No, Fasting Is Probably Not Healthy

I’ve recently heard arguments from various religious folk that fasting is “good” for health. There is also no end to health gurus recommending it. There may be some exceptions; for instance, in recovery from some illnesses. This is clearly rare. This trend, then, strikes me as odd. My brief knowledge of human biology says this: there is probably no way that starving oneself increases bodily health. Some modern scholars have attempted to explain religious phenomena as physically wealth-maximizing (such as the Israelite diet being disease-ridden), but this is one instance where, I think, the buck stops.

However, there is vast empirical literature supporting the healthiness of fasting. Studies on Jehovah’s witnesses, for example, correlate their long lives with their strict adherence to fasting. I have yet to find a study that does not merely correlate fasting with some vague variable representing health. An astute reader may already see my point: correlation does not equal causation. It is far more likely that individuals who fast also happen to be healthy, and that the former does not cause the latter.

If an individual is willing to undergo the sacrifice of fasting, they may also be willing to sacrifice other pleasures for the sake of their health. In fact, the act of sacrifice itself is a mark of lower time preference. If we were to place all people in two buckets – those who fast and those who don’t – it should be no surprise that those who fast tend to be more self-disciplined, more caring about their future health, and therefore healthier. We can make this assumption about the first bucket because, if anything, we know those who lack the determination to finish a fast (that is, who tried and failed) are in the second bucket. Should we expect those who fail to be healthier?

Of course, unhealthy persons may still successfully fast. But we would not expect, ceteris paribus, that they would engage in low-time-preference behavior more than those with demonstrably lower time preferences (healthier people).

This is also not to say that religious fasting is misguided. On the contrary, religious fasting must (demonstrably) serve a purpose other than health; and that’s okay! Health is not the ultimate end, and we often make trade-offs that leave us less healthy but wealthier. If religious fasting were for health, that would imply the incentives for fasting lie merely in the non-spiritual, which seems contradictory for any religion to claim of its practices.