What is Intermittent Fasting, and Why Do People Do It?
Every so often, a new diet surfaces, appearing to offer a variety of health benefits, and is touted as the healthiest way to eat. Whether seeking weight loss, improved energy levels and cognitive function, detoxification, or something else entirely, people are quick to adopt these new diets hoping to reach their health goals. Intermittent fasting is one of these diets, having gained significant popularity in recent years. Fueling public enthusiasm, the 2016 Nobel Prize for Physiology or Medicine was awarded to Dr. Yoshinori Ohsumi for his research in autophagy, a key benefit of intermittent fasting. Intermittent fasting (IF) consists of going without food for extended periods of time, whether for a few days a week or the more common application of an extended stretch each day, such as a 16-hour break between dinner and breakfast.
Research has shown that many beneficial processes begin to take place when the body is deprived of food -another way to think of it is as a rest from digestion - for an extended period of time. Autophagy (translates to “self-eating”) is a cellular process stimulated by fasting whereby cells begin to break down any of their components that are damaged. Once these pieces are broken down, the cell recycles them for energy or building new molecules. This process has been shown to slow signs of aging and has even been suggested as a potential therapy for cancer and neurodegenerative diseases such as Parkinson’s. Research has also shown that IF can help regulate insulin levels, thereby reducing the risk of developing type 2 diabetes and improving insulin sensitivity in those who already have developed the disease.
Is Intermittent Fasting Dangerous for Women?
The research on intermittent fasting is heavily sex-biased, with a much greater focus on men than on women. The aforementioned benefits have all come from studies on men only. Moreover, the few studies conducted on women examined only the short-term effects of fasting (1 & 2). What is most concerning is that the few animal studies that researched the long-term effects of fasting on females have not demonstrated the same benefits that we see in men; female rodents studied during extended periods of fasting showed significant hormone disruptions. These hormonal imbalances resulted in absent menstrual cycles, decreased size of ovaries, and heightened stress responses (3). Anecdotal evidence suggests a similar impact on humans; we recently wrote an article on why the Keto diet may be harmful for women, but intermittent fasting can trigger similar mechanisms in disrupting a woman’s hormonal balance. If you have tried intermittent fasting and experienced irregular menstrual cycles, abnormal fatigue, insomnia or cystic acne, it may be a sign that your hormones are unbalanced and that IF may not be the right diet for your body.
The Science Behind the Adverse Effects of Intermittent Fasting
An important hormone known as gonadotropin releasing hormone (GnRH) is signals to our pituitary gland to release two reproductive hormones known as luteinizing hormone (LH) and follicular stimulating hormone (FSH). In women, LH and FSH trigger production of estrogen and progesterone, the two hormones that stimulate ovulation. Studies have shown that release of GnRH is extremely sensitive to weight loss, stress, and fasting (4). Although men also release GnRH, they do not experience the adverse effects of fasting that women do, although this is not yet well understood. It could be due to the female reproductive system’s more sensitive dependence on a regular hormonal cycle. Another proposed hypothesis, although not confirmed due to lack of research, is due to the hormone kisspeptin. Kisspeptin is very dependent on the metabolic system and is released in response to the hormones ghrelin, insulin, and leptin. Leptin is the hormone that is released after a meal to signal to your brain that you are full; it also stimulates GnRH release. When fasting, even briefly, leptin levels decrease and dysregulate the GnRH pathway. Studies have shown that kisspeptin levels can decline in females after skipping just one meal. Ghrelin, the “hunger hormone”, rises when the body is hungry and actually suppresses kisspeptin. Expression of kisspeptin much higher in females than in males, which may explain why women’s hormones can be more prone to dysregulation in response to fasting (5).
Interestingly, although an increase in insulin sensitivity is a reported benefit of intermittent fasting, this may actually be the opposite case for women. According to the few human studies done on IF in females, women saw no significant improvement in insulin sensitivity, which was observed for the male study group. Therefore, it’s possible that IF may only be effective in reducing the risk of type 2 diabetes in men.
So, Should Women Avoid Intermittent Fasting?
The research on intermittent fasting in women is too scarce to give any definitive conclusions on its effects. However, the studies conducted on female rats and the few studies conducted on female humans have shown significant adverse effects, especially on reproductive hormone levels. The reported benefits of intermittent fasting may be much more available to men than to women, and some research indicates that these benefits may not occur in females at all. That being said, many women who try IF do not experience a loss of menstrual cycles or any adverse effects at all. If you have tried IF and you notice any adverse effects, it may be a good idea to try shortening your window of fasting fewer hours in the day and see if that improves your symptoms. There are plenty of other diets that do not signal to your body that it is starving, and may be a safer option for women (especially if you’re of reproductive age.)