How do I tell dizziness from an energy deficit on 1,200 kcal a day?

The particulars: dizziness · 1,200 kcal.

Something has gone wrong and I would like to know how badly before I decide what to do.

Nothing else in the setup changed, which is what makes this puzzling.

What would you check first, and what would you conclude from each outcome?

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 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 1,200. 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.

Answer first: fatigue in this context is usually an energy-intake problem before it is a drug effect, and the arithmetic is the first place to look.

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.

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.

Attributing a symptom with a wide differential to the most recent change is a common and expensive error.

If it persists at an adequate intake, get bloods rather than more theories.

edited 29 Mar 2026 by v_ramaswamy — corrected a unit error in the worked example

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.

Put another way, 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.

Nothing here is medical advice.

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.

Fatigue that appeared abruptly, rather than gradually with the deficit, is a different pattern and points away from intake.

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

Sleep is a variable here too, and no amount of eating fixes sleep debt.

The relevant physiology is that a large deficit reduces both available substrate and spontaneous activity, and the second is often mistaken for the first.

Sleep quality often changes during rapid weight loss in both directions, and sleep debt produces fatigue that no amount of dietary adjustment will fix.

Ferritin as an acute-phase reactant is a recognised limitation and is why it is interpreted alongside an inflammatory marker.

Check fluid and sodium before anything more exotic.

Start with the actual intake, because a substantially suppressed appetite produces deficits far larger than intended and fatigue is the first symptom.

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.

Sleep restriction produces measurable decrements in subjective energy and in training performance independently of energy intake.

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