Is your brain making you fat? Well, not exactly. A healthy diet without a lot of fat and sugar is a good idea, however, sometimes the brain can interfere with even the best efforts at losing weight. New research on a mouse model has suggested that certain brain cells can become active in response to dieting and this activation can prevent the body from burning calories.
The body, controlled of course by brain activity, tends to burn fewer calories when fewer calories are consumed, and burn more calories when consumption goes up. Dr. Clémence Blouet from the Metabolic Research Laboratories at University of Cambridge where the research was conducted explains, "Weight loss strategies are often inefficient because the body works like a thermostat and couples the amount of calories we burn to the amount of calories we eat. When we eat less, our body compensates and burns fewer calories, which makes losing weight harder. We know that the brain must regulate this caloric thermostat, but how it adjusts calorie burning to the amount of food we've eaten has been something of a mystery."
The mechanism by which the body slows caloric burn in response to reduced intake was studied in mice, since the mouse brain operates much like the human brain. Looking at specific neurons in the hypothalamus, the team focused on 'agouti-related neuropeptide' (AGRP) neurons. They are known to be a main part of how appetite is processed in the brain. When they are active, they cause the brain to signal hunger and the mice seek food. When they are not active, the brain does not signal hunger or the urge to find food.
Using genetic manipulation to switch the AGRP neurons on and off, the team studied the mice closely to see what would happen. The mice were housed in specially equipped cages that could track their energy output. In addition, probes were implanted in the mice so that internal temperatures could be monitored remotely, without having to handle or disturb the mice
The team documented that the AGRP neurons were a significant part of the thermostatic process that regulates weight. When these neurons fired, the mice were hungry and would seek food. When no food was available, the neuron's purpose was changed to cause the mice to limit energy expenditure and thus burn less calories. The exact opposite of what most dieters want. If limiting the intake of food causes caloric burn to slow down, strict dieting might not be the best way to lose weight. As soon as food becomes available and we start eating, the action of the AGRP neurons is interrupted and our energy expenditure goes back up again to normal levels. This is likely related to why yo-yo dieting almost never works long-term.
Dr. Blouet added, “While this mechanism may have evolved to help us cope with famine, nowadays most people only encounter such a situation when they are deliberately dieting to lose weight. Our work helps explain why for these people, dieting has little effect on its own over a long period. Our bodies compensate for the reduction in calories.”
Exercise is one way to offset the lowered calorie burning that the AGRP neurons can cause. Study first author Dr Luke Burke stated, "This study could help in the design of new or improved therapies in future to help reduce overeating and obesity. Until then, best solution for people to lose weight -- at least for those who are only moderately overweight -- is a combination of exercise and a moderate reduction in caloric intake.” The research is published in the journal eLife. In addition, the video below offers more insight on this newly-described mechanism of caloric intake and burn, check it out.