Gym huwezi kosa, kuna moja hua naona hapo just after Tanners ya chini (Kamiti Road)...think it is 100 per day. I was there last year. In addition, they had a jogging group.
Supplements: Know your health status first, i.e body type, metabolism etc. Doctor can advise. Maintain health check up. I stopped using supplements because of some health issues.
Finally, discipline.