It turns out that when we eat may be as important as what we eat.
Led by Satchidananda Panda, an associate professor in the Regulatory Biology Laboratory, scientists at the Salk Institute for Biological Studies have found that regular eating times and extending the daily fasting period may override the adverse health effects of a high-fat diet and prevent obesity, diabetes and liver disease in mice.
They fed two sets of mice, which shared the same genes, gender and age, a diet comprising 60 percent of its calories from fat (like eating potato chips and ice-cream for all your meals). One group of mice could eat whenever they wanted, consuming half their food at night (mice are primarily nocturnal) and nibbling throughout the rest of the day. The other group was restricted to eating for only eight hours every night; in essence, fasting for about 16 hours a day. Two control groups ate a standard diet comprising about 13 percent of calories from fat under similar conditions.
Mice limited to eating during an 8-hour period are healthier than mice that eat freely throughout the day, regardless of the quality and content of their diet
After 100 days, the mice who ate fatty food frequently throughout the day gained weight and developed high cholesterol, high blood glucose, liver damage and diminished motor control, while the mice in the time-restricted feeding group weighed 28 percent less and showed no adverse health effects despite consuming the same amount of calories from the same fatty food. Further, the time-restricted mice outperformed the ad lib eaters and those on a normal diet when given an exercise test.
Their findings suggest that regular eating times and fasting for a significant number of hours a day might be beneficial to our health.
Fasting Time Important
"By eating in a time-restricted fashion, you can still resist the damaging effects of a high-fat diet, and we did not find any adverse effects of time-restricted eating when eating healthy food," says Megumi Hatori, a postdoctoral researcher in Panda's laboratory and a first author of the study. However, she cautioned that people should not jump to the conclusion that eating lots of unhealthy food is alright as long as we fast. "What we showed is under daily fasting the body can fight unhealthy food to a significant extent," she says. "But there are bound to be limits."
The Salk study suggests an option for preventing obesity by preserving natural feeding rhythms without altering dietary intake.
The Salk study found the body stores fat while eating and starts to burn fat and breakdown cholesterol into beneficial bile acids only after a few hours of fasting. When eating frequently, the body continues to make and store fat, ballooning fat cells and liver cells, which can result in liver damage. Under such conditions the liver also continues to make glucose, which raises blood sugar levels. Time-restricted feeding, on the other hand, reduces production of free fat, glucose and cholesterol and makes better use of them. It cuts down fat storage and turns on fat burning mechanisms when the animals undergo daily fasting, thereby keeping the liver cells healthy and reducing overall body fat.
The daily feeding-fasting cycle activates liver enzymes that breakdown cholesterol into bile acids, spurring the metabolism of brown fat -- a type of "good fat" in our body that converts extra calories to heat. Thus the body literally burns fat during fasting. The liver also shuts down glucose production for several hours, which helps lower blood glucose. The extra glucose that would have ended up in the blood -- high blood sugar is a hallmark of diabetes -- is instead used to build molecules that repair damaged cells and make new DNA. This helps prevent chronic inflammation, which has been implicated in the development of a number of diseases, including heart disease, cancer, stroke and Alzheimer's. Under the time-restricted feeding schedule studied by Panda's lab, such low-grade inflammation was also reduced.
"Implicit in our findings," says Panda, "is that the control of energy metabolism is a finely-tuned process that involves an intricate network of signaling and genetic pathways, including nutrient sensing mechanisms and the circadian system. Time-restricted feeding acts on these interwoven networks and moves their state toward that of a normal feeding rhythm."
Simple, Effective Lifestyle Intervention
"The take-home message," says Panda, "is that eating at regular times during the day and overnight fasting may prove to be beneficial. If following a time-restricted eating schedule can prevent weight gain by 10 to 20 percent, it will be a simple and effective lifestyle intervention to contain the obesity epidemic.”
The above story is based on the My 17, 2012 news release by SalkInstitute for Biological Studies.
The scientific findings has been published in Cell Metabolism which focuses on reports of novel results in any area of metabolic biology, from molecular and cellular biology to translational studies: Hatori M, Vollmers C, Zarrinpar A, DiTacchio L, Bushong EA, Gill S, Leblanc M, Chaix A, Joens M, Fitzpatrick JAJ, Ellisman MH, Panda S. Time-Restricted Feeding without Reducing Caloric Intake Prevents Metabolic Diseases in Mice Fed a High-Fat Diet. Cell Metab, 2012; DOI: 10.1016/j.cmet.2012.04.019
The National Health and Morbidity Survey in 2006 showed that two out of every five adults or 43%, were either overweight or obese and an alarming situation where the number of obese adults had more than tripled over a decade, from 4% in 1996 to 14% in 2006.
Obesity increases the risk of a number of health conditions including: high blood pressure, high cholesterol and type 2 diabetes. Lifestyle modifications, including eating a healthy diet and daily exercise, are first-line interventions in the fight against obesity.