Our Longevity Diet

One of the few Intermittent Fasting studies to use human subjects was Effect of intermittent fasting and refeeding on insulin action in healthy men by Nils Halberg, Morten Henriksen, Nathalie Söderhamn, Bente Stallknecht, Thorkil Ploug, Peter Schjerling, and Flemming Dela, published in July 2005. In this study a very small population of eight healthy men undertook an alternate day 20 hour fast for two weeks (kind of like Fast-5, but only every other day). They fasted from 10:00 PM one night to 6:00 PM the following night, every second day, so there was a total of seven 20 hour fasts over the 15 day period. They were instructed to eat more than normal on the non-fasting days, to maintain their weight, but not to change the types of foods they ate.

There was no significant weight-loss (as one might expect given the compensatory over-eating on non-fasting periods). Yet they did find significant improvement in glucose metabolism, especially insulin sensitivity.  They did not find evidence for the muscle-loss that had been observed in long-term fasts of 72 hours. According to the researchers:

This experiment is the first in humans to show that intermittent fasting increases insulin-mediated glucose uptake rates, and the findings are compatible with the thrifty gene concept.

By ‘thrifty gene’ they mean that our bodies are likely adapted to Late-Paleolithic eating habits. Indeed, in their introduction, the authors state:

Insulin resistance is currently a major health problem. This may be because of a marked decrease in daily physical activity during recent decades combined with constant food abundance. This lifestyle collides with our genome, which was most likely selected in the late Paleolithic era (50,000–10,000 BC) by criteria that favored survival in an environment characterized by fluctuations between periods of feast and famine. The theory of thrifty genes states that these fluctuations are required for optimal metabolic function.

Our take on this is that even very limited fasting, such as imposed by their study, can be beneficial for health. Our fasting schedule is really not much different, except it is slightly longer, 23 hours instead of 20, and our schedule is more balanced — which we find easier and much more comfortable — and we maintain it fairly constantly, not just for a couple weeks.

I find no reason to suspect our genetic adaptation to food intake during the Late-Paleolithic was substantially different from earlier times, when hunting-gathering also prevailed, so it might be more accurate to suggest we are still largely adapted to pre-agricultural food habits. No doubt we have undergone substantial adaptation during the past 10,000 years, but probably not enough to overcome the preceding 200,000 or more years.