Observation:- Athletes that do middle to long distance are wiry or slim. Athletes who require explosive power are bulky with extra muscle mass.
The above also involves different forms of dietetics - that's true.
1) Eat foods containing essential fatty acids rather than saturated fats
2) Avoid meats that have a possibility of hormone enrichment > rapid weight gain before market
3) Cardio of a middle distance - but also using upper body strength would help answer your Q
4) Eating pumpkin seeds (for aging men over 35) helps to maintain testosterone levels and avoids i) a splitting off into oestradiol (a female hormone) and ii) a splitting off into dihydroxytestosterone (which causes benign prostatic hypertrophy - or even some forms of prostate cancer). A herb called Saw Palmetto does the same - but I wouldn't start that until after 40.
5) Alcohol slows down BMR (basal metabolic rate)
I'm missing out on more, which other guys here will fill you in on, but Nick, TTT and I have started you off I guess.