A major benefit of losing excess weight is that it lowers high blood sugar levels to reduce your chances of becoming diabetic and suffering a heart attack. However, high-protein diets such as Atkins, Dukan or Paleo do not lower blood sugar levels as much as normal-protein diets do and therefore do not prevent diabetes as effectively as diets that are not high in protein (Evid Based Med, 2013;18(4):e37).

For the first time a major article explains why high-protein weight-loss diets are far less likely to prevent diabetes (Cell Reports, October 11, 2016):
• weight lost while eating moderate amounts of protein makes your cells more sensitive to insulin and therefore insulin becomes more effective in lowering high blood sugar levels, while
• weight lost on a high-protein diet does not improve insulin sensitivity.

In this study, 34 obese, non-diabetic women, 50 to 65 years old, were assigned to three groups:
1) A weight-loss diet with a moderate daily protein intake of 0.8 grams/kg body weight
2) A high-protein weight-loss diet with 50 percent extra protein
3) A control group that was told not to change their existing diet.

After 28 weeks, both weight-loss groups had lost about 10 percent of their body weight. The women on the high-protein diet had no improvement in their sensitivity to insulin, while the moderate-protein group had a 25-30 percent improvement in their sensitivity. This much improvement markedly reduces risks for diabetes, heart attacks and kidney damage. The results were surprising because getting rid of fat almost always improves insulin sensitivity, but the high-protein diet did not improve insulin sensitivity even a little bit.

The high-protein diet also did not help the women retain significantly more muscle than those in the moderate-protein group. When a person loses weight, two-thirds of weight loss is usually fat and one third is lean tissue including muscle. The high-protein dieters retained less than a pound more muscle than the moderate-protein dieters.

Insulin Insensitivity
Most cases of diabetes in North America are caused by insulin insensitivity, in which cells are not able to respond to insulin, so the pancreas keeps on putting out insulin and blood insulin levels rise to very high levels. When you lose excess weight, you are expected to improve your sensitivity to insulin, so insulin levels and blood sugar levels go down. However, when you eat a lot of protein-rich foods, your insulin levels go up just as they do when you eat sugar-rich foods, even if you are reducing your total intake of calories and thus are losing weight.

Insulin, Protein and Fatty Liver
Another study showed that eating a lot of meat is associated with higher fasting blood sugar and insulin levels (Am J Clin Nutr, Nov 2015;102(5):1266-78). Most people do not know that insulin is supposed to do more than just lower high blood sugar levels. Insulin drives certain amino acids from protein into cells just as it drives sugar into cells (Diabetes Res Clin Pract, August 2011;93(Suppl 1):S52-9), so your pancreas releases insulin to lower high blood protein levels as well as to lower high blood sugar levels. Excess insulin drives the extra protein building blocks into your liver where they are converted to fat to fill the liver with fat. A fatty liver cannot accept much sugar from your bloodstream, so blood sugar levels remain high to damage all the cells in your body and increase your risk for diabetes. This helps to explain why eating a lot of protein can raise blood sugar and insulin levels.

When you lose weight, you get some of the accumulated fat out of your liver, so your liver can then pull sugar out of the bloodstream more effectively. The high-protein diet reduces the amount of fat removed from the liver to block the effects of insulin.

High Protein Diets and Athletes
High protein diets are associated with increased risk for heart attacks (BMJ. June 26, 2012;344:e4026). Elite body builders and competitive athletes in sports requiring great strength are at a markedly increased risk for dying from heart attacks and diabetes (J of Urology, April 2016;195(Supplement):e633). I believe that the extra protein these athletes tend to eat may explain this risk.
• Eating lots of high protein foods does not help athletes to grow muscles larger than when they take in moderate amounts of protein (Journal of Sports Sciences, 2004;22(1)), even though athletes will absorb more protein on the high-protein diet (Journal of Applied Physiology, Aug 1992;73 (2): 767–75). Taking in less protein than you need (approximately 0.7g/kg/day) will cause loss of muscle size (Journal of the American Medical Association, Jan 2012;307(1):47–55).
• Eating lots of protein does not help non-athletes grow larger muscles, despite the claims made for various protein supplements and high-protein diets.

My Recommendations
• I do not recommend high-protein diets, either for weight loss or for building muscle in athletes. High-protein diets will not make your cells more sensitive to insulin, so they are less likely than normal-protein diets to help prevent diabetes.
• If you are trying to lose weight, I believe that you should eat plenty of carbohydrates as nature made them, in fruits, vegetables, whole (unground) grains, beans, nuts and other seeds. Restrict refined carbohydrates: sugar-added foods, sugared drinks including fruit juices, and foods made from ground-up grains (flour) — bakery products, pasta and most dry breakfast cereals. Limit animal products to keep your total protein intake to a moderate amount.
• If you are an athlete and are trying to build muscle, eat a moderate amount of protein shortly after you finish a hard workout. Timing of meals may be more important than the amount of protein you take in.
• Whether you are trying to lose weight or just to maintain your existing healthful weight, I recommend intermittent fasting.

Checked 7/27/23