Think living on doughnuts is the worst thing you can possibly do for your weight?
Nope. According to researchers with the Salk Institute for Biological Studies in California, when you eat those doughnuts could make a huge difference in how your body responds to them.
A study published in the journal Cell Biology in December 2014 found that mice eating unhealthy foods at all times of day gained twice as much weight as mice eating the same diet in the same amounts but in nine-hour eating windows. The study backed up earlier Salk research.
The dietary approach is called time-restricted feeding (TRF), and the idea is simple. Food intake takes place only between certain hours of the day — say, 9 a.m. to 6 p.m. — rather than whenever the feeling strikes. The 2014 study, led Dr. Satchin Panda, associate professor in the Salk Regulatory Biology Laboratory, found this eating pattern to have dramatically positive health effects under certain conditions.
Panda and colleagues divided 392 male mice into four groups and fed each a different type of diet:
· High-fat/high-sucrose (table sugar)
· Low-fat/high-fructose (fruit sugar)
· Regular mouse food
Each group ate the same number of calories, just from different food sources.
Within each of the four dietary groups, half of the mice ate whenever they wanted, and half of the mice ate on TRF schedules with feeding windows ranging from eight to 15 hours. After 12 weeks, researchers checked their weights.
In the low-fat/high-fructose and mouse-food groups, differences in weight gain between the anytime mice and the TRF mice were unremarkable, according to an analysis by PubMed Health. But in the high-fat and high-fat/high-sucrose groups, the differences were staggering.
For the high-fat/high-sucrose diet, the nine-hour TRF mice gained 21.5 percent of their body weight, while the anytime mice gained 42.9 percent.
For the high-fat diet, the nine-hour TRF mice gained 26.4 percent of their body weight, compared to 43.9 percent for the 15-hour mice and 61.6 percent for the anytime mice.
The effects went beyond weight, though. Non-TRF mice eating the high-fat diets eventually developed high cholesterol, high blood sugar and liver damage. TRF mice eating the same diets had "nearly normal" levels in all three categories, Panda told Science NetLinks in January.
Scientists aren't entirely sure how this all works, but it seems to be at least partly related to circadian rhythms, the "body clock"-driven timing of daily biological processes. Metabolic systems have evolved to work most efficiently during hours of greatest activity, and animals haven't evolved to be active at all times of day. Eating during periods of low activity — at night, for humans — "disturbs this fine control of which genes are to be turned on at what time," says Panda.
"TRF fixes this timing issue, which is similar to having a good timing belt in a car so that every moving part of the engine moves in synchrony," he explains.
The other side of the issue is fasting. Dr. Mark Mattson, chief of the cellular and molecular neurosciences section at the National Institutes of Health, told the Wall Street Journal in February that fasting speeds up weight loss. After an extended period without caloric intake, the body runs out of glucose (blood sugar) to convert to energy, so it starts converting body fat instead. Fasting may also trigger liver functions that lead to reduced blood sugar, cellular-repair activity and cholesterol breakdown.
TRF's possible implications for human health are significant. Evidence derived from mice doesn't apply to humans, though, and human TRF studies are few. One from August 2015 did find that overweight women who fasted for longer periods overnight and started fasting by 6 p.m. had lower blood concentrations of a protein linked to Type 2 diabetes and breast cancer. And in a new pilot study out of the Salk Institute, overweight people who reduced their eating windows from about 14 hours to about 10 hours lost weight, slept better and had more energy.
"However," Panda says," when they reduced eating intervals, they also (unknowingly) reduced their caloric intake." So the exact role TRF played in the findings is unclear.
For that study, which is ongoing, the researchers developed a smartphone app to track subjects' eating patterns. They're offering it to any adult who wants to track and share their eating, sleeping and activity patterns.
Ultimately, only controlled studies can provide hard evidence for the health benefits of TRF in humans, and those might be a ways off. Still, those living on doughnuts who want to reduce their risks of metabolic illness might try paying attention to when they eat them.
Those living on doughnuts who want to be generally healthy will still need to stop living on doughnuts.