From what I understand, several of the body’s systems go higgledy-piggledy when you crash diet. If someone quickly transitions from a long-term lack of cardiovascular exercise to a relatively demanding routine, do various systems (endocrine, hormonal, etc.) also react in counter-intuitive ways?[sup]*[/sup]
There are really two questions here. If sudden dieting kind of ‘tricks’ the body into thinking it’s facing a famine, does sudden exercise ‘trick’ the body into thinking it’s on the run? And second, though the number of ‘calories burned’ is an estimate at best, there is still a non-trival amount of calories burned per day. Is it possible that the net reduction could result in triggering the body’s ‘famine’ response?
[sup]*[/sup]By ‘relatively demanding routine’, I mean relative to zero; a basic, somewhat rigorous cardio workout 4 to 5 times per week that keeps the heart rate (approximately) between 40 and 50 percent of its theoretical maximum for 20 to 30 minutes, and then between 80 and 90 percent of its theoretical maximum for 40 to 50 minutes (as measured by a basic chest-strap Polar heart rate monitor). There’s 15 to 20 minutes of warm-up/cool-down in there too.
This assumes no physical injury (i.e. heart attack, pulled muscle, etc.), a two-week ramp-up, at least eight to ten months of continual exercise, and a very modest-to-minimal change in diet or other activities (I’m trying to narrow the question, so assume there’s no substantial addition of strength training).
ETA: oops, self-reported for forum change from GD to GQ~