While some of these factors appear to be genetic, others appear to be environmental. For example, a lack of adequate amounts of sleep has been linked to one's risk for obesity and can impact dieting success. A potentially related nighttime phenomenon, "light at night", has recently been suggested to impact body weight.
A new obesity research study examined the potential relationship between nighttime light exposure (or "light at night") and body mass in male mice[1]. The obesity researchers housed mice under different lighting conditions (standard light/dark cycle, dim light, or bright light) over the 8-week study period and measured changes in body weight, food intake, physical activity, and metabolism. The study investigators reported:
Mice housed in bright light and dim light showed an increase in body weight as early as the first week of the study compared to mice housed in a normal light/dark cycle.
The increase in body weight was at least partly due to an increase in fat mass in the mice exposed to light at night.
Total daily physical activity and food intake was not different between mice housed in different lighting conditions; however, differences were noted in the timing of eating.
Mice housed in dim light consumed about 55% of their food during the light phase, which is a shift in the normal eating habits of nocturnal mice. The mice housed in normal light conditions consumed only about 36% of their food during the light phase.
Limiting food consumption of mice housed in dim lighting conditions to only normal eating times prevented weight gain.
This is a fascinating study that suggests even low amounts of light at night, about equivalent to twilight with a clear sky, alters metabolism, alters the timing of regular food consumption, and promotes weight gain. While these are interesting results, it will be more interesting to see if this holds true in human beings. Our internal body clock helps to determine many of the schedules we keep including when we eat and when we sleep. Because the hormone melatonin is closely involved in our internal clock and is affected by light exposure, changes in melatonin might be partly responsible for this disruption in normal metabolism and eating behaviors. As a population, we are typically exposed to high amounts of light at night from computers, television, and other artificial sources of light. While watching television and sitting in front of a computer can increase our chances of gaining weight due to a lack of physical activity, these results imply that exposure to their artificial light might negatively effect our dietary habits. However, much more research will be needed to clarify this relationship as well as the level of impact it might have.
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