A new study is raising questions about the age-old belief that a calorie is a calorie.
The research finds that dieters who were trying to maintain their
weight loss burned significantly more calories eating a low-carb diet
than they did eating a low-fat diet.
The study, funded by the National Institutes of Health, was designed
to see if changing the type of diet people consumed helped with weight
maintenance because dieters often regain lost weight.
So scientists had 21 obese participants, ages 18 to 40, lose 10% to
15% of their initial body weight (about 30 pounds). After their weight
had stabilized, each participant followed one of three different diets
for four weeks. Participants were fed food that was prepared for them by
diet experts. The dieters were admitted to the hospital four times for
medical and metabolic testing.
The diets had the same number of calories, but the fat, protein and carbohydrate content varied. Those diets:
- A low-fat diet which was about 20% of calories from fat and emphasized whole-grain products and fruits and vegetables.
- A low-carb diet, similar to the Atkins diet, with only 10% of
calories from carbohydrates. It emphasized fish, chicken, beef, eggs,
cheese, some vegetables and fruits while eliminating foods such as
breads, pasta, potatoes and starchy vegetables.
- A low-glycemic index diet, similar to a Mediterranean diet, made up
of vegetables, fruit, beans, healthy fats (olive oil, nuts) and mostly
healthy grains (old-fashioned oats, brown rice). These foods digest more
slowly, helping to keep blood sugar and hormones stable after the meal.
Findings, published in this week's Journal of the American Medical
Association: Participants burned about 300 calories more a day on a
low-carb diet than they did on a low-fat diet. “That's the amount you'd
burn off in an hour of moderate intensity physical activity without
lifting a finger,” says senior author David Ludwig, director of the New
Balance Foundation Obesity Prevention Center at Boston Children's
“Participants burned 150 calories more on the low-glycemic index diet
than the low-fat diet. That's about an hour of light physical activity,”
The reason for the low-carb advantage is unclear, he says.
“We think the low-carb and low-glycemic index diets, by not causing
the surge and crash in blood sugar, don't trigger the starvation
response. When the body thinks it's starving, it turns down metabolism
to conserve energy,” he says.
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Most people can count calories. Many have a clue about where fat lurks
in their diets. However, fewer give carbohydrates much thought, or know
why they should.
But a growing number of top nutritional scientists blame excessive
carbohydrates — not fat — for America's ills. They say cutting
carbohydrates is the key to reversing obesity, heart disease, Type 2
diabetes and hypertension.
“Fat is not the problem,” says Dr. Walter Willett, chairman of the
department of nutrition at the Harvard School of Public Health. “If
Americans could eliminate sugary beverages, potatoes, white bread,
pasta, white rice and sugary snacks, we would wipe out almost all the
problems we have with weight and diabetes and other metabolic diseases.”
It's a confusing message. For years we've been fed the line that
eating fat would make us fat and lead to chronic illnesses. “Dietary fat
used to be public enemy No. 1,” says Dr. Edward Saltzman, associate
professor of nutrition and medicine at Tufts University. “Now a growing
and convincing body of science is pointing the finger at carbs,
especially those containing refined flour and sugar.”
Americans, on average, eat 250 to 300 grams of carbs a day,
accounting for about 55% of their caloric intake. The most conservative
recommendations say they should eat half that amount. Consumption of
carbohydrates has increased over the years with the help of a
30-year-old, government-mandated message to cut fat.
And the nation's levels of obesity, Type 2 diabetes and heart disease
have risen. “The country's big low-fat message backfired,” says Dr.
Frank Hu, professor of nutrition and epidemiology at the Harvard School
of Public Health. “The overemphasis on reducing fat caused the
consumption of carbohydrates and sugar in our diets to soar. That shift
may be linked to the biggest health problems in America today.”
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Study out of University of Pennsylvania School of Medicine,
University of Colorado Health Sciences Center and Washington University
School of Medicine randomly assigned participants to either a
low-carbohydrate, high-protein, high-fat diet or a low-calorie,
high-carbohydrate, low-fat diet.
- FINDINGS: The low-carbohydrate diet produced a greater weight loss
and was associated with a greater improvement in some risk factors for
coronary heart disease.
Foster, G. D., Wyatt, H. R., Hill, J. O., et al., “A Randomized Trial
of a Low-Carbohydrate Diet for Obesity,” The New England Journal of
Medicine, 348(21), 2003, pages 2082-2090. hydrate, high-protein,
high-fat diet or a low-calorie, high-carbohydrate, low-fat
Study out of the University of Cincinnati assigned obese, healthy
women to follow either a low carbohydrate or low fat diet for four
months. Both groups were given nutrition counseling and were instructed
to record energy expenditure using a pedometer.
- FINDINGS: The women on the low carbohydrate diet lost significantly
more weight, even though there was no difference in calorie intake or
energy expenditure. This supports the metabolic advantage phenomenon in
controlled carbohydrate nutrition.
Study out of the University of Cincinnati instructed obese women to
follow either a low fat, calorie restricted diet or a low carbohydrate
diet for six months.
- FINDINGS: The women lost significantly more weight and body fat on
the low carbohydrate diet than women instructed on the low fat diet at
three and six months. Additionally, blood pressure, triglycerides,
cholesterol, fasting blood sugar, and insulin improved.
Study out of Harvard University recruited twenty-one participants who
were randomly assigned to separate diets for 12 weeks: a low fat diet
and two different low carbohydrate diets, one allowing 300 more calories
- FINDINGS: Participants consuming the higher calories on the very low
carbohydrate diet were able to lose more weight compared to the lower
calorie, low fat diet. The low carbohydrate diet improved several risk
factors for heart disease.
Study out of Duke University Division of General Internal Medicine
determined the effect of a six month very low carbohydrate diet program
on body weight and other metabolic parameters.
- FINDINGS: Participants included overweight or obese healthy
participants, who lost up to 20 percent of their body weight on a very
low carbohydrate diet, unrestricted in calories. There were also
significant improvements in total cholesterol, LDL cholesterol, HDL
cholesterol, and triglycerides. The results suggest that a short-term,
low carbohydrate diet produces weight loss with improvements in the
blood lipid profile.