Iwan eats lots of burgers but doesn't eat much fresh fruit. Some types of food are countable nouns and others are uncountable. Burgers are countable but fruit is an uncountable noun. When we use countable nouns, we usually say 'a lot of' or 'lots of' in the positive form and 'not many' in a negative sentence. When we use uncountable nouns, we also use 'a lot of' in positive sentences but in negative sentences we usually use 'much', e.g. Iwan doesn't eat much fruit.