I saw this link on another thread, it discusses the average household spend, pre lockdown, but the interesting part is how it breaks down average spend by income bracket and states that the average spend for households with incomes in the highest 10% bracket, which a lot of Mumsnetters will fall into is more than four times that of the lowest 10%, which is as expected.
Low income households need to stick to a smaller budget, but still need to spend a higher percentage of their income on food. People with more money are less constrained by a budget, so are able to afford higher priced products that are probably not even on the radar of lower income people who can't afford them.
But level of spending is not an indicator of the quality of a family's diet. Eating well can cost very little, as illustrated by foodbills receipts, entirely made up of fruit, vegetables, pulses, fish etc from a cheaper supermarket.
You could pay several times more for exactly the same food, simply by buying the premium versions from a more expensive supermarket, and it's unlikely that food will be five times more nutritious or five times nicer, but those who can afford it might be happy with the cost.
Similarly you could eat a high calorie, nutritionally poor diet for not very much or for a lot of money, depending on whether your premade food is the standard Aldi versions or the Premium ones from Waitrose. A Charlie Bighams macaroni cheese or Waitrose 1 pizza will almost certainly be nicer than the standard budget supermarket versions, but the macaroni cheese at least will have far more calories, fat and probably salt than the cheaper one.