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Same calories, more protein
The Studies
The studies ran in the early 2000s at the University of Illinois, where Gabrielle Lyon worked on them as a student. Calories were controlled in both groups. One group followed the food guide pyramid, which is 0.8 grams of protein per kilogram of body weight, roughly 60 to 70 grams a day for a woman. The other group ate 1.6 grams per kilogram, at least 100 grams a day, with breakfast around 30 to 50 grams.
The Results
With no change in overall calories, only a shift in macronutrients that put protein near 30 percent of intake, the higher-protein group improved body composition. Their fasting insulin dropped, their blood glucose improved, and their triglycerides improved.
The Threshold
Below 100 grams of protein, the effect on insulin, glucose, and triglycerides seemed to disappear. The current recommendation of 1.2 to 1.6 grams per kilogram sits much closer to the second group's intake than to the pyramid's.
Why does extra protein change insulin and triglycerides?
Protein carries a high thermic effect: the body spends roughly 20 to 30 percent of its calories digesting it, against 5 to 10 percent for carbohydrate and under 3 percent for fat, according to reviews of the thermic effect of food. Protein also triggers satiety hormones, which tend to lower appetite. Shifting calories from carbohydrate to protein reduces the glucose load of each meal, which lowers the insulin response.
Where does the 0.8 grams per kilogram figure come from?
The figure comes from nitrogen balance studies, which track how much nitrogen from protein goes in versus how much leaves in urine. The US Institute of Medicine set the RDA in its macronutrient report of 2002 at the intake that meets the needs of nearly all healthy adults. The average requirement in those studies was closer to 0.66 grams per kilogram.
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