For a while now, researchers have been able to show an association between fasting in mice and extended lifespan and improvement in age-related diseases. And not just in mice, but in many other species whose lifespans are generally short enough for us to study from beginning to end. Yup, I’ll say it again – calorie restriction seems to extend life in many species. Researchers are now starting to study whether the same is true for humans.
But since even researchers admit that daily fasting isn’t sustainable for most people, intermittent fasting – severe calorie restriction every other day in this case – is being looked at as a viable option to produce the effects of daily fasting. In the study I referenced above, researchers at the University of Florida recruited 24 participants to eat 25% of their caloric needs one day and then 175% of their needs on alternating days for six weeks. After six weeks on the diet (three weeks without antioxidant supplementation and three weeks with), researchers found a “marginal” (their lingo) increase in “SIRT 3, a well-known gene that promotes longevity and is involved in protective cell responses.” They also found a slight a decrease in plasma insulin levels (none of the participants had diabetes). The researchers also determined that, after only six weeks, the “intermittent fasting dieting paradigm is acceptable in healthy individuals.” It’s not clear what criteria they used to determine acceptability.
Never mind that six weeks is a ridiculously short time to determine whether a diet will have long-term adverse effects, is sustainable for most people, or that a small increase in a gene that is associated with longevity will actually produce longevity or to what degree…never mind all that. Let’s say it all works and maybe you’ll live a few years longer.
Now you’ve decided you want to take a gamble on longer life and you’ll take a stab at this diet. So on one day you eat 650 calories, and on the next you eat 4,550 calories. Rinse and repeat ad nauseam. How much of your time, on a daily basis, is now devoted to getting this diet right? Study participants reported that they actually had a harder time meeting the intake requirements on the feast days. What if you’re not hungry on feast day? What if you’re really really hungry on famine day?? And do I get more years in my 20s or 30s? Or just tacked on to the end, in my 70s or 80s?
And now let’s talk about those mice. It’s easy to put them on a fasting diet, because we didn’t ask their opinion about how they wanted to eat and we gave them only what was allowed. But people aren’t mice. We live in a world where we go to work, raise children, drive by McDonald’s, experience joy and stress, share food with loved ones…I don’t want to judge, but I’m pretty sure the daily life of a mouse is not quite as complex as that of a human. I’m willing to bet that if we took those mice out of the cage and let them have at it on the kitchen table after a 9 year-old’s birthday party, very few would choose to fast over hoovering every last cake crumb. I’ve had some up-close-and-personal experiences with free-range mice in my lifetime and they are remorseless in their eating habits. So this isn’t even a sustainable diet for your average house mouse when you think about it.
It’s really too soon to see how all of this calorie restriction is going to play out in humans. We need to study people long enough to:
- Get to the end of their lives to see if they actually lived longer or suffered fewer diseases, and
- See if more than a tiny of fraction of people are able to live their lives on this diet.
UCSF has already done some research in this area, check it out here. Fun fact: one of my friends was in the control group!
In the meantime, I’ll stick to listening to my internal cues of hunger and satiety to guide my nutrition. Because even if intermittent fasting could give me a longer life, I’m pretty sure I wouldn’t enjoy any of it. I’m sure any mouse would agree.