I'm curious about how men keep their calories up on a plant based diet, especially when other restrictions are in place?

You'll need to add more high calorie and high fat foods to your diet -- more raw nuts and raw seeds, coconut and avocado. You also want to make sure you're eating healthy foods like brown rice, which are high in calories. When I was a personal trainer, I had a client who couldn't seem to go beyond 90lbs. She was naturally very thin due to a high metabolism, but she was also very athletic -- a marathon runner. She wanted to get pregnant and her doctor thought she might have better luck if she'd gain 10 lbs. Within weeks of eating handfuls of raw almonds and cashews (her favorites) and adding avocado (which she loved!) she'd gained weight. She ended up having a baby and was a healthy, glowing mama her entire pregnancy.