Bipolar : could severely reduced calories or not eating trigger mania / hypomania?

Interesting question: Not sure from a metabolic standpoint, but decreased appetite is often part of mood changes, sometimes people cycle from depression where appetite is low, into mania. It may also be someone is becoming so manic they are not stopping to ear, or the stress of some extreme diet acts generally to trigger a manic episode. In any event it is serious and requires a medical/psychiatric consult.

Causality?: Reduced appetite is a part of a manic state. The mind, brain and body form a unity that we perceive (somewhat artificially, maybe) as separate. So the impulse to restrict food may seem freely willed, but may actually be part of an elevating mood. Rather than seeing the one as "causing" the other, they interact as a whole.

If it became enough: Of stress on the person it may. There are many types of stressors which may trigger mania or hypomania. Prescription medications are one (antidepressants, stimulants, steroids, decongestants, asthma inhalers ; antabuse) as well as caffeine ; illicit drugs. Lack of sleep, menses, head injury, ms ; infectious diseases are other causes. Psychosocial stressors may include death of loved one, divorce, .