Luke Stanaway

Registered Nutritionist

Why Intermittent Fasting May Not Work For Women 

Why Intermittent Fasting May Not Work For Women 

Why Intermittent Fasting May Not Work For Women 

Key Takeways

  • Intermittent fasting is a popular health trend that involves fasting for extended periods of time.

  • The practice of intermittent fasting can have health benefits such as regulating blood glucose and lowering the risk of disease.

  • However, for some women, it can lead to serious health issues such as binge eating, metabolic disruption, missed menstrual periods, and early menopause.

  • Intermittent fasting can negatively impact reproductive hormones by disrupting the gonadotropin-releasing hormone (GnRH) secretion in the hypothalamic-pituitary-gonadal axis.

  • Factors such as negative energy balance caused by poor nutrition, excessive exercise, stress, illness, and lack of rest can increase the risk of hormonal disruption caused by fasting.

What is Intermittent Fasting

Intermittent fasting (IF) is the practice of fasting for extended periods of time. Meal skipping, alternate-day fasting, and other strategies are available. When done correctly and by the right people, intermittent fasting may help to: regulate blood glucose, lower the risk of coronary disease, manage body weight, assist you in gaining (or maintaining) lean mass, lower the risk of cancer, and so on. 

As a result, a large number of people are attempting it. However, a concerning trend has emerged in which some women report serious issues such as binge eating, metabolic disruption, missed menstrual periods, and menopause at an early age. It seems that intermittent fasting differs for men and women... 

Intermittent Fasting and Hormones

In the grand scheme of health decisions, experimenting with intermittent fasting may appear insignificant. So what's the harm in trying it? For some women, it's a bigger deal than you might think. It turns out that the hormones that regulate vital functions such as ovulation, metabolism, and even mood are extremely sensitive to your energy intake. Changing your eating habits can have a negative impact on your reproductive hormones. This has the potential to have far-reaching consequences, resulting in a slew of health issues. 

How exactly does this happen? 

Fasting affects reproductive hormones in both men and women via the hypothalamic-pituitary-gonadal axis. Fortunately, this is known more commonly as the HPG axis. Here's how the HPG axis works: 

  1. Gonadotropin-releasing hormone (GnRH) is secreted by the hypothalamus in regular bursts known as "pulses." 

  2. GnRH pulses signal your pituitary gland to secrete LH and FSH (FSH). 

  3. The gonads are then stimulated by LH and FSH. 

  4. LH and FSH stimulate oestrogen and progesterone production in women, which is necessary for the release of a mature egg (ovulation) and the maintenance of a pregnancy. They boost male testosterone and sperm production. 

GnRH pulses must be precisely timed because this chain of events occurs on a very specific, regular cycle in women. Otherwise, everything can go wrong. If no eggs are released, the period ends. The main point is that GnRH pulses appear to be highly sensitive to environmental factors and that fasting can disrupt them.

The Immediate Effects of Fasting

Fasting for three days can alter these hormonal pulses in some women. There's even evidence that missing a single meal, which isn't necessarily an emergency, can set off our hormonal system. This may explain why some women have difficulty with intermittent fasting. But why does eating less make our bodies more alert? For many years, scientists believed that a woman's reproductive system was controlled by her body fat percentage. The theory was that if your fat stores fell below a certain percentage, around 11%, hormones would be disrupted and your period would stop. From an evolutionary standpoint, this made a lot of sense. For our forefathers, who did not have access to Costco or Amazon, a lack of food would be a major concern. As a result, if you're losing body fat, your body may believe there's not much to eat and attempt to prevent reproduction. The situation, however, is more complicated than that. Even before body fat levels drop, female bodies appear to be on high alert. Women who aren't particularly thin may stop ovulating and miss their periods as a result. Scientists believe that overall energy balance, or how many calories you consume versus how many you "burn," is more important than body fat percentage in this process. 

Long-Term Fasting

When you consistently consume less energy than you expend, you have a negative energy balance. Weight loss necessitates a negative energy balance. That is exactly what many people try to achieve through dieting. However, when it is extreme or lasts for an extended period of time in the context of other stressors, it may be to blame for the hormonal spiral seen in some fasting women. Negative energy balance is caused by factors other than simply eating less. 
Poor nutrition, excessive exercise, excessive stress, illness, infection, chronic inflammation, and insufficient rest and recovery can all contribute to it. 

Fasting and Stress = Alarm!

Any combination of stressors can cause an abnormally negative energy balance and prevent ovulation. Training for a marathon while sick with the flu, going to the gym too many days in a row without eating, eating enough fruits and vegetables, intermittent fasting, and dealing with financial stressors are all examples. Psychological stress can affect your hormonal health. Our bodies are unable to tell the difference between a genuine threat and something created by our thoughts and feelings. These "threats" can cause our bodies to produce more of the stress hormone cortisol. What about cortisol levels? It suppresses GnRH. And as we have already discussed, disrupting GnRH causes a cascade effect that can suppress oestrogen and progesterone production by your ovaries—hormones required for reproduction. 

As a result, even though you may have a body fat percentage of 30%, if you are experiencing a negative energy balance for an extended period of time, particularly if you are extremely stressed, reproductive functions may stop.