Vegan diets are low in saturated fat, B12, EPAs and DHAs (essential fats). These things are all pretty much absent. Coconut oil won't cut it, and aside from olive oil, most other vegetable oils are hard on the body, even carcinogenic.
I'm not trying to sound rude or mean, but honestly vegan diets are a surefire road to poor health. They're good for short term, not for long term. Veganism is a non-historical diet with no proof of efficacy. We're only just starting to find out what is happening to older vegans in our society because until the mid 21st century veganism pretty much didn't exist, and the research is not encouraging.
You'd be way, way better off becoming a vegetarian. There's lots of evidence for that being a good way of life. It's going to be hard to gain weight if you aren't consuming saturated fat from animal products. No meat required, but even something like clarified butter would be immensely helpful.
I used to be a lot more yielding toward vegans but after seeing so many health disasters come through my practice I can't openly support it anymore.
