Hypothyroidism and weight loss
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Hypothyroidism and Weight Loss: Understanding the Connection
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 weight gain is typically modest and primarily involves an increase in lean body mass rather than fat mass. The relationship between hypothyroidism and weight is complex and influenced by various factors, including thyroid hormone levels and physical activity.
Mechanisms of Weight Loss in Hypothyroidism Treatment
Excretion of Excess Body Water
One of the primary mechanisms for weight loss following hypothyroidism treatment is the excretion of excess body water associated with myxoedema, a condition characterized by swelling of the skin and underlying tissues . Studies have shown that treatment with levothyroxine (L-T4) leads to a significant decrease in body weight, primarily due to the loss of water weight rather than fat .
Changes in Resting Energy Expenditure
Treatment of hypothyroidism with L-T4 also results in an increase in REE, which contributes to weight loss. This increase in energy expenditure helps to counteract the reduced metabolic rate seen in untreated hypothyroidism.
Physical Activity and Energy Expenditure
While physical activity levels, as measured by daily steps, may not significantly change, self-reported physical activity often increases following treatment, further contributing to weight loss. This suggests that patients may engage in more spontaneous physical activities, which can enhance overall energy expenditure.
Subclinical Hypothyroidism and Weight Change
Modest Impact on Weight
Subclinical hypothyroidism, a milder form of thyroid dysfunction, has a less clear impact on weight. Research indicates that subclinical hypothyroidism does not significantly affect weight change or body composition in the elderly. However, some studies suggest a modest increase in weight associated with subclinical hypothyroidism, though the evidence is not definitive .
Influence of Thyroid Hormone Levels
Higher levels of thyroid-stimulating hormone (TSH) and free T3 are often observed in obese individuals, which may be mediated by leptin, a hormone involved in regulating energy balance . Weight loss induced by treatments such as bariatric surgery can lead to normalization of TSH levels, indicating a potential bidirectional relationship between thyroid function and obesity .
Long-Term Weight Regulation
Weight Stability Post-Treatment
Long-term studies have shown that body weight tends to stabilize after initial treatment for hypothyroidism, with patients often returning to their pretreatment weight within a few years. This suggests that effective management of thyroid function can help maintain weight within narrow limits over time.
Role of Adaptive Thermogenesis
Interestingly, hypothyroid mice models have demonstrated a leaner phenotype due to increased adaptive thermogenesis in skeletal muscle, highlighting the complex metabolic adaptations that can occur in hypothyroidism. These findings may provide insights into potential therapeutic targets for weight loss in humans.
Conclusion
In summary, weight loss in hypothyroidism treatment is primarily driven by the excretion of excess body water and an increase in REE. While subclinical hypothyroidism has a modest impact on weight, effective management of thyroid function can help maintain long-term weight stability. Understanding the intricate relationship between thyroid function and weight can aid in developing better strategies for managing weight in patients with thyroid disorders.
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