A new study published in the journal Cell Metabolism by scientists at the Salk Institute in La Jolla (California) has found that metabolic disorders, such as obesity, can be corrected by a type of intermittent fasting, wherein a person eats all of his/ her calories for a day within a 10-hour window.
The study concluded that the type of intermittent fasting called ‘time-restricted feeding,’ or TRF, not only prevented obesity in mice, but it did so without changing the type of foods they ate, or their level of physical activity. “For many of us, the day begins with a cup of coffee first thing in the morning and ends with a bedtime snack 14 or 15 hours later. But restricting food intake to 10 hours a day, and fasting (for) the rest, can lead to better health, regardless of our biological clock,” said Professor Satchidanada Panda at Salk’s Regulatory Biology Laboratory and senior author of the study.
In mammals’ bodies, every cell operates on a 24-hour cycle known as the circadian rhythm - cellular cycles that govern when various genes are active. This helps the body determine where, and when, certain genes should be active, such as the genes for digestion. In humans, for example, the genes for digestion are more active earlier in the day while genes for cellular repair are more active at night. In an earlier study, the researchers had discovered that mice allowed 24 hours access to a high-fat diet became obese and developed a slew of metabolic diseases including high cholesterol, fatty liver and diabetes. These same mice, when restricted to a high-fat diet for a daily 8- to 10-hour window, became learn, fit and healthy. The study attributes these health benefits to keeping the mice in better sync with their cellular clocks - for example, by eating most of the calories when the genes for digestion were more active.
In the latest study, researchers aimed to better understand the role of circadian rhythms in metabolic diseases by disabling genes responsible for maintaining the biological clock in mice, including in the liver which regulates many metabolic functions. The genetic defects in these clock-less mice make them prone to obesity, diabetes, fatty liver disease and elevated blood cholesterol. These diseases are known to further escalate when the animals are allowed to eat fatty and sugary food.
For the study, the scientists had split mice into two groups - one that had 24-hour access to food and another that had access to the same amount of calories, but only for 10 hours a day. The group that could eat at any time became obese and developed metabolic diseases, but the group that was limited to the 10-hour window remained lean and healthy, even though they lacked the biological clock and were thought to be destined to be unhealthy.
“From the previous study, we had been under the impression that the biological clock was internally timing the process of turning genes for metabolism on and off at predetermined times,” said Amandine Chaix, a staff scientist at Salk. “And while that may still be true, this work suggests that by controlling the animals’ feeding and fasting cycles, we can basically override the lack of an internal timing system with an external timing system.”
According to the new research, the primary role of circadian clocks may be to tell the animal when to eat and when to stay away from food. This internal timing strikes a balance between sufficient nutrition during the fed state and necessary repair or rejuvenation during fasting. Disruption of this circadian clock, for instance, when humans do shift work or when it is compromised due to genetic defects, skews the balance between nutrition and breaks down rejuvenation, allowing diseases to set in. Age is also known to weaken circadian clocks. Age-dependent deterioration of circadian clock parallels our increased risk for metabolic diseases, heart diseases, cancer and dementia.
However the scientists did have some good news that a simple lifestyle, such as eating all food within 10 hours, can restore balance, stave off metabolic diseases and maintain health. “Many of us may have one or more disease-causing defective genes that make us feel helpless and destined to be sick. The finding that a good lifestyle can beat the bad effects of defective genes opens new hope to stay healthy,” says Professor Panda.
The researchers are planning to further study whether eating within 8-10 hours can prevent or reverse many diseases of aging, as well as looking at how the current study could apply to humans. By potentially collecting daily eating and health status data from thousands of people, the lab hopes to gain a better understanding of how a daily eating-fasting cycle sustains health.
