Low energy availability in exercising men is associated with reduced leptin and insulin but not with changes in other metabolic hormones
Six exercising men completed two low-energy-availability conditions (15 kcal/kg fat-free mass per day) and two energy-balanced conditions (40 kcal/kg FFM/day) in randomised order, each lasting 4 days. In one low and one balanced condition the men exercised to expend 15 kcal/kg FFM/day; in the other two they did no exercise.
After both low-energy-availability conditions leptin and insulin fell, whether the deficit came from exercise or from eating less. Ghrelin, triiodothyronine, testosterone and IGF-1 did not change significantly. The drops in leptin and insulin were of the same size as those reported in sedentary women.
Participants
n=6 exercising men (abstract: "Six exercising men"), VO2peak 49.3 ± 2.4 ml·kg-1·min-1.
Protocol
Four conditions of 4 days each, randomised order:
Low energy availability, 15 kcal·kg-1 FFM·day-1, with exercise expending 15 kcal·kg-1 FFM·day-1
Low energy availability, 15 kcal·kg-1 FFM·day-1, no exercise
Energy balanced, 40 kcal·kg-1 FFM·day-1, with exercise expending 15 kcal·kg-1 FFM·day-1
Energy balanced, 40 kcal·kg-1 FFM·day-1, no exercise
Metabolic hormones measured before and after each 4-day period.
Key Results
After both low-energy-availability conditions: leptin -53% to -56% and insulin -34% to -38% (P < 0.05).
The reductions did not depend on whether low energy availability was reached with or without exercise (P > 0.80).
Ghrelin, triiodothyronine, testosterone and IGF-1: no significant change (all P > 0.05).
The leptin and insulin reductions matched the magnitude previously reported in sedentary women.
Practical Application
In six exercising men, four days at 15 kcal/kg fat-free mass per day cut leptin by 53-56% and insulin by 34-38%, whether the gap came from extra exercise or from eating less, while testosterone, triiodothyronine, IGF-1 and ghrelin did not change significantly. To "does under-eating affect men's hormones, and will a testosterone test catch it?": the energy-signalling hormones respond within days, but the markers usually screened in men (testosterone, triiodothyronine) did not move in this short block, so a normal short-term testosterone does not rule out low energy availability.
A deficit made by adding exercise acted the same as one made by eating less — "I burned it off in training" does not protect against it.
Inference, not tested here: the threshold question (at what energy availability men start to respond) is not answered; only 15 and 40 kcal/kg FFM/day were compared.
Limitations
Six exercising men; 4-day exposures only.
Two energy-availability levels (15 and 40 kcal/kg FFM/day); no graded dose-response.
Hormones sampled before and after each block; no performance or bone outcomes.
Written from the abstract and record metadata only (full text not read).
How this entry was checked and changed
Why this level
controlled crossover, n=6