Don't blame yourself for failure. Sometimes there's a medical reason for weight gain or the inability to lose weight! Here is a list of key tests that can determine if there's a physiological cause for your weight problems.

Thyroid hormone imbalance

An imbalance of thyroid hormones, specifically hypothyroidism or thyroid hormone conversion disorders, can make it difficult or impossible to lose weight. To determine if you have thyroid issues, ask your doctor to test TSH, Free T4, Free T3, and reverse T3 (RT3). Since reverse T3 can block cell receptors for thyroid hormone, it is critical to test this hormone to properly determine your thyroid health. In fact, RT3 is the best test to measure tissue levels of thyroid hormone. In healthy individuals, Reverse T3 is typically less than 250 pg/ml, with a Free T3/Reverse T3 ratio greater than 1.8 if free T3 is measured in ng/dl, or 0.018 if Free T3 is in pg/ml.

Sex Hormone Binding Globulin

Another hormone that is related to proper thyroid functioning is sex hormone binding globulin (SHBG). SHBG is stimulated in the liver in response to thyroid hormones and estrogen, and thus can be a good indicator of tissue levels of thyroid hormones. In premenopausal women, SHBG should be greater than 70, especially if the woman is on oral thyroid hormone replacement. Due to first pass metabolism, the liver will have a much higher level of thyroid hormones than the rest of the tissues. If SHBG is low, the rest of the body is low thyroid.

SHBG is not a useful test, however, if a woman is taking oral estrogen replacement therapy, because this estrogen will artificially elevate SHBG due to high estrogen levels in the liver. Conversely, this test is not affected by transdermal estrogen preparations, such as bioidentical hormone creams.


Homocysteine is a non-protein amino acid that is produced when methionine is broken down in the body. Elevated homocysteine levels can cause irritations of the blood vessels. Levels less than 9 are an indicator of low thyroid hormone levels and low B vitamins.


Iodine is a critical element for healthy thyroid function. Levels that are too low or too high can cause low thyroid hormones. Urinary iodine is the most reliable measure of iodine levels in the body.

C-reactive Protein (CRP)

C-reactive protein is a measure of inflammation in the body, which decreases cellular T3 production. In a healthy individual, C-reactive protein should be less than 1.

Iron and Ferritin

Adequate iron and ferritin levels are required to activate thyroid hormones, so levels that are low can contribute to weight loss difficulty. Many symptoms that are attributed to anemia, such as fatigue and sensitivity to cold, also can be seen in patients with low thyroid hormone levels. If ferritin levels are low, it can take several months for them to return to normal. However, iron supplementation and thyroid supplementation can be done simultaneously while your doctor monitors blood levels.

Thyroid Antibodies

A common cause of hypothyroidism is an autoimmune disease called Hashimoto's disease. If you are having symptoms of hypothyroidism, including fatigue and weight gain, it is important to test your levels of thyroid peroxidase antibodies (TPO) and antithyroglobulin antibodies to make sure you aren't dealing with an autoimmune thyroid disorder.

Glucose and Insulin

Insulin resistance can be a key factor in weight gain or difficulty in losing weight. To rule out these issues, your doctor should test your glucose and insulin levels, as well as HgA1C, which measures average glucose levels over a period of time. These tests can help determine if you are suffering from insulin resistance, which is a treatable imbalance.


Lipids such as cholesterol and triglycerides can be an indicator of metabolic problems. For example, high cholesterol can indicate low thyroid hormone levels, which could make it difficult to lose weight, while high cholesterol is a marker for insulin resistance.


Leptin is a protein hormone that plays a key role in regulating energy intake and expenditure. Leptin levels greater than 12 indicate leptin resistance, which can hinder weight loss efforts. Note that normal laboratory ranges cannot be used for determining leptin resistance, because these ranges include both overweight and insulin resistant individuals.

Vitamin D

Vitamin D is not a vitamin at all, but is actually an important hormone in the body that is critical to multiple body functions, including weight management. Optimal vitamin D levels should be greater than 80. Low levels of vitamin D are often seen in people who are overweight. It is thought that the hypothalamus may sense low levels of vitamin D and respond by releasing hunger-stimulating hormones and increasing the body weight set point. Vitamin D also may work at the cellular level to prevent the growth and maturation of fat cells.

Basal Metabolic Rate

The basal metabolic rate, or BMR, indicates the number of calories burned while the body is at rest. The BMR can be tested using a device that measured using a device that measures the amount of oxygen burned over a ten-minute period. If the BMR is low, it can indicate that the body burns significantly fewer calories than normal during exercise.

Muscular Reflex Time

Decreased muscle reflex time can be used as a diagnostic indicator of low thyroid hormone levels. A delayed return phase of the ankle jerk reflex can indicate hypothyroidism at the tissue level, and is actually a more sensitive test of thyroid tissue levels than standard lab tests.

Weight loss success isn't always as simple as calories in versus calories burned. Often it can be directly attributed to specific physiological functions in the body, including hormone levels and thyroid function. Before you give up your efforts to reach a healthy weight, ask your doctor to run a full metabolic panel that includes tests such as TSH, free T3, free T4, reverse T3, leptin levels, HgA1c, insulin and glucose, c-reactive protein, antithyroid antibodies, homocysteine, SHBG, lipids, and sex hormone such as estrogen and testosterone. You may find the answer to your weight loss success can be controlled with a little help from your doctor. More importantly, your overall health may depend on it.

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