Can Intermittent Fasting Affect Female Hormones?

Intermittent fasting has been shown to be an effective way to lose weight, but critics worry the practice could have a negative impact on women’s reproductive hormones. A team of researchers from the University of Illinois Chicago has published a study on obesity that brings new evidence to the table.

Intermittent Fasting and the Effects on Hormone Levels

The researchers, led by Krista Varady, UIC Professor of Nutrition, followed a group of obese pre- and postmenopausal women on the “warrior diet” method of intermittent fasting over a period of eight weeks. The Warrior Diet mandates a four-hour time-limited food window per day during which participants can eat without counting calories before returning to a water-only fast until the next day. They measured the differences in hormone levels, evident by analysis of blood sample data, in groups of women who adhered to four- and six-hour meal times versus a control group who followed no dietary restrictions.

The researchers found that levels of sex hormone-binding globulin, a protein that carries reproductive hormones around the body, were unchanged after eight weeks in the women who fasted. The same was true for both testosterone and androstenedione, a steroid hormone that the body uses to produce both testosterone and estrogen. DHEA, a hormone that fertility clinics prescribe to improve ovarian function and egg quality, was significantly lower in both premenopausal and postmenopausal women at the end of the study, falling about 14 percent. While the decrease in DHEA levels was the most significant finding of the study, DHEA levels remained within the normal range in both pre- and postmenopausal women through the end of the eight-week period.

Weight Loss and Decrease in Insulin Resistance

The drop in DHEA levels in women after menopause could be of concern since menopause already causes a dramatic drop in estrogen and DHEA is a major component of estrogen. However, a survey of participants found no adverse side effects associated with low estrogen levels after menopause, such as sexual dysfunction or skin changes. Since high levels of DHEA have been linked to the risk of breast cancer, the researchers see an added benefit here, as modestly lowering levels may help to reduce this risk in both pre- and postmenopausal women. The study also measured levels of estradiol, estrone and progesterone — all hormones vital to pregnancy — but only in postmenopausal women, since levels of these hormones change during the menstrual cycle of premenopausal women. In postmenopausal women, there was no change in these hormones after eight weeks. In both the four- and six-hour fasting groups, the women experienced a weight loss of 3 to 4 percent of their baseline weight over the course of the study, compared to the control group, who had almost no weight loss. Fasters also saw a decrease in insulin resistance and oxidative stress biomarkers.

Intermittent Fasting has Positive Impact on Health

In a review article published in the New England Journal of Medicine, Mark Mattson, professor of neuroscience at Johns Hopkins University School of Medicine, concludes that intermittent fasting offers many health benefits and may be part of a healthy lifestyle. Intermittent fasting diets generally fall into two categories: daily time-restricted food intake, which limits meal times to 6-8 hours per day, and what is known as 5:2 intermittent fasting, in which people focus on a moderate diet with large meals only during two days a week.

A number of animal and some human studies have shown that alternating between periods of fasting and eating supports cellular health, likely by triggering an age-old adaptation to times of food scarcity called metabolic switchover. Such a switch occurs when cells deplete their stores of readily available sugar-based fuel and begin converting fat into energy in a slower metabolic process. According to Mattson, studies have shown that this switch improves blood sugar regulation, increases resistance to stress, and suppresses inflammation. Some studies have also found that intermittent fasting reduced blood pressure, blood lipid levels, and resting heart rate.

There is also mounting evidence that intermittent fasting can alter risk factors associated with obesity and diabetes. Two studies at the University Hospital of South Manchester NHS Foundation Trust of 100 overweight women showed that those who followed the 5:2 intermittent fasting diet lost the same amount of weight as women who restricted calories, but they performed better on measurements of insulin sensitivity and reduced abdomen.

In fact, even the brain is said to benefit from this nutritional strategy. A multi-center clinical study at the University of Toronto found that 220 healthy, non-obese adults who followed a calorie-restricted diet for two years showed signs of improved memory in a battery of cognitive tests. Although much more research needs to be done to prove the effects of intermittent fasting on learning and memory, this strategy could help to counteract neurodegenerative diseases in the future.