At night, when a mouse in its cage runs on the wheel, an automated feeder opens and dispenses a portion of food. That is how an experiment began in which 528 mice lived their entire lives under the watch of sensors and scales. The scientists were testing a simple idea: if food enters the body only during waking hours, the internal clocks run more precisely and the body ages more slowly. Time-restricted feeding does not force you to eat less, but it does force you to eat at the right time.
Two years ago, these mice were divided into three groups. Some ate whenever they wanted, others received food within a 12-hour nighttime window, and a third group had a narrower 8-hour window. Every six months, the mice were weighed, scanned, had blood drawn, and were checked for how quickly they became frail. It turned out that both windowed regimens slowed weight gain and fat accumulation, and also delayed frailty. This was especially noticeable in males: those that ate for only 8 hours lived to 916 days on average, while their counterparts with free access to food lived to 818. A difference of 12% sounds modest, but for a mouse it is almost three months of life.
The females, by the way, became healthier but did not live longer. That is an important twist: better health does not always mean a longer life. Scientists do not yet know why. Perhaps females need more severe calorie restriction or longer fasting to trigger the same mechanisms as in males. Or perhaps their internal clocks respond differently to meal timing.
At the same time, mice on the 8-hour window ate 9–23% less on their own, even though food was plentiful. This is called spontaneous calorie restriction: the animal is not starving, but appetite drops by itself. That effect makes the method practical for people who find strict diets hard to follow. You just shift your meals to daylight hours, and your body asks for less food on its own.
The window into the night that opened for the mice at the start of the experiment turned into a window into healthy old age by the end of their lives. Those that ate on schedule suffered less from age-related diseases and stayed strong longer. Now scientists want to test whether this regimen works if started in old age rather than in youth. After all, most people do not need to overhaul their entire lives from a young age to benefit from a simple rule: eat when the sun is up, not when it is dark.
Contrary to popular belief, in this experiment male mice outlived females: median lifespan was 818 days for males versus 694 for females. In mammals, females usually live longer, but in C57BL/6J mice the results are inconsistent. Perhaps the females were cold in individual cages without nesting material and spent more energy on heating.
Not published on arXiv. Here are its page, the PDF and the formalization: you can check it yourself, not only read our account.