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High-Pro Diet Danger?

Is a long-term high-protein diet hazardous to your health?

Bodybuilding diets change according to short-term goals. The changes manipulate various dietary constituents, including calories, fat and carbohydrates, and incorporate various food supplements. A diet designed to promote muscle increase differs from a diet focused on bodyfat loss. The one aspect that remains constant, however, is an emphasis on high protein.

Eating plenty of protein is considered essential for anyone who wants to add muscle. If you want to lose bodyfat, a high-protein diet offers several benefits. Protein suppresses the appetite better than fat or carbohydrate, which makes dieting easier. Dietary protein spares muscle tissue under decreased-calorie conditions. It also helps retain muscle when other nutrients, such as carbs, are drastically reduced.

Although extra protein makes sense from a physiological point of view, many scientists and mainstream nutrition authorities still warn athletes that a high-protein diet may lead to eventual health problems. The most immediate danger, they warn, is dehydration. That’s because the body needs more water to eliminate nitrogen waste products left over from protein metabolism. While dehydration is a possibility with high-protein diets, it rarely, if ever, occurs.

The long-term dangers of a higher protein intake, say critics, are increased burdens on liver and kidneys, the organs most involved in protein metabolism. But much of the data that relate a high-protein intake to liver or kidney problems stem from cases involving hospitalized patients who already have such problems. Besides, protein is never the initial culprit in causing them.

Animal-based studies have shown that a high-protein diet doesn’t lead to adverse effects on any organs or systems. In one study rodents were put on a diet that consisted of a whopping 85 percent of calories from protein. The rats handled that huge amount with no apparent problems, other than a minor enlargement of the liver. They didn’t succumb to any diseases related to protein intake.

A new study, again using rats as subjects, verifies the notion that high-protein diets are not only safe but also have other benefits.1 The study lasted six months, the equivalent of about 25 human years. The 48 rats in the study were divided into groups, with one group getting about 14 percent protein, and the other group getting 50 percent. Tests on the rats included body composition, liver, kidney, oxidative stress and calcium balance.

Among problems linked to a high-protein intake are insulin resistance, increased oxidative stress and impaired cortisol secretion. None of those problems occurred in the study. Instead, the rats on the high-protein diet went through a number of beneficial changes.

Foremost among them was a 58 percent reduction in white adipose tissue, or common bodyfat. After six months the rats in the high-protein group had bodyweights 18 percent lower than those in the normal-protein group. The high-protein rats also showed an average 13 percent reduction in calorie intake, a factor likely related to the appetite-suppressing effects of eating more protein. They also had lower blood insulin, triglyceride and leptin levels than the others.

Calcium balance wasn’t adversely affected. The decreased carb intake was linked to the lower insulin levels, which also foster decreased total bodyfat. Both groups of rats were given milk protein. That’s significant because one type of milk protein, casein, has been linked to elevated cholesterol levels in some animal studies. Despite getting three times more protein than those in the normal-protein group, the high-protein rats showed no increases in blood lipids. Those in the normal-protein group did show an increase in blood triglycerides, which was attributed to their higher carb intake.

Examination of the rats at the conclusion of the study found no liver or kidney abnormalities, other than a slight increase in enzyme activity related to amino acid metabolism. The rats on the high-protein diet drank more water, which likely offered some kidney protection by helping them eliminate any protein metabolic waste products more efficiently. Those in the normal-protein group showed a massive hepatic steatosis, or infiltration of fat in the liver. That didn’t occur in the higher-protein rats.

Thus, despite getting a diet containing three times more than the suggested level of protein, the rats in the high-protein group not only thrived but showed long-term health benefits as well. Those changes included a significant fat loss and greater insulin sensitivity. Although results in a rat study may not be completely applicable to humans, rats handle protein in a manner similar to humans.

Speaking of insulin sensitivity, another new study, also using rats as subjects, compared the effects of milk protein, as whey concentrate, to those of red meat.2 Once again, the rats in the study got either a moderate- or high-protein diet. At the end of six weeks all the rats getting higher-protein diets showed a 26 percent loss of fat throughout their bodies. Those in the whey group gained 4 percent less bodyweight and had 40 percent less plasma insulin than the ones in the red-meat group.

The fat loss was attributed to a 19 percent increased activity level, coupled with a 160 percent increased energy expenditure needed to process the higher-protein intake. The higher-protein group also showed a sparing of lean mass, primarily muscle, that doesn’t occur in diets high in carbs or fat. The beneficial effects on insulin levels and sensitivity didn’t occur in the rats on the red-meat high-protein diet. That led the authors to suspect that elements in whey foster those beneficial changes.


1 Lacroix, M., et al. (2004). A long-term high-protein diet markedly reduces adipose tissue without major side effects in Wistar male rats. Am J Physiol Regul Integr Comp Physiol. In press.
2 Belobrajdic, D.P., et al. (2004). A high whey-protein diet reduces bodyweight gain and alters insulin sensitivity relative to red meat in Wistar rats. J Nutr. 134:1454-1458.

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