[QUOTE=Frylock]
…people are bringing up the idea that hyperhthyroidism and other hormone problems can cause it to be very difficult to lose weight, no matter how much is eaten and how much one exercises…I don’t understand how this can be. If you eat very little, and exercise a lot, how can you still gain weight?..
Alternatively, is the claim false, or only half-true, in the first place?..
[/QUOTE]
To repeat, elements of the claim are true. A well known symptom of hyperthyroidism is weight loss, even despite ravenous eating. The prevalence and symptom are especially striking among hyperthyroid domestic cats, who often waste away, become skeletal and die, despite eating ravenously.
That said, the part 'no matter how much you eat or exercise’ is not true – if you mean that literally and not as hyperbole. Such persons if trapped in the wilderness or a concentration camp would never die from lack of food. That obviously doesn’t happen. They become thin, emaciated and eventually die.
Observationally we know there’s a significant variation in body weight that accompanies certain medical conditions and treatments. Something biochemical changes to cause weight gain/loss, despite unchanging caloric intake and exercise levels.
Re PCOS in human females, it’s often associated with body weight gain. The underlying biological mechanisms aren’t totally understood:
“Obesity is a prominent feature of PCOS; at least 50% of patients with PCOS are obese” Obesity and weight loss in polycystic ovary syndrome, Hoeger K., Obstetrics and Gynecology Clinics of North Am, 2001 March, PMID: 11293006
Another cause of weight gain (or difficulty losing weight) are commonly-used antidepressant and antipsychotic medications. Lithium, Remeron, etc. often cause this. The underlying mechanism isn’t well understood, but a recent paper said this about Remeron (Mirtazapine): “…Weight gain is a frequent and important side effect of psychopharmacotherapy…Recent studies suggest that the fat-cell-derived hormone leptin and the tumor necrosis factor-alpha (TNF-alpha) cytokine system are pathophysiologically involved.” Kraus T, et al, Pharmacopsychiatry, 2002 November, PMID: 12518269.
Anabolic steroids are often legally used in patients who can’t gain weight, no matter what they eat. One example are AIDS patients. The drugs obviously cause weight gain, since that’s why they’re prescribed.
Here’s a key thought: What you induce artificially with anabolic steroids, some people may already naturally have within their bodies. E.g, there’s a wide range of normal, naturally-occurring testosterone levels within adult males, ranging from 300 ng/dl to 1000 ng/gl. It’s no great leap to hypothesize that one with a high level can gain weight (esp muscle mass) faster than one with a low level.
None of this means you could feed such patients 100 calories per day and they’d still gain weight. Obviously there’s a point weight loss would still happen. However there’s ample evidence that some common hormonal factors and pharmaceutical treatments will cause weight gain, even despite moderate caloric intake control and regular exercise.