Recent research provides new insight into how the body reduces burning calories during a diet. A new piece in the puzzle that should explain why losing weight sometimes seems so damn hard or increasingly difficult.
Slowing down calorie burning: Diet resistance
It remains difficult; to lose weight you need to create an energy deficit and thus a negative energy balance. You have to eat less than you consume. However, your body reacts by lowering consumption. You receive less, so your body becomes ‘more efficient’ and ensures that you also consume less. When exactly this happens and to what extent can cause significant differences in how people respond to a diet. Some have to put in relatively much more effort for the same result because their body is ‘smarter’ in adjusting to the environment.
I call ‘more efficient’ and ‘smarter’. Terms that normally sound positive, but now cause an unwanted effect. Once and somewhere, it’s fantastic if your body starts consuming less when less food is coming in. In times and places when and where that means that there is also less food available. Here and now, however, in a time when it often takes more effort not to eat too much than to eat enough, makes losing weight a lot harder.
A new study by the University of Cambridge shows insight into a way the body achieves this saving effect[1]. Important brain cells that act as a trigger when food is ‘scarce’.
“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.
In their research with mice, researchers identified a new mechanism by which the body adjusts to low calorie intake and thereby limits weight loss. The researchers tested a group of neurons in the hypothalamus, the so-called ‘agouti-related neuropeptide’ (AGRP) neurons. These neurons are known for their significant role in regulating appetite. When activated, they increase appetite. However, if they are completely deactivated, they would lead to anorexia.
The researchers used a method to turn the AGRP neurons on and off in mice. The mice themselves stayed in special chambers to measure energy consumption. Sensors were implanted to measure temperature, an indicator of energy consumption. Here, the effects were observed under various conditions of available food.
With their research, the team was able to demonstrate that AGRP neurons make a significant contribution to body temperature and the way it facilitates calorie burning. Their study shows that AGRP neurons increase appetite when activated, but ensure that calorie burning is reduced when no food is available. As soon as eating resumes, this function of the AGRP neurons is stopped, and calorie burning rises back to a normal level.
In addition, they also discovered a mechanism by which AGRP neurons can determine how much energy the body has and then decide how much needs to be burned.
Eat a little less, move a little more
The researchers hope to provide more insight into why eating less yields diminishing returns. Smaller calorie deficits combined with more physical activity would be the best approach.
In addition, it would also be nice if we could make it clear to those neurons in the future when reducing calorie burning is not efficient but undesirable.
References
- Luke K Burke, Tamana Darwish, Althea R Cavanaugh, Sam Virtue, Emma Roth, Joanna Morro, Shun-Mei Liu, Jing Xia, Jeffrey W Dalley, Keith Burling, Streamson Chua, Toni Vidal-Puig, Gary J Schwartz, Clémence Blouet . mTORC1 in AGRP neurons integrates exteroceptive and interoceptive food-related cues in the modulation of adaptive energy expenditure in mice. eLife, 2017; 6 DOI: 10.7554/eLife.22848
