A Body Blow to High-Protein Diets
They can lead to kidney stones and possibly bone loss, study finds
WEDNESDAY, Aug. 7, 2002 (HealthDayNews) -- The choice is yours: If you follow a high-protein, low-carbohydrate diet such as the Atkins Diet, you'll probably shed pounds.
However, you're also putting yourself at risk for excruciating kidney stones and possibly bone loss, new research has found.
"This is not a healthy way to lose weight," says Dr. Chia-Ying Wang, co-author of the study and an assistant professor of internal medicine at University of Texas Southwestern Medical Center in Dallas.
The study appears in the August issue of The American Journal of Kidney Diseases.
Wang and her colleagues put 10 healthy, not overweight, adults on the Atkins Diet, one of several popular weight-loss plans that prescribe a diet mainly of meats, dairy products and some vegetables but very little fruit, bread or other grains.
During the first two weeks of the study, the subjects ate their normal diet. During the second two weeks, they ate a highly restricted "induction" diet that followed the Atkins plan and included less than 20 grams of carbohydrates daily. That's about what you'd find in one slice of bread.
During the next four weeks, participants were allowed to eat slightly more carbohydrates (40 grams a day), the same amount called for in the Atkins Diet. Each person also took a multivitamin tablet daily.
The researchers measured the level of citrate in the urine. Urinary citrate inhibits kidney stones, rock-like accumulations of calcium and other minerals in the kidneys that can cause extreme pain and, in some cases, severe illness, Wang says.
They found levels of urinary citrate dropped by 25 percent during the first phase of the diet. The level of urinary citrate increased slightly when the carbohydrates were increased during the next four weeks.
At the same time, researchers found acid excretion in the blood rose by as much as 90 percent during the phase of the diet in which carbohydrates were most restricted. Acid load fell only slightly during the next phase of the diet, when slightly more carbohydrates were permitted.
The acid level rose for two reasons, Wang says. The first is that animal proteins have a high acidic content. The second has to do with the body's metabolism of fats.
Carbohydrates are a ready source of energy for the body. When you restrict those, the body turns to other sources of energy, including fat. When the body burns fat, ketone bodies are formed. An overload of ketone bodies can lead to a condition called ketoacidosis, when the blood is excessively acidic.
Chronic acid load in the blood suppresses osteoblasts, cells that help build bone, and stimulates osteoclasts, cells that break down bone. If bone is broken down faster than it's built up, bone strength decreases. To maintain bone strength, these processes have to be in balance.
And yet, the subjects did lose weight on the diet.
The average weight loss during the first two weeks of the diet was 6 to 7 pounds. After two weeks, they lost, on average, an additional 1 to 2 pounds a week.
"We are not questioning the value of the diet in producing weight loss," says Dr. Kashayer Sakhaee, co-author of the study and a professor of internal medicine at the medical center. "We are investigating a countermeasure so that subjects can benefit from weight loss without experiencing the side effects of increased risk of stones and bone loss."
The researchers did not measure the actual number of cases of kidney stones or the change in bone density.
Dawn Jackson, a spokeswoman for the American Dietetic Association, says plenty of previous research has linked diets high in animal proteins and sodium to kidney stones.
"Everybody is trying all sorts of fad diets," Jackson says. "At any time, you've got 45 percent of women and 25 percent of men trying to lose weight. This is a very vulnerable time for people. They are willing to try anything."
Jackson recommends a diet of moderation. If you're trying to lose weight, cut back a little on what you're eating and give it a little time to see the results.
"The bottom line is small changes you can make to the diet you're currently eating are best, and so is a diet that has a lot of variety, a lot of balance and moderation," she says.
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