Why do we sometimes feel hungry soon after a meal, why do certain foods keep us feeling full for longer, and how do insulin, ghrelin and leptin play a part in regulating our appetite?
Appetite is much more than just the sensation that our stomach is empty. It is the result of complex communication between the brain, the digestive system, adipose tissue and metabolic signals, which inform the body when it needs energy and when it has enough.
This system is known as brain-spinal axis and plays an important role in regulating eating behaviour, satiety and energy balance. This is precisely why hunger cannot be explained solely by a person’s willpower or discipline.
Ghrelin is a hormone produced mainly in the stomach. Its levels usually rise before a meal and fall after eating. It plays a role in signalling hunger and affects the brain structures associated with eating behaviour.
Interestingly, the composition of the diet can also influence this response.
Protein, for example, can help to suppress hunger in the short term. A systematic review and meta-analysis of randomised controlled trials found that, following protein intake, participants reported feeling less hungry and more full, whilst a reduction in ghrelin was also observed. The long-term effects, however, are less clear-cut.
A breakfast containing eggs, yoghurt or another suitable protein-rich food may provide a greater feeling of fullness than a meal consisting mainly of easily digestible carbohydrates and little protein. The effect depends on the overall composition and quantity of the meal, as well as on individual characteristics.
Unlike ghrelin, leptin is produced mainly by adipose tissue. It provides information about the body’s energy reserves and plays a role in the long-term regulation of appetite and energy balance.
When energy stores are sufficient, leptin helps signal to the brain that the body has energy available. During a prolonged energy deficit, its levels usually fall, which can increase hunger and trigger physiological adaptations that make it difficult to maintain weight loss.
There is one important point to note here: in people with obesity, leptin levels are often elevated, but this does not necessarily mean that its signal is transmitted effectively. In some people, the following is observed: leptin resistance — a reduced response to leptin despite its presence in the bloodstream.
This is one of the reasons why regulating body weight is more complicated than the simple equation „less food = less weight“.
It is important to note that there is no specific food which, on its own, can „reverse“ leptin resistance. The approach must take into account overall metabolic health, diet, physical activity, sleep and individual clinical factors.
Insulin is a hormone produced by the beta cells of the pancreas. Its main role is to regulate glucose metabolism, but it also plays a part in signalling to the brain regarding energy status and appetite.
After a meal, particularly one containing carbohydrates, insulin levels usually rise. This is a normal physiological response and not necessarily a sign of a metabolic problem.
Insulin interacts with other signalling molecules, including ghrelin and leptin. However, the relationship between these hormones is complex and cannot be reduced to the assertion that any rise in insulin levels leads to subsequent hunger.
In the case of insulin resistance, the body responds less effectively to the action of insulin, and the pancreas may compensate by secreting larger amounts of it. Chronically elevated insulin levels may accompany this condition, but do not in themselves prove that hormonal control of appetite is impaired.
It is therefore important to distinguish between the normal postprandial insulin response and chronic hyperinsulinaemia in the context of metabolic health.
It is not a question of avoiding certain macronutrients, but of understanding how the composition of our diet affects satiety, digestion and the metabolic response.
1. Proteins
Eggs, fish, yoghurt, meat and pulses can help promote a feeling of fullness. Protein influences ghrelin and the release of gut signals of satiety, including GLP-1 and cholecystokinin. The evidence is most consistent for the short-term effect following a meal.
2. Fibre
Oats, pulses, vegetables, fruit, nuts and whole grains provide fibre, which can influence digestion and the glycaemic response. Some types of fibre are fermented by the gut microbiota and produce short-chain fatty acids, which play a role in signalling between the gut and the brain.
The effect depends on the type of fibre, the amount of fibre and the overall composition of the diet.
3. Carbohydrates
Not all carbohydrate-rich foods elicit the same glycaemic response. Wholemeal foods, pulses and whole fruits provide a different nutritional profile compared with refined, low-fibre products.
Combining carbohydrates with protein, fibre and appropriate amounts of fat can alter the rate of digestion and the postprandial glycaemic response. This does not mean that carbohydrates should be restricted across the board, but rather that the quality and composition of the diet matter.
The feeling of hunger does not depend solely on hormones. Other factors also play a part:
Consequently, feeling hungry shortly after a meal is not, in itself, sufficient grounds to conclude that there is insulin resistance, a hormonal imbalance or any other metabolic problem.
Rather than looking for foods that „balance hormones“, it is more beneficial to develop a diet that promotes satiety and metabolic health:
There is no one-size-fits-all meal frequency that optimally regulates appetite in all people. For some, three main meals are suitable, whilst for others, additional snacks between meals are recommended, depending on their hunger levels, lifestyle and clinical needs.
Hunger is not simply a signal from an empty stomach, but the result of the interaction between the brain, hormones, the gut, energy reserves and the environment in which we eat.
Ghrelin plays a role in signalling hunger, leptin provides information on energy reserves, and insulin regulates metabolism and is involved in communication with the brain. Gut hormones such as GLP-1 and PYY complement this system.
Understanding these mechanisms helps us to view nutrition in terms of more than just calories, and weight management in terms of more than just willpower. The aim is not to „outsmart“ our hormones, but to create conditions in which the physiological signals of hunger and satiety can be supported through sustainable, personalised and scientifically sound eating habits.
Take a look at the online course „REMISSION | The DietitianMED Method“, where you will find structured training and practical resources on the nutritional approach to these conditions.
