You can be strong and still be losing muscle mass. Make sure you eat back ALL the calories you burn (especially since you aren't overweight) and be sure to eat a variety of foods. Include beans, nuts, and whole grains in your diet to get a variety of protein (amino acids) and a variety of vitamins. Humans cannot sustain on fruits and vegetables alone!

I think about a whole new set of food groups as a vegan (which I have been for 8 years). I always choose a variety of foods from each of these five groups: nuts, beans, grains, fruits, vegetables. Since you don't have dairy and meat as food groups anymore, rather than just exclude them, you need to REPLACE them with something else. Do lots of research before going vegan and make sure you are staying healthy!!... especially with how much weight you are lifting!!

Good luck

This maybe because previous to being vegan you ingested lots of saturated fats. Most of these fats are in animal products like cheese, milk, and meat. I have found that since I became vegan I can be less strict about what I eat and still lose fat and build muscle. I lost lots of belly fat but have had an easier time gaining muscle (I am a fitness instructor as of last week). I used to have this bloated nasty pregnant looking belly when I ate animal products no matter what I did. Now I don't and am rarely bloated. Friends have commented on how I've lost weight,while I've only lost about 5lbs, it was pure fat and I've been gaining muscle.