A recent study in mice showed that increasing dietary protein from 15 percent to 46 percent of calories caused the mice to develop 30 percent more arterial plaques than mice on their normal-protein diet, even though they did not gain more weight (Nature Metabolism, Jan 23, 2020;2:110-125). Furthermore, the mice on the high-protein diet were at very high risk for heart attacks because the plaques were unstable. This study could explain why high-protein diets are associated with increased risk for heart attacks in humans.

Unstable plaques are likely to break off, while stable plaques are likely to adhere to the artery walls. Heart attacks are caused by plaques breaking off, followed by bleeding and clotting, and the clot extends to block the flow of blood to part of the heart muscle so that part of the heart muscle dies. Plaques in arteries contain dead cells that must be removed or the dead cells can accumulate to such high levels that they cause a plaque to break off and cause a heart attack. To prevent the dead cells in plaques from accumulating, your immune system produces certain cells called macrophages that eat the dead cells and remove them from plaques. However, a high protein diet can cause the macrophages to die and accumulate in the plaques to further weaken the plaque and increase its likelihood to break off to cause a heart attack. This research showed that a high-protein diet activated a protein in macrophages called mTOR, which stopped the macrophages from cleaning up and removing dead cells in plaques.

More High-Protein Diet Concerns
High-protein diets can:
• raise blood TMAO levels that increase heart attack risk (European Journal of Nutrition, July 5, 2019:1-14)
• damage healthy kidneys (Nephrology Dialysis Transplantation, Nov 27, 2019; June 7, 2019)
• increase risk for diabetes (Am J Clin Nutr, Nov 2015;102(5):1266-78; Nov 2004;80(5):1246-53)

High-Protein Diets Do Not Prevent Loss of Muscle When You Lose Weight
High-protein weight loss diets do not prevent loss of muscle size and strength significantly more than weight-loss diets with a normal protein content. For example, in one study, postmenopausal women who restricted calories to lose weight lost almost the same amount of muscle whether they ate an average-protein diet or a high-protein diet (Obesity, May 2018;26(5):854-861). Weight loss diets normally make your cells more sensitive to insulin, but if you try to lose weight with added dietary protein, you do not increase insulin sensitivity. Therefore high-protein weight loss diets may actually increase risk for diabetes and heart attacks (Cell Reports, October 11, 2016;17:849-861). Almost all other weight loss programs help to increase insulin sensitivity because they reduce fat, which helps both to prevent and to treat diabetes (Lancet, Feb 10, 2018;391(10120):541-551).

Eating a lot of high-protein foods does not help athletes grow larger muscles than when they take in moderate amounts of protein (Journal of Sports Sciences, 2004;22(1)). Athletes in power sports not only follow high protein diets, they also often eat large amounts of added protein powders. Two scoops of protein powder in a milkshake or a smoothie would contain about 40 grams of protein, which provides a large part of the recommended dietary allowance of protein for most people.

My Recommendations
If you are trying to lose excess weight, or to prevent or treat diabetes:
• Avoid all of the various popular diets that encourage you to load on high-protein foods such as meat, chicken, fish, eggs, or dairy products.
• Avoid or restrict refined carbohydrates: sugared drinks including fruit juices, sugar-added foods, and foods made from flour (ground up grains) such as bakery products, pastas, and most dry breakfast cereals.
• Eat lots of unprocessed or minimally processed carbohydrates in plants as nature made them: vegetables, fruits, whole (unground) grains, beans, nuts and other seeds.