USA Today, 2012

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 Hospital.

“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,” he says.
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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The Los Angeles Times, 2010

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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The New England Journal of Medicine, 2003

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.

Randomized Trial of a Low-Carbohydrate Diet for Obesity

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 (conventional) diet.

The Journal of Clinical Endocrinology and Metabolism, 2005

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.

The Journal of Clinical Endocrinology and Metabolism, 2003

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.

Obesity Research, 2003

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 a day.

  • 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.

The American Journal of Medicine, 2002

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.