Your brain gathers information from many different parts of your body. It uses some of this information to decide whether you need to eat (or stop eating). So if your brain decides you need extra food or energy, your brain "tells you" you're hungry.

• For instance, your brain gets messages from your stomach about whether it's full or empty. So if your stomach is full, you feel less hungry.
• A part of your brain also checks how much sugar there is in your blood. You'll start to feel hungry if the amount of sugar drops too low.
• The cells in your body that store fat make a chemical called leptin. Scientists think that leptin tells your brain how much fat you have in your body.¹ If there's enough fat in the body, leptin tells your brain that you have enough. This makes you stop eating. A few obese people have a condition where they don't make enough leptin. These people may be helped by treatment with leptin.
• Researchers also think that another hormone, called ghrelin (pronounced "grellin'), may affect your weight. Ghrelin makes you feel hungry. It's made mainly in your stomach, although your brain also produces a small amount. The level of ghrelin in your blood rises just before you eat and drops after you eat.^{2 3 4} Researchers are looking to see if blocking ghrelin helps people to eat less and lose weight.

This information is for educational use only, and is not a substitute for prompt professional medical advice. Readers should always consult a physician or other professional for advice and treatment. ©BMJ Publishing Group Limited 2008. All rights reserved.