Why does sema make me SO tired?? — my results so far

Read the primary source rather than the write-up and the two do not agree, so here is what is actually in it.

Mostly the deficit, and the useful part of that answer is that it is testable. Fatigue driven by a deficit tracks intake, improves within a day or two of eating properly, and worsens on the days you eat least. Fatigue that is flat regardless of intake, or that arrives on a fixed day after dosing, is behaving like a drug effect. Before assuming either, rule out the boring causes — iron, B12, thyroid, and sleep — because a fast deficit unmasks deficiencies that were previously subclinical.

Where I think it is weakest: the comparator does most of the work in how this gets reported, and it is not the comparator most people think they are citing.

The narrow version of the question is whether the fatigue is a direct drug effect or simply the caloric deficit, because the answer changes what you do about it. Practical detail welcome, however dull — the duller the better.