Cancer
Cancer increases inflammation, and this promotes muscle wasting and disrupts appetite-regulating hormones. A growing tumor may also increase your resting energy expenditure (REE), or how much energy your body burns at rest.
Addison’s disease
Addison’s disease develops when the immune system attacks the adrenal glands. In turn, the adrenal glands can’t make enough hormones like cortisol and aldosterone. Cortisol regulates many functions, including metabolism and appetite. Low levels of cortisol may lead to poor appetite and weight loss.