What is hunger?
Hunger is our bodies' response to having eaten less than normal. It is caused by the brain reading changes in the levels of hormones and nutrients in the blood.
It is our reaction to this feeling that can make us overeat or eat the wrong things. So if we understand our hunger, can we control it better?
Why do I not feel full?
How full we feel is strongly influenced by what we eat. If we do not feel full our brains want to keep searching for food.
Different types of food we eat affect the brain in various ways. For example, fatty foods trick the brain into believing that you have eaten fewer calories than you actually have, causing you to overeat. This is because fatty foods such as butter and fried foods contain a lot of densely packed energy.
However, other foods give a lasting sense of fullness. Fibre triggers the release of gut hormones that make you feel full. A low fibre diet though, with little or no wholemeal produce or fruit and vegetables, may leave you open to feelings of hunger.
Foods with a low GI (glycaemic index) such as nuts, vegetables and beans release energy more slowly than high GI food such as white bread and sugar. Eating more low GI foods will suppress your hunger by increasing levels of gut hormones that help you feel fuller for longer.
Am I eating the right food?
The type of food you eat can make a great deal of difference to how hungry you feel and for how long you feel full.
On What's the Right Diet for You: A Horizon Special participants took part in an experiment to investigate how the type of food you eat affects your hunger and hunger hormones. A group made up of Feasters, those who don't feel full after meals, were given different meals. One group was given food with high GI and the other group food with low GI. They then picked strawberries until they felt hungry again. The number of strawberries collected is used as an indicator of how long they stayed full.
Is my body make-up to blame?
Hormones can have a very powerful effect on our diets too. Hormones are molecules which regulate biological processes and act as chemical signals between our organs.
Two hormones, called GLP-1 and PYY, send messages from the gut to the brain to say when you are full. Levels increase after eating, telling your brain that you are full. Some people with low amounts of these hormones, such as the Feasters in our programme, need to be even more careful about eating the right diet as they are less likely to feel full after eating a normal meal.
Several other hormones influence hunger. Two major ones which tip the balance between hunger and fullness are leptin and ghrelin. Leptin is released from the body's long term fat stores, which we all have, and suppresses hunger while ghrelin causes stomach rumblings as a physical reminder to eat.
Obese people have often built up a resistance to the effects of leptin. This is because over a long period their bodies have got used to such high levels diminishing its effect. For an overweight person trying to diet the drop in leptin that accompanies any fall in body fat stores can feel like starving as the reduced leptin levels feel too low.
Am I a comfort eater?
We are also affected by other hormones which influence our appetite.
One of those hormones is serotonin which makes you feel happy after eating. Sugary foods produce a quick boost of energy which can elevate mood temporarily.
Food is like a drug, and the same areas of the brain are activated by food as by drug addiction. Food can be strongly linked to social situations such as going out for a meal with friends, so it can be difficult to eat less as this would impact on your social life.
Emotional eating can also be a response to stress. The stress hormone cortisol triggers a craving for foods that give you a fast release of energy – including sugary and fatty food. Stress hormones encourage fat cells to form which gives the body more space to store fat.
Some people overeat when they are stressed or depressed, but others overeat when they are happy. However, there are huge individual differences, and seasonal changes – most people eat more in winter.
Good and bad habits
Hunger is caused by a number of factors. The feeling of hunger itself is the result of interactions between the brain and digestive system. But there are ways we can control it.
The context in which you eat is important and habit forming. Eating at regular times can help reduce irresistible feelings of hunger.
Quick diets won't make you feel less hungry, but changing habits can help reduce hunger. Make small, long-lasting changes to diet and exercise. Stick to a list when shopping and don't shop when stressed.
Eating smaller portions from smaller plates can also help you eat less while not feeling hungry any quicker. However, breaking bad habits can be psychologically difficult and can trigger a return to poor eating or a worsening of diet.