PHYS-03 · Principle
Will fasted rides or Zone 2 make me leaner?
Not by themselves. They burn more fat during the ride, but body fat follows energy eaten and spent over days and weeks; fasted against fed exercise made a trivial difference to body mass.
How the body works, agreed across the reviews below; a study entry shows what one experiment measured.
Practical Application
Will fasted rides or Zone 2 make me leaner? Not by themselves. They burn more fat during the ride, but body fat follows energy eaten and spent over days and weeks; fasted against fed exercise made a trivial difference to body mass.
Mechanism
Fat gain needs a positive energy balance: the energy-balance model calls this a law of physics (Hall 2022), and the carbohydrate-insulin model accepts it, disputing only which way causation runs (Ludwig 2021, full text). Intake and expenditure are linked, and counter-regulation resists weight loss (Hall & Guo 2017).
Exercise raises muscle's capacity to oxidise fat, yet up to about an hour of moderate exercise changed 24-h fat oxidation little (Melanson 2009); in 5 studies of 96 adults fasted and fed aerobic exercise differed trivially for body mass (Hackett & Hagstrom 2017).
Common misreading
"Zone 2 burns the fat off"; "fasted cardio burns more fat, so I lose more"; "eat less, move more is all there is" (intake and expenditure push back on each other, Hall & Guo 2017).