Eating at the wrong time can cause obesity
It doesn't matter if you're not taking in more calories - eating at the wrong time can also cause weight gain. A new study in Nature Medicine shows that removing the clock gene in fat cells causes mice to become obese, with a shift in the timing of when the animal normally eats.
The study is surprising in two respects. "The first is that a relatively modest shift in food consumption to what is normally the rest period for mice can favour energy storage," says Georgios Paschos, study author and a research associate at the University of Pennsylvania. "Our mice became obese without consuming more calories."
Indeed, the researchers could also cause obesity in normal mice by replicating the altered pattern of food consumption observed in mice with a broken clock in their fat cells.
This behavioural change in the mice is somewhat akin to night-eating syndrome in humans, also associated with obesity and originally described by Dr Albert Stunkard, a professor at the University of Pennsylvania, in 1955.
The second surprising observation relates to the influence the fat cell clock has. Clocks in peripheral tissues were thought to follow the lead of the "master clock" in the part of the brain that controls circadian rhythms.
Daily intake of food is driven by genes that drive and suppress appetite in the hypothalamus, the brain area that controls certain metabolic processes. When the clock was broken in fat cells, this rhythm was disrupted to favour food consumption at the wrong time.
When the typical daily rhythm is thrown off, changes in metabolism also happen. For example, in people, night shift workers have an increased prevalence of obesity and metabolic syndrome, and patients with sleep disorders have a higher risk for developing obesity. Also, less sleep means more weight gain in healthy men and women.