Do you have any suggestions on how I can support him?
It is great that James is interested in his diet as eating the right kinds of food can have a big effect on a person's health.
The NHS inform website has an Easy Info zone which has printable Easy Read material that you can share with him. It offers guidance on what a portion size actually means.
l 1 heaped tablespoon of small fruit such as berries.
l 3 heaped tablespoons of vegetables.
l Matchbox-sized piece of cheese.
l 1 medium slice of bread.
You will find there is also information on swapping certain foods for lower fat options on the website.