Simple sugars that are found in candy, cakes, desserts, etc. cause our bodies to produce more insulin and insulin encourages cell growth.....healthy ones and cancerous ones so it's best to try to limit the amount that we eat. To counteract the insulin production when eating sugars, try to make sure protein, fats, and fiber are eaten at the same time. Maybe some nuts with the chocolate or fruits instead of fruit juice.
Everyone reacts to chemo and radiation differently. Some are able to work in the beginning and slow down as the effects accumulate. Maybe even an abbreviated work schedule would be appropriate so as to not overly tax the immune system.
I hope I've helped a little
Be sure to keep us updated on his progress and take care