Carbs won't be an issue because I can guarantee that he'll lose a good 10 pounds by the end of the first month. If he's only doing this for a short term (1-3 months), then it's perfectly fine. The meals won't be half bad, he'll still have enough to eat a solid meal from time to time, it'll save him tons of money, and it's a guaranteed way to lose weight.

I do agree that it's pretty bad long term (Over 5 months) and will have a negative impact on your health. But if this is your only option, then I suggest you take lots of vitamin supplements on a daily basis and find a way to borrow more money.