He plans to do it for two weeks. You cannot lose a bunch of fat in two weeks.
Also, things don’t always to be extreme- carnivore vs vegan is a false dichotomy.
A balanced diet of fruits, whole grains, veggies and lean meat is best for most people.
Slow and sustainable changes beat drastic and temporary ones every time. I strongly suggest not going into one of these yoyo diet cycles to temporarily lose weight- your weight will jump up again once you go back to your old diet.
Why? A bunch of animal fat and protein ain’t gonna help you lose any weight.
Just walk more, add some greens to your diet (veggies keep you full and have almost no calories) and drink more water and you’ll be fine.