Does my menstrual cycle affect my weight, appetite and training?

Most of what the menstrual cycle does to the scale is fluid, not fat. White and colleagues followed 765 cycles in 62 healthy women with a daily diary and found that self-reported fluid retention, what many people call bloating, was greatest on the first day of menstrual flow and lowest in the mid-follicular phase. A rise of a few hundred grams to a kilo around your period is therefore expected, temporary, and says nothing about how much fat you carry.

Appetite moves too. In a review of how the sex hormones govern energy balance, Davidsen and colleagues describe how both energy intake and cravings, especially for carb- and fat-rich food, tend to increase in the luteal phase, meaning the weeks after ovulation and before your period, compared with the follicular phase. This is a genuine physiological shift, not a lapse in willpower.

What about metabolism? Benton and colleagues pooled 26 studies covering 318 women and found a small but significant rise in resting metabolism during the luteal phase. The effect was small, and in the newer and better-controlled studies it shrank and was no longer statistically reliable. So the cycle raises your metabolic rate by a few percent at most, not enough to explain large swings on the scale.

Training is affected least of all. McNulty and colleagues reviewed 78 studies, 51 of which could be pooled, and found only a negligible dip in performance early in the follicular phase, that is, during your period itself. The evidence was rated low and the variation between studies was large, so the conclusion was not to schedule the month around phases but to go by how your own body feels. Taken together, the cycle moves water and appetite in a predictable, passing way, but it does not change how fat is stored or what you are actually able to do.

The scale rises in the days before your period, right when your mood is already more tender, and the number gets read as fat gain even though it is water. The bloating can be seen and felt, which makes the interpretation convincing, and confirmation bias fills in the rest: you remember the time it lined up and forget the times it didn't. On top of that sits a whole market. Apps selling cycle-synced eating and training, teas and supplements against bloating, and products promising to balance your hormones all profit when a normal shift in fluid and appetite is framed as a problem to fix. The fear that a couple of kilos means fat keeps the buying going, even though the body is only doing what it should.

Expect the scale to read a little higher in the days before and during your period. That is fluid, and it clears on its own within a few days, so compare the same phase of the cycle across months rather than day against day. Feeling hungrier in the week before your period is expected, and a bit more protein and fibre makes it easier to meet without treating it as a failure. Train as usual. If you feel weaker at the start of your period, adjust that one session to how you feel on the day; you don't need to plan the whole month around the cycle.