There is too much canned food in his diet. or There are too many canned foods in his diet. Pls adv food/s use.

Answer 1

Both sentences are grammatically correct.

Use "much" for singular nouns, and for verb actions:
I don't have much time.
Do you eat much for breakfast?

Use "many" for plural nouns (that can be counted).
I don't have many days to study.
Do you eat many meals in restaurants?

However... I like your first sentence better. "Canned food" is a general term that fits the 'singular noun' category.

Answer 2

Some nouns are mass nouns, some are count nouns. "Food" can be either, depending on meaning and context.

Contrast/compare your sentences with another noun- water. "Water" means the liquid that you drink; "waters" can be rivers or lakes. So I could correctly say, "Wisconsin has many waters." But it would be incorrect to say, "I drank too many waters."

Check this cite below:
Some nouns are only one kind, so it's easier. However, "food" can mean "that which sustains you nutritionally" and is thus a mass noun. If you speak of Thai food and Mexican food, then you can speak of international "foods."

In the context you cite, I'd say the former is the correct thing to say- too much of what he eats comes from cans.

The confusing things is that many grocery stores used to have a "canned foods" aisle, where you chose various foods beans, soup, tuna, etc. In your example, the unspoken contrast is with food that is cooked/prepared from fresh commodities. Thus it sounds right for one to say, "There is too much canned food in his diet."