Weight loss with hypothyroidism
Pro Research Analysisby 
Searched over 200M research papers
Weight Loss with Hypothyroidism: Mechanisms and Outcomes
Introduction to Hypothyroidism and Weight Gain
Hypothyroidism, a condition characterized by an underactive thyroid gland, often leads to weight gain due to a reduction in resting energy expenditure (REE) and other metabolic changes . This article explores the mechanisms behind weight loss in hypothyroid patients undergoing treatment and the outcomes of various weight loss strategies.
Mechanisms of Weight Loss in Hypothyroidism
Role of Levothyroxine (L-T4) Therapy
Levothyroxine (L-T4) therapy is a common treatment for hypothyroidism. Studies have shown that L-T4 therapy leads to a significant decrease in body weight, primarily due to the excretion of excess body water associated with myxoedema, rather than a reduction in fat mass 17. This weight loss is accompanied by an increase in REE and physical activity levels, although the number of daily steps may not change significantly .
Short-Term Weight Changes
In the short term, weight loss in hypothyroid patients treated with levothyroxine is often due to diuresis. A study involving 99 newly diagnosed hypothyroid patients found that 90.3% of participants experienced weight loss within six weeks of starting levothyroxine therapy, with a significant reduction in both body weight and body mass index (BMI) . This early weight loss is primarily attributed to the loss of water weight rather than fat.
Long-Term Weight Regulation
Long-term studies indicate that weight regulation in hypothyroid patients stabilizes over time. For instance, a study on hypothyroid subjects showed a small decline in body weight during the first six months of treatment, with weight returning to pretreatment levels by 24 months . This suggests that, in the absence of significant metabolic derangement, body weight is regulated within narrow limits over many years.
Weight Loss Strategies and Their Efficacy
Alternate Day Fasting vs. Daily Calorie Restriction
For individuals with subclinical hypothyroidism, both alternate day fasting (ADF) and daily calorie restriction (CR) have been shown to produce similar reductions in body weight without affecting thyroid hormone levels . This indicates that intermittent fasting and daily caloric restriction are both viable strategies for weight loss in this population.
Impact of Bariatric Surgery
In morbidly obese patients with subclinical hypothyroidism, weight loss induced by Roux-en-Y gastric bypass (RYGBP) surgery has been associated with a significant decrease in TSH levels and normalization of thyroid function . This suggests that substantial weight loss through surgical means can improve thyroid function and potentially reverse subclinical hypothyroidism.
Body Composition Changes
Lean Body Mass vs. Fat Mass
While weight loss in hypothyroid patients is often due to water loss, changes in body composition also occur. Studies have shown that lean body mass (LBM) decreases significantly after correction of hypothyroidism, without a corresponding change in fat mass . This indicates that the reduction in body weight is not due to fat loss but rather a decrease in lean tissue.
Subclinical Hypothyroidism in the Elderly
In elderly individuals with subclinical hypothyroidism, there is no significant difference in weight change or body composition compared to euthyroid individuals . This suggests that subclinical hypothyroidism does not have a clinically significant impact on weight status in older adults.
Conclusion
Weight loss in hypothyroid patients undergoing treatment is primarily due to the excretion of excess body water rather than fat loss. Levothyroxine therapy, alternate day fasting, daily calorie restriction, and bariatric surgery are all effective strategies for weight loss in this population. However, changes in body composition, particularly the reduction in lean body mass, should be considered when evaluating the outcomes of these treatments. Understanding these mechanisms can help clinicians better manage weight loss in hypothyroid patients.
Sources and full results
Most relevant research papers on this topic