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Health Options
Our last column described potential problems related to high-carbohydrate (low-protein/low fat) weight loss diets. This column focuses on the possible adverse effects associated with high-protein (high-fat/low-carbohydrate) weight loss diets. High-protein
diet endangers
overall healthWithout a doubt, many individuals lose significant amounts of weight on high-protein diets. However, the initial quick weight loss with this type of diet consists primarily of water loss, glycogen loss, and possibly muscle loss. Glycogen, the body's form of carbohydrate storage, is surrounded by water molecules. When we eat normal amounts of carbohydrate, we have about a 24-hour reserve of glycogen in the body.
If our diet does not contain carbohydrates in the form of starches and sugars, glycogen is broken down to supply the brain and red blood cells with the glucose they require. When this happens, the water associated with glycogen is also lost, accounting for much of the initial three-to-five pound rapid weight loss often seen with high-protein diets.
High-protein diets usually do not contain adequate carbohydrate. When inadequate carbohydrate is consumed, the body must form glucose from some of the amino acids in protein. Even though the diet is high in protein, muscle protein can be broken down to provide some of these amino acids. Also, this process is only about 50 percent efficient and some amino acids from muscle protein can be converted to fat. So, although weight is lost, it is not primarily fat.
Despite the fact that blood cholesterol levels usually drop with weight loss on a diet high in protein and fat, there are still problems with the high fat intake. Keep in mind that blood cholesterol generally drops with virtually any type of weight loss.
The high levels of fat often observed with these diets can bind with calcium to form soap in the intestinal tract, greatly reducing the absorption of this mineral. To make matters worse, excess dietary protein causes increased loss of calcium in the urine. The long-term end result of too much fat and protein is the increased risk of developing osteoporosis.
In the 1950s Dr. Roy Swank showed that a single high-fat meal can cause red blood cells to aggregate or clump together, causing blood flow to slow. This allows more time for certain forms of circulating fat to contribute to the plaque that gradually clogs blood vessels. It also increases the risk of blood vessels clogging up for several hours after the high fat meal.
In 1997, research by Dr. Vogel, head of cardiology at University of Maryland, indicated that a single high-fat meal (greater than 50 grams of fat) caused blood vessels to narrow. For some unknown reason, blood vessels constricted to only 50 percent of normal size. This could put even healthy individuals at more potential risk of a heart attack or stroke after a high-fat meal. Vogel commented after this study that people need to keep the fat out of the diet each and every meal.
Dr. Baba showed in another study that even though total blood cholesterol decreased with weight loss of any type, the high density lipoprotein (the good cholesterol) decreased greater during high-protein weight loss diets than lower-protein diets.
There are also concerns that high-protein diets may add to the workload of the kidneys and aggravate kidney problems. Whether high protein intake can cause kidney problems remains questionable.
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Alan Titchenal, Ph.D., C.N.S., is a sports nutritionalist in the
Department of Food Service and Human Nutrition,
University of Hawaii-Manoa.Joannie Dobbs, Ph.D., C.N.S., is a food and nutrition consultant
and owner of Exploring New Concepts, a nutritional consulting firm.
She is also responsible for the nutritional analyses indicated
by an asterisks in this section.