I think I want to go back to eating red meat?

Eat meat if you want - there is no law against it and if you buy freedom farming or organically reared meat the animals have lived a decent life. Other than that you need to increase your intake of eggs, cheese, pulses and if you still eat them fish and chicken. Just eating red meat again won't cure your dietary deficiency you need to look at your entire diet and increase your protein intake across the board.