There's a ton of problems when you're dealing with food though. Calculating calories of a recipe you find online can be tough. On one side, it's a natural language problem to extract the ingredient, the amount, the unit, and the prep/notes. On the other side, it's a data/data matching problem, where you need good data on a ton of ingredients, and then need to pick a reasonable one for "1 cup of milk".
And of course everyone eats and prepares food so differently that suggesting meals they'll actually enjoy is hard without asking them a bunch of questions first.