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02.08.2012

Low-carb diet makes it easier to maintain weight loss

Once you've lost weight, it's easier to maintain your weight loss if you switch to a diet with a bit more protein and a lot fewer carbohydrates. Researchers at Children's Hospital Boston published their findings in the prestigious medical journal JAMA. Does it sound a bit too extreme? A diet consisting of slow-burning carbohydrates also works.

Long-term weight-loss
It's difficult to lose weight, but maintaining your weight loss is even more difficult. Perhaps because attempts to lose weight change the body's metabolism and reduce its energy expenditure.

Study
The researchers wanted to test this theory on 21 obese young adults in their 20s and 30s whose average BMI was 34.4. The subjects first lost 12.5 percent of their body weight by following a diet that was moderately rich in protein. The composition is shown below.

Then the real experiment began. The researchers had the subjects maintain their weight loss for 3 periods of 4 weeks each. In the first period, the subjects followed a diet that had very little fat [Low Fat] and an accent on full-grain products.

In the second period, the subjects followed a diet of slow-burning carbohydrates [Low Glycemic Index] in which a number of the grain products were replaced by beans or fruit with little starch.

In the third period, the subjects followed a diet with a bit more protein and a very few carbohydrates [Very Low Carb], a diet inspired by the Atkins diet.

Results
As you can see below, a diet with slow-burning carbohydrates didn't reduce energy expenditure as much as the diet with little fat did. But the best results were from the low-carb diet. Physical activity didn't play a significant role in this study.

The researchers found an increased concentration of the stress hormone cortisol in the subjects' urine when they followed the protein-rich diet. That came as no surprise. When obese people eat protein-rich food, the activity of the enzyme 11-beta-HSD1 increases and the activity of the enzymes 5-alpha and 5-beta reductase decreases. [J Clin Endocrinol Metab. 2007 Nov;92(11):4480-4.] The first enzyme raises the concentration of cortisol in the body, and the other two lower it.

Conclusion
This is why the researchers feel that people who have lost weight should switch to a diet rich in slow-burning carbohydrates. Although a very low-carb diet is the best method for maintaining weight loss, the researchers are concerned that the increased concentration of cortisol could be a health risk.

If you check the researchers' references on this, you might question their caution. They base their concern on a Dutch study in which the expectation of mortality among people 65 and older is higher when there is more cortisol in their urine. [J Clin Endocrinol Metab. 2010 Nov;95(11):4959-64.]

The figure below, which comes from that study, shows the relation between the expectation of mortality, cardiovascular disease [CVD] and the amount of of cortisol in the urine. The quantity of cortisol at which the expectation of mortality rises is much higher than is the amount of cortisol in the subjects of the JAMA study. [Table]

Source:
JAMA. 2012 Jun 27;307(24):2627-34.

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