In modern times, eating at all times of day and night has become quite common. We often graze and snack until the time we go to bed, also leaving little time between each episode of eating and drinking. So, could this type of eating pattern have any impact on the risk of obesity and metabolic syndrome, including type 2 diabetes?
A new study in mice published in the journal Cell Metabolism suggests that it could. In this study, mice prevented from eating all hours reduced their risk of obesity and metabolic problems even when the diet was sometimes unhealthy or ad libitum feeding was allowed for short periods, say at weekends. Time restricted feeding also stabilised and reversed the progression of metabolic diseases in mice with pre-existing diabetes and obesity.
Researchers at the Salk Institute for Biological Studies in San Diego and elsewhere began experimenting with the eating patterns of laboratory mice in a study published in 2012. In that study, some mice consumed high-fat food whenever they wanted; others had the same diet but could eat only during an eight-hour window. None exercised. The mice that ate at all hours soon grew fat and unwell, with symptoms of diabetes. But the mice on the eight-hour eating programme gained little weight and developed no metabolic problems.
For the new study, the researchers fed groups of adult male mice one of four diets: high-fat; high-fructose; high-fat and high-sucrose; and regular mouse kibble. Some of the mice in each dietary group were allowed to eat whenever they wanted throughout their waking hours; others were restricted to feeding periods of nine, 12 or 15 hours. The energy intake for all the mice was the same.
Over the course of the 38-week experiment, some of the mice in the time-restricted feeding groups were allowed on weekends to eat whenever they chose. A few of the mice who could eat anytime were shifted to the restricted eating pattern midway through the study.
By the end, the mice eating at all hours were generally obese and metabolically ill, reproducing the results of the earlier 2012 study. But those mice that ate within a nine- or 12-hour window each day remained slim and healthy, even if they ate as they liked occasionally on weekends, a regimen particularly relevant to human lifestyles. In addition, mice that were changed from an eat-anytime schedule to a restricted time feeding schedule lost some of the weight they had gained.
Time-restricted eating both prevented and reversed obesity in the mice. Mice that consumed regular kibble in fixed time periods also had less body fat than those that ate the same food whenever they chose. Time restricted feeding reduced inflammation and improved glucose and insulin homeostasis.
How a time-restricted eating pattern prevented weight gain and metabolic illness in mice is not fully understood, but the researchers think that the time at which food is eaten influences a body’s internal clock. Meal times have more effect on circadian rhythm than dark and light cycles. Circadian rhythm in turn affects the function of many genes in the body that are known to involve metabolism.
To date, the Salk Institute studies have been conducted with only mice, but the researchers think the findings could apply to humans. A large-scale clinical intervention trial could show whether this time restricted eating pattern, ie over a period of 12 hours, could also reduce the risk of obesity, type 2 diabetes and other metabolic disorder in humans.