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Researchers nix low-carb diet

December 14, 2007

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. ASU 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 affected by the severely low-carbohydrate intake.

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 into what’s called ketosis, or the inefficiency of the body to oxidize fat,” says 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, such as 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,” Johnston says. “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 significantly affected.

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

They also note 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 for those individuals who are taking in an extremely low amount of carbohydrates and only receiving energy from protein, intense exercise is harming their bodies more than it’s helping. 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,” says 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 a person’s body is not getting the nutrients it needs to function, that person’s 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,” Swan says.

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

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