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The news media has highlighted a fascinating study published in the Annals of Internal Medicine that compared  Low-Carb with Low-Fat Diets. It is terrific  that they measured weight loss and cardiovascular risk factors. Of course, the media only got the message half right.

Before you hear the results, you need to understand what the people in the study actually did, something the media failed to understand.

The investigators randomized 148 obese men and women to follow two diets:

Diet #1: Less carb, higher fat, higher protein 

These subjects increased fat intake from 34% of calories to 40% of calories and increased their protein from 17% of calories to 24% of calories. They were supposed to increase their fiber, but didn’t (their fiber intake stayed the same). The biggest increase in fat was from nuts and olive oil (monounsaturated fat), and they were asked to eliminate hydrogenated fat. They were also given shakes to help them follow the plan.

Diet #2: Less fat, higher carbs, same protein

These subjects decreased their fat intake from 34% to 28-30% (not really low fat enough to be a low-low fat diet), and increased their carb intake from 46% to 54% of calories. They didn’t increase their fiber (they were asked to, but it stayed the same) instead, they added more starch (potatoes, white bread, white rice and pasta).

Both groups were asked to not change their activity and they were given meal plans to reduce their calorie intake and lose weight.

The low-carb, higher fat, higher protein group dropped form eating 2000 calories per day to only 1200-1400 calories per day for 12 months. They lost 12 pounds in the first 3 months, and then their weight stayed the same for the rest of the year. Their cholesterol profile improved nicely.

The higher refined carb, lower fat, same protein group dropped form eating 2000 calories per day to only 1400-1500 calories per day for 12 months. They lost 5 pounds in the first 3 months, and then gained half that weight back over the rest of the year, and their cholesterol profile worsened.

What did this study really show?

Bazzano et al, Effects of Low-Carb and Low-Fat Diets, Ann Int Med;161:309-318.

When you look at the real results, you can see that eating more “healthy” fat, more protein, and less refined carbs (less potatoes, rice, bread, and pasta) helped people lose weight and improve their cholesterol profile. They were also given a shake a day to help change their eating habits.

Asking people to eat less fat and more refined carbs (sugar and starch) without fiber isn’t very effective for weight loss and increases your risk for heart problems.

The bottom line from this study is that you should eat more “healthy” fat and protein, and less refined carbs.

I suspect the reason the subjects in the higher refined carb diet gained their weight back despite following the low calorie intake, is that without extra protein, their metabolic rate (calorie burn rate) decreased. Adding more protein to the low-carb, higher fat plan boosts calorie burn and was a smart idea!

Notice that the people in this study were obese, yet they only lost 12 pounds. They likely would have lost twice as much weight if they had added more FIBER (fiber makes you full and satisfied and improves your cholesterol profile), but the fiber must come from eating more vegetables, beans, nuts, and fruits–not from eating more flour!

If they had added more activity, they would have kept losing weight after 12 months and their cholesterol profile would have looked even better. So unlike the results in this study,  the ideal plan would have been more “healthy” fat and protein, less refined carbs, more fiber, and more activity.

I wish you the best of health!

Steven Masley, MD, FAHA, FACN, FAAFP, CNS


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