In an earlier blog, we discussed the ‘hunger hormone’ ghrelin, which directs us to eat when the stomach is empty. Today we’re looking at another key hormone that regulates appetite: leptin.
What is leptin?
Leptin helps the body maintain its weight by signalling the brain to tell it how much is stored in the body’s fat cells.
A 167 amino acid hormone, Leptin is released from fat cells, circulates in the blood and, like ghrelin, signals the hypothalamus in the brain. This helps to regulate food intake and bodyweight.
- Leptin is believed to help with cognitive function, in particular learning and memory
- Studies have found that high levels of leptin are linked with a lower risk of Alzheimer’s disease and other forms of dementia
- Leptin regulates the onset of puberty and affects ovulation: underweight women reach puberty later and may fail to release an egg during menstruation
When leptin was first detected and characterised in 1994, there was excitement that the discovery could provide the key to weight gain and loss, revolutionising the diet industry. However, since then it has been found that leptin deficiency only explains obesity in a small number of people and that leptin resistance is more relevant to weight gain.
What are leptin deficiency and leptin resistance?
Leptin regulates how much we eat and our fat stores, stimulating appetite when fat mass decreases and supressing it when it increases, to keep us within a balanced weight range.
Congenital leptin deficiency is a rare condition when leptin is not produced, causing uncontrolled hunger and eating, as the brain believes that the body has no fat. It is often seen early in childhood obesity and can be treated with leptin injections.
Leptin resistance is when there is too much leptin circulating in the bloodstream. Instead of the brain telling you to stop eating, the body loses its sensitivity to the hormone, causing increased appetite and weight gain over time. Your brain also reduces your energy expenditure and tries to conserve energy, burning fewer calories when at rest.
As well as high levels of leptin causing leptin resistance, it can be affected by inflammatory signalling in the hypothalamus and high levels of free fatty acids in the bloodstream.
What part does leptin play in yo-yo dieting?
Leptin resistance is a major cause of obesity. The factors that lead to leptin resistance are also made worse by obesity, leading to a vicious cycle of weight gain and further leptin resistance.
This is thought to be the reason why a lot of diets struggle to see long-term success. Restricting food intake leads to the brain believing you are starving and encouraging you to regain the body fat you have lost. The result is yo-yo dieting, where someone loses a lot of weight but soon puts it all back on again.
Can leptin resistance be reversed?
Some research has indicated that reducing inflammation brought on by particular foods could help to reverse leptin resistance. This would mean steering clear of processed foods that cause inflammation, reducing carbohydrate intake, eating plenty of protein and soluble fibre, getting lots of exercise and a sound night’s sleep.