They both mean the same thing but the structuring of these statements do not sound perfectly natural.
The most correct simple version would be the imperfect conditional setup:
If you WERE to eat less, [then] you would not get fat.
The simple formula is:
IF (subject) you/he (imperfect form of to be) were/was (infinitive verb) to exercise regularly, THEN (subject) you/he (conditional) would look healthier.
If you were to exercise regularly, then you would look healthier.
If he was to exercise regularly, then he would look healthier.