How to live longer: the different effects of fasting on men and women

Fasting has become the weight loss diet du jour thanks to the fat burning benefits of ketosis, as well as the benefits to health, antiaging and longevity from autophagy. While in today’s modern society sex and gender exist on a spectrum, the effects of fasting on men and women are more binary. Find out how best to optimise your fast based on your sex.

Fasting for health and longevity

Caloric restriction has been practised for millennia for a variety of purposes: meditative, religious and therapeutic. Today, there exist several styles of modern fasting for health and weight loss that differ in intensity and effectiveness. These vary by timeframe and include intermittent, periodic and prolonged fasts. In prehistoric days before the advent of agricultural farming, human beings adapted to survive for long periods without food. Much has changed in the modern era, where high-income countries have almost limitless access to high-fat, low-nutritional convenience food.
Fasting works for weight loss by reducing overall calorie consumption as well as harnessing the additional fat burning benefits of ketosis. Around 12-16 hours into a fast, blood glucose and insulin levels dramatically drop. This deactivates nutrient signalling pathways regulated by mTOR kinase, forcing the body into the fasting state. To prevent starvation, the body switches from using glucose from food for energy to metabolising its own fat stores, known as the G to K switch. Ketosis can promote weight loss, as well as improve metabolic function, reduce inflammation and enhance immune functioning [1].
The health benefits of fasting are related to its ability to induce autophagy, during which cells reuse their old and damaged organelles to achieve cellular rejuvenation. Autophagy is an ongoing cellular process that can be accelerated by longer fasts since it also balances energy sources during nutrient stress. Around 24 hours into a fast, autophagy is initiated through the TOR kinase pathway. Cellular renewal is thought to protect against age-related disease like cardiovascular disease, neurodegeneration, diabetes and cancer, safeguarding longevity [2].
Read more about what happens to your body during fasting here.

The fasting differences between men and women

While regularly fasting can benefit weight loss, health and longevity its effects can differ between men and women. Physiological differences in how men and women’s bodies respond to fasting can be traced back to prehistoric gender roles of the hunter-gatherer lifestyle. While men hunted, women generally gathered, which may explain the differences in body size, metabolism and muscle and fat composition between men and women. Unfortunately, over time, it is women who have become the main subjects of modern day’s toxic dieting culture. While research in this area is limited, there is some evidence that men are better adapted to caloric restriction and thus may experience heightened fasting benefits compared with women.
While fasting is generally safe and most women who fast are happy with its results, in very extreme cases some women have reported side effects like binge eating, metabolic disruption and changes in menstrual periods. There are several possible explanations for these extreme responses, and may involve the intricate balance of hormones that controls essential functions in both men and women. Hormones in men and women seem to respond differently to fasting; changes in caloric intake and even the timing of caloric intake can disrupt hormonal functioning in women, effecting ovulation, metabolism and mood [3].
This could be related to the molecule kisspeptin, which stimulates production of sex hormones like gonadotropin-releasing hormone (GnRH) and consequently follicle stimulating hormone (FSH) and luteinizing hormone (LH). Kisspeptin can be sensitive to other hormones like leptin, insulin and ghrelin that effect hunger and fullness. Women have more kisspeptin than men and may therefore be more sensitive to changes in energy intake that can affect their hormonal cycle [4]. Hormonal imbalances can have further implications than just in reproduction, and disruptions in sex hormones like oestrogens can echo throughout the body. For example, imbalances in oestradiol, a type of oestrogen, effect metabolism by increasing appetite and possibly promoting fat storage [5].
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How to optimise your fast

Considering these differences, it is important to optimise your fast depending on your sex. While it is important to be aware of the different responses the female body can have when fasting, it should in no way prevent women from completing their fasts. Luckily, there are endless fasting variations to suit everybody, male or female. While male bodies appear to be more resilient to most types of fasting, for women it may be prudent to avoid extreme types of fasting like the OMAD, or one meal a day fast.
For all fasting beginners of both sexes, it is best to start slow, for example by gradually extending the natural fast everyone experiences when they sleep into the daylight hours. Women may be more suited to time restricted eating (TRE), which alternates between periods of fasting and feasting within one day. Beginners can start with the 12:12. Gradually, as your body adapts to fasting, this can be extended to the 16:8, or even the more intensive 20:4 best suited to experienced fasters.
While sex and gender lie on a spectrum, certain physiological differences between men and women are more fixed and our bodies respond differently to fasting. However, women can still unlock the health and longevity benefits of fasting by being aware of these differences and matching their fasts accordingly.