Research Stories

by Christine Lambrakis

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 people still swear by them.

However, research on these diets has been limited if not 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. They have found that severely low carbohydrate intake may lead to bone loss, high cholesterol and low energy.

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 intake–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.

Their research also suggests 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," says Johnston. "Diets that severely restrict carbohydrates, particularly potassium-rich fruits and vegetables, may have deleterious effects on bones."

Another study looked at the metabolic advantage of one diet over the other. They found that fat loss and weight loss were 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, or "bad," cholesterol than those following the NLC diet. HDL (good) 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," says Johnston.

The researchers also noted that dieters on the NLC diet had more energy than those on the KLC diet. 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," 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 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," says Swan.

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

This research was supported by a grant from the Inflammation Research Foundation. For more information, contact Christine Lambrakis, Office of Public Affairs at the Polytechnic campus, 480.727.1173 or Lambrakis@asu.edu