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Low carb diets may stress body too much, studies find

December 06, 2007

MESA, Ariz. — For most of the past decade, there was much hubbub about the Atkins and Zone diets. Both focus on quick, effective ways to lose weight through high protein and low carbohydrate foods. Today, many still swear by them.

However, research on these diets has been limited if nonexistent, until now. Arizona State University scientists from the departments of Nutrition and Exercise and Wellness along with other colleagues have been studying the diets since 2005, and find many biomarkers being negatively impacted by the severely low carbohydrate intake.

The ASU researchers Carol Johnston and Pamela Swan, along with collaborators Sherrie Tjonn and Andrea White, both registered dieticians, and Barry Sears, of the Inflammation Research Foundation and creator of the Zone diet, have published three papers during the last two years, appearing in Osteoporosis International, The American Journal of Clinical Nutrition and most recently in the Journal of the American Dietetic Association.

The biggest difference in these types of diets is the amount of carbohydrate prescribed. The Atkins diet entails very low carbohydrate, less than 20 grams daily, whereas the Zone promotes a more moderate intake of carbohydrates, up to 180 grams daily.

“The downside of severely low carbohydrate intake is that dieters go in to what’s called ketosis or the inefficiency of the body to oxidize fat,” said Johnston, chair and professor in the Department of Nutrition, School of Applied Arts and Sciences.

The term used to describe diets that produce this biological effect is ketogenic; hence, Atkins is a ketogenic, low carbohydrate (KLC) diet and the Zone diet is considered a nonketogenic low carbohydrate (NLC) diet.

With these studies, their research uncovered that the ketogenic diet may increase bone loss because of an increase in acid in the body and not enough intake of alkalizing minerals like potassium to neutralize this effect. In addition, a higher percentage of calcium was found in the urine of those on the KLC diet, leading the researchers to believe that the bones are “leaching” calcium.

“The public should realize that these diets have differing effects on biomarkers,” said Johnston. “Diets that severely restrict carbohydrates, particularly potassium-rich fruits and vegetables, may have deleterious effects on bones.”

Another study by these researchers looked at the metabolic advantage of one diet over the other. They found that the reduction in fat loss and weight loss was about the same for both diets over a six-week trial. In addition, body mass index was significantly lower after six weeks in both diet groups. However, those following the KLC diet experienced a greater increase in LDL cholesterol than those following the NLC diet. HDL cholesterol did not seem to be impacted significantly.

“With a higher fat concentration with the KLC diet, the increase in the LDL cholesterol is not really that surprising,” said Johnston.

They also noted that dieters on the NLC diet versus the KLC diet experienced more energy. Their most recent article published in October explains that the body needs carbohydrates for energy so if you are taking in an extremely low amount of carbohydrates and only receiving energy from protein, intense exercise is actually harming your body more than helping it. Without adequate amounts of carbohydrate stores, or glycogen, muscles rapidly fatigue during sustained exercise.

“And because there is an overall lack of energy, the KLC diets actually may thwart attempts to combine diet modifications with increased physical activity,” said Swan, acting chair and associate professor in ASU’s Department of Exercise and Wellness, School of Applied Arts and Sciences.

The researchers note that when your body is not getting the nutrients it needs to function, your body goes into a state of stress which causes systematic inflammation.

“120 grams of carbohydrates is enough for an average person who does moderate exercise, but endurance athletes should eat more carbs, especially for long bouts of exercise like a marathon,” said Swan.

“The KLC diets restrict carbohydrates too much; at minimum, carbohydrate intake should be moderate,” recommends Johnston.

All the research was supported by a grant from the Inflammation Research Foundation.