The goal of this study was to determine if the presence or absence of food had an effect on the circadian patterns of mammals. The scientists who conducted this study believed that there would be a mild effect on thee circadian patterns of the rats studied. Activity was measured to determine the circadian. The food anticipatory activity was the unit of measure and allowed the scientists to compare the various cohorts with one another.

In all these graphs, the x-axis is made of time while the y-axis is made of activity. These graphs show the change in circadian pattern due to food consumption only being allowed at odd times. The rats were withheld food until the middle of the day, as such the rats began to wake up during the day to eat. Eventually this began to change their circadian pattern causing them to switch over from nocturnal to diurnal effectively confirming the hypothesis that food intake alters circadian rhythm. It was found that food intake changes the release time and abundance of various hormones. This alteration includes melatonin. Essentially, the rats were more likely to wake up and stay awake with a regular morning meal and the rats were more likely to sleep longer if a meal was presented only sporadically or not at all.

I would like to ask the author of this study if there is any evidence that a lunchtime and evening meal have different effects on activity.

Mendoza, J. (2007), Circadian Clocks: Setting Time By Food. Journal of Neuroendocrinology, 19: 127–137. doi: 10.1111/j.1365-2826.2006.01510.x