Numbers first: dizziness · 800 kcal.
Before I write this off, I want to check whether it is a known failure mode.
I have the lot number, the certificate and the date, and I am happy to compare them against anything.
What is the most likely explanation, and how would I confirm it?
Start with what 800 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 — 50 per cent of the entire day's energy — and everything else has to come out of the remaining 400. A day that misses protein at 800 kcal has missed it by a wide margin, and dizziness 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 800. Log intake, protein and dizziness on the same daily row for a fortnight and the two patterns separate without any further cleverness. Nothing here is medical advice.
The relevant physiology is that a large deficit reduces both available substrate and spontaneous activity, and the second is often mistaken for the first.
Hypothyroidism, sleep apnoea, depression and anaemia all present as fatigue and all become more likely rather than less in this population, so attribution to the compound should be a diagnosis of exclusion.
Iron deficiency is common, particularly in menstruating women, and low intake plus a reduced red-meat share makes it more likely. Ferritin is the test, and it is an acute-phase reactant so it needs interpreting alongside CRP.
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.
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Visit GL BiochemThe relevant detail is that this is the complaint with the widest differential and the one most often attributed too quickly.
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.
Sleep quality often changes during rapid weight loss in both directions, and sleep debt produces fatigue that no amount of dietary adjustment will fix.
Attributing a symptom with a wide differential to the most recent change is a common and expensive error.
Check fluid and sodium before anything more exotic.
edited 23 May 2025 by sunniva_dahl — tightened the wording; no substantive change
The underlying point is that if it persists at an adequate intake, it needs blood work rather than more speculation.
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.
On the detail: fatigue that appeared abruptly, rather than gradually with the deficit, is a different pattern and points away from intake.
Research-use compounds are not approved for human use.
If it persists at an adequate intake, get bloods rather than more theories.
Answering this needs to know the size of the deficit, since fatigue tracks it closely and predictably.
Dehydration from reduced fluid intake alongside reduced food intake produces headache, lethargy and postural dizziness, and is the cheapest thing on the list to correct.
Ferritin as an acute-phase reactant is a recognised limitation and is why it is interpreted alongside an inflammatory marker.
Abrupt onset points away from the deficit and towards something else.
The honest answer is that this is usually fixable by eating more, which is unwelcome advice in this context.
Three days of honest weighed intake usually settles this. Estimated intake in this situation is systematically wrong and usually wrong in the direction that hides the problem.
Nothing here is medical advice.
Sleep is a variable here too, and no amount of eating fixes sleep debt.
Ask PeptideStack is a static archive. Posting is closed, but the norms are worth stating: answer the question that was asked, show your working, cite the trial or the certificate, and say plainly where the evidence runs out.