I recently got to know someone with a resting heart rate of 45, who will pretty frequently do 8+ mile trail runs and 100 mile bike rides. He is also an amazing cook who makes decadent and delicious foods. He says he consumes 4,000 calories a day. He still has a sizeable belly. I'd say he is at like 10/10 on exercise, but 3/10 on diet. I was surprised at his extreme cardiovascular fitness while still managing to be overfat.