Just from reading through various health topics on Wikipedia, I'm now pretty sure that exercise influences much more than just fat and muscle mass. All the way to having anti-inflammatory effect because muscle secretes some stuff, working as an endocrine organ.
So if you decide to sleep more, perhaps you want to sacrifice something other than exercise.
Also I don't know how anyone can take BMI by itself seriously.
> Also I don't know how anyone can take BMI by itself seriously.
BMI is very useful if you're looking at large data sets. BMI for individuals is not very useful. I'm not sure of the efficacy of BMI for ~1200 data points.
So the entire use of BMI starts with the assumption that its increase can only mean more fat. I practically can see the headlines: ‘BMI on the rise for the past decade, obesity epidemic in Jocktown! We need even more gyms!’
Excluding massive biological changes (we're not going to start carrying more water or drastically increasing bone density), you gain weight by adding muscle or fat. Adding muscle is generally healthy (not in the case of heart disease, organ growth from steroid abuse, etc.) and also very hard. Adding fat is very easy. It would incredible if our population was adding a substantial amount of lean body mass.
Are there any other causes you could think of that would cause a BMI increase across a sufficiently large data set that would not be caused by fat?
So if you decide to sleep more, perhaps you want to sacrifice something other than exercise.
Also I don't know how anyone can take BMI by itself seriously.