Why you should reconsider intermittent fasting if you plan on having babies

Women in their 40s, who are perimenopausal, were not included in the study.

In Summary
  • While intermittent fasting is an effective way to lose weight, experts are worried that the practice may have a negative impact
  • •They found that there was a drop in DHEA, which has also been postulated to improve egg and embryo quality, pregnancy rates and time to conception and reduce miscarriage rates.

What is intermittent fasting?

‘How to lose weight fast?’ ‘Get rid of belly fat,’ Do this to lose weight overnight’ we have all come across these topics on social media platforms.

But there is one common method that scientists are beginning to shed more light on, intermittent fasting.

While intermittent fasting is an effective way to lose weight, experts are worried that the practice may harm women's reproductive hormones.

Researchers from the University of Illinois Chicago have published a study on Obesity, that brings new evidence to the table.

Intermittent fasting prescribes a time-restricted feeding window of four hours per day, during which those on the diet can eat without counting calories before resuming the water fast until the next day.

The lead author and nutrition Prof Krista Varady followed a group of pre- and post-menopausal obese women for eight weeks on the "warrior diet" method of intermittent fasting.

After observing them, they measured the differences in hormone levels, obtained by analysing blood sample data, in groups of dieters who stuck to four- and six-hour feeding windows against a control group that followed no diet restrictions.

Varady and her team found that levels of sex-binding globulin hormone, a protein that carries reproductive hormones throughout the body, were unchanged in the dieters after eight weeks.

The same holds for both testosterone and androstenedione, a steroid hormone that the body uses to produce both testosterone and estrogen.

However, they found that dehydroepiandrosterone or DHEA, a hormone that fertility clinics prescribe to improve ovarian function and egg quality, was significantly lower in both pre-menopausal and post-menopausal women at the end of the trial, of those who observed the warrior diet.


“This suggests that in pre-menopausal women, the minor drop in DHEA levels has to be weighed against the proven fertility benefits of lower body mass,” Varady said.

“The drop in DHEA levels in post-menopausal women could be concerning because menopause already causes a dramatic drop in estrogen, and DHEA is a primary component of estrogen. However, a survey of the participants reported no negative side effects associated with low estrogen post-menopause, such as sexual dysfunction or skin changes.”

In the study, they also measured levels of estradiol, estrone and progesterone.

These are the hormones vital to pregnancy and found that among post-menopausal women, there was no change in these hormones at the end of eight weeks.

Women in their 40s, who are perimenopausal, were not included in the study.

Good news?

Women in both the four-hour and six-hour dieting groups experienced weight loss of 3 per cent to 4 per cent of their baseline weight throughout the course of the study, compared with the control group, which had almost no weight loss.

“I think this is a great first step. We have observed thousands of pre-and post-menopausal women through different alternate-day fasting and time-restricted eating strategies,” Varady said.

“All it's doing is making people eat less. By shortening that eating window, with this, you just naturally cut calories.”

Much of the negative information on intermittent fasting reported has come from studies on mice or rats.

More research is needed to look at the effects of intermittent fasting on humans.

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