Quick answer: Insulin moves glucose into cells and signals fat storage; leptin, made by fat cells, tells your brain you have enough energy. Over time, a diet high in processed foods and sugar can contribute to insulin resistance and leptin resistance, leading to higher blood sugar and hunger. An anti-inflammatory diet low in sugar and rich in fiber, protein and healthy fats may support both hormones.
Key takeaways
After a meal, the pancreas releases insulin to move glucose into cells, and insulin resistance develops when cells stop responding well.
Leptin is made by fat cells and tells the brain you are full, but in leptin resistance hunger can persist despite enough stored energy.
Food, sleep and movement are important levers for both hormones, and insulin resistance is linked with many age-related conditions.
Insulin
How insulin is made and works
After a meal, glucose rises, and beta cells in the pancreas make proinsulin, which becomes insulin. Insulin is then released into the blood, where it binds to cells and lets glucose in.
Insulin sensitivity and resistance
Sensitive cells respond well to insulin. In insulin resistance, cells respond poorly, so the pancreas makes more. See insulin sensitivity.
Supporting healthy insulin levels
Limit processed foods and added sugars, eat protein and fiber with meals, choose healthy fats, and move after meals.
Leptin
Leptin is made by fat cells and signals fullness to the brain. In leptin resistance, the brain stops responding, so hunger persists despite enough energy stored.
Supporting healthy leptin levels
Prioritize sleep, limit sugar and processed foods, eat protein and fiber, and exercise regularly.
Healthy aging lens
Insulin resistance is linked to many age-related conditions. Food, sleep and movement are important levers. See hormones, part 1.
When to see a naturopathic doctor
It may be time to see a naturopathic doctor if you have a chronic inflammatory, autoimmune or digestive condition, or if you have diabetes, kidney disease or take medications affected by diet changes. The same is true if you are pregnant, breastfeeding, or have a history of disordered eating, or if you want a plan tailored to your labs, symptoms and goals.
See a medical provider promptly for severe abdominal pain, signs of an allergic reaction such as swelling or trouble breathing, or fainting.
What the research shows
Leptin resistance helps explain why high leptin does not always curb appetite. In a 1996 study by Caro and colleagues, researchers measured leptin in the blood and spinal fluid of 31 people across a range of body weights. Blood leptin was more than four times higher in people with obesity (about 40 ng/mL versus 10 ng/mL), but spinal-fluid leptin was only about 30% higher. That suggests leptin’s transport into the brain becomes saturated, so the brain may not get the full signal. The study was small and measured a single point in time.
Meal timing can affect insulin even when weight stays the same. In a 2018 controlled feeding trial by Sutton and colleagues, men with prediabetes ate all their meals within 6 hours, finishing before 3 p.m., for 5 weeks, and also spent 5 weeks on a 12-hour eating window. Because they were fed enough to keep their weight stable, any change could not be explained by weight loss. The early eating window improved insulin sensitivity, beta-cell response and blood pressure. The trial was small and included only men.
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Questions to bring to your clinician
These questions can help you get the most out of your next visit.
Should we check my fasting insulin or other markers of insulin resistance?
How might my eating habits be affecting my insulin and leptin?
Would checking my fasting insulin help guide my food choices?
Which meal habits might help me feel fuller and more balanced?
Frequently asked questions
What is insulin resistance?
When cells respond poorly to insulin, raising blood sugar and insulin.
What does leptin do?
Signals fullness and energy stores to the brain.
Can diet improve insulin sensitivity?
It can help, together with movement and sleep.
What is leptin resistance?
When the brain stops responding to leptin’s fullness signal.
Sources
- Caro JF, Kolaczynski JW, Nyce MR, et al. Decreased cerebrospinal-fluid/serum leptin ratio in obesity: a possible mechanism for leptin resistance. Lancet 1996. PMID: 8684156. https://pubmed.ncbi.nlm.nih.gov/8684156/
- Sutton EF, Beyl R, Early KS, et al. Early Time-Restricted Feeding Improves Insulin Sensitivity, Blood Pressure, and Oxidative Stress Even without Weight Loss in Men with Prediabetes. Cell Metab 2018. PMID: 29754952. https://pubmed.ncbi.nlm.nih.gov/29754952/
- Malik VS, et al. Sugar-sweetened beverages and risk of metabolic syndrome and type 2 diabetes: a meta-analysis. Diabetes Care 2010. PMID: 20693348. https://pmc.ncbi.nlm.nih.gov/articles/PMC2963518/
- Petersen MC, Shulman GI. Mechanisms of Insulin Action and Insulin Resistance. Physiol Rev 2018. PMID: 30067154. https://pmc.ncbi.nlm.nih.gov/articles/PMC6170977/
- Myers MG, et al. Obesity and leptin resistance: distinguishing cause from effect. Trends Endocrinol Metab 2010. PMID: 20846876. https://pmc.ncbi.nlm.nih.gov/articles/PMC2967652/
- Spiegel K, et al. Brief communication: Sleep curtailment in healthy young men is associated with decreased leptin levels, elevated ghrelin levels, and increased hunger and appetite. Ann Intern Med 2004. PMID: 15583226. https://pubmed.ncbi.nlm.nih.gov/15583226/
- Facchini FS, et al. Insulin resistance as a predictor of age-related diseases. J Clin Endocrinol Metab 2001. PMID: 11502781. https://pubmed.ncbi.nlm.nih.gov/11502781/
- MedlinePlus: Hormones
This article is for educational purposes only and is not medical advice. It does not replace an individual evaluation. Talk with your healthcare provider before starting supplements or changing medications, especially if you are pregnant, nursing, or managing a health condition.
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