https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5466941/
Yeah pedantically you can nothing but Oreos and be "vegan". But FTA:
"In a cohort of 4384 Taiwanese Buddhists, vegetarian men had approximately half of the rate of diabetes (OR: 0.49, 95% CI: 0.28–0.89), and vegetarian post-menopausal women had one-quarter the rate of diabetes (OR: 0.25, 95% CI: 0.15–0.42), compared with their omnivorous counterparts, despite statistical adjustment for body mass index and other factors. Interestingly, the omnivores in this study consumed a predominantly plant-based diet with little meat or fish, again implying that small amounts of meat contribute significantly to the development of insulin resistance"
And the idea that fat = calories in - calories burned is a simplistic view that no serious nutritionist on either side of the debate believes.