Help for a friend

I have been doing keto for the last 2 months and it has done me wonders. greatest thing I've decided to do. I have a buddy who wants to start doing it but he is currently 535 lbs and is about 5'7. I am curious if anyone has any info on a larger guy starting a diet like this with any potential risks. I told him to ask his doctor for obvious reasons but he is worried about his heart and cholesterol potentially going up. if anyone has any insight it would be greatly appreciated!