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Low-Carb Diet War: High-Protein vs. High-Fat

Both Work for Weight Loss -- But How Healthy Is High-Fat?
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WebMD Health News

June 16, 2004 -- Low-carb dieters can go high-protein or high-fat. Either way, weight loss will happen, new research shows.

The report, from a group of Australian researchers, is being presented at the annual meeting of The Endocrine Society being held in New Orleans this week. But it hasn't settled the "which diet is best" dilemma yet. Some nutritionists are bristling, saying that a high-fat diet is never a good idea.

Pitting Fat Against Protein

At issue is a two-phase study involving 57 men and women -- all obese, all between ages 40 to 60. In addition, they had high levels of insulin in their blood -- a sign of prediabetes.

They were divided into two low-carb groups; each assigned the same number of calories:

  • The high-protein group ate 34% protein calories, 29% fat calories, 37% carbs.
  • The high-fat group ate 45% fat calories, 18% protein calories, 37% carbs.

All 57 volunteers completed the study's first 12 weeks; 19 of the dieters in each group continued their dietary regimen until a full year had passed. Their weight and various other health factors were tracked the entire time.

At week 16:

  • Dieters in both low-carb groups had lost about 10% of their weight.
  • All dieters' blood sugar and insulin levels improved, as would be expected with weight loss.
  • The high-protein group felt less hunger than the high-fat group did; the high-protein group also burned a few more calories after each meal.
  • Metabolism at rest decreased in both groups -- dieting without exercise commonly decreases metabolism.

At week 52:

  • Weight loss was the same in both groups -- 5% to 8% -- possibly caused by a decrease in calorie intake.
  • Blood pressure, blood sugar, insulin, and cholesterol levels were the same across both groups.

Statistically speaking, the weight loss differences were close enough to call it a draw, says researcher Natalie Luscombe, with the University of Adelaide. Also, dieters in both groups reported having difficulty following their diet program, she notes.

Forget High-Fat

But a high-fat diet is never a good idea, says Althea Zanecosky, MS, RD, a spokeswoman for the American Dietetic Association and professor of sports and nutrition at Drexel University in Philadelphia. She agreed to comment on the findings.

"Getting half your daily calories from fat is not conducive to good health in the long run, with the kind of lifestyle Americans lead," Zanecosky tells WebMD. "Even if you're getting the healthiest of fats -- the omega-3s and the monounsaturateds -- it's still not a good idea. There are lots of good, scientific data showing that high-fat diets are not good for the long term."

The diet's carb content is healthy, says Zanecosky. "But 45% of calories from fat is too high. Even though cholesterol levels and other factors weren't changed, this study doesn't make me comfortable recommending a high-fat diet."

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