I'm a health coach as a side job. I earned $7700 while helping 10 ppl with their weight loss program. I spent ~$3000 on food for my own program. Can I deduct this?

It depends.  You cannot deduct any food for yourself, but you can deduct food for your customers if you purchased it for them.

They also are not deductible for medical reasons: Although diet foods may also be part of a weight-loss program, these are substitutes for the food the taxpayers normally consume and satisfy their nutritional requirements. As such, they are not deductible medical expenses, even for taxpayers whose disease qualifies them to deduct weight loss program costs.