Two recent studies compared the effects of both diets on groups of obese women. The first one looked at the effects of high-protein and high-carb diets on blood glucose and insulin levels during dieting conditions.1
Twenty-four adult women, all of whom were at least 15 percent above ideal bodyweight, were divided into two groups: a high-protein group that ate 1.6 grams of protein per kilogram of bodyweight, with 40 percent of total calories derived from carbs; and a high-carb group that ate half as much protein (0.8 grams of protein per kilogram of bodyweight), with 55 percent of calories coming from carbs. Both diets contained the same number of total calories and fat (50 grams per day), and the study lasted 10 weeks.
While the high-protein group lost slightly more weight than the carb group, the real advantage emerged when the groups ate test meals at the end of the study. Those in the carb group had lower blood glucose levels and an elevated insulin response to meals. Lower blood glucose levels set the stage for increased hunger, which generally leads people to have trouble following a diet consistently and to indulge in high-calorie binges that defeat the purpose of dieting.
The authors explain that a higher-protein intake promotes a more stable blood glucose level through the actions of the amino acids in the protein. With more amino acids available, the body produces glucose precursors that it uses to maintain stable blood glucose levels while avoiding the excess insulin output that occurs with increased carb intake. As blood glucose levels decline, appetite increases, making dieting more onerous.
The second study compared high-protein and higher-carb intakes and their effects on body composition and blood lipids.2 Like the first study, this one featured overweight female subjects who followed either a high-protein or high-carb diet for 10 weeks. Once again, both diets contained the same number of total daily calories and fat, differing only in their protein and carb contents.
Those in the high-protein group showed body-composition changes, pointing to retention of lean mass coupled with loss of fat that was greater than what the high-carb group experienced. Both groups showed a 10 percent average drop in blood cholesterol, but only the high-protein group showed a 21 percent drop in blood triglyceride (fat) levels and a superior ratio of triglycerides to high-density lipoprotein, a pattern that favors cardiovascular health. The women in the high-carb group had higher insulin responses to meals, with a tendency toward decreased blood glucose (hypoglycemia) following meals. Those in the high-protein group reported greater satiety after meals, likely due to better insulin responses.
The researchers note that a higher-protein intake maintains thyroid hormone levels while reducing insulin responses to meals, a pattern that would favor more bodyfat losses. The higher protein intake also blunts or prevents the loss of muscle that otherwise would accompany a reduced-calorie diet. The branched-chain amino acids isoleucine, leucine and valine are particularly potent in the anticatabolic effect, as are other aminos, including glutamine.
Another interesting aspect of this study is the lack of adverse cardiovascular effects in the higher-protein group. If anything, the changes conferred cardiovascular protection. That’s notable in light of the frequent admonitions about cardiovascular “dangers” linked to higher-protein diets.
The same held true for that old bugaboo about high protein and kidney disease. The theory behind this idea is that waste products of protein metabolism, such as urea, impose increased stress on kidneys, eventually leading to renal failure. The notion was originally derived from observations of patients with existing kidney disease—hardly applicable to healthy people.
In this study the subjects showed rapid adaptation to the higher-protein intake, with urea values similar in both groups. That suggests the body can easily upregulate renal function to deal with the additional metabolic waste products. Although not discussed in the study, the best way to protect your kidneys during a high-protein diet is simply to drink enough water to help flush out nitrogen waste products efficiently.
References
1 Layman, D.K., et al. (2003). Increased dietary protein modifies glucose and insulin homeostasis in adult women during weight loss. J Nutr. 133:405-410.
2 Layman, D.K., et al. (2003). A reduced ratio of dietary carbohydrate to protein improves body composition and blood lipid profiles during weight loss in women. J Nutr. 133:411-417.
©,2013 Jerry Brainum. Any reprinting in any type of media, including electronic and foreign is expressly prohibited.
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