There are thousands of studies out there. The vast majority with similar results.
As the son and grandson of butchers I ignored most of them, until being sent home “palliative care only” 6 years ago, with a 2% chance of making 2 years.
That was enough to give me the incentive to seriously investigate for myself.
As a result of that intensive investigation I went strict vegan, and high dose vitamin c. Tumours went away.
I have been tumour free for 5.5 years.
A case study of one, and all medical records and some of the data I found are on my blog site – if anyone is interested.
And going vegan was one of the hardest things I have done.
Nothing I ate tasted even vaguely palatable for 6 months.
Now I have retrained my neural networks, and I am really enjoying what I eat – but it was two years before I could say I really enjoyed eating vegan, even occasionally. Now it is consistent.
So yes – lots of evidence, and also vast amounts of monied interests out there doing their best to disguise, obfuscate, and otherwise distort the reality for financial gain – dairy industry, meat industry, fishing industry, etc.
A very strange system we live in.
And there are real risks with being vegan – serious risks to health from Vit B12 deficiency (supplements needed in most cases) and also from omega3 oil deficiency – I ensure I have about 3 tablespoons per day of a mix of chia and linseed ground up.
I also take a single low dose multivitamin and mineral supplement – just to be on the safe side.