Weight loss in patients with hypothyroidism treated with medication
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Weight Loss in Hypothyroid Patients Treated with Medication
Levothyroxine (LT4) Therapy and Weight Change
Research shows that most patients with hypothyroidism experience some weight loss after starting levothyroxine (LT4) therapy, but the amount is generally modest and varies between individuals. In one study, 90% of patients lost weight after six weeks of LT4 treatment, with an average loss of about 3.2 kg, while a small number gained or maintained their weight. The reduction in body mass index (BMI) was also significant, and these changes did not depend on age, gender, baseline weight, or thyroid hormone levels at the start of treatment . However, another study found that only about half of patients lost weight after LT4 therapy, with an average loss of 3.8 kg, and the overall change in weight and BMI was not statistically significant for the group as a whole .
Nature of Weight Loss: Water vs. Fat
Several studies agree that the weight loss seen with LT4 therapy is mainly due to the loss of excess body water, not fat. This is because untreated hypothyroidism often leads to fluid retention (myxoedema), and correcting thyroid hormone levels helps the body get rid of this extra water. Fat mass and bone mass usually remain unchanged during treatment, even though resting energy expenditure increases 49.
Long-Term Weight Regulation
Long-term studies indicate that any initial weight loss after starting hypothyroidism treatment is usually small and may not be sustained. Over a period of two years, patients often return to their pretreatment weight, suggesting that the body regulates weight within a narrow range once thyroid function is normalized .
Weight Loss in Obese Hypothyroid Patients
For patients with both obesity and hypothyroidism, achieving normal thyroid hormone levels with LT4 therapy leads to weight loss responses similar to those seen in people without thyroid disease. When combined with calorie restriction and exercise, hypothyroid women on LT4 lost weight at the same rate as women with normal thyroid function .
Effects of Other Thyroid Hormone Therapies
Switching from LT4 to liothyronine (LT3) or to combination therapies (LT4/LT3 or desiccated thyroid extract) has been studied for potential additional weight loss benefits. LT3 therapy resulted in greater weight loss compared to LT4, but did not show differences in cardiovascular or insulin sensitivity outcomes . Desiccated thyroid extract also led to modest weight loss (about 1.4 kg), and nearly half of patients preferred it over LT4, though quality of life improvements were not significant . However, switching to combination therapy did not result in weight loss, even though patients reported better quality of life .
Mechanisms Limiting Fat Loss
Despite increases in resting energy expenditure with LT4 therapy, fat mass loss is rarely observed. One reason may be that LT4 treatment increases hunger sensations, which could offset the potential for fat loss by leading to higher food intake .
Conclusion
In summary, most hypothyroid patients treated with medication experience modest weight loss, primarily due to water loss rather than fat reduction. Achieving normal thyroid hormone levels allows for weight regulation similar to individuals without thyroid disease. Alternative therapies may offer slight additional weight loss for some patients, but overall, significant fat loss is uncommon, and increased hunger may limit further weight reduction.
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