TSH is thyroid stimulating hormone, which is secreted by your pituitary gland when your body is running low on its active thyroid hormones, T3 and T4. T3 and T4 are involved in metabolism as well as other critical functions in your body. High TSH is often, although not necessarily, indicative of low active hormones and thus low thyroid function. Weight gain is a common consequence. Losing weight with an underactive thyroid is difficult, but not impossible.
The pituitary will secrete more TSH when you have inadequate levels of the active thyroid hormones. Having high TSH can lead to potential concerns, as your body's metabolism depends on T3 and T4 levels to function properly. In other words, without these hormones, the rate at which you use fats and carbohydrates is altered. High levels of TSH are often associated with weight gain and obesity.
TSH and Weight Gain
Weight gain occurs when your body has more calories then it needs to perform its daily tasks, so it stores this energy for later use. Although you may watch your calorie intake, with high TSH levels, weight gain remains a possibility. Low T3 and T4 levels mean your metabolic rate is lower, which can increase your risk for putting on pounds. According to a study published in the "Journal of Clinical Endocrinology and Metabolism" in July 2005, there is a positive correlation between body mass index -- BMI -- and TSH levels. However, TSH may not be the only factor in weight gain and it is therefore not the only factor in weight loss.
A Little About Leptin
One reason TSH is correlated with weight gain is its connection to leptin, a hormone that is secreted by your adipose, or fat, tissue. If you have energy -- i.e. fat -- in reserve, leptin gives your brain a "full" signal; too little fat, and leptin tells your brain you need to eat. However, excessive fat will cause leptin to transmit signals too often, resulting in a malfunctioning signal and potential hunger signaling.
TSH and Leptin
Elevated leptin levels occur in individuals with high BMI's. According to a 2008 study in "Nuklearmedizin," high levels of leptin will increase TSH levels. However, the study states that it is unclear whether high TSH or leptin levels are responsible for obesity and weight gain.
TSH and Weight Loss
Since a high TSH level is indicative of other imbalances in the body, like low active thyroid hormones, weight loss is more difficult. Hypothyroidism changes your metabolism, so calorie counting alone may not work for you. You may need help balancing your thyroid hormones. Your doctor can prescribe medications that increase your active thyroid hormones, which can result in lower TSH levels and a speedier metabolism. Reducing body fat can lower TSH levels without the need for medication. Diet and exercise are helpful tools in weight and fat reduction. Talk to your doctor about your condition and what methods are available to help you lose weight.