Leptin is a hormone that is produced by fat cells in the body. Its main role is to signal to the brain when you have eaten enough and to help control your appetite. Leptin sends signals to the hypothalamus, the part of the brain that manages hunger and body weight.

When leptin levels are high, the brain understands that there is enough stored energy in the body and reduces the feeling of hunger. Conversely, low levels of leptin tell the brain that the body needs more food.

This hormone plays an important role in regulating metabolism and fat storage. It is not limited to the management of hunger, but also contributes to energy balance, thus helping to prevent obesity or undernutrition.

Doctors use leptin levels to diagnose disorders related to metabolism, such as obesity, leptin resistance, or hormonal imbalances that can lead to conditions like diabetes or cardiovascular problems.

A leptin test may be prescribed when there are concerns about the body's management of hunger and fat storage. This test is generally requested if there are signs of leptin resistance, obesity, or unexplained weight changes.

The following situations may require a leptin test:

• Body mass index (BMI) greater than 25: In people who are overweight or obese, leptin levels are checked for possible resistance to the hormone.
• Type 2 diabetes risk: In the case of abdominal obesity, a family history of diabetes, or gestational diabetes, leptin levels can provide valuable clues.
• High levels of LDL (bad cholesterol) or C-reactive protein (CRP): These heart disease risk factors may also indicate problems with leptin.
• Unexplained persistent hunger: If you experience constant hunger despite eating enough, a leptin test can be helpful in understanding the cause.
• Testosterone suppression in men: Obese men with reduced testosterone levels may have abnormal leptin levels contributing to the problem.

The leptin test is done by taking a blood test. A blood sample is taken from a vein, usually from the arm, and sent to the laboratory for analysis.

The most common method used to measure leptin is enzyme immunoassay. This test assesses the concentration of leptin in the blood. It's important to note that leptin levels can vary throughout the day, often peaking in the morning and evening.

Normal leptin levels vary depending on age, gender, and body fat percentage. The following are general reference ranges:

Kids

• Boys
  • Up to 10 years: 0.6—16.8 ng/mL
  • 10-14 years: 1.4—16.5 ng/mL
  • Ages 14 to 18:0.6—24.9 ng/mL
• Girls
  • Up to 10 years: 0.6—16.8 ng/mL
  • 10-14 years: 1.4—16.5 ng/mL
  • Ages 14 to 18:0.6—24.9 ng/mL

Adults

• Men: 0.3—19.9 ng/mL
• Women: 4.7—38.9 ng/mL

Note: Normal measurement units and ranges may differ depending on the specific laboratories and methods used.

High levels

High levels of leptin can occur when the body makes too much of this hormone but the brain doesn't respond properly. This condition is known as leptin resistance. Despite high levels, hunger persists, leading to overeating and weight gain.

Common causes of high leptin levels:

• Overfeeding: Consuming large amounts of food increases fat storage, leading to increased production of leptin.
• Leptin resistance: The brain stops responding to leptin signals, and hunger is not suppressed.
• Obesity: People who are obese often have very high levels of leptin because their fat cells produce more of it.
• Metabolic syndrome: High levels of leptin are also linked to disorders like insulin resistance, high blood pressure, and cholesterol problems.
• Testosterone suppression in men: Obese men with high levels of leptin may experience a decrease in testosterone.

Recommendations:

• Work with a doctor to identify the underlying cause and develop a plan.
• Avoid overeating, especially heavy meals in the evening.
• Reduce carbohydrate consumption.
• Exercise regularly to improve the body's response to leptin.
• Maintain a healthy weight through gradual weight loss.

Low levels

Low levels of leptin, although less common, can lead to constant hunger and overeating. This can contribute to weight gain and obesity.

Common causes of low leptin levels:

• Leptin deficiency: A rare condition where the body cannot produce enough leptin.
• Underweight or extreme dieting: People who are very thin or on strict diets have low levels of leptin.
• Malnutrition: A lack of nutrients can affect hormone production, including leptin.
• Excessive physical activity: Excessive exercise without adequate nutritional intake can lower leptin levels.

Recommendations:

• Maintain a regular schedule of balanced meals.
• Avoid overeating, even when there is an intense feeling of hunger.
• Ensure adequate nutritional intake, including healthy fats and proteins.

If there are concerns about your leptin levels, it is advisable to see an endocrinologist. These specialists focus on hormonal and metabolic imbalances and can provide personalized advice.