1lb_fatThis is one of those ‘makes perfect sense on paper’ ideas that just don’t stack up in real life.  The simple premise is that because 1lb of stored body fat has about 3,500 calories of energy; ergo, a 3,500 calorie deficit should equal 1lb of fat loss – perfect sense, yes? Well no; unfortunately, there’s a massive hole in this proposition.  Namely, it’s assumed that every single calorie that is accounted for comes from your fat stores and this simply does not happen!  Human metabolism can, at very best, only ever achieve about 80% efficiency at fat burning, which means you can only get 80 calories per 100 from your unwanted wobbly bits, with the other 20 calories derived from existing carbs and protein stores; making your 3,500 calorie deficit accounting for only a 2,800 calorie loss from your fat cells (3,500 x80% = 2,800). And notice we said ‘at very best’, because this 80% figure is also dependant upon a number of factors: activity levels, what you’ve just eaten, the ebb and flow of certain hormones, etc., so sometimes it may be as low at 30 or 40%. fat-burnerThe metabolic processes of energy creation within every cell is extremely complex but when your cells decide to use fat for energy it’s the breakdown of a simple sugar called glucose that’s ‘triggers’ this specific process; hence the old nutritional term: fat burns in a carbohydrate fire.  Simply put; you cannot burn fat without some carbs being present with the cell; therefore you cannot be 100% efficient at purely burning body fat for fuel. But if you’re on, for example, a very low or zero-carb diet, where do the carbs come from?  The answer is your protein intake.  Your liver is very capable of converting amino-acids (the building blocks of proteins) into carbs (glucose).  It does this by both converting the proteins that you’ve just eaten OR breaking down existing proteins within your muscles back into amino-acids and converting them into the glucose (a process called neoglucogenesis) that is required to initiate the fat burning process. bicep-calf-workoutSo, for arguments sake, if we applied the same 3,500 calorie deficit to just your muscle tissue and nothing else, then as muscles carry about 750 calories per pound of weight (muscles are heavy but are approx. 70% water), then you would lose about 4½lbs (2kg) of weight.  This is purely hypothetical because it would be almost impossible to just burn muscle but hopefully, it proves a point. It’s also worth noting that we’re talking about fat loss and not just a reduction in weight because you have to bear in mind that your total bodyweight – taking a broad average – consists of about 55-60% water.  Even your fat cells carry about 5-10% water So, how many calories do you need to burn off 1lb of body fat?  Well, if you’re purely looking a dietary deficit, then aim for about 4,500.  With exercise it will depend on the intensity but a safe amount would be around 6,000 and there will be more info about fat burning and exercise in future posts. On a final note, the aforementioned 5-10% water content of your fat cells is now considered to be one of the reasons why weight loss is never straight forward when dieting.  It’s thought that the water content goes up leaky_buckettemporarily as the fat content goes down, giving rise to the common effect of not losing a pound one week and then three pounds the next week despite little or no change in diet, activity, etc.  Again, this makes a lot of sense, but then so did the 3,500 calorie/1lb of fat loss model; so watch this space and we’ll see what future research brings. Paul Lonsdale Oct 2014