We all know that diet can dramatically affect our health, both mentally and physically. But a new study shows that an off-kilter eating schedule could also affect well-being, too. Here's why.

Illustration from a poster by Abram Games

Our sleep cycles are governed by a complex biological mechanism called circadian rhythms. Put simply, all your cells contain biological clocks. The circadian clock is the most fundamental, and it's set by the Earth's night and day cycles. As the hours pass each day, these biological clocks send chemical signals to your body that trigger everything from wakefulness to cellular repair. When your sleep cycles are interrupted, or you aren't exposed to sunlight during waking hours, the clock can get thrown off and cause any number of health problems (including, most famously, jet lag).

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But some parts of your body rely on other cues to determine what time it is. Your gut microbiome — that massive collection of microbes in your intestines that regulate health — also operate on a 24-hour clock. But without any light, their only signals come from the food that you eat. When you're eating, those microbes behave in certain ways; when you're not eating they often go into repair mode (just like your body's cells do). And if your eating cycles get wonky, this could impact your health.

Writes Ed Yong on his blog Not Exactly Rocket Science:

Christoph Thaiss from the Weizmann Institute of Science has discovered that the communities of microbes in out guts vary on a daily cycle. Some species rise to the fore during daylight hours and recede into the background at night, while others show the opposite pattern.

These cycles are a lot like our own body clocks, or circadian rhythms. Over a 24 hour period, the levels of many molecules in our body rise and fall in predictable fashion. These rhythms affect everything from our body temperature to our brain activity to how well we respond to medicine. But these clocks tick by themselves. You can reset them by exposing yourself to light at different times of day (which is what we do when we cross time zones and get jetlag), but they are still self-sustaining.

Our microbiome clock is not. The microbes aren't waxing and waning of their own accord. Their world is completely dark. There's no way for them to tell what time of the day it is, except for clues provided by us. The most important of these clues is food. Thanks to our own rhythms, we eat at regular times of the day, and it's these feeding patterns that drive the cycles in our microbiome. Diet is the gear that synchronises the ticks of our clocks with those of our microbes.

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Yong explains how Thaiss and his colleagues tested the microbiome's clock cycle, and discovered some terrifically interesting things. In mice, there are measurable fluctuations in the composition of the microbiome on a daily cycle — and it's correlated with eating schedules. The researchers also found that mice who had been artificially "jetlagged" using irregular light schedules tended to have a harder time processing sugar and put on weight.

There is evidence that the same holds true for humans, too. Yong reports:

Does the same apply to humans? To find out, the team analysed the gut microbes of two volunteers, before and after a flight from the USA to Israel. Sure enough, crossing the time zones changed the make-up of their microbiomes. In particular, they had a higher proportion of Firmicutes—a major group of gut bacteria, whose overabundance has been linked to obesity. Two weeks later, when the volunteers had recovered from their trip, their microbes had also reverted to their usual cycles.

When the team transplanted these human communities into germ-free mice, the rodents that got the jetlagged microbes put on weight, while those that got the normalised ones did not.

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More research needs to be done to understand the relationship between eating schedules and the microbiome, but these preliminary findings indicate that losing weight isn't just about changing your diet. It's about finding a regular eating schedule, and sticking to it.

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