Hunger Hormone Leptin Influences Mice To Choose Sex over Food

Summary: Since the discovery of leptin and ghrelin, our understanding of obesity has improved considerably. These are hormones with opposing actions on appetite, with leptin increasing satiety. However, leptin has other influences on animal behavior, too. A new study shows leptin influences acutely hungry mice to choose sex over food. However, this action was not seen in mice chronically deprived of food. These findings may suggest why chronic food deprivation or dietary measures often fail to counter obesity.

 Obesity and metabolic disorders have risen considerably in the last few decades. Fortunately, our understanding of gut and brain health and its role in metabolic disorders has also improved significantly in the last few decades.

Humans have always known that obesity occurs due to increased food intake and low-calorie expenditure, which is pretty simple to guess. However, doctors know that there is more to obesity. Therefore, they knew that they needed to understand better food addiction, the role of mood, hormones, and so on in obesity.

In the last few decades, researchers have developed a much better understanding of the endocrinal role of the gastrointestinal tract. Since, now, we know that the gut not only secretes digestive enzymes but it is also an active endocrinal organ. The gut releases a range of hormones that influence brain health, mood, food choices, appetite, metabolic rate, etc. These actions occur both due to the local action of these hormones and their impact on the brain and even other body organs.

Thus, in the 1990s, they discovered gut hormones like leptin and ghrelin. Leptin is often described as a hormone that suppresses appetite, and ghrelin is a hormone that boosts appetite. But, researchers know that there is much more to learn about these hormones, as they have a much broader impact on animal behavior.1

Now a new study published in the Cell Metabolism shows that leptin is not only good for enhancing satiety and suppressing appetite, but it may also influence the sexual behavior of animals. It can influence social behavior, eating, drinking, and other choices. This is perhaps because leptin acts on a certain population of neurons in the hypothalamus that have multiple roles in the body.2

It means that hormones like leptins are not just for controlling hunger but play a broader role in well-being by balancing socializing, mating, and so on. These hormones help balance social needs and nutrition.

Thus, their study found that if they stimulated the neurons that are generally stimulated by leptin, this forced acutely hungry mice to prioritize social interaction over hunger or thirst. Researchers say this makes sense as mating partners are difficult to find, so socializing with a partner is preferred over acute hunger. After all, skipping a meal or two won’t do much harm.

But that is not all. Researchers have many other interesting findings. For example, they found that leptin promoted socialization in acutely hungry mice but not chronically hungry mice. Chronic hunger occurs due to prolonged scarcity of food. In such cases, leptin did not promote socialization. This is logical, too. If hunger is chronic, then getting sufficient nutrition is more important than socializing or having sex.

All this means that how leptin influences animal behavior will depend on the kind of food deficiency. For example, mice can neglect acute food deficiency and prefer socializing over food. However, chronic food restriction alters the effect of leptin, and it does not cause an increase in socialization or preference for sex over food.

This has some practical implications for humans, too. Researchers say this partially explains why highly restrictive diets practiced for a long often fail to help people lose weight successfully since leptin fails to boost mood or increase socialization in those chronically deprived of food. 

It also means that chronic food deprivation may negatively affect brain health. In addition, chronic food restriction may negatively influence mood. People deprived of food for a long may start losing interest in sex and socializing. 

Of course, we still need to understand much about the hormones that influence appetite. Nonetheless, this study shows that things are quite complex. Hence, managing obesity and metabolic disorders would need a multi-dimensional approach.