moving away from population-based nutritional research to more personalized approaches. With 30 million Americans currently diagnosed with type 2 diabetes, and tens of millions more at risk for developing the disease, this personalized approach may be quite challenging. Because diabetes is the seventh leading cause of death in the United States, research into the influence of dairy on diabetes is a worthwhile challenge to accept.
-- "Emerging Evidence for the Importance of Dietary Protein Source on Glucoregulatory Markers and Type 2 Diabetes: Different Effects of Dairy, Meat, Fish, Egg, and Plant Protein Foods," by Kevin B. Comerford and Gonca Pasin, was published in Nutrients 2016, 8(8), 446; doi:10.3390/nu8080446
The CDRF is an independent non-profit organization that leads and delivers research and science-based programs towards a more innovative and sustainable California and U.S. dairy industry. For more information about the CDRF and the research it supports, visit www.cdrf.org