We do not decide to be hungry or full after a meal, do we? We just feel either one of those sensations in a due time and then proceed with relevant actions.

Nor can we comprehend why we prefer a chocolate bar over a green apple for a late afternoon snack, when in the morning we firmly intended to persevere with healthy choices.

So, if our eating behaviour and food choices are not entirely in our conscious control and sometimes run counter to our intentions, what are the other forces at play, how do they work, and why do they often seem to ruin our plans?
 

“The need to find fuel to generate energy is a profound drive within the biology of all living organisms: we all need food to survive. So, it’s not surprising that our bodies have such a complex system to control food intake, driven by hormones,” explains Joseph Proietto, professor of medicine at University of Melbourne

It appears that hormones act like chemical messengers between the body and the brain that coordinates our eating behaviour and food choices.

These hormones circulate in the blood and come from tissues in various parts of the body that deal with energy intake and storage, including the gut (which receives and digests food), fat tissue (which stores the energy as fat), and the pancreas (which makes hormones that are involved in energy storage, such as insulin).

These hormones circulate in the blood and come from tissues in various parts of the body that deal with energy intake and storage, including the gut (which receives and digests food), fat tissue (which stores the energy as fat), and the pancreas (which makes hormones that are involved in energy storage, such as insulin.
 

Some hormones are responsible for stimulating hunger (let’s call them “hunger hormones”) while others responsible for making us feel full (let’s call them “satiety hormones”).

Below is a simplified overview of the hormones involved in appetite regulation. In it you can see where the different hormones are released by the body, and how they affect your appetite.
 

Once full, the stomach reduces our desire to eat by producing less of the hunger hormone and sending a message to the brain to make us stop eating. At the same time, the levels of satiety hormones increase following a meal and reach a peak between 30 and 60 minutes later.

This dynamic interplay of messages from the hunger and satiety hormones helps our brain to regulate our eating behaviour. Another set of hormones can steer our food choices and motivate us to eat, even in the absence of physical hunger.
 

It seems that hormone levels also change when we lose weight. Several studies have found that diet-induced weight loss is associated with hormonal changes that promote weight regain.

Following weight loss, levels of satiety hormones decrease and levels of hunger hormones increase. These changes lead to a persistent increase in hunger, reduced feelings of fullness and burning fewer calories. These changes may last for up to three years and are probably part of the reason why 8 out 10 people end up regaining lost weight in the long run.

These findings suggest that suppressing hunger after weight loss, may help people to maintain their new weight.
 

It’s important to remember that we cannot control our hormones. When we feel hungry, it is very hard not to eat – no matter how much we might not want to. But learning how our hormones work can help us understand what types of interventions and strategies may be needed to effectively manage our weight.