Leptin is secreted by fat cells after a meal. This hormone sends a message to your brain indicating you are full. The leptin brain receptors secrete substances that suppress appetite signals (neuropeptide Y), so the body stops being hungry and starts burning calories. Therefore, when leptin works properly, it helps to reduce fat storages, but when it doesn’t, our brain keeps asking for food because there are not signals to stop being hungry, so the hunger signals are on all the time.
When glucose levels are too low (too many hours between meals or we skip a meal) or after following very restrictive diets, leptin is not secreted and therefore neuropeptide Y keeps activated and we feel an intense hunger and an unstoppable desire to eat, especially carbohydrates, because the brain knows carbohydrates will give it glucose quickly and therefore it asks for them.
The more fat cells you have, the more leptin you produce, but contrary to what you would think, it doesn’t help us on our weight management mission. You would think the more fat cells, the more leptin, and therefore the easier to make you feel you are full. But when you are overweight, it is for a reason. If you are overweight, it is because you haven’t paid too much attention to all the mechanisms and hormones that are telling you to stop eating so you have kept going on. Well, leptin can have a similar effect as insulin. If you keep stimulating leptin production over the years by eating constantly, you can become leptin-resistant. Although levels of leptin are still high after a meal, its receptors no longer recognize it, so neuropeptide Y is never shut off and therefore our sense of hunger is still on, plus the fat burning result never takes place.
When you lose some weight, your body recovers its sensitivity to leptin and its ability to control your hunger. Also, your organism can now activate your fat-burning machine much easier.
When under restrictive dieting, our body thinks we are starving so they stop leptin production to make us feel hungry and EAT. Poor sleep also decreases leptin levels