I wouldn't generalise...some of us have much faster or slower matabolisms to start with...then there is the question of how much gut you have left (and most nutrients are absorbed through the small intestine and ileum which we mostly have) plus transit time and finally your level of physical activity added to the whole thing and that gives you a ton of variables...
You must be particularly active with a good metabolism and a healthy lifestyle that needs a little 'plus' to keep up your calorie count...others can eat half of what you do and gain weight.
You have found the 'trick' that works for you...you are fortunate.
I have a very high activity level (no car, running around all day up/downhill on foot, carrying groceries, books...) plus I work out at least 4xs/week...nothing helps other than 900cal/day protien diet.
You might want to look into making smoothies with extra protien, maybe soya or other vegetable based protiens...and eating more small high protien meals a day.
Sharon

I'm having the same issues gaining and even maintaining weight. I lost over 35 lbs. and am attempting to gain at least some of it back. I am 27 years old and just about 6'5". All that lost weight does matter to me, because as you mentioned it does appear like I am malnourished.

It's been almost a year since my takedown. I recently began lifting weights and drinking protein smoothies. Any other suggestions for others that have effective to gain weight? Thanks.

For those who are a bit concerned about absorption, there is a chewable vitamin called Forvia. I take two per day, and have done so for years. This supplement was developed for folks like us who have or had bowel disease. Check out this website http://www.inovera.com/default.aspx

peanut butter (natural no-hydrogenated oil types), nut butters, cream of rice, and ground meats. I have noticed normal carbs kind of cause me to bloat. As for meats chicken and fish seem to go through me too quick and I have a high metabolism. I found ground pork, boar, buffalo, venison, lamb and rabbit seem to absorb good. In all honesty you have to figure out what works for you. When I eat i dont drink anything until about 30 minutes after i eat to help my body try and absorb as much as possible....but you need to figure out your body. I had also mentioned peptide supplementation early this year...people where skeptical about it on these forums however the one i take (GHRP-6) and Impamorelin are now being utilized pre-post surgery for colectomys and for people with chrons/UC but thats a whole other ball of wax.