'What's that, Mummy?'

When your three-year-old asks this question about an item of food on his/her or your plate, you are likely to reply:
'That's chicken / cheese / watermelon / broccoli / brown bread, darling.' 
You wouldn't give a description such as:
'Oh, that's animal protein / a combination of animal protein and saturated fat / a high-GI simple carbohydrate with a relatively low-GI load / brassica oleracea / a partially refined grain product, sweetheart. It's yummy. Eat up.'
We tend to think of food items in terms of their 'common' names, rather than considering the botanical family, genus and species, or the chemical composition. From habit, experience and the 'collective unconscious', you will go to the butchery section of the supermarket for animal protein, the veg section for brassica and (a lot of) other carbohydrates, and the bakery section for bread.
What I'm getting at is the fact that foods fall into fairly distinct groups, but as with any form of categorisation, the borders of the groups are a bit fuzzy. Few food products belong exclusively to one food group - at least, not by the time they reach your plate. But as the old adage has it, it all goes down the same way, anyway.
Food used to be categorized into three broad groups:
Carbohydrates; protein; and fats.
The carbohydrate group was the biggest and most complex: it covered vegetables, fruits, sugars and grains.
Proteins appeared to be reasonably straightforward, covering meat, poultry, fish, dairy and eggs - but wait, there's more - beans, legumes, quinoa, nuts and seeds are protein as well, although you can quite correctly group them with the carbohydrates.
The fats category comprised vegetable oils, animal fats, and dairy - though dairy also comes under protein!
No wonder people were - and still are! - confused about what they are eating!
Maybe a better approach is the new style 'food pyramid' (http://www.mypyramid.gov/), which has six categories: grains, vegetables, fruits, milk, oils and meat and beans.
Lessons start tomorrow - I will take you through each of the food groups, as designated by the food pyramid, and - I hope - help you to make healthier food choices.