Your body is keeping time, all the time.
Deep inside the brain, a master clock synchronizes thousands of molecular clocks scattered throughout the body, and together, they anticipate signals such as the rising sun, the coming night and the daily rhythms of life.
But Texas A&M University researchers have discovered that the liver is also listening for another signal, one tuned to something much closer to home: the dinner bell.
A new study led by associate professor Dr. Jerome Menet at the College of Arts and Sciences uncovered how meal timing triggers a nutrient-signaling pathway that drives rhythmic gene activity in the liver, independently of its circadian clock.
In other words, the liver isn't simply waiting for instructions from the brain about whether it's day or night; it's taking cues from the dinner table, too.
The findings, published in Science Advances and supported by the National Institutes of Health, suggest that when we eat may be just as important as what we eat, raising new questions about what happens when our feeding schedule is out of sync with our body's circadian clock.
"We've shown that the liver is keeping time not just with molecular clocks, but also using food signals. And when the timing of food signals is disrupted, it can potentially have serious metabolic and health consequences," Menet said.
Eating against the clock
For millions of people, eating doesn't always happen on the body's schedule.
A night shift worker may eat dinner at 2 a.m., a frequent flyer crossing different time zones may have breakfast while their circadian clock is stuck in the middle of the night and a habitual late-night snacker may reach for food long after the sun's gone down.
Different circumstances, same basic mismatch: food is arriving when the body's internal clock is winding down to sleep.
"That mismatch matters," Menet said. "Food isn't just a source for calories; it also acts as a biological signal."
When nutrients arrive, they activate metabolic pathways in our bodies that tell cells to shift gears and turn genes that process energy either on or off.
"The liver sits at the center of that metabolic work. It processes nutrients, then stores and releases them when the body needs energy," Menet said.
Put simply, picture a factory with a carefully timed production schedule. After hours, its master clock says it's time to close shop. Then, suddenly, a truck arrives at midnight carrying a fresh delivery of materials.
The factory can still work but now its delivery schedule is out of sync with its production schedule, and the workers are putting in overtime when the factory is supposed to be winding down.
That's the biological tension of the new research. If the circadian clock is telling the body that it's nighttime while food is commanding the liver to launch a full production shift, the two start to send conflicting signals.
The conflicting signals, over time, could have serious health consequences, particularly among those who routinely live against the body's natural day-night cycle.
"Our results can help explain why night-shift workers, habitual late-night eaters and frequent travelers with irregular sleeping schedules are at higher risks for conditions like fatty liver disease, cardiovascular disease and even cancer," Menet said.
Conversely, the research team's findings also provide a powerful biological foundation for chrononutrition, or how the timing, frequency and distribution of food interact with the body's 24-hour rhythm to influence metabolism and health.
Specifically, the research could help explain why popular diet strategies like intermittent fasting, or more precisely, time-restricted eating, have attracted so much attention. That is, a consistent eating window creates a predictable schedule of nutrient signals that keep metabolism on rhythm.
"Eating on restricted feeding schedules, like we see in intermittent fasting, can be vital for cellular longevity and liver health, not just for calorie counting," Menet said.
Looking ahead, mapping the exact molecular machinery behind the liver's food-driven rhythms opens compelling clinical possibilities.
"It opens the door for the idea that equally as important as the medicine is the timing of its administration, in alignment with the nutrient-signaling pathway of the liver's rhythms and not just time of day," Menet said. "That could have an impact, no matter how small, in the success of pharmaceutical interventions."
The signal behind the rhythm
Menet and his team focused on a nutrient-signaling pathway called mTOR, short for mechanistic target of rapamycin.
"mTOR is one of the body's major nutrient-signaling systems," Menet said. "It responds to signals that indicate nutrients and energy availability, regulating processes like protein production, growth and metabolism."
When food arrives, nutrients activate mTOR, passing along signals that influence which genes in the liver switch on and off, and when.
The researchers were interested in knowing whether rhythmic food intake was doing more than simply feeding the liver: was food actually helping set the liver's daily rhythms?
To find out, the team gave their models access to food only during their normal active periods, creating a predictable schedule of feeding that corresponds to the rhythm of mTOR activity.
Then, the researchers blocked mTOR, and the result was dramatic.
"We observed that the mTOR inhibitor reduced rhythmic gene expression by 50%," Menet said.
Hundreds of genes that normally rise and fall throughout the day suddenly lost their rhythmic patterns.
Even more surprising, the liver's core circadian clock kept ticking.
"It suggests that the liver's daily rhythmic expression operates on two pathways: the intrinsic molecular circadian clock and rhythmic signals created by feeding," Menet said.
In other words, food may provide the cue but mTOR carries the signal, and the liver responds by keeping time.
Resynchronizing the clocks
Once they had established that mTOR helps carry the signal behind the liver's food-driven rhythms, the team asked a more difficult question.
"Is mTOR responding to rhythmic feeding or was it actually initiating gene rhythms?" Menet said.
To answer this question, they disrupted the models' normal feeding schedule, deliberately making it irregular and throwing it out of sync with their core circadian clock.
"As the feeding rhythm became more irregular, so too did the liver's rhythmic mTOR activity," Menet said.
The team then manipulated mTOR directly, and in doing so, they found the liver's rhythmic gene expression patterns were restored.
"It's an exciting finding," Menet said. "We created a situation where the liver's mTOR rhythm became arrhythmic, and yet we were able to restore it to its baseline so that it resynchronizes with the circadian rhythm."
This finding provides evidence that mTOR isn't just a passive responder to feeding. Instead, it acts as an intermediary between when food arrives and when genes in the liver switch on and off — a distinction that could be important for understanding what happens when the body's internal rhythms and daily behaviors like feeding fall out of sync.
"It's significant because we live in a modern world that constantly affects our biological timing. What's exciting is that we've found a way to help resynchronize those rhythms when they become disrupted," Menet said.
A lifetime spent chasing time
For Menet and his students at the Menet Lab , biological timing is more than a research interest; it is a scientific passion and wonder that has shaped their careers.
Before joining the Texas A&M's Department of Biology in 2013, Menet spent years studying the molecular machinery that keeps biological clocks ticking, examining how thousands of genes orchestrate rhythmic activity across cells and throughout the body.
"My background is in neuroscience, which is what I earned my first credentials in," Menet said. "But in that pursuit, I became fascinated with the processes behind the internal biological clocks that we have."
That elegant, yet impactful, curiosity is also at the heart of Texas A&M's Center for Biological Clocks Research , where biologists work alongside neuroscientists, geneticists with physicians, and professors with students, all to unravel the molecular mysteries of our hidden clocks, deepen our understanding of how life moves through time and lay the groundwork for potentially life-changing interventions.
"The Center for Biological Clocks Research's aim is to promote and accelerate discoveries in chronobiology research, all the while developing the next generation of researchers," Menet said. "In my lab, it's my passion to train and teach my students."
For over a decade at Texas A&M, Menet has continued chasing the mystery of biological time, even as the clock — as it always has — keeps ticking.
Ultimately, sunlight helps set our internal clock while food sends its own signals through the body, too — and our liver listens to both. When the dinner bell rings, what matters most may be whether these signals are in sync, so that our metabolism can stay in rhythm.
