Usually your brain sabotages your fitness and weight loss goals in not-so-subtle ways like filling your head with doubts, killing your motivation, or telling you it’s OK to eat all of the Pringles in the can. And it also does it by compensating when you eat fewer calories by burning less of those calories, kind of like a thermostat, but how it did that is a mystery.

A new study from the Metabolic Research Laboratories at the University of Cambridge, though, has discovered how your brain cells can keep you from losing weight at a microscopic level. Researchers tested how certain neurons in the hypothalamus region of mice brains affect appetite by using a genetic manipulation technique that allowed them to turn them on and off quickly and frequently. They then tracked the mice’s energy expenditure, and found that these neurons are essential to adjusting the caloric thermostat central to regulation of our weight.

"If food is available, [these neurons] make us eat, and if food is scarce, they turn our body into saving mode and stop us from burning fat,” said study lead Clémence Blouet, Ph.D. "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."