Asked by: Richard Kemp, Jersey
It's tempting to think that giving in to a craving is simply correcting a nutrient imbalance in the body, but there isn't any good evidence to support this. Chocolate, for example, contains magnesium, and low magnesium levels have been shown to worsen premenstrual symptoms in women. However, you would need to eat 20 bars of chocolate to get enough magnesium that way.
Chocolate also contains many mood-altering compounds, including caffeine, theobromine, serotonin and tryptophan. But dairy products also contain these, and at higher concentrations, yet we are much less likely to crave them.
In some societies, pregnant women may eat clay, soil or termite mounds, but this seems to have a cultural, rather than a nutritional basis. Indeed, women who eat dirt, or 'geophagy' as it is called, often cause their malnutrition, rather than cure it.
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.
