We often talk about what we eat.
About proteins, carbohydrates, fats, vitamins, minerals – and, quite incorrectly, very often about calories.
I, too, used to focus on this constantly.
That was until I understood the connections of chronobiology.
Our organism follows rhythms. And one of the most important biological pacemakers in this interplay is a hormone that is surprisingly little known: leptin.
Leptin is often referred to as the "satiety hormone." But this description is far too simplistic. Leptin is not a small signal that just says, "I'm full." Leptin is a central hormone of energy metabolism. It connects our adipose tissue with the brain and influences hunger, energy expenditure, temperature regulation, hormonal processes, fertility, the immune system, bones, muscles, and the circadian rhythm.
In other words: Leptin helps the body recognize whether enough energy is available – and whether this energy can be used.
For BARAU, this topic is so exciting because it shows: health, energy, and skin regeneration do not begin with a cream or a serum.
Before we look at the significance of leptin in more detail, we must understand some fundamental connections.
Circadian Rhythms and Chronobiology
Chronobiology is the science that studies the biological rhythms of living beings, as our organism does not function the same way at every time of day. It possesses an internal clock – or more precisely: many internal clocks. The central control center is located in the brain, in the so-called suprachiasmatic nucleus of the hypothalamus. But organs such as the liver, pancreas, adipose tissue, muscles, and skin also follow their own rhythms.
For these systems to work together harmoniously, they need external signals. In chronobiology, these are called zeitgebers. The most important natural zeitgeber is sunlight: morning light, daylight brightness, sunset, and darkness help the body adapt to the time of day and the season.
You can find more on this in the article "Sunlight".
It becomes problematic when these natural signals are replaced by artificial stimuli. Artificial light in the evening destroys the circadian rhythm and causes chronodisruption, with the following metabolic effects:
- Glucose intolerance: The consumption of carbohydrates in the evening or at night can exacerbate hyperglycemia and make insulin secretion more difficult, increasing the risk of developing diabetes.
- Accumulation of toxins: The brain cleanses itself during the night, partly through neuronal autophagy, breaking down waste products such as beta-amyloid plaques, which are linked to Alzheimer's. Chronodisruption impairs this process and promotes the accumulation of toxins.
- Changes in appetite: Poor sleep increases levels of ghrelin, the hunger hormone, and lowers levels of leptin, the satiety hormone. This leads to more food being consumed the next day.
“Food interacts with our circadian rhythm to impact disease risk.” - Malin, The Journal of Clinical Endocrinology & Metabolism, 2020, “Timing Is Everything, Right? Meal Impact on Circadian Related Health”
Melatonin: The Silent Order of the Night
Melatonin is also important for understanding leptin.
Melatonin is a central molecule of nightly regeneration. It is linked to sleep, antioxidant protection, immune function, body temperature, hormonal processes, and the alternation between activity and rest.
Falling melatonin levels and disrupted circadian rhythms flatten the leptin signal curve – thereby influencing energy, hunger, and regeneration.
More about melatonin in our article "Sun-Kissed".
Leptin – The Hormone of Energy Metabolism
The Discovery of Leptin
In 1994, a pleiotropic hormone consisting of 167 amino acids was discovered: leptin.
"Pleiotropic" refers to a hormone's ability to trigger several different – and at first glance seemingly unrelated – effects in various body systems.
The name leptin comes from the Greek word leptos, which means "thin." Leptin first became known in connection with body weight, hunger, and satiety. Earlier studies showed that animals without functional leptin gained significant weight, developed metabolic problems, and displayed other physiological disorders. This initially created the hope that obesity could be easily treated by administering leptin.
In humans, however, a crucial difference emerged: many people with obesity do not have too little, but often very high levels of leptin in their blood. The problem, therefore, does not necessarily lie in a deficiency, but in the fact that the signal is no longer being received correctly.
This is exactly where the term leptin resistance arises: leptin is present, but the brain does not recognize its message clearly. The adipose tissue signals, "There is enough energy." But the brain does not hear it. The body then behaves as if energy were scarce.
What Leptin Does in the Body
Leptin is primarily produced by fat cells. Adipose tissue is not just a passive storage facility. It is a hormonally active organ that communicates with the brain. It informs the body about its energetic status.
Leptin is one of the most important signals in this regard, as it is involved in many processes:
- It regulates hunger and satiety.
- It influences energy expenditure.
- It plays a role in temperature regulation.
- It is connected to the immune system.
- It influences fertility and hormonal axes.
- It is relevant to bone and muscle metabolism.
- It communicates with the brain regarding the body's energetic status.
Especially important is that leptin does not function in isolation. It is embedded in a network of light, darkness, melatonin, insulin, cortisol, thyroid hormones, inflammatory processes, and mealtimes.
That is why it is shortsighted to describe leptin only as a "satiety hormone." Leptin is the central control hormone of energy metabolism.
It does not just tell the body whether enough has been eaten.
It tells it whether enough energy is available for life, warmth, repair, and regeneration.
What Disrupts Leptin Function
Leptin function can be disrupted by several modern factors. Particularly relevant are:
- eating late
- artificial light in the evening
- non-native electromagnetic fields
- poor sleep
The most important point in connection with nutrition is timing. In chrononutrition – or chrono-dieting – it is not just about what we eat, but above all when we eat. Because food does not have the same effect at all times of the day. During the day, the body is more geared toward activity, digestion, and energy utilization. At night, it should shift toward rest, repair, cell maintenance, and regeneration.
“DIT is clearly higher in the morning than in the evening, irrespective of the consumed calorie amount.” - Richter et al., The Journal of Clinical Endocrinology & Metabolism, 2020, “Twice as High Diet-Induced Thermogenesis After Breakfast vs Dinner on High-Calorie as Well as Low-Calorie Meals”.
If we eat late in the evening or at night, the body receives food at a time when it actually has other tasks. Particularly interesting here is the connection between triglycerides and leptin. After eating, triglycerides in the blood rise – a process that is normal at first. However, if this rise falls into the night, the transport of leptin to the brain is disrupted. Exactly when leptin would be particularly important at night, its message does not arrive.
“Triglycerides are an important cause of leptin resistance.” - Banks et al., Diabetes, 2004, “Triglycerides Induce Leptin Resistance at the Blood-Brain Barrier”.
“LD induces nocturnal glucose intolerance, and reduces fatty acid oxidation and mobilization.” - Gu et al., The Journal of Clinical Endocrinology & Metabolism, 2020, “Metabolic Effects of Late Dinner in Healthy Volunteers—A Randomized Crossover Clinical Trial”.
Also very important is how often we eat. A study using a mobile app showed that many people eat up to 10 times within 16 hours – including snacks. This constant eating is one of the central causes of metabolic problems. Although insulin is often the focus, leptin is at least as decisive for energy metabolism. Leptin resistance arises before insulin resistance and influences both fat loss and muscle building.
Added to this are modern habits such as artificial light at night, non-native electromagnetic fields – for instance from mobile phones, Wi-Fi, or artificial light environments – and a chronically high carbohydrate consumption, which further burden the metabolism. Artificial light at night causes cortisol and glucose levels to rise sharply the next morning and causes hyperglycemia and hyperinsulinemia as well as changes in other hormones such as leptin and ghrelin. Studies by Nora Volkow prove this connection: in one of her studies, the part of the brain exposed to the phone antenna increased its glycolysis activity and demanded more carbohydrates.
Another decisive factor is sleep. Too little recovery disrupts the hormonal hunger and satiety regulation. It takes only 2 nights with too little sleep to throw ghrelin and leptin out of balance – leading to more appetite and a stronger inclination toward unfavorable foods.
More on the topic of sleep in our article "Night's Rest".
Leptin Resistance: When the Signal No Longer Arrives
As already described, leptin signaling is part of a finely tuned system: the fat cells detect the energetic status of the body, leptin transmits this information to the brain, and the brain decodes the signal and reacts accordingly. Additionally, leptin is also involved in the regulation and modulation of the immune system in the brain.
Resistance to this hormone means that the brain no longer recognizes the leptin signal sent by the fat cells. This is a crucial difference: in the case of a leptin deficiency, the signal is missing. In the case of leptin resistance, the signal is present – but is not recognized.
The result is that the body behaves as if energy were scarce, even though enough energy is actually stored. Hunger is perceived more strongly, energy expenditure drops, and fat metabolism and hormonal processes can shift unfavorably. Leptin regulates the entire metabolism of the body. If its function is disrupted, the remaining hormones can show medical pathology.
Possible consequences of disrupted leptin signaling can be:
- increased hunger
- less satiety
- lower energy expenditure
- disruption of fat metabolism
- insulin resistance
- increased tendency toward inflammation
- disrupted sleep
- altered cortisol rhythms
- problems with temperature regulation
- hormonal imbalance
It is important to note: This is not a matter of willpower. If the brain does not correctly recognize the energy status, the body works with different internal information. That is why, from this perspective, the statement "just eat less and move more" falls short for people with obesity.
Reference values for leptin in fasting blood are: women 3.9–30ng/ml, men 0.5–12.7ng/ml. Very high levels can indicate leptin resistance; very low levels can indicate a lack of or insufficient leptin production. In both cases, an endocrinological clarification is sensible.
These are the signs that a person is leptin resistant:
- Overweight
- If the person is thin, an increased reverse T3 is a clear symptom
- Constant hunger and cravings for carbohydrates and/or ultra-processed foods, especially at night
- Unusually elevated cortisol levels toward the afternoon/night
- Poor sleep
- Having high insulin levels
Reversing Leptin Resistance
The good news is: Many of the most important signals that can support healthy leptin function are simple, natural, and often free. It is not about making everyday life perfect, but about giving the body clear biological orientation again. According to our research, the following measures are a proven way to reverse leptin resistance.
13 Natural Approaches
1. Consciously reduce carbohydrates
Low-carbohydrate diet: less than 50g of carbohydrates per day.
2. Consciously set the first meal early
Eat 30 minutes after waking up – provided it is already light outside.
3. Choose natural, seasonal, and regional foods
The body benefits from real food: as unprocessed, seasonal, regional, and close to nature as possible.
4. No snacks in between
Do not eat snacks. This means for the rest of your life. Snacks completely stress the liver's metabolism. The liver must learn again how to use gluconeogenesis normally during the day and at night. Eating snacks destroys the circadian clocks that function in harmony with leptin.
5. Start with three meals, reduce to two later
Initially, three meals a day can make sense. When hunger and cravings subside, the rhythm can be reduced to two meals – ideally by omitting dinner. In fact, fasting improves leptin signaling. By reducing the number of meals, leptin receptors work better, which can make people feel fuller with fewer meal intakes.
More on this in the article "Fasting".
“eTRF improved insulin sensitivity, β cell responsiveness, blood pressure, oxidative stress, and appetite.” - Sutton et al., Cell Metabolism, 2018, “Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes”.
6. Do not count calories
The focus is not on the mathematical quantity, but on the biological information: nutrients.
7. Leave four to five hours before going to sleep
There should be at least four to five hours between the last meal and sleep so that the body can switch to nightly regeneration more easily.
“Moving the dinner to an earlier time may result in better glucose tolerance.” - López-Minguez et al., Clinical Nutrition, 2018, “Late Dinner Impairs Glucose Tolerance in MTNR1B Risk Allele Carriers”.
“...relationships between food timing, fasting duration, and adipose tissue metabolism.” - Arredondo-Amador et al., The Journal of Clinical Endocrinology & Metabolism, 2020, “Circadian Rhythms in Hormone-sensitive Lipase in Human Adipose Tissue: Relationship to Meal Timing and Fasting Duration”.
8. Plan exercise for the afternoon or early evening
Training on an empty stomach right after getting up is a common practice and may be suitable for a metabolically flexible person. For people with insulin resistance or leptin resistance, however, training times become more important. In the initial phases, exercise can even be counterproductive or harmful, especially for people who are overweight. If the person has the energy and willingness to exercise, it is preferable to do so after 5:00 PM. Studies show that glucose is better regulated by exercise in the afternoon compared to the morning. In addition, afternoon exercise helps improve sleep quality, provided it does not take place right before bedtime, to avoid negative effects. The ideal is to train 3 to 4 hours before going to bed.
“Choosing the ideal time of day seems to be an emerging strategy to enhance the benefits of physical activity on glucose metabolism.” - Clavero-Jimeno et al., Obesity, 2024, “Impact of lifestyle moderate-to-vigorous physical activity timing on glycemic control in sedentary adults with overweight/obesity and metabolic impairments”.
“These results suggest that late afternoon endurance exercise may be more effective than morning endurance exercise at improving 24-h glucose and triglyceride levels.” - Kim et al., Frontiers in Endocrinology, 2022, “Late-afternoon endurance exercise is more effective than morning endurance exercise at improving 24-h glucose and blood lipid levels”.
“...performing most MVPA in the afternoon or evening was associated with up to 25% reduced insulin resistance...” - van der Velde et al., Diabetologia, 2022, “Timing of physical activity in relation to liver fat content and insulin resistance”.
9. Integrate HIIT or strength training
The important thing remains: the intensity should suit your current metabolic state and physical resilience.
10. Consciously utilize sunlight
Expose yourself to natural light for as long as possible.
11. Respect darkness after sunset
About an hour after sunset, your environment should be as dark as possible. Less artificial light, lower screen brightness, and dimmed rooms signal to the body that the day is ending.
12. If you have trouble falling asleep, use short bodyweight exercises with caution
3 to 5 minutes of light bodyweight exercises before sleeping, such as squats or push-ups. However, if you have elevated nighttime cortisol, this should be avoided.
13. Utilize meditation and stress reduction
Meditation, conscious breathing, and calm evening rituals can help lower cortisol and prepare the body for regeneration.
How leptin affects skin health: Understanding well-aging holistically
At first glance, leptin seems far removed from skincare. But the skin is not an isolated organ. It is part of the entire body and reacts to sleep, stress, hormones, inflammation, blood sugar, nutrition, light, the nervous system, and regeneration.
If leptin is a central signal for energy, rhythm, and metabolism, then impaired leptin function also affects the conditions under which skin can regenerate.
Because skin needs energy for:
- Cell division
- Repair processes
- Barrier function
- Collagen production
- Antioxidant defense systems
- Regulation of inflammation
Skin that needs to regenerate therefore requires more than just good external care. It also requires a body that can internally switch to a state of regeneration. This is exactly where leptin, melatonin, and skin health meet.
That is why at BARAU, well-aging does not begin with the idea of controlling the skin. It begins with the idea of supporting its natural regenerative capacity: with less unnecessary strain, clear rhythms, high-quality ingredients, conscious rituals, protection during the day, and regeneration at night.
The skin does not always need more active ingredients. It also needs better conditions. Healthy skin is not created only by what we apply to it. It is also created by the rhythm in which we live.
My Conclusion
I, too, have integrated all these measures into my everyday life—with the exception of points 2 and 5 of the approaches mentioned above, as I have been practicing OMAD for about six years. Not because of a diagnosed leptin resistance, but from the desire to support my body more consistently in maintaining a state of balance and general health that feels natural to me.
For me, the focus is on a regulated circadian rhythm—and this includes, above all, light hygiene: natural light in the morning, as much daylight as possible during the day, less artificial brightness in the evening, and true darkness at night. Since then, my sleep is deeper, my digestion is calmer, my body fat percentage is maximally reduced—and my general state of health is optimal.
My skin has also changed visibly. For me, this is closely linked to the fact that I do not unnecessarily stress it from within and consciously nourish it from the outside with high-quality organic natural cosmetics. Five minutes of quality time in the morning and evening—a ritual I wouldn't want to miss today. Skin blemishes, herpes, redness, pigment spots, and feelings of tightness in my face are no longer an issue for me today.
The studies show a clear pattern: the body processes food depending on the time of day. With the same amount of calories, a meal in the morning can have different effects on thermogenesis, glucose, insulin, triglycerides, fat metabolism, and hunger hormones than the same meal in the evening.
This does not mean that the quality of food is unimportant. But:
When we eat is more decisive for our metabolism than what we eat.
Sources of the mentioned studies
• Malin, S. K. (2021). Timing Is Everything, Right? Meal Impact on Circadian Related Health. The Journal of Clinical Endocrinology & Metabolism, 106(2), e1050-e1051. DOI: 10.1210/clinem/dgaa533.
• Richter, J., Herzog, N., Janka, S., Baumann, T., Kistenmacher, A., Oltmanns, K. M. (2020). Twice as High Diet-Induced Thermogenesis After Breakfast vs Dinner on High-Calorie as Well as Low-Calorie Meals. The Journal of Clinical Endocrinology & Metabolism, 105(7), e2683-e2690. DOI: 10.1210/clinem/dgaa125.
• Banks, W. A., Coon, A. B., Robinson, S. M., Moinuddin, A., Shultz, J. M., Nakaoke, R., Morley, J. E. (2004). Triglycerides Induce Leptin Resistance at the Blood-Brain Barrier. Diabetes, 53(5), 1253-1260. DOI: 10.2337/diabetes.53.5.1253.
• Gill, S., Panda, S. (2015). A Smartphone App Reveals Erratic Diurnal Eating Patterns in Humans that Can Be Modulated for Health Benefits. Cell Metabolism, 22(5), 789-798. DOI: 10.1016/j.cmet.2015.09.005.
• Volkow, N. D., Tomasi, D., Wang, G. J., Vaska, P., Fowler, J. S., Telang, F., Alexoff, D., Logan, J., Wong, C. (2011). Effects of Cell Phone Radiofrequency Signal Exposure on Brain Glucose Metabolism. JAMA, 305(8), 808-813. DOI: 10.1001/jama.2011.186.
• Spiegel, K., Tasali, E., Penev, P., Van Cauter, E. (2004). Brief Communication: Sleep Curtailment in Healthy Young Men Is Associated with Decreased Leptin Levels, Elevated Ghrelin Levels, and Increased Hunger and Appetite. Annals of Internal Medicine, 141(11), 846-850. DOI: 10.7326/0003-4819-141-11-200412070-00008.
• Sutton, E. F., Beyl, R., Early, K. S., Cefalu, W. T., Ravussin, E., Peterson, C. M. (2018). Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metabolism, 27(6), 1212-1221.e3. DOI: 10.1016/j.cmet.2018.04.010.
• López-Minguez, J., Saxena, R., Bandín, C., Scheer, F. A. J. L., Garaulet, M. (2018). Late Dinner Impairs Glucose Tolerance in MTNR1B Risk Allele Carriers: A Randomized, Cross-over Study. Clinical Nutrition, 37(4), 1133-1140. DOI: 10.1016/j.clnu.2017.04.003.
• Clavero-Jimeno, A., et al. (2024). Impact of Lifestyle Moderate-to-Vigorous Physical Activity Timing on Glycemic Control in Sedentary Adults with Overweight/Obesity and Metabolic Impairments. Obesity. DOI: 10.1002/oby.24063
• Kim, H. K., Furuhashi, S., Takahashi, M., Chijiki, H., Nanba, T., Toyoda, Y., ... Shibata, S. (2022). Late-afternoon endurance exercise is more effective than morning endurance exercise at improving 24-h glucose and blood lipid levels. Frontiers in Endocrinology, 13, 957239. DOI: 10.3389/fendo.2022.957239.
• van der Velde, J. H. P. M., Boone, S. C., Winters-van Eekelen, E., et al. (2023). Timing of physical activity in relation to liver fat content and insulin resistance. Diabetologia, 66, 461-471. DOI: 10.1007/s00125-022-05813-3.
