when you use "there is lots of food", the "food" is uncountable noun. when you use "there are lots of foods",you emphasize "food" on category,which means lots of kinds things to eat. however,the second usage is rare.that's what I've learnt in grammatical books several years ago.

"There is lots of food in the fridge." Food is an uncountable noun. Food = is.

There is lots of food... There may be a reason, but native speakers don't typically know the rules. They just know how to say it.

Phrases with "a lot of" and "lots of" often present agreement problems. Technically the verb should agree with "lots" rather than "food,' but "There are lots of food in the fridge" sounds unnatural. I would avoid the problem and say "There is a lot of food in the fridge." When the object of the preposition is countable, as in "lots of people," it sounds more natural to say "There are lots of people."

There IS lots of food in the fridge. We use "is" because "food" is singular. The plural "foods" is almost never used, and most people would consider it incorrect. Hopefully that helps.