This might be why we are attracted to 'healthy looking' people. People who are far out of shape, extremely overweight, extremely underweight, etc are less likely to find mates.
Health and strong reproductive traits are what our sex drives are based upon.
The problem is, many people these days are starting to develop skewed opinions because of society(unnaturally skinny woman as 'healthy', extremely ripped men as attractive, and on the opposite side of the spectrum - being obese is okay, etc).
Being skinning is not healthy.
Being 'totally ripped' is not a good thing.
Being obese is not okay.