It’s been known for a long time that when you begin to diet and consciously drop your calorie intake, the body progressively begins to compensate as it drops your metabolic rate to ensure your energy abundance is sufficient (1).
Although well documented, the role of the brain in activating this metabolic down-regulation is something that has less clear.
A recent study carried out by a team of researchers at the University of Cambridge has made some inroads in understanding the brains role on the metabolic switch whilst dieting.
The study was conducted on mice, who share many similar physiological and psychological characteristics as humans.
The study focused on the bundle of neurons within the brain, collectively known as the hypothalamus. This area plays a pivotal role on appetite. When these neurons are up-regulated, your appetite also increase, likewise when they the hypothalamus is disengaged, your appetite will drop.
The team used a genetic trick to switch the AGRP neurons (hypothalamus) ‘on’ and ‘off’ in mice so that they could rapidly and reversibly manipulate the neurons’ activity.
They studied the mice in special chambers, measuring energy expenditure, and implanted them with probes to remotely measure their temperature, a proxy for energy expenditure, in different contexts of food availability.
The teams finding suggest that it is this region of the brain that is responsible for regulating our caloric expenditure and consequently, weight loss.
The study revealed that the hypothalamus region of the brain being responsible for the amount of calories we consume and also limiting our caloric expenditure when food isn’t available, however as soon as you eat this region engages and calorie output returns to baseline.
In effect, the findings have highlighted a feedback loop that can detect available energy and make calorie output adjustments where necessary.
Although this is an essential evolutionary trait, in the modern world where food is abundant and calorie restriction are made consciously explaining why calorie restrictive diets can lead to weight loss plateaus.
Understanding the brains relationship with calorie expenditure is valuable for constructing and optimising weight loss therapies for the future by reducing overeating.
1. Josephine Connolly Theresa Romano Marisa Patruno. Effects of dieting and exercise on resting metabolic rate and implications for weight management. Family Practice, Volume 16, Issue 2, 1 April 1999, Pages 196–201