Leptin is a hormone that was only discovered in 1994. A hormone is a chemical messenger that carries instructions from one part of your body to another. Leptin is produced in fat cells. Fat cells release leptin when they have gathered enough energy from calories in your diet. Leptin then travels to your brain where it tells your brain that you are full. Your brain then shuts down hunger so you stop eating. [1-3]
Researchers thought this discovery would be a blockbuster for weight loss. If they could just increase leptin in people who were overweight, it could be the long-wanted cure for obesity. Unfortunately, the leptin-obesity connection turned out to be complex. Although research continues, there have been no successful weight loss therapies derived from leptin yet. [2,3,4] One exception is in rare genetic conditions where children are born without leptin. This may cause childhood obesity. For these children, leptin treatment has shown some promise. [1,2]
What Is Leptin Resistance
One big reason why giving people leptin to lose weight has not worked is leptin resistance. Most people who are obese have too many fat cells and these cells produce large amounts of leptin. This level of leptin makes the brain become resistant to leptin. Even though fat cells are trying to tell the brain to stop eating, the message does not get through and people keep eating and they keep making more fats cells, a vicious cycle. Giving them even more leptin does not help. [1-4]
Although you can find leptin supplements and diets on the internet, it is important to know that leptin is not found in foods or in supplements. Even if you could add leptin to your diet, you could not absorb it into your blood, so neither leptin foods or leptin supplements would work. In any case, increasing leptin doesn’t help if you have leptin resistance. 
Is There Any Hope for Leptin as an Obesity Treatment?
A 2019 study, led by researchers as Baylor University may be a breakthrough. The researchers were able to discover a natural way to reduce leptin resistance, at least in mice. They found that a hormone secreted in the digestive system, called gastric inhibitory polypeptide (GIP) increases when mice are fed a high fat diet. GIP then travels to the brain and blocks the action of leptin, causing hunger. This may explain how leptin resistance develops. 
The research is published in the Journal of Clinical Investigation. The researchers were able to block the effect of GIP in the brain with a man-made antibody. Mice that were made obese through a high-fat diet and were given the antibody ate less and lost weight. More research is needed, but if GIP is a cause of leptin resistance and the mouse study leads to successful human studies, there may come a day when a leptin-based therapy will help people with obesity. 
Is There Anything You Can Do Now?
The Baylor researchers found that mice eating a balanced diet did not develop leptin resistance. Only mice fed a high-fat diet developed leptin resistance.  Previous research suggests that leptin resistance may be linked to higher levels of blood fats called triglycerides and to high levels of sugar. Rather than trying leptin diets or leptin supplements, your best bet may be to stick to a balanced diet that reduces fats and sugar. This type of diet is safe and time-tested: 
- Avoid fats and oils like butter, margarine, shortening, lard, and oils of palm or coconut. Stick to vegetable oils.
- Limit fats from mayonnaise, salad dressings, gravies, and sauces. Chose low-fat products for these foods.
- Chose lower fat proteins like fish, poultry, beans, and soy. Limit red meat and egg yolk.
- Chose non-fat or low-fat dairy products.
- Eat lots of fruits and vegetables.
- Chose whole grain breads, cereals, and pastas.
- Avoid sugar added drinks and foods. Watch out for sugar in snacks and baked goods.
If you are struggling to lose weight, ask your doctor to help you with a plan to lose weight through exercise and diet. For now, the best ways to avoid leptin resistance and a cycle of hunger and obesity is to lose weight and maintain a healthy weight with a healthy diet. [3-5]
- The Endocrine Society, Leptin, https://www.hormone.org/your-health-and-hormones/glands-and-hormones-a-to-z/hormones/leptin
- American Association for Clinical Chemistry, Leptin, https://labtestsonline.org/tests/leptin
- WebMD, The Facts on Leptin: FAQ, https://www.webmd.com/diet/obesity/features/the-facts-on-leptin-faq#5
- AARP, Are Hormones Causing Your Weight Gain? https://www.aarp.org/health/conditions-treatments/info-2020/hormones-and-weight-loss.html
- ScienceDaily, Gut-brain connection helps explain how overeating leads to obesity, https://www.sciencedaily.com/releases/2019/08/190812160533.htm
- University of California San Francisco, Guidelines for a Low Cholesterol, Low Saturated Fat Diet, https://www.ucsfhealth.org/education/guidelines-for-a-low-cholesterol-low-saturated-fat-diet