I ran 2:38 in 1980, then two things caused my running to unravel:
1) High carb/low-fat diet. Every day was "carbo-loading" day. Wreaked havoc throughout my body with inflammation, illness, injuries.
2) High-heeled, overbuilt running shoes. Encouraged overstriding, heel-strike and wrecked my knees.
It took almost 20 years to get back to a reasonable state of fitness and health (had a great masters career in my 40's, but at shorter distances). Today I eat very low-carb, enjoy trail runs up to 25-30 mils, and still can do speed work, however slow, without undue trauma to body. I don't compete, but if I chose to do so, I have a renewed base and appreciation of the sport and what true health feels like. It is NOT eating tons of pasta and bashing out 100-mile weeks.