PHYS-32 · Principle

My period stopped while I was losing weight. Is that just hard training?

Probably not. When food falls short of what training uses, the body turns down reproduction, metabolism and bone, in men too. Fuel up and see a sports doctor.

How the body works, agreed across the reviews below; a study entry shows what one experiment measured.

established physiologyApplies to everyone who trains, women and menEstablished — hormones shift within days in prospective studies, mostly of 5 days or less in women (Areta 2021), and low availability goes with menstrual dysfunction and bone loss (REF-341, REF-1066); well supported…

Practical Application

My period stopped while I was losing weight. Is that just hard training? Probably not. When food falls short of what training uses, the body turns down reproduction, metabolism and bone, in men too. Fuel up and see a sports doctor.

What it means for training: a missed period, low libido or falling power during a cut is a fuelling question first; the screen and the stop rules are in SYNTH-54, a severity level is a physician's call (REF-341).

What it does not mean: that a calorie formula sets a safe line (diaries did worse than reproductive signs, REF-343), that a normal short-term testosterone rules it out (REF-878), or that every deficit harms (REF-341: adaptable vs problematic).

Mechanism

Energy availability is intake minus exercise expenditure per kg of fat-free mass (REF-341); unlike energy balance it counts what is left for everything else, and weight can settle at a lower expenditure that masks the gap (Areta 2021, a hypothesis).

In sedentary women LH pulsatility held at 30 kcal/kg lean mass and broke down at 20 and 10 over 5 days (REF-342); over three cycles the odds of a menstrual disturbance fell 9% for each extra kcal/kg (35 sedentary women, Lieberman 2018).

In men, 4 days at 15 kcal/kg fat-free mass cut leptin and insulin, not testosterone or T3 (6 men, REF-878); 14 days near 22 cost explosive power before hormones moved (12 trained men, REF-545).

Amenorrhoea and low testosterone went with about 4.5 times more bone injuries in elite distance athletes (cross-sectional, REF-343); in 18 of 21 overload studies with diet data, energy or carbohydrate availability fell during the overload (REF-344).

Common misreading

"A women's problem": pooled, men were classed as low no less often (REF-1317). "Under 30 is the line." "My weight is stable, so I eat enough."

Backs

SYNTH-24 "alongside energy-sparing responses (immune suppression, menstrual disruption, elevated fatigue driving more rest)" (the hormonal and menstrual part) · SYNTH-54 "So watch the signs, not the arithmetic." · SYNTH-37 "Missing cycles → low energy availability until proven otherwise" · SYNTH-54 "A normal short-term testosterone does not rule out low energy availability"