Slight Shifts in Thyroid TSH Linked to Weight Gain

If your weight loss efforts are failing, get a full thyroid evaulation

Woman weighing herself on scale.
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Experts know that an overactive thyroid (hyperthyroidism) can cause weight loss, and a slower thyroid -(hypothyroidism) can contribute to weight gain, but experts have often claimed that the relationship is not significant in many cases. Research has now pinpointed that there is even more of a thyroid-weight connection.

A study reported in the Archives of Internal Medicine explored the connection between Thyroid Stimulating Hormone (TSH) levels and body weight.

The researchers found that even slight increases in TSH within the normal range, over time, appear to be associated with weight gain.

Patients studied had levels that fell within the reference or normal range of TSH. For the purposes of this study, they used the range of 0.5 to 5.0. The research found that even small increases in TSH were clearly associated with increases in body weight.

The study authors summarized their findings:

"Thyroid function (as assessed by serum TSH concentration) within the reference range is associated with body weight in both sexes. Our findings raise the possibility that modest increases in serum TSH concentrations within the reference range may be associated with weight gain."

The researchers offered two possible reasons that might explain their findings.

First, lower energy expenditure—known as thermogenesis—is associated with lowered thyroid function. Lowered thyroid function can lower metabolism, which means that fewer calories are needed in order to maintain body weight, which can make weight loss more difficult, or even impossible in some cases.

Second, triiodothyronine (T3) is the active thyroid hormone at the cellular level. It delivers oxygen and energy to cells. Lower T3 levels are associated with lowered resting metabolic rates. And again, when metabolism is lower, lower calorie intake and more activity to burn calories are both needed in order to maintain current body weight or lose weight.


The implications of these findings aren't clear because while they suggest that increased TSH levels— even within the normal reference range—may play a role in weight gain, there is no definite cause and effect. It's not clear that lowering the TSH level (for example, with thyroid hormone replacement therapy) would reverse any impact and result in weight loss.

The main conclusion, therefore, is that while increases in TSH may be associated with weight gain, further research is needed to understand why, and whether this is preventable or treatable.

When You Need to Lose Weight

If you are overweight and can't lose weight despite a healthy diet and exercise, you should have a full thyroid evaluation to rule out hypothyroidism. An underactive thyroid can sabotage even the best diet and exercise plans.

If you are overweight, and being treated for a thyroid problem, but finding it hard or impossible to lose weight, you'll want to learn about optimizing your thyroid treatment, and tactics thyroid patients can follow for effective weight loss


Fox, Caroline S. et. al. "Relations of Thyroid Function to Body Weight: Cross-sectional and Longitudinal Observations in a Community-Based Sample," ​Archives of Internal Medicine. 2008;168:568-569, 587-592. Vol. 168 No. 6, March 24, 2008