I don't understand the calorie in and out theory

I consumed 1,100 calories today.  How can I burn 1,100 calories?  I walked for about 40 min and only burned 300-400 calories. It is impossible to burn that many calories in one day.

Your body burns calories daily even at rest.  This is your resting metabolic rate.  There are formulas for determing what your RMR is.  Mine is 1288 calories per day.  That is at total rest without any activity.  Then you can add activity based on your lifestyle.  I eat about 1300 calories per day and with my activity I am still loosing about 1 lb per week.  It takes 3500 calories burned to lose one pound.  Google Resting Metabolic Rate and look for a site that will help you determine yours.  This will tell you what you burn each day then add exercise on top of that.  These formulas are not as accurate as if you go to a center that will measure your CO2 output and give you a specifric number based on your actual output.  Burning an extra 500 calories per day over your RMR will result in about 1 lb loss per week of body fat.  Remember if you are building muscle that will affect the scale as well.  Hope this helps.  Shelli

Your body burns calories even when you are completely at rest. 

You would even burn calories if your body was in a coma, laying perfectly still at all times - even on a respirator.

Every cell function burns calories.  Every beat of your heart is work for the body that burns calories.  Every breath you take in and out burns calories.

My Basal Metabolic Rate (BMR) is about 2500 calories. That means I burn that much in a day doing nothing. It doesn't necessarily mean if I eat less than that I'll lose weight or more that I'll gain weight. There are a lot of factors involved not the least of which is weight isn't just fat or an adequate indicator of activity or health.

You can burn 1100 calories in a day too. Walk a half marathon or bike a century ride.

You should look at your calories over 1 weeks time.  If you reduce you calorie consumption by 500 calories (not recommended post WLS) or exercise and burn 500 calories you should burn 3500 calories in one week.  You do not burn all the calories (1,100) you eat in one day unless you are VERY active!