How do I tell injection-site erythema from an energy deficit on 1,200 kcal a day?

Accepted answer

Start with what 1,200 kcal a day leaves you room for, because at that intake the deficit is a live competing explanation rather than a footnote. Protein is 4 kcal per gram, so 100 g costs 400 kcal — 33 per cent of the entire day's energy — and everything else has to come out of the remaining 800. A day that misses protein at 1,200 kcal has missed it by a wide margin, and injection-site erythema that tracks those days is a nutrition signal. Then separate the two by timing: a dose effect is periodic and phase-locked to the injection or to an increase, and a deficit effect is monotonic and gets worse the longer the intake stays at 1,200. Log intake, protein and injection-site erythema on the same daily row for a fortnight and the two patterns separate without any further cleverness. Nothing here is medical advice.

The short version: check intake, check hydration, check iron and thyroid if it persists, and only then attribute it to the compound.

A deficit beyond about a thousand kilocalories a day reliably produces fatigue, reduced training performance and reduced spontaneous movement. With appetite suppressed, deficits of that size arrive by accident rather than by plan.

Carbohydrate intake specifically affects training performance and perceived energy at a given total intake, which is why very low carbohydrate approaches feel worse in the gym at matched energy.

Energy deficits above roughly a thousand kilocalories a day are associated with measurable reductions in resting metabolic rate, spontaneous activity and subjective energy in controlled studies.

The caveat is that fatigue with breathlessness, chest symptoms or sudden onset needs assessment rather than dietary adjustment.

Weigh three days of intake honestly. That answers this most of the time.