Leptin, your energy accountant
Leptin is made mainly by white fat tissue and acts as one of the body’s key energy messengers.
It travels through the blood to the hypothalamus, which is the part of the brain that helps regulate hunger, satiety, metabolism, body temperature, fertility, thyroid signalling and sleep timing.
In simple terms, leptin tells the brain how much stored energy the body has available.
Leptin regulates hunger, increases satiety
When leptin signalling is working well, the brain receives the message that energy is available. This helps reduce hunger, increase satiety and support a healthy metabolic rate.
Leptin resistance
When leptin signalling is not working well, the brain may not hear the message clearly. This is often called leptin resistance.
In that state, the body may have plenty of stored energy, but the brain acts as if energy is low. This can increase hunger, cravings and food seeking behaviour, while also making the body more likely to conserve energy.
The Leptin Pathways
Leptin works in the hypothalamus through several appetite pathways, including POMC, AgRP and NPY.
POMC stands for pro opiomelanocortin. In plain English, POMC can be thought of as one of the brain’s appetite brake pathways. When leptin activates POMC neurons, this helps reduce appetite and supports the feeling of being satisfied after eating. But the POMC pathway needs ultra violet light (UV) on the skin and through the eyes to be activated.
AgRP and NPY work more like food seeking pathways. They are important survival signals. They help drive hunger when the body senses low energy or food scarcity.
Hunger is important
The aim is not to shut hunger down. Hunger is healthy when it comes at the right time. The aim is to help the brain receive accurate energy information so hunger and satiety can return to a natural rhythm.
Leptin a circadian hormone
Leptin is also connected to circadian rhythm.
This means leptin does not work randomly across the day and night. It follows timing. Studies show that leptin has a daily rhythm, with levels often rising during the night, especially during sleep.
This night time rise makes sense when we look at the body through a circadian lens.
Night is not meant to be a feeding window. It is meant to be a repair window.
During sleep, the body should be digesting less, repairing more and deciding how to use stored energy. Leptin helps inform this process by telling the brain whether the body has enough energy available.
Eating late is an issue
This is why late night eating can become a problem.
If insulin is high from a late meal or snack, leptin signalling may be disrupted at the very time the brain needs that energy message. Insulin is not bad. It is necessary. But it belongs mostly in the daytime feeding window, not close to sleep.
ALAN and Leptin
Artificial light at night can also affect this rhythm.
Light is not just something we see. It is information for the brain.
Morning sunlight helps set the master clock in the brain, known as the suprachiasmatic nucleus. This master clock helps organise the timing of hormones, digestion, appetite, sleep and repair.
When the eyes receive natural morning light, the brain gets a clear message that the day has begun. This helps anchor the rhythm for cortisol, melatonin, hunger hormones and metabolic signals, including leptin.
Research has shown that light exposure can affect leptin and ghrelin in sleep restricted adults. Ghrelin is often called the hunger hormone because it increases appetite and food seeking behaviour.
This matters because many midlife women are not just dealing with food choices. They are dealing with disrupted signals.
Poor sleep, artificial light at night, late meals, stress, snacking and too little morning sunlight can all make the hunger system feel louder.
Blue light, why it’s important to notice
Blue enriched light has also been studied in relation to hunger and metabolism.
Blue light from the sun during the day is part of the natural light spectrum. It helps tell the brain it is daytime. But blue heavy artificial light at night sends a confusing message.
The brain may receive a daytime signal when the body should be preparing for darkness, melatonin and repair.
This can affect sleep timing, hunger, blood sugar, insulin and appetite regulation.
It is a light story.
It is a timing story.
It is a sleep story.
It is a circadian hormone story.