Yes. Generally speaking, women will find a person who is healthy and reasonably physically fit more attractive than someone who is obese or unhealthily thin.

The problem is that the point of diminishing returns on actual body building happens pretty fast. Some women do prefer guys who are big piles of muscle, but that's a minority.

I learned that from experience. The reason "work out until somebody loves me" works is because you're giving yourself time and learning to be a person who is fine being alone, not because of hours in the gym.