Can eating too little disrupt your hormones, even if you do not have an eating disorder?

Even a short-term, moderate calorie deficit (roughly half of your daily energy needs) can disturb sleep and lower reproductive hormones such as oestrogen, progesterone and leptin (the 'satiety hormone') in healthy, lean women. That effect was strongest in the late phase of the menstrual cycle. This has been demonstrated in controlled research involving women without an eating disorder or excess weight.

Calorie restriction also disrupts the hunger hormones ghrelin, leptin and insulin. In people with excess weight or metabolic problems, restoring those levels can actually be beneficial. In healthy, lean people, however, it is unclear whether those same shifts are desirable: the research on this does not give a consistent picture.

Not only how much you eat matters, but also when. Eating at irregular times, or having meals that do not align with your biological day-night rhythm (such as late in the evening or at night), disrupts hormonal rhythms and reduces insulin sensitivity. This effect occurs independently of whether you are eating too little or too much.

The situation is somewhat different for men. Obesity disrupts the hormonal axis that regulates testosterone, causing testosterone to drop. Calorie restriction and improved nutrition can help restore that. However, this applies specifically to men with excess weight or a metabolic problem; in healthy, lean men the effects of calorie restriction on sex hormones have not yet been well mapped out.

In short: eating too little does not have to mean you have an eating disorder in order to still feel hormonal effects. Women in particular are sensitive to even short-term energy deficits, and the timing of your meals also plays an independent role.