It is an interesting challenge, but optimizing income sources goes better for me rather than doing extreme saving. You may do better saving writing a specialty post every day for 30 days on Hive, for example.
It's about health and whether you can have a healthy diet on a fixed budget.
It is an useful exercise, but how somebody already pointed out, the one able to do that are already disciplined enough to have a good enough diet. But as an exercise, it is good.
I do something similar by fasting one day a week, so that is 52 days a year, like more or less 7 week with no money spent on food. If we talk about finances. But it is good for health too.