Protein and Metabolic Rate

Protein intake may positively affect body composition. Since all food requires metabolic processing, all macronutrients increase metabolism. However, the metabolic increases seen when eating protein are double those seen when eating carbohydrates or fat. Therefore a high protein intake may in fact be thermogenic and may lead to increased calorie burning and fat loss.

During dieting, this may enhance calorie expenditure and therefore the rate of fat loss [Blacklevin et al. 1975, Ballor and Poehllman 1994, Skov et al. 1999, Alford et al. 1990]. As I said above, more protein is needed on a low calorie diet anyway; especially when working out. During overeating in an attempt to gain muscle, although higher protein intake may not be needed for positive nitrogen status, it's likely better to eat excess protein rather than carbohydrates or fats. Since overeating leads to both some muscle and some fat gain, eating more calories as protein may lead to more lean weight and smaller gains in fat weight.

Did you know that eating protein might increase your metabolic rate and nutrient balance? By virtue of this phenomenon, a higher protein diet may contribute to body fat losses. Since protein foods require more "metabolic processing" than carbohydrates and fat it only stands to reason that the metabolic increases seen when eating protein would be higher than those seen when eating fat or carbohydrate. In fact, several research investigations have shown just that. The metabolic increase seen with eating protein is just about double that of eating carbohydrates or fats [Welle et al. 1981, Robinson et al. 1990, Nair et al. 1983].

Protein and Hormones

In addition to the calorie burning effects of protein, higher protein intakes can increase the release of the hormone glucagon from the pancreas [Guntiak et al. 1986, Linn et al. 2000)]. The hormone insulin prevents fat loss from adipose (fat) tissue, but glucagon is responsible for reversing this effect [Yamauchi et al. 1988]. Glucagon also does a nice job of decreasing the enzymes responsible for making fats and building up the fat stores in the liver and in the fat cells [Girard et al. 1994].

So again, higher protein intakes may lead to losses in body fat due to the thermogenic effects as well as the hormonal effects of eating protein. During dieting, this may lead to a greater rate of fat loss [Blacklevin et al. 1975, Ballor and Poehllman 1994, Skov et al. 1999, Alford et al. 1990]. And, during overfeeding, it may lead to a smaller increase in fat mass relative to lean mass gains.

Additionally, in applicable human studies, protein and branched-chain amino acid supplements have been shown to increase the IGF-1 response to eating and to exercise [Kraemer et al. 1998, Thissen et al. 1994, and Carli et al. 1992]. Therefore both protein and calorie intake may be responsible for raising IGF-1 levels. Since IGF-1 can regulate the muscle growth [Adams 1998], I believe that a high protein intake may assist in muscular development.

Protein and Cardiovascular Disease Risk

Finally, increasing the percentage of protein in the diet while decreasing the percentage of carbohydrates and fats may have some real health advantages. Increasing protein intake from 11% to 23% can lead to very favorable changes in blood lipids and cardiovascular disease risk.

So, there may be some real health and body composition benefits to higher (even "excessive") protein intakes. More research on these topics is needed but until this research is done, the reports of hundreds of athletes, bodybuilders, and weightlifters have confirmed my speculation.

We have data showing that increasing protein intake from about 10 to 20% while decreasing carbohydrate intake from 55 to 45% (with fats kept constant at 35%) can lead to favorable changes in blood lipids. However, with athletes, increasing protein to levels higher than 20% might not offer much more benefit in terms of blood lipids and may actually decrease performance since either carbohydrate and/or fat would have to be reduced in order to do so. For the majority of athletes, since carbohydrates and fats are essential for athletic performance, I would not recommend decreasing either in favor of more protein [Len Piche, Ph.D, RD. Nutrition Program, Brescha College, University of Western Ontario, Ontario, CA].

Safety of A High-Protein Diet

In the previous section I suggested that not only a high protein intake, but also an excess protein intake might have some benefit to those interested in changing body composition and decreasing cardiovascular disease risks. Again, an important distinction has to be made. High protein diets aren't necessarily in excess. In fact, according to the data discussed earlier, high protein diets in athletes are just enough to get these individuals to nitrogen balance. So this isn't an excess of protein at all!

Replacing Carbs with Protein

Why are nutritionists recommending high carbohydrate diets when research has demonstrated that replacing some dietary carbohydrates with protein can lead to favorable blood lipid profiles?

Dr B.M. Wolfe, a nutrition researcher at the University of Western Ontario, has been asking himself this very question for several years. In three separate studies, Dr Wolfe has shown that when increasing protein intake from about 11% of the diet to about 23% of the diet, blood markers associated with heart disease took a turn for the better [Wolfe and Piche, 1999, Wolfe, 1995, Wolfe and Giovannetti, 1991]. This benefit occurs in both healthy and high-risk people.

As the protein intake increased, Dr Wolfe made sure that the fat content of the diet stayed the same (25-35% fat) while the carbohydrate content was reduced (from about 63% to about 48%).

The exact magnitude of the changes was pretty large as in one particular study, the bad fats like LDL cholesterol decreased by between 6% and 9%, while the good fats like HDL cholesterol increased by between 12% and 17% [Wolfe, 1995]. In addition, in this study, the ratio of plasma total cholesterol to HDL cholesterol (the lower the ratio the better) decreased by between 15% and 16%. Finally, in this study, the total triglyceride levels decreased by between 18% and 23%.

Another interesting effect of the protein increase in these studies was that the satiety levels of subjects tended to be higher with the high protein diet. Therefore they felt fuller at the same calorie intake. Protein is well known to have this effect on appetite.

Protein and Kidney Strain

The kidneys ultimately process chemicals derived from protein breakdown. Because of this, some have theorized that extra protein break down could cause strain and therefore damage to the kidney. From the research, though, there is no data (in healthy rats or in healthy humans) that support such theories.

In fact a new study directly contradicts this theory. In this study protein intakes up to 1.27g/lb. (or 2.8g/kg) did not cause kidney damage. Some rat studies have revealed that when rats were given an 80% protein diet for long periods of time, none of the rats showed any signs of kidney damage [Zaragoza et al. 1987].

Protein and Osteoporosis

Past research has revealed that high protein intake was associated with increased calcium loss in the urine. From this researchers thought that this could lead to osteoporosis. Recently, though, such concerns have been dismissed. Recent studies have shown that higher protein intakes usually lead to a higher bone mineral content instead [Cooper et al. 1996, Freudenheim et al. 1986]. Since exercise is known to increase bone mass, a high protein diet coupled with exercise training leads to a net increase in bone mass despite any potential losses in calcium.

The Purported Hazards of Eating Lots of Protein

So what is the truth? Are high protein diets dangerous? Look and see what the research has to say.

Impaired Kidney Function?

Although studies have been published showing that in individuals with unhealthy kidneys, an excessive protein intake could place undue strain on their kidneys, healthy individuals have little to worry about with high protein diets. To demonstrate this, a recent study revealed that when bodybuilders consumed up to 1.3 grams of protein/lb. (2.8g/kg) of body weight kidney function was not impaired [Poortmans and Dellalieux 2000]. In fact, in an older study conducted with female rats, kidney function seemed to be improved with high protein diets [Sterck et al. 1992].

Calcium Loss?

A few original studies demonstrated that when protein intake was raised to 140-225g per day, excess calcium was lost from the urine at a faster rate than normal [Hegsted et al. 1991]. However, in these studies, calcium intake as well as phosphorus intake was restricted and not allowed to increase in proportion to the protein intake. Since whole-food proteins contain both calcium and phosphorous and even protein supplements are fortified with calcium and phosphorous, it only makes sense that increases in protein intake are typically accompanied by increased dietary calcium and phosphorous. In this scenario, the research has demonstrated that when taking in additional protein, there is actually a positive calcium balance and there are no adverse affects on bone calcium content [Hegsted et al. 1991, Zigler and Filer, Jr. 1996, National Academy of Sciences National Research Council 1989].

If protein supplements are used, they should be fortified with calcium and phosphorous.

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