I am going to say no, as the powders etc do not in themselves produce a body image. Good health is normal human requirement. Just as it is not possible to claim medical treatment expenses to make person fit to continue trading.
Edit to add link: While not completely the same as your case, this link is the page of that covers it
Need a little advice: could a self employed personal trainer (PT) claim supplements such as protein powders as a business expense? It could be argued that body image is very important for a PT and that it is one of the ways of getting and keeping new clients and therefore is allowable?!?!
I've been umming and arring over this for the last couple of weeks and then - lightbulb - decided to ask you good folk
Any help/advice on this matter greatly appreciated.
Has your client thought about retailing the dietary supplemts? Free samples and then they'd save more than the tax - might be worth contacting the manufacturer or supplier. An even longer shot would be to have them re-branded to his own business/logo.