How Much Fat Can You Burn?


I find it fascinating that some of the smartest people I know understand so little about the physics of weight loss.


I have a friend who is an engineer.  He is responsible for projects that include production and testing of systems and components for the military.  On one occasion our conversation turned to exercising.  He matter-of-factly explained to me that he worked out for an hour 3 times per week and burned 2 pounds of fat during each workout.  Obviously he based this on the fact that his “pre-workout” and “post-workout” weight typically varied by 2 pounds.  I didn’t have the heart to challenge him at the time, and a debate was really not something I was interested in getting into.  I simply took notice and pondered on the all-too-familiar occurrence of someone making that kind of a statement.


You see, intelligence is not the issue here – it is misinformation accepted as truth and not questioned.


The reality is that his 3 hours of working out likely netted him an extra 900 calories worth of combustion per week, not the 21000 calories worth of combustion he believed he was netting.  He was overestimating the calorie burning potential of his workout by a factor of 23X. 


Interestingly enough, a 200 lb male needs approximately 21000 calories total to operate for one week.  If his assumption were true, he could eat twice as much as a person the same size who was not working out at all.  Undoubtedly he did not believe that he could eat twice as much, however, most folks who work out believe that the net calories burned are much greater than the actual. 


Maybe an even more startling fact is that his 900 calories per week combustion would only net a total burning of 6.4 lbs of fat for the entire year.  You read that right!  If you add to your regimen a 1 hour moderate workout 3 times per week – all other factors being constant – you will only burn 6.4 pounds of fat per year.


Like my buddy, most people have a really hard time believing this to be true, yet it can be mathematically proven using physics.  If one believes that the net combustion (fat burning capability) of working out it more, it is not wonder that folks work out like crazy and become very disappointed when their “weight does not seem to budge.”  Furthermore, research has proven that the psychological effects of working out, often more than “undo” the fat burning effects.  Simply stated, it seems that after a workout people subconsciously feel they have “earned” the right to eat more, or maybe the “survival mechanism” inside of each of us signals the brain to seek more food because a deficit is sensed.  Whatever the case may be, folks do in fact eat more after a workout, often negating the calorie burn – and then some.


Of course exercise should be an important component of any physique management system, it is not my desire to promote the idea that working out is of little benefit.  Rather, I am aiming this discussion squarely at knowing precisely what is happening within the human body.  Variations in daily weight are largely due to water, not fat.  Even if a 200 lb man ate nothing at all it would still take almost 12 days to lose 10 lbs.  His body (needing approx 3000 calories per day) would take almost 12 days (11.6 to be exact) to burn the 35,000 calories that are contained in 10 lbs of body fat.   Conversely, the same man would have to double his calorie intake to 6000 for 12 days to gain 10 lbs.  This feat would be nearly impossible for several reasons.


First, a man who is used to eating 3000 calories a day would have to work pretty hard to somehow take in twice that many calories – that is a lot of food (but it can be done.)  Second, the human body is not geared combust that many calories at 100% efficiency.  Simply put, a certain percentage of those extra calories will pass through the body un-combusted (un-digested.) 


My research has proven that doubling the caloric intake does not double the amount of fat your body will “put on.”  In fact, I have found a “threshold” for fat gain from over-eating.  Adding calories beyond that threshold does not seem to affect fat gain over time. 


Using data from my own research it appears I can “lose 11 lbs” in 5 days.  Stated more precisely, I can make my weight vary quite a bit in a 5 day period – either up or down.  But the variance is attributed mainly to water gain/loss or simply the mass of food that is in my body (more accurately somewhere in my digestive tract) at any point in time. 


All Rights Reserved.  Copyright: November 2008.  Take Charge Counseling and Consulting. 

Author: Miles Nitz, MS, LMFT