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17.01.2011

More than half a kg weight loss per week lowers testosterone levels

If athletic women want to lose weight they are probably better off confining the weight loss to a pound a week. Finnish sports scientists at the University of Jyvaskyla discovered that testosterone levels take a dive if weight loss is faster.

Study
The researchers did an experiment with 15 women with an average age of 28 years. The women had all been training for at least six months, using weights and doing aerobics. They were put on a diet for 4 weeks that included a daily 1.4 g protein per kg bodyweight.

Half of the women ate 1100 kcal less daily than the women burned. On a diet like this you'll lose 1 kg a week in theory. The other half of the women ate 550 kcal less daily than the women burned. This is a diet that in theory results in half a kilogram weight loss per week.

Results
And indeed. When the 4 weeks were up, the 1KG group had lost 3.9 kg, and the 0.5KG group had lost 2.2 kg. The effect on total bodyweight is shown below.

As a result of their training and protein-rich diet the women lost almost no lean body mass. The 1KG group lost 3.8 kg fat and the 0.5KG group lost 2.0 kg fat. The second figure below shows the effect of the diet on the fat mass.

The training results remained the same for both groups, except for one thing: because the women became lighter they were able to jump higher.

But the women in the 1KG group felt worse than the women in the 0.5KG group. They reported more often feeling sleepy and tired. Their testosterone levels went down dramatically.

The more weight the women lost per week, the more their testosterone levels plummeted.

Conclusion
The researchers write that women are better off losing weight slowly rather than too fast. You need to be alert in daily life, and hormonal changes like this probably have negative effects.

"A weight reduction of 0.5 kg per week with approxiamtely 1.4 g protein/kg/day can be recommended to normal weighted, physically active women instead of a larger weight reduction, because the latter may lead to a catabolic hormonal state", the Finns conclude.

Source:
J Int Soc Sports Nutr. 2010 Jan 25;7(1):4.

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