The Science of Fasting for Women

Fasting for women: why your body works differently

Many women who begin fasting find that their bodies react differently than men's. This is because the female body is much more sensitive to fluctuations in energy intake, particularly due to hormonal influences. However, when used correctly, fasting can be a powerful tool not only for fat burning but also for recovery and cell renewal.

From sugar burning to fat burning

When you begin fasting, your body first switches from burning glucose to fat. Over the first 12 to 24 hours, your glycogen stores (stored sugar in the liver and muscles) are gradually depleted. This is the first step: the body loses its immediate energy source and must search for alternative fuel. It finds this in fatty acids. Simultaneously, your insulin levels drop, which enables fat burning. For women, it's important not to force this process, as excessively low insulin levels can disrupt the balance of estrogen and progesterone during a strict fasting schedule.

Autophagy: internal detox and cell renewal

After about 24 to 48 hours, an interesting process occurs: autophagy. This is the body's natural mechanism by which old or damaged cellular material is cleared and recycled. Autophagy is like an internal detox: cells that no longer function properly are broken down and the usable building blocks are reused for repair. It's an evolutionary mechanism that sustains your body during periods of scarcity. Researchers, including Nobel Prize winner Yoshinori Ohsumi, have shown that this process is essential for preventing aging and chronic diseases such as Alzheimer's and even certain forms of cancer.

Fasting and chemotherapy for breast cancer

The effect of fasting on health goes far beyond just weight loss. A growing number of studies are focusing on the influence of fasting during disease processes, such as chemotherapy. Small clinical studies in women with breast cancer have shown that a so-called "fasting mimicking diet"—a fasting-like diet low in calories, sugars, and proteins—during the days surrounding chemotherapy can reduce side effects, better preserve healthy cells, and even increase treatment effectiveness. The theory behind this is that healthy cells enter a protective mode during fasting, while cancer cells become more vulnerable to the attack of chemotherapy. Large-scale studies like the DIRECT trial in the Netherlands are now investigating whether this also makes a difference on a large scale.

Fasting and the Female Cycle: Why Timing is Everything

Yet, all of this requires nuance. Fasting is a stressor; it challenges your body, and for women, especially in the second half of the cycle (the luteal phase), this additional stress can lead to hormonal issues or even the absence of menstruation. During this phase, women are more sensitive to blood sugar fluctuations, their energy needs increase, and they are less resilient to stress. That's why fasting works best for women when applied cyclically: longer fasting periods in the first half of the cycle (after menstruation through ovulation), and shorter or no fasting at all in the second half (from ovulation to menstruation). This way, your hormonal balance remains intact and you benefit from the advantages of fat burning and cell repair.

Those who fast for longer periods, for example, one or more days, will notice that the body switches to fat burning more efficiently, that inflammation levels decrease, and that mental clarity often increases. However, these deeper forms of fasting should be used with caution, and only when the body is already well-trained to shorter forms of intermittent fasting.

In summary

Fasting can be a powerful tool for women, both physically and cellularly, provided it's aligned with the female cycle and includes sufficient recovery periods. It's not the strictness of the fast that determines its success, but the intelligence with which you apply it.

Cyclical fasting schedule for women

Note: This is a general guideline. Always listen to your body. Reduce your fasting immediately if you notice a missed period, fatigue, or obsession with food. Fasting should not dominate your life.