Nerves are to blame: yo-yo effect decoded
Those who have stuck to a diet are often only at the beginning: because it becomes really difficult to keep the weight off in the long term. A new study has now uncovered the cause of the yo-yo effect and thus opened up a starting point for the development of medication to combat unwanted weight gain.
Diets are a dime a dozen: low-carb, ketogenic diets, intermittent fasting, paleo diets, FdH (eat your half)... the list could go on and on. What all these diets usually have in common is that they involve going without, eating fewer calories than you burn: the body is starving.
Scientists from the Max Planck Institute for Metabolism Research and Harvard Medical School have now been able to decipher the neuronal processes that often lead to the yo-yo effect, i.e. renewed weight gain, after a diet: In their study, they explain how the reduced calorie intake boosts the activity of "hunger neurons" in the brain, which then leads to an increased urge to eat and renewed weight gain in the long term, even after the diet.
Diet changes neuronal processes in the brain in the long term
So far, studies on the topic of dieting have mainly focussed on the short-term consequences for the body. Now, for the first time, it has been shown that the reduced calorie intake continues to affect neuronal processes in the brain even after the diet has ended:
Weight loss, when fewer calories are consumed than the body needs, increases the activation of so-called AgRP neurones (colloquially known as hunger neurones) in the hypothalamus. This signal ensures that we eat more to compensate for the lack of food. What is new is that AgRP activity, i.e. the feeling of hunger, remains elevated long after the diet - namely until the lost weight has been regained.
Important for survival for our ancestors - fatal for any dieting success today
As unfavourable as this mechanism is for us today in a world of abundance, it was important for our ancestors to ensure their survival. If there was a prolonged period of hunger back then, it was essential for survival to make up for the weight loss as quickly as possible. The fat reserves had to be replenished in order to be prepared for the next period of scarcity. From this perspective, it is only logical that metabolic processes have developed that cause people to eat more again after starvation until their original weight is restored.
However, this is fatal when trying to get rid of excess weight. A problem that played no role in the evolution of these metabolic processes. As a result, our brain specifically works against our intention to reduce fat reserves, as this makes little sense from an evolutionary perspective. The diet and the associated weight loss signal to our brain that there is a deficiency situation that needs to be compensated for as soon as possible. The long-lasting reinforcement of the hunger signal then leads to the yo-yo effect after the diet, as our brain is only satisfied once the fat reserves have been replenished - and the success of the diet has been cancelled out.
Results provide a starting point for drugs that prevent the yo-yo effect
Although the study results are sobering for anyone hoping to lose weight in the long term with diets, they also represent the starting point for the development of drugs to prevent subsequent weight regain. The authors of the study have already succeeded in suppressing the reinforcement effect of the hunger signal in mice after a period of reduced calorie intake. These mice did not regain the weight they had lost after their "diet". The next goal is now to develop drugs that will also enable us humans to maintain our weight permanently after a diet.
Caption photo: Lee Charlie/Shutterstock
Science editor and biologist. I love animals and am fascinated by plants, their abilities and everything you can do with them. That's why my favourite place is always outside - somewhere in nature, preferably in my wild garden.