Why You Can’t Lose Weight: The Hidden Role of Leptin Resistance, Thyroid Function, and Metabolism

June 04, 2026 Essential Metabolic Health

Weight gain is often explained as eating too much and moving too little. But if that were the full story, many people who carefully track calories, exercise consistently, and even use GLP-1 medications would not continue struggling. One of the most overlooked reasons behind stubborn weight gain and difficulty losing weight is a hormone called leptin.

What leptin actually does

Leptin is hormone produced primarily by fat tissue and acts as a messenger between the body and the brain. As body fat increases, leptin levels rise. The brain, specifically the hypothalamus, should interpret this as a signal that energy stores are sufficient. In response, appetite decreases, metabolism increases, fat burning improves, and the body naturally becomes more willing to use stored energy.

In a healthy system, gaining body fat should trigger mechanisms that help reduce excess fat.

For many people, this signaling becomes dysfunctional.

Check your Leptin status through individual or panel testing.

Blood test Biomarker

Leptin

Individual Leptin test.

Leptin $53.49

Leptin is a hormone produced by fat cells that helps regulate appetite and energy balance by signaling satiety to the brain. Abnormal leptin levels can be associated with obesity, metabolic disorders, and appetite regulation issues.

Laboratory: Labcorp
Sample type: Serum
Avg. sample processing time: 5 Business days
Require fasting: No

Biomarkers

Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.

Leptin in panel tests.

Functional Health Panel with AMH (Male) $896.49

This comprehensive panel assesses biomarkers related to hormonal health, thyroid function, metabolism, cardiovascular health, inflammation, nutrient status, and environmental exposures. The results can help provide a broader picture of overall health and support personalized wellness and treatment strategies.

Laboratory: Labcorp
Sample type: Plasma Serum Whole Blood
Avg. sample processing time: 18 Business days
Require fasting: Yes

Biomarkers

Prostate-Specific Antigen (PSA), % Free The percentage of your PSA that's unbound to blood proteins. A lower percentage raises suspicion for prostate cancer, helping refine an elevated total PSA result.
Estradiol The main and most potent form of estrogen. Key for reproductive health in women and also present in men; used to evaluate menstrual, fertility, and hormone-related concerns.
Lipase An enzyme that helps digest fat, produced mainly by the pancreas. Elevated levels are a key marker for pancreatitis.
Sex Hormone-Binding Globulin (SHBG) A protein that binds and transports testosterone and estrogen in your blood, determining how much hormone is 'free' and active. Important for interpreting sex hormone results.
LDL Size Measures the average size of your LDL ('bad' cholesterol) particles; smaller, denser particles are considered more likely to contribute to artery plaque.
LDL Small
Testosterone The primary male sex hormone, also present in women in smaller amounts. Evaluated for low testosterone symptoms, fertility, and reproductive hormone imbalances.
Free Testosterone The small portion of your testosterone that's unbound and biologically active, considered a more accurate reflection of usable hormone than total testosterone.
Large VLDL-P Counts the largest VLDL particles, which carry a high amount of triglycerides and are associated with greater cardiovascular risk.
Rh Type Identifies whether your blood is Rh-positive or Rh-negative, an important factor for blood transfusions and pregnancy management.
T3, Free (fT3) The unbound, biologically active portion of triiodothyronine (T3), the more potent thyroid hormone. Used to evaluate thyroid function.
T4, Free (fT4) The unbound, biologically active portion of thyroxine (T4), your main thyroid hormone. A core marker for evaluating thyroid function.
Homocysteine An amino acid byproduct of protein metabolism. Elevated levels are linked to increased cardiovascular risk and can reflect low B vitamin (B12, folate, B6) status.
Luteinizing Hormone (LH) A pituitary hormone that triggers ovulation in women and stimulates testosterone production in men. Used to evaluate fertility, menstrual irregularities, and reproductive hormone disorders.
Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.
C-Reactive Protein, High Sensitivity (hs-CRP) A sensitive marker of low-grade inflammation in the body, commonly used to help assess cardiovascular disease risk.
Prostate-Specific Antigen (PSA), Free The unbound portion of prostate-specific antigen. Used alongside total PSA to help assess prostate cancer risk, especially when total PSA is borderline.
Prostate-Specific Antigen (PSA) A protein made by the prostate gland. Used to help screen for and monitor prostate cancer, though it can also rise with benign prostate conditions.
Follicle-Stimulating Hormone (FSH) A pituitary hormone that drives egg development in women and sperm production in men. Key marker for fertility and menopause evaluation.
Iron % Saturation The percentage of transferrin (your iron-carrying protein) that's currently occupied by iron — a key marker for detecting iron deficiency or overload.
Unsaturated Iron Binding Capacity Unsaturated Iron-Binding Capacity — reflects how much additional iron your blood's transferrin could still carry, used with iron and TIBC to assess iron status.
Lipoprotein(a) A genetically-determined, LDL-like particle. Elevated levels are an independent, largely inherited risk factor for cardiovascular disease.
Prolactin A pituitary hormone best known for stimulating milk production; also checked to evaluate menstrual irregularities, fertility issues, or pituitary conditions in men and women.
LP-IR Score Lipoprotein Insulin Resistance Score — a composite score derived from lipoprotein particle measurements that estimates insulin resistance.
Total Iron Binding Capacity (TIBC) Total Iron-Binding Capacity — reflects how much transferrin (the iron-carrying protein) is available in your blood, used with iron and ferritin to evaluate iron status.
Uric Acid A waste product from the breakdown of purines. Elevated levels are linked to gout and kidney stones, and can also reflect metabolic health.
Thyroglobulin Antibodies (Anti-Tg) An autoantibody against thyroglobulin. Elevated levels are associated with autoimmune thyroid conditions like Hashimoto's thyroiditis, and checked before using thyroglobulin to monitor thyroid cancer.
Dehydroepiandrosterone Sulfate (DHEA-S) The sulfated, more stable form of DHEA. A reliable marker of adrenal androgen production, used to evaluate adrenal function and androgen excess.
Cortisol, Total Your main stress hormone, produced by the adrenal glands. Reflects adrenal function and helps evaluate conditions like Cushing's syndrome or adrenal insufficiency.
Methylmalonic Acid A compound that builds up when vitamin B12 is deficient. A more sensitive marker of B12 status than a B12 blood level alone.
HDL Size Measures the average size of your HDL ('good' cholesterol) particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Antinuclear Antibodies Antibodies that target structures inside your own cells' nuclei. A positive result is a key screening marker for autoimmune conditions like lupus.
Rheumatoid Factor
Albumin The main protein made by your liver, which helps balance fluids and carries hormones, vitamins, and medications through your blood. Low levels can point to liver, kidney, or nutrition issues.
Iron, Total Measures the iron circulating in your blood, used along with other markers (like ferritin and TIBC) to evaluate for iron deficiency or overload.
HDL Large
Apolipoprotein B The main protein found on LDL and other 'bad' cholesterol particles. Considered a strong indicator of cardiovascular risk, since each particle carries one ApoB molecule.
Amylase An enzyme that helps digest carbohydrates, produced mainly by the pancreas and salivary glands. Elevated levels can signal pancreatitis or salivary gland problems.
Mercury Measures mercury levels in your blood, used to assess exposure to this toxic heavy metal, often from certain fish or environmental sources.
Thyroid Peroxidase Antibodies (Anti-TPO) An autoantibody that's the most common marker of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease.
Lead (Venous) Measures lead levels in your blood, used to assess exposure to this toxic heavy metal.
Gamma-Glutamyl Transferase (GGT) Gamma-glutamyl transferase, a liver enzyme sensitive to bile duct problems and alcohol use, often used alongside other liver tests.
Vitamin D, 25-OH, Total The combined measure of both major forms of vitamin D (D2 and D3) in your blood — the standard test used to assess overall vitamin D status.
Thyroid-Stimulating Hormone (TSH) A pituitary hormone that signals your thyroid to produce hormone. The primary screening test for both underactive and overactive thyroid conditions.
Ferritin Reflects your body's stored iron levels. Low levels point to iron deficiency; high levels can indicate iron overload or, since it's also an inflammation marker, other conditions.
VLDL Size Measures the average size of your VLDL particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Anti-Mullerian Hormone (AMH) A hormone produced by developing egg follicles that reflects ovarian reserve — an estimate of how many eggs remain. Commonly used in fertility evaluations.
HDL Particle Number (HDL-P) HDL particle number — counts your actual HDL ('good' cholesterol) particles rather than just the cholesterol they carry, offering a more detailed cardiovascular risk picture.
LDL Particle Number LDL particle number — counts your actual LDL ('bad' cholesterol) particles rather than just the cholesterol they carry, often a stronger cardiovascular risk indicator than standard LDL cholesterol.
Magnesium Measures magnesium, a mineral essential for muscle, nerve, heart, and bone function.
ABO Group Identifies your blood type (A, B, AB, or O) based on antigens on your red blood cells. Essential for safely matching blood for transfusions or transplants.
Zinc Measures zinc, a trace mineral essential for immune function, wound healing, and taste/smell.

Functional Health Panel with AMH (Female) $821.49

Laboratory: Labcorp
Sample type: Plasma Serum Whole Blood
Avg. sample processing time: 18 Business days
Require fasting: Yes

Biomarkers

Iron % Saturation The percentage of transferrin (your iron-carrying protein) that's currently occupied by iron — a key marker for detecting iron deficiency or overload.
Magnesium Measures magnesium, a mineral essential for muscle, nerve, heart, and bone function.
HDL Large
Uric Acid A waste product from the breakdown of purines. Elevated levels are linked to gout and kidney stones, and can also reflect metabolic health.
Zinc Measures zinc, a trace mineral essential for immune function, wound healing, and taste/smell.
T4, Free (fT4) The unbound, biologically active portion of thyroxine (T4), your main thyroid hormone. A core marker for evaluating thyroid function.
Thyroid Peroxidase Antibodies (Anti-TPO) An autoantibody that's the most common marker of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease.
Thyroid-Stimulating Hormone (TSH) A pituitary hormone that signals your thyroid to produce hormone. The primary screening test for both underactive and overactive thyroid conditions.
Vitamin D, 25-OH, Total The combined measure of both major forms of vitamin D (D2 and D3) in your blood — the standard test used to assess overall vitamin D status.
Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.
C-Reactive Protein, High Sensitivity (hs-CRP) A sensitive marker of low-grade inflammation in the body, commonly used to help assess cardiovascular disease risk.
LDL Particle Number LDL particle number — counts your actual LDL ('bad' cholesterol) particles rather than just the cholesterol they carry, often a stronger cardiovascular risk indicator than standard LDL cholesterol.
Anti-Mullerian Hormone (AMH) A hormone produced by developing egg follicles that reflects ovarian reserve — an estimate of how many eggs remain. Commonly used in fertility evaluations.
HDL Size Measures the average size of your HDL ('good' cholesterol) particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Follicle-Stimulating Hormone (FSH) A pituitary hormone that drives egg development in women and sperm production in men. Key marker for fertility and menopause evaluation.
Apolipoprotein B The main protein found on LDL and other 'bad' cholesterol particles. Considered a strong indicator of cardiovascular risk, since each particle carries one ApoB molecule.
Prolactin A pituitary hormone best known for stimulating milk production; also checked to evaluate menstrual irregularities, fertility issues, or pituitary conditions in men and women.
VLDL Size Measures the average size of your VLDL particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Antinuclear Antibodies Antibodies that target structures inside your own cells' nuclei. A positive result is a key screening marker for autoimmune conditions like lupus.
Dehydroepiandrosterone Sulfate (DHEA-S) The sulfated, more stable form of DHEA. A reliable marker of adrenal androgen production, used to evaluate adrenal function and androgen excess.
Sex Hormone-Binding Globulin (SHBG) A protein that binds and transports testosterone and estrogen in your blood, determining how much hormone is 'free' and active. Important for interpreting sex hormone results.
HDL Particle Number (HDL-P) HDL particle number — counts your actual HDL ('good' cholesterol) particles rather than just the cholesterol they carry, offering a more detailed cardiovascular risk picture.
Lipase An enzyme that helps digest fat, produced mainly by the pancreas. Elevated levels are a key marker for pancreatitis.
T3, Free (fT3) The unbound, biologically active portion of triiodothyronine (T3), the more potent thyroid hormone. Used to evaluate thyroid function.
LDL Small
Thyroglobulin Antibodies (Anti-Tg) An autoantibody against thyroglobulin. Elevated levels are associated with autoimmune thyroid conditions like Hashimoto's thyroiditis, and checked before using thyroglobulin to monitor thyroid cancer.
ABO Group Identifies your blood type (A, B, AB, or O) based on antigens on your red blood cells. Essential for safely matching blood for transfusions or transplants.
Gamma-Glutamyl Transferase (GGT) Gamma-glutamyl transferase, a liver enzyme sensitive to bile duct problems and alcohol use, often used alongside other liver tests.
Methylmalonic Acid A compound that builds up when vitamin B12 is deficient. A more sensitive marker of B12 status than a B12 blood level alone.
Lead (Venous) Measures lead levels in your blood, used to assess exposure to this toxic heavy metal.
Testosterone The primary male sex hormone, also present in women in smaller amounts. Evaluated for low testosterone symptoms, fertility, and reproductive hormone imbalances.
Albumin The main protein made by your liver, which helps balance fluids and carries hormones, vitamins, and medications through your blood. Low levels can point to liver, kidney, or nutrition issues.
Homocysteine An amino acid byproduct of protein metabolism. Elevated levels are linked to increased cardiovascular risk and can reflect low B vitamin (B12, folate, B6) status.
Unsaturated Iron Binding Capacity Unsaturated Iron-Binding Capacity — reflects how much additional iron your blood's transferrin could still carry, used with iron and TIBC to assess iron status.
Free Testosterone The small portion of your testosterone that's unbound and biologically active, considered a more accurate reflection of usable hormone than total testosterone.
Large VLDL-P Counts the largest VLDL particles, which carry a high amount of triglycerides and are associated with greater cardiovascular risk.
Estradiol The main and most potent form of estrogen. Key for reproductive health in women and also present in men; used to evaluate menstrual, fertility, and hormone-related concerns.
Amylase An enzyme that helps digest carbohydrates, produced mainly by the pancreas and salivary glands. Elevated levels can signal pancreatitis or salivary gland problems.
Luteinizing Hormone (LH) A pituitary hormone that triggers ovulation in women and stimulates testosterone production in men. Used to evaluate fertility, menstrual irregularities, and reproductive hormone disorders.
Rheumatoid Factor
Mercury Measures mercury levels in your blood, used to assess exposure to this toxic heavy metal, often from certain fish or environmental sources.
Total Iron Binding Capacity (TIBC) Total Iron-Binding Capacity — reflects how much transferrin (the iron-carrying protein) is available in your blood, used with iron and ferritin to evaluate iron status.
Cortisol, Total Your main stress hormone, produced by the adrenal glands. Reflects adrenal function and helps evaluate conditions like Cushing's syndrome or adrenal insufficiency.
Rh Type Identifies whether your blood is Rh-positive or Rh-negative, an important factor for blood transfusions and pregnancy management.
Lipoprotein(a) A genetically-determined, LDL-like particle. Elevated levels are an independent, largely inherited risk factor for cardiovascular disease.
Ferritin Reflects your body's stored iron levels. Low levels point to iron deficiency; high levels can indicate iron overload or, since it's also an inflammation marker, other conditions.
LP-IR Score Lipoprotein Insulin Resistance Score — a composite score derived from lipoprotein particle measurements that estimates insulin resistance.
Iron, Total Measures the iron circulating in your blood, used along with other markers (like ferritin and TIBC) to evaluate for iron deficiency or overload.
LDL Size Measures the average size of your LDL ('bad' cholesterol) particles; smaller, denser particles are considered more likely to contribute to artery plaque.

Functional Health Panel (Male) $753.99

Laboratory: Labcorp
Sample type: Plasma Serum Whole Blood
Avg. sample processing time: 18 Business days
Require fasting: Yes

Biomarkers

Lipase An enzyme that helps digest fat, produced mainly by the pancreas. Elevated levels are a key marker for pancreatitis.
Rh Type Identifies whether your blood is Rh-positive or Rh-negative, an important factor for blood transfusions and pregnancy management.
Free Testosterone The small portion of your testosterone that's unbound and biologically active, considered a more accurate reflection of usable hormone than total testosterone.
Thyroid Peroxidase Antibodies (Anti-TPO) An autoantibody that's the most common marker of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease.
Follicle-Stimulating Hormone (FSH) A pituitary hormone that drives egg development in women and sperm production in men. Key marker for fertility and menopause evaluation.
LDL Size Measures the average size of your LDL ('bad' cholesterol) particles; smaller, denser particles are considered more likely to contribute to artery plaque.
LP-IR Score Lipoprotein Insulin Resistance Score — a composite score derived from lipoprotein particle measurements that estimates insulin resistance.
Dehydroepiandrosterone Sulfate (DHEA-S) The sulfated, more stable form of DHEA. A reliable marker of adrenal androgen production, used to evaluate adrenal function and androgen excess.
Thyroglobulin Antibodies (Anti-Tg) An autoantibody against thyroglobulin. Elevated levels are associated with autoimmune thyroid conditions like Hashimoto's thyroiditis, and checked before using thyroglobulin to monitor thyroid cancer.
Prolactin A pituitary hormone best known for stimulating milk production; also checked to evaluate menstrual irregularities, fertility issues, or pituitary conditions in men and women.
Apolipoprotein B The main protein found on LDL and other 'bad' cholesterol particles. Considered a strong indicator of cardiovascular risk, since each particle carries one ApoB molecule.
HDL Size Measures the average size of your HDL ('good' cholesterol) particles, used alongside particle number for a more detailed cardiovascular risk assessment.
HDL Particle Number (HDL-P) HDL particle number — counts your actual HDL ('good' cholesterol) particles rather than just the cholesterol they carry, offering a more detailed cardiovascular risk picture.
Thyroid-Stimulating Hormone (TSH) A pituitary hormone that signals your thyroid to produce hormone. The primary screening test for both underactive and overactive thyroid conditions.
Unsaturated Iron Binding Capacity Unsaturated Iron-Binding Capacity — reflects how much additional iron your blood's transferrin could still carry, used with iron and TIBC to assess iron status.
Gamma-Glutamyl Transferase (GGT) Gamma-glutamyl transferase, a liver enzyme sensitive to bile duct problems and alcohol use, often used alongside other liver tests.
Lipoprotein(a) A genetically-determined, LDL-like particle. Elevated levels are an independent, largely inherited risk factor for cardiovascular disease.
Mercury Measures mercury levels in your blood, used to assess exposure to this toxic heavy metal, often from certain fish or environmental sources.
HDL Large
Estradiol The main and most potent form of estrogen. Key for reproductive health in women and also present in men; used to evaluate menstrual, fertility, and hormone-related concerns.
Albumin The main protein made by your liver, which helps balance fluids and carries hormones, vitamins, and medications through your blood. Low levels can point to liver, kidney, or nutrition issues.
Testosterone The primary male sex hormone, also present in women in smaller amounts. Evaluated for low testosterone symptoms, fertility, and reproductive hormone imbalances.
Homocysteine An amino acid byproduct of protein metabolism. Elevated levels are linked to increased cardiovascular risk and can reflect low B vitamin (B12, folate, B6) status.
Prostate-Specific Antigen (PSA) A protein made by the prostate gland. Used to help screen for and monitor prostate cancer, though it can also rise with benign prostate conditions.
Lead (Venous) Measures lead levels in your blood, used to assess exposure to this toxic heavy metal.
Rheumatoid Factor
Luteinizing Hormone (LH) A pituitary hormone that triggers ovulation in women and stimulates testosterone production in men. Used to evaluate fertility, menstrual irregularities, and reproductive hormone disorders.
Large VLDL-P Counts the largest VLDL particles, which carry a high amount of triglycerides and are associated with greater cardiovascular risk.
Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.
T3, Free (fT3) The unbound, biologically active portion of triiodothyronine (T3), the more potent thyroid hormone. Used to evaluate thyroid function.
Cortisol, Total Your main stress hormone, produced by the adrenal glands. Reflects adrenal function and helps evaluate conditions like Cushing's syndrome or adrenal insufficiency.
Zinc Measures zinc, a trace mineral essential for immune function, wound healing, and taste/smell.
Vitamin D, 25-OH, Total The combined measure of both major forms of vitamin D (D2 and D3) in your blood — the standard test used to assess overall vitamin D status.
Ferritin Reflects your body's stored iron levels. Low levels point to iron deficiency; high levels can indicate iron overload or, since it's also an inflammation marker, other conditions.
Prostate-Specific Antigen (PSA), Free The unbound portion of prostate-specific antigen. Used alongside total PSA to help assess prostate cancer risk, especially when total PSA is borderline.
ABO Group Identifies your blood type (A, B, AB, or O) based on antigens on your red blood cells. Essential for safely matching blood for transfusions or transplants.
Sex Hormone-Binding Globulin (SHBG) A protein that binds and transports testosterone and estrogen in your blood, determining how much hormone is 'free' and active. Important for interpreting sex hormone results.
Prostate-Specific Antigen (PSA), % Free The percentage of your PSA that's unbound to blood proteins. A lower percentage raises suspicion for prostate cancer, helping refine an elevated total PSA result.
LDL Small
Iron, Total Measures the iron circulating in your blood, used along with other markers (like ferritin and TIBC) to evaluate for iron deficiency or overload.
Uric Acid A waste product from the breakdown of purines. Elevated levels are linked to gout and kidney stones, and can also reflect metabolic health.
Amylase An enzyme that helps digest carbohydrates, produced mainly by the pancreas and salivary glands. Elevated levels can signal pancreatitis or salivary gland problems.
C-Reactive Protein, High Sensitivity (hs-CRP) A sensitive marker of low-grade inflammation in the body, commonly used to help assess cardiovascular disease risk.
Magnesium Measures magnesium, a mineral essential for muscle, nerve, heart, and bone function.
T4, Free (fT4) The unbound, biologically active portion of thyroxine (T4), your main thyroid hormone. A core marker for evaluating thyroid function.
Iron % Saturation The percentage of transferrin (your iron-carrying protein) that's currently occupied by iron — a key marker for detecting iron deficiency or overload.
LDL Particle Number LDL particle number — counts your actual LDL ('bad' cholesterol) particles rather than just the cholesterol they carry, often a stronger cardiovascular risk indicator than standard LDL cholesterol.
Antinuclear Antibodies Antibodies that target structures inside your own cells' nuclei. A positive result is a key screening marker for autoimmune conditions like lupus.
Total Iron Binding Capacity (TIBC) Total Iron-Binding Capacity — reflects how much transferrin (the iron-carrying protein) is available in your blood, used with iron and ferritin to evaluate iron status.
VLDL Size Measures the average size of your VLDL particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Methylmalonic Acid A compound that builds up when vitamin B12 is deficient. A more sensitive marker of B12 status than a B12 blood level alone.

Functional Health Panel (Female) $747.99

Laboratory: Labcorp
Sample type: Plasma Serum Whole Blood
Avg. sample processing time: 18 Business days
Require fasting: Yes

Biomarkers

Ferritin Reflects your body's stored iron levels. Low levels point to iron deficiency; high levels can indicate iron overload or, since it's also an inflammation marker, other conditions.
ABO Group Identifies your blood type (A, B, AB, or O) based on antigens on your red blood cells. Essential for safely matching blood for transfusions or transplants.
Sex Hormone-Binding Globulin (SHBG) A protein that binds and transports testosterone and estrogen in your blood, determining how much hormone is 'free' and active. Important for interpreting sex hormone results.
Lead (Venous) Measures lead levels in your blood, used to assess exposure to this toxic heavy metal.
Rh Type Identifies whether your blood is Rh-positive or Rh-negative, an important factor for blood transfusions and pregnancy management.
Albumin The main protein made by your liver, which helps balance fluids and carries hormones, vitamins, and medications through your blood. Low levels can point to liver, kidney, or nutrition issues.
Amylase An enzyme that helps digest carbohydrates, produced mainly by the pancreas and salivary glands. Elevated levels can signal pancreatitis or salivary gland problems.
Uric Acid A waste product from the breakdown of purines. Elevated levels are linked to gout and kidney stones, and can also reflect metabolic health.
HDL Size Measures the average size of your HDL ('good' cholesterol) particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Estradiol The main and most potent form of estrogen. Key for reproductive health in women and also present in men; used to evaluate menstrual, fertility, and hormone-related concerns.
Free Testosterone The small portion of your testosterone that's unbound and biologically active, considered a more accurate reflection of usable hormone than total testosterone.
Follicle-Stimulating Hormone (FSH) A pituitary hormone that drives egg development in women and sperm production in men. Key marker for fertility and menopause evaluation.
C-Reactive Protein, High Sensitivity (hs-CRP) A sensitive marker of low-grade inflammation in the body, commonly used to help assess cardiovascular disease risk.
Testosterone The primary male sex hormone, also present in women in smaller amounts. Evaluated for low testosterone symptoms, fertility, and reproductive hormone imbalances.
Methylmalonic Acid A compound that builds up when vitamin B12 is deficient. A more sensitive marker of B12 status than a B12 blood level alone.
HDL Large
Thyroid Peroxidase Antibodies (Anti-TPO) An autoantibody that's the most common marker of autoimmune thyroid disease, including Hashimoto's thyroiditis and Graves' disease.
Lipoprotein(a) A genetically-determined, LDL-like particle. Elevated levels are an independent, largely inherited risk factor for cardiovascular disease.
HDL Particle Number (HDL-P) HDL particle number — counts your actual HDL ('good' cholesterol) particles rather than just the cholesterol they carry, offering a more detailed cardiovascular risk picture.
VLDL Size Measures the average size of your VLDL particles, used alongside particle number for a more detailed cardiovascular risk assessment.
Total Iron Binding Capacity (TIBC) Total Iron-Binding Capacity — reflects how much transferrin (the iron-carrying protein) is available in your blood, used with iron and ferritin to evaluate iron status.
Lipase An enzyme that helps digest fat, produced mainly by the pancreas. Elevated levels are a key marker for pancreatitis.
Large VLDL-P Counts the largest VLDL particles, which carry a high amount of triglycerides and are associated with greater cardiovascular risk.
Dehydroepiandrosterone Sulfate (DHEA-S) The sulfated, more stable form of DHEA. A reliable marker of adrenal androgen production, used to evaluate adrenal function and androgen excess.
Thyroglobulin Antibodies (Anti-Tg) An autoantibody against thyroglobulin. Elevated levels are associated with autoimmune thyroid conditions like Hashimoto's thyroiditis, and checked before using thyroglobulin to monitor thyroid cancer.
T4, Free (fT4) The unbound, biologically active portion of thyroxine (T4), your main thyroid hormone. A core marker for evaluating thyroid function.
Thyroid-Stimulating Hormone (TSH) A pituitary hormone that signals your thyroid to produce hormone. The primary screening test for both underactive and overactive thyroid conditions.
Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.
Zinc Measures zinc, a trace mineral essential for immune function, wound healing, and taste/smell.
Cortisol, Total Your main stress hormone, produced by the adrenal glands. Reflects adrenal function and helps evaluate conditions like Cushing's syndrome or adrenal insufficiency.
Apolipoprotein B The main protein found on LDL and other 'bad' cholesterol particles. Considered a strong indicator of cardiovascular risk, since each particle carries one ApoB molecule.
Antinuclear Antibodies Antibodies that target structures inside your own cells' nuclei. A positive result is a key screening marker for autoimmune conditions like lupus.
LDL Particle Number LDL particle number — counts your actual LDL ('bad' cholesterol) particles rather than just the cholesterol they carry, often a stronger cardiovascular risk indicator than standard LDL cholesterol.
Rheumatoid Factor
Iron, Total Measures the iron circulating in your blood, used along with other markers (like ferritin and TIBC) to evaluate for iron deficiency or overload.
Gamma-Glutamyl Transferase (GGT) Gamma-glutamyl transferase, a liver enzyme sensitive to bile duct problems and alcohol use, often used alongside other liver tests.
LDL Small
T3, Free (fT3) The unbound, biologically active portion of triiodothyronine (T3), the more potent thyroid hormone. Used to evaluate thyroid function.
Vitamin D, 25-OH, Total The combined measure of both major forms of vitamin D (D2 and D3) in your blood — the standard test used to assess overall vitamin D status.
LDL Size Measures the average size of your LDL ('bad' cholesterol) particles; smaller, denser particles are considered more likely to contribute to artery plaque.
Magnesium Measures magnesium, a mineral essential for muscle, nerve, heart, and bone function.
Mercury Measures mercury levels in your blood, used to assess exposure to this toxic heavy metal, often from certain fish or environmental sources.
Luteinizing Hormone (LH) A pituitary hormone that triggers ovulation in women and stimulates testosterone production in men. Used to evaluate fertility, menstrual irregularities, and reproductive hormone disorders.
Homocysteine An amino acid byproduct of protein metabolism. Elevated levels are linked to increased cardiovascular risk and can reflect low B vitamin (B12, folate, B6) status.
Iron % Saturation The percentage of transferrin (your iron-carrying protein) that's currently occupied by iron — a key marker for detecting iron deficiency or overload.
Unsaturated Iron Binding Capacity Unsaturated Iron-Binding Capacity — reflects how much additional iron your blood's transferrin could still carry, used with iron and TIBC to assess iron status.
LP-IR Score Lipoprotein Insulin Resistance Score — a composite score derived from lipoprotein particle measurements that estimates insulin resistance.
Prolactin A pituitary hormone best known for stimulating milk production; also checked to evaluate menstrual irregularities, fertility issues, or pituitary conditions in men and women.

CIRS Panel $853.49

The CIRS panel measures markers associated with Chronic Inflammatory Response Syndrome (CIRS). It aids in evaluating systemic inflammation and immune dysregulation, facilitating accurate diagnosis and tailored treatment plans for patients with CIRS-related conditions.

Laboratory: Labcorp
Sample type: Plasma Serum
Avg. sample processing time: 13 Business days
Require fasting: No

Biomarkers

Transforming Growth Factor Beta 1 (TGF-β1) A signaling protein (cytokine) involved in tissue repair, immune regulation, and inflammation; studied in various chronic inflammatory and fibrotic conditions.
Antidiuretic Hormone Also called vasopressin, this hormone helps your kidneys regulate how much water your body retains. Abnormal levels are linked to conditions affecting fluid balance, like diabetes insipidus or SIADH.
Complement C3a desArg An activation fragment produced when complement protein C3 is triggered. Reflects how active your complement immune pathway currently is.
Matrix Metalloproteinase-9 (MMP-9) An enzyme involved in breaking down tissue, including artery plaque, and contributing to inflammation. Studied in cardiovascular and certain chronic inflammatory conditions.
Melanocyte-Stimulating Hormone (MSH) A pituitary-derived hormone involved in skin pigmentation and, more recently, studied for roles in appetite and inflammation regulation.
Vascular Endothelial Growth Factor (VEGF) A signaling protein that promotes new blood vessel growth. Studied in cancer, wound healing, and certain inflammatory or eye conditions.
Osmolality Measures the concentration of dissolved particles in your blood, reflecting hydration and fluid balance.
Leptin A hormone released by fat cells that helps regulate appetite and energy balance. Levels generally rise with increased body fat.
Complement C4a An activation fragment produced when complement protein C4 is triggered. Reflects how active your complement immune pathway currently is.

View biomarker

Leptin resistance means more leptin, not less

The majority of overweight individuals who struggle to lose weight do not have low leptin levels. In fact, they often have elevated leptin. The problem is that the brain stops responding appropriately to leptin’s message. This condition is known as leptin resistance.

When leptin resistance develops, the brain behaves as if the body is starving, even when there are substantial fat stores available. The body shifts into survival mode. Hunger increases, satiety decreases, metabolic rate slows, and fat storage becomes prioritized over fat burning.

This helps explain why some people report eating less than before while continuing to gain weight or being unable to lose it.

Why this reaches the thyroid

Leptin resistance does not only affect appetite. It has significant effects on thyroid physiology and cellular metabolism.

Research suggests that elevated leptin and leptin resistance may reduce intracellular active thyroid hormone, specifically T3, while altering thyroid signaling pathways. This means that thyroid hormones measured in blood may appear normal while thyroid activity inside tissues is reduced.

This is one reason some individuals experience symptoms commonly associated with hypothyroidism despite having “normal” thyroid labs. They may struggle with chronic fatigue, brain fog, fluid retention, feeling cold, hair loss, constipation, slow recovery, and difficulty losing weight.

Reverse T3

One important mechanism involves Reverse T3. Reverse T3 is an inactive form of thyroid hormone produced under stress, inflammation, calorie restriction, chronic illness, and metabolic dysfunction. Instead of converting thyroid hormone into active T3 that supports energy production, the body converts more into Reverse T3, effectively slowing metabolism.

From an evolutionary perspective, this response protects survival during famine.

In modern life, chronic stress, poor sleep, inflammation, insulin resistance, repeated dieting, nutrient deficiencies, and metabolic dysfunction may keep individuals trapped in this adaptation.

The result is a body that behaves as though it must conserve energy.

Why TSH alone can look normal

This is also why TSH alone may not provide a complete picture of thyroid function in people struggling with weight. Elevated leptin combined with increased Reverse T3 may reduce cellular T3 while suppressing TSH, making standard thyroid testing less informative in some cases.

Why GLP-1 medications may not be enough on their own

People often ask why they cannot lose weight despite taking GLP-1 medications. While GLP-1 therapies can significantly reduce appetite and improve blood sugar regulation, appetite suppression does not automatically correct leptin resistance, chronic inflammation, impaired thyroid conversion, elevated Reverse T3, mitochondrial dysfunction, or nutrient deficiencies.

Reducing calorie intake alone does not always restore normal metabolic signaling.

Weight loss depends not only on how much someone eats but also on whether the body feels safe enough to increase energy expenditure.

Leptin levels themselves matter

An important point rarely discussed is that leptin levels themselves matter. While laboratory reference ranges vary, many functional medicine practitioners consider leptin levels above 10 ng/mL is an indicator of impaired leptin sensitivity, especially in individuals struggling with weight loss, elevated Reverse T3, or symptoms of slowed metabolism. Elevated leptin does not automatically mean leptin resistance, but persistently high levels may suggest the body is no longer responding efficiently to leptin signaling.

Where to start

The question then becomes: where should someone start?

The goal is not simply lowering leptin levels. The goal is improving leptin sensitivity.

This often begins by reducing chronic inflammation, improving sleep quality, supporting insulin sensitivity, optimizing protein intake, correcting iron and micronutrient deficiencies, reducing chronic stress, and evaluating thyroid function beyond TSH alone.

For some individuals, restoring normal thyroid conversion and improving leptin sensitivity becomes the turning point where metabolism begins functioning differently and weight loss finally becomes possible.

At Hormunity, we believe that understanding the deeper physiology behind weight regulation allows for more personalized strategies rather than relying solely on standard ranges or simplified approaches to metabolism.

Bibliography

Perello, M., Çakir, I., Cyr, N. E., Romero, A., Stuart, R. C., Chiappini, F., Hollenberg, A. N., & Nillni, E. A. (2010). Maintenance of the thyroid axis during diet-induced obesity in rodents is controlled at the central level. American Journal of Physiology-Endocrinology and Metabolism, 299(6). https://doi.org/10.1152/ajpendo.00448.2010
Obradovic, M., Sudar-Milovanovic, E., Soskic, S., Essack, M., Arya, S., Stewart, A. J., Gojobori, T., & Isenovic, E. R. (2021). Leptin and obesity: Role and clinical implication. Frontiers in Endocrinology, 12, 585887. https://doi.org/10.3389/fendo.2021.585887
El Amrousy, D., El-Afify, D., & Salah, S. (2022). Insulin resistance, leptin and adiponectin in lean and hypothyroid children and adolescents with obesity. BMC Pediatrics, 22(1), 245. https://doi.org/10.1186/s12887-022-03318-x
Calvino, C., Souza, L. L., Costa-e-Sousa, R. H., Almeida, N. A., Trevenzoli, I. H., & Pazos-Moura, C. C. (2012). Hypothyroidism reduces ObRb-STAT3 leptin signalling in the hypothalamus and pituitary of rats associated with resistance to leptin acute anorectic action. Journal of Endocrinology, 215(1), 129–135. https://doi.org/10.1530/JOE-11-0476

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June 04, 2026 Essential Metabolic Health

Why You Can’t Lose Weight: The Hidden Role of Leptin Resistance, Thyroid Function, and Metabolism

What leptin actually does

Leptin resistance means more leptin, not less

Why this reaches the thyroid

Reverse T3

Why TSH alone can look normal

Why GLP-1 medications may not be enough on their own

Leptin levels themselves matter

Where to start

Bibliography

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