Researchers Nix Low-carb Diet
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
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.
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
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.
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.
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)
these studies, their research uncovered that the ketogenic diet may
increase bone lossbecause 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.
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."
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.
a higher fat concentration with the KLC diet, the increase in the LDL
cholesterol is not really that surprising," Johnston says.
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.
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
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.
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.
For more information on Arizona State University, visit www.asu.edu.