Fasting for Active Women

Fasting for Women and Why it’s controversial

Of all the subjects I discuss, fasting is by far one of the most divisive. Yet it’s also one I feel strongly about—because the evidence is clear, and I want to help women avoid the many traps it sets. Whilst some women report feeling well when fasting, the longer-term research paints a very different picture. Why is that?

Women Are Not Small Men

For far too long, women have been following health and fitness advice based on male

physiology. Whether it’s training, weight management, or even medical treatment, most of the recommendations stem from studies carried out on men.

Fasting is no exception. Some studies suggest benefits for active men, yet the data shows fasting often has the reverse effect for active women.

Research is conclusive: there are sex- specific differences in energy metabolism and metabolic balance. Women, compared with men, are more efficient at conserving fat and protein (for fuel, rather than to protect lean tissue) during times of food shortage or prolonged exertion.

(A quick note: I’m talking here about active women—those who exercise with purpose. In sedentary populations, fasting may offer some benefits. But for active women, it tends to cause more harm than good.)

The Role of the Hypothalamus

So why does fasting affect women more negatively than men?

Neuropeptides play a crucial role in reproductive health, hormone regulation, blood sugar control, appetite, and body composition.

Here’s the key point—those that stimulate appetite, such as Neuropeptide Y, are naturally lower in women at rest and in non-stressful situations, but they rise more sharply in response to food restriction than they do in men.

When the brain senses a drop in nutrients—especially carbohydrates—neuropeptide

production shifts, driving the body to conserve energy more aggressively. Add the stress of exercise, and further hormonal changes occur. In the short term, women experience a stronger physiological drive to eat. Over time, if energy needs remain unmet, thyroid function can decline, menstrual cycles may become irregular, and increases in body fat are often observed.

Sound familiar? This is why women who fast alongside male partners or friends often feel disheartened: he gets leaner, trains well, and feels mentally sharp—while she gains weight, feels anxious, and struggles with energy and performance.