Everyone has an internal clock, called the circadian rhythm, that controls wake/sleep cycles, body temperatures, brain activity, and changes in hormone levels throughout the day. Disruption in these circadian rhythms can alter metabolism. In the latest issue of Cell Metabolism (epub ahead of print June 2012 DOI 10.1016/j.cmet.2012.04.019), Dr. Megumi Hatori and colleagues investigated how feeding patterns, in particular time restrictions to eating, can alter metabolism and the expression of genes that control the circadian rhythm.
Mice were divided into four groups as follows:
- Normal calorie diet, freely accessible all day
- Normal calorie diet, limited access
- High fat diet, freely accessible all day
- High fat diet, limited access
Mice are nocturnal and were placed on a 12 hour light/dark cycle. For groups 2 and 4, food was available from 1 hour after lights off (waking) until 3 hours before lights on (sleeping).
Their data were intriguing. Mice in both high fat diet groups consumed equivalent numbers of calories over a 24 hour period. Those with free access appeared to eat all day with no spike in intake at any regular time period, while those with limited access consumed their calories only during the 8 hour period.
As expected, mice with unlimited access to the high fat diet gained significant weight compared with either of the normal calorie diet groups. Conversely, the mice on the high fat diet with limited access did not have the same weight gain as the unlimited access group. Indeed, mice in the time restricted groups were lower weight than those with unlimited access. When comparing the high fat diet groups, the mice with limited food access did not become obese as did the unlimited access mice. In fact, their weight was only slightly higher than the normal calorie diet groups. In addition, the time restricted high fat diet group also retained sensitivity to insulin and did not exhibit liver problems as seen in the unlimited high fat diet group.
This very interesting study suggests that circadian rhythms control metabolism and restricting food intake to regimented periods during the day can help to keep the metabolism strong and avoid excessive weight gain. This is a small study in mice, but could have implications in human dieting and the control of weight gain.