Across a Northwestern laboratory, mice fed the same rich diet grew heavier when they were allowed to eat during their resting hours than when they ate in their waking dark, even though they consumed about the same amount. The work, reported in Science, suggests that the body's internal clocks may govern how fat tissue releases energy as heat, a quiet process that could help explain why when we eat seems to matter as much as what we eat. It is a discovery still confined to mice, but it reopens an old human question about the hours we choose for our meals.
Mouse Study Links Late-Night Eating to Weight Gain Through Fat-Tissue Heat Release
The same food, eaten at the wrong hour, left mice heavier within a week.
Mark
So what did the researchers actually do here?
Mimi
They fed mice the same high-fat diet, but limited some to the dark period, when mice are active, and others to the light period, when they sleep. Within a week the light-fed mice had gained more weight.
Mark
And the food amounts were the same?
Mimi
The team describes the mice as eating the same amount at different times, which is what pushed them to look at energy expenditure instead.
Luke
I'd keep that in view: the setup points to timing, not calories. But this is mice, and the article doesn't say how many or how large the effect was.
Mark
What's the proposed mechanism?
Mimi
Thermogenesis, heat release through fat cells. Mice engineered for enhanced thermogenesis didn't gain the weight and were healthier. Hepler also found creatine cycling in fat tissue, which may drive that heat.
Luke
Careful with the word "may." Creatine as the driver is an implication, not a demonstrated cause. Hepler herself says they still need to work out how the clock controls creatine metabolism.
Mark
Why does Bass bring up feeding tubes?
Mimi
Those patients are often fed overnight, when energy release is lowest, and diabetes and obesity rates are high among them. Bass thinks this could explain it.
Luke
It's a hypothesis from the lead author, not a finding. Nobody has tested it in patients here, and the same goes for his question about timing insulin around meals.
Mark
So what's solid?
Luke
That in these mice, with temperature held at 30 degrees, meal timing changed weight gain. Everything about people is still a question.
Le Pouls
- Mice eating the same high-fat diet gained noticeably more weight when fed during their inactive light hours than when fed in their dark, active hours.
- Food intake was matched across groups, so researchers are asking what hidden energy burn is slipping away at the wrong hour.
- The team traced the effect into fat cells, where heat release through thermogenesis appears to protect against weight gain.
- Creatine cycling in fat tissue is a leading suspect for driving that heat, and the team is working to learn how the clock controls it.
- Clinicians are weighing whether night feeding for tube-fed patients and insulin timing in Type II diabetes deserve the same scrutiny, though every result so far comes from mice.
Across a Northwestern laboratory, mice fed the same rich diet grew heavier when they were allowed to eat during their resting hours than when they ate in their waking dark, even though they consumed about the same amount. The work, reported in Science, suggests that the body's internal clocks may govern how fat tissue releases energy as heat, a quiet process that could help explain why when we eat seems to matter as much as what we eat. It is a discovery still confined to mice, but it reopens an old human question about the hours we choose for our meals.
In a Northwestern University lab, mice were given the same high-fat diet and sorted by one variable: the hours when they were allowed to eat. Some ate only during their active dark period, when nocturnal mice are naturally awake. Others were restricted to the light period, when they would normally sleep. Within a week, the mice fed in the light had gained more weight than those fed in the dark.
The finding, published in Science, offers a candidate explanation for something researchers have long observed. Late-night eating has been tied to weight gain and diabetes, and overnutrition is known to disrupt circadian rhythms and alter fat tissue. The team reports that the release of energy as heat may be the molecular route by which the body's internal clocks regulate energy balance, with daytime appearing to be the best window for burning energy this way.
Dr. Joseph T. Bass, an endocrinologist at Northwestern's Feinberg School of Medicine, led the work. Chelsea Hepler, a postdoctoral fellow in his lab, ran many of the biochemistry and genetics experiments, and Rana Gupta, now at Duke, was a key collaborator. The room was held at 30 degrees, the temperature at which mice expend the least energy, so the environment would not skew results.
Because the mice ate similar amounts regardless of timing, the team looked for differences in energy expenditure and found them in fat tissue. Mice engineered for enhanced fat-cell thermogenesis were protected from weight gain and showed better health. Hepler also identified futile creatine cycling in fat tissue, a process in which creatine stores and releases chemical energy, which may be what drives the heat.
Bass noted that disruptions to the body clock are disruptions to metabolism, and that Western-style diets scramble that clock. Fat tissue is especially sensitive to meal timing, and as animals grow obese they begin eating when they should be sleeping. The implications reach toward clinical care: patients on night-time feeding tubes, who often release the least energy while asleep, have high rates of diabetes and obesity, and Bass wonders whether meal timing belongs in insulin dosing for Type II diabetes.
All of these findings come from mice, and the human questions remain open. Hepler plans to keep studying how the circadian clock controls creatine and whether that control can be boosted. Clocks, she said, do a great deal for metabolic health at the level of fat tissue, and how much is still unknown.
In a Northwestern University lab, mice were given the same high-fat diet and sorted by a single variable: when they were allowed to eat. Some had access to food only during their active period, the dark hours when mice, as nocturnal animals, are awake. Others could eat only during the light period, when they would normally be asleep. Within a week, the mice fed during the light hours had gained more weight than those fed in the dark.
The finding, published in the journal Science under the title "Time-restricted feeding mitigates obesity through adipocyte thermogenesis," offers a candidate explanation for something researchers have long observed. Eating late at night has been linked to weight gain and diabetes, and over-nutrition is known to disrupt circadian rhythms and alter fat tissue. The connection between meal timing, sleep and obesity has been well documented but poorly understood. The Northwestern team reports, for the first time, that the release of energy as heat may be the molecular route by which the body's internal clocks regulate energy balance. Daytime, in the light environment created by the Earth's rotation, appears to be the optimal window for dissipating energy this way.
The corresponding author is Dr. Joseph T. Bass, the Charles F. Kettering Professor of Medicine at Northwestern's Feinberg School of Medicine, an endocrinologist, director of the Center for Diabetes and Metabolism and chief of endocrinology in the department of medicine. Chelsea Hepler, a postdoctoral fellow in his lab, was first author and ran many of the biochemistry and genetics experiments behind the team's hypothesis. Rana Gupta, now at Duke University, was a key collaborator. To keep room temperature from skewing the results, the researchers held the environment at 30 degrees, the point at which mice expend the least energy.
The mice ate comparable amounts of food regardless of timing, so the team suspected the difference lay in energy expenditure. Hepler said they wondered whether the animals burned more energy when eating at particular times, which could explain why the same amount of food leaves them healthier when eaten during active periods. That led the researchers to examine metabolism in fat tissue, and they found the same effect there. Mice genetically engineered for enhanced thermogenesis, meaning heat release through fat cells, were protected from weight gain and showed improved health.
Hepler also identified futile creatine cycling in fat tissue. In this process creatine, a molecule that helps maintain energy, stores and releases chemical energy, which suggests it may be what drives the heat release. The work builds on research by Bass and colleagues at Northwestern more than 20 years ago, which linked the internal molecular clock to body weight, obesity and metabolism in animals.
Bass said it is well known that disruptions to the body clock are disruptions to metabolism. Western-style cafeteria diets, high in fat and carbohydrate, scramble the clock, he said, and fat tissue is particularly sensitive to when people eat. Why high-fat diets throw off that sensitivity remains unexplained, but as animals become obese they begin eating when they should be asleep. This research, he said, shows why that matters.
The implications Bass raises reach into clinical care. Patients with gastric feeding tubes are commonly fed at night while they sleep, when they release the least energy, and rates of diabetes and obesity run high among them. Bass thinks timing could be part of the reason. He also asks whether meal times should be factored into when insulin is given in Type II diabetes treatment.
All of the findings so far come from mice, and the clinical questions remain questions. Hepler plans to keep studying creatine metabolism, aiming to learn how the circadian clock controls it and how it might be boosted. Clocks do a great deal for metabolic health at the level of fat tissue, she said, and how much is not yet known.
Citations marquantes
As animals become obese, they start to eat more when they should be asleep. This research shows why that matters.— Dr. Joseph T. Bass, Northwestern University Feinberg School of Medicine
We need to figure out how, mechanistically, the circadian clock controls creatine metabolism so that we can figure out how to boost it.— Chelsea Hepler, postdoctoral fellow, Bass Lab
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