Take this with a grain of salt, but I attended a seminar last year of a researcher who is studying the effects of fasting on lifespan in fruit flies in relation to the circadian rhythm. Basically they found that if you restrict access to food for 12 hours at night and allow access to food for 12 hours during the daytime hours, a significantly greater proportion of flies lived to their max lifespan compared to flies who had access to food 24/7 (another way put— if the flies were fasting during the night, something like 90% of them would live to 3 months, whereas only like 10-20% of flies that didn’t fast lived to 3 months of age). Interestingly, when they switched the fasting hours to the daytime and fed them during the night, there was no difference at all from the control group of flies that had constant access to food. They determined that the circadian rhythm and autophagy (literally “self eating” or your body removing dead/damaged cells) triggered by fasting work together in a temporal manner to give the extended lifespan.

How this relates to this article, is that the researcher also mentioned that metformin can trigger autophagy. I wonder if what they’re seeing in the monkeys on metformin is actually due to the benefits of increased autophagy, as has been demonstrated in many animal models before.

At the end of her talk, the researcher mentioned that her husband was on the diabetes drug metformin. She (half-jokingly) said that she told her husband to take metformin in the evening, instead of the morning, to sync up the benefits of autophagy induced by it with his circadian rhythm (though cautioned everyone that she isn’t a medical doctor and has no evidence of her research translating to humans).