Wednesday, March 4, 2009

Which diet is best?

Diet composition does matter after all ?

According to a new study, diets with reduced carbs and higher protein are more effective.

The low carb blogs have been alight in the last few days with deconstructions of a recent study from the New England Journal of Medicine. It purports to show that:

Reduced-calorie diets result in clinically meaningful weight loss regardless of which macronutrients they emphasize.
So it doesn't matter what your diet is as long as you cut calories. The composition of the diet - protein%, carb%, fat% doesn't matter....

Well the study was picked up by the media - but has been well and truly demolished by some very capable doctors and bloggers. e.g. Dr Briffa, Dr Eades and Eugene. At the most basic level it is worth noting that the low carb diet was not low carb. As Dr Briffa says:

Because the diets were so similar in composition, it seems inappropriate to use it to vindicate the ‘calorie is a calorie’ concept.

And what this study certainly can’t be used for (though some have tried) is to suggest that low-carb diets have no particular merit.

One reason for this is that diet 4 - the ‘low-carb’ diet – was most certainly not low in carb. Individuals in this group were getting about 43 per cent of their calories from carb. Let’s for argument sake say a low-carb diet contains no more than 40 g of carb a day (the induction phase of the Atkins diet allows just half this amount). This 40 g equates to about 10 per cent of calorie intake. That’s less than a quarter of the percentage of calories contributed by carb in diet 4.

Also, those eating diet 4 were consuming, on average, 152 grams of carbohydrate a day (almost four times as much as someone eating a true low-carb diet containing 40 g of carb a day).

While the authors of this study mention low-carb diets several times, it seems they were not necessarily keen to test the effectiveness of such a diet. If they had been, then they would have done well to include a diet that was actually low in carb.

However there is a new study that says that diet composition does matter.

Here is the abstract: A Moderate-Protein Diet Produces Sustained Weight Loss and Long-Term Changes in Body Composition and Blood Lipids in Obese Adults

There is a commentary here too with some interesting points:

"The additional protein helped dieters preserve muscle. That's important for long-term weight loss because muscle burns calories—if you lose muscle, and you used to be able to consume 2,000 calories without gaining weight, you'll find that now you can only eat, say, 1,800 calories without weight gain," he said.

This is the first study to show that short-term changes in LDL cholesterol are not maintained with long-term weight loss. Most scientists believe that high cholesterol is more a factor of genetics than of diet," he said.

But the moderate-protein diet had by far the bigger effect on lowering triglycerides, and that lasted as long as individuals remained on the diet, he said.

"Of the two types of lipid problems, high triglycerides pose a greater risk for heart disease. Approximately twice as many people have high triglycerides, and people with this condition are approximately four times more likely to die from heart disease," the scientist said.

The protein diet was easier to follow and maintain long-term, with 64 percent of the moderate-protein dieters completing the study compared to 45 percent of dieters using the high-carbohydrate diet, Layman said.

"Subjects on the moderate-protein diet reported that they weren't as interested in snacks or desserts, and they didn't have food cravings. When you eat protein, you feel full longer," he said.

(Just to be fair before someone points this out....the study was funded by the National Cattlemen's Beef Association, The Beef Checkoff, and Kraft Foods.)

No comments: