Food is a social construct. For a social construct to exist you have to have a social category with shifting goalposts based on different context and cultural factors that are not rigidly defined. Like "Fat" - what is considered fat for a person is based on context. A supermodel is fat for being 5'9 and 145lbs but we would call a constructiom labourer skinny as fuck at those same dimensions. Each culture constructs it's own version of what defines "fat" which is different and distinct from something than the medical guidelines for obesity or an expectation of reasonable health. "Fat" is in the eye of the beholder and represents overlapping cultural circles with varying degrees of consideration of what is excluded from the category.

The scientific concept of nutritional substance is not how we always define "food". Culturally people contest what is considered food vs non food items based on cultural factors. Like eating mice for instance does have nutritional value but there are a lot of people who would contest them as being a valid food item even if they were raised in clean conditions due to cultural adversions. "That isn't food." has been uttered in all sincerity by people encountering strange delicacies that their culture has taboos against eating beliving it dangerous, unpleasant or just categorically not something intended to be eaten. Thus "food" would be in part a sociologically constructed category.