Why didn't I gain weight when I ate 4,000 calories a day?
I'm about 6 feet tall and weigh 175 pounds, 26 years old.
  
For the past several years, I have lived a fairly sedentary
    lifestyle, easily consuming around 4,000 calories per day.
  
What I'd like to know is why if I don't burn more calories than
    I take in, I don't seem to gain weight. The only time in my life that I
    gained weight was a period when, after moving to a new place, I ate a lot of
    fried food for a few months.
  
According to various online calculators, I need about 2,000
    calories for my body to function.
  
Should the extra 2,000 calories I've eaten contribute to weight
    gain? Why don't they seem to? Estimates say that on my diet I should weigh
    over 200 pounds, but I weigh 175.
  
I calculated my daily calorie intake based on the
    myfitnesspal.com website
  
Why wouldn't you gain weight in the usual way, especially
    with less exercise or physical activity than usual?
  
I would recommend eating smaller meals more often. Eating
    a very large meal and a small meal is not good in my experience
  
I'm the same way, except I only eat about 3,800 calories a day.
    I am 6'2' (1.88m) and 155lbs (70kg), although my body weight before I
    started lifting weights and when I was only eating about 2200 calories per
    day was 130lbs (59kg). BMI calculators, at my level that's anorexia, so
    there's no luck in having an overactive metabolism.
  
Almost every day, I have to force-feed myself until I can't
    even swallow. At that time, I will drink a glass of whole milk and still
    have trouble gaining weight. I've been to the doctor and according to the
    blood tests I'm completely normal, but I'm not eating
  
"What I'd like to know is why if I don't burn more
    calories than I take in, I don't seem to gain weight? ... Should the extra
    2,000 calories I've consumed contribute to weight gain?"
  
 If you're not gaining weight, you're burning as many
    calories as you take in and not taking in an extra 2,000 calories.
  
"Why wouldn't I be gaining weight in the typical way,
    especially with less exercise or physical activity than normal?"
  
One of your assumptions is wrong. You are either burning 4,000
    calories per day or you are not consuming 4,000 calories per day. You said
    that you know for a fact that you are consuming 4,000 calories per day, so
    the website you used underestimated your daily burn. 

 
 
 
 
 
 
 
 
 
