When rats are fed a high-fat diet, it disturbs the body clock in their brain that normally controls satiety, leading to overeating and obesity. This is according to new research published in the Journal of Physiology.
The number of people with obesity has nearly tripled worldwide since 1975. Obesity can lead to several other diseases such as type 2 diabetes, heart disease, stroke and some types of cancer.
This research conducted by the Jagiellonian University in Krakow and the University of Bristol may be a cornerstone for future clinical studies that could restore proper functioning of the body clock in the brain to avoid overeating.
Dr Lukasz Chrobok, lead author of the study said, “I’m really excited about this research because of the possibilities it opens up to tackle the growing health issue of obesity.”
Historically researchers believed that the master body clock was located in the brain’s hypothalamus.
However, further research over the years has shown that some control of our body’s daily rhythms (hormone levels, appetite, etc.) lies in several other parts of the brain and body, including a group of neurons in the evolutionary ancient brainstem, called the dorsal vagal complex (DVC).
Specifically, the DVC controls food intake by inducing satiety.
Research found that fat-fed rats, before they started to gain weight, showed changes in the DVC’s daily neuronal rhythms and the response of these neurons to appetite hormones.
What it means for humans
Research has also shown that in obesity, daily rhythms in food intake and the release of eating-related hormones are blunted or eliminated.
However, it has not been clear if the malfunctioning of brain centres controlling appetite is a cause or the result of obesity.
Thus, the researchers propose that disturbance in the DVC’s timekeeping leads to obesity, rather than being the result of excessive body weight.
The research was performed on two groups of rats: those fed a well-balanced control diet (10% kcal from fat) and a high-fat diet (70% kcal from fat).
To mimic the impact of an unhealthy diet on humans, the researchers introduced the new diet to adolescent (4-week-old) rats and monitored their food intake across 24 hours for four consecutive weeks.
While the human and mouse brainstem shares common features, the major limitation of the study for its immediate translation to humans is that it was performed on nocturnal animals (rats).
The peak of the DVC activity was observed at the end of the day, which is the rest phase for rodents, but an active phase for people.
Thus, it remains to be established if the phase of the brainstem clock is set to day and night, or whether it depends on patterns of rest and activity.
This study opens new research opportunities for trying to establish the strategy how to restore body clock function of the DVC, and therefore help tackle obesity.
Chrobok added, “We still do not know what are the time cues which are able to reset or synchronise the brainstem clock. Hopefully, the restoration of daily rhythms in this satiety centre before or after the onset of obesity may provide new therapeutic opportunities.”