A Fat Burning Metabolism

We hear this term thrown around a lot in LC circles.  The frequency of this seemed to have picked up in 2011 with the mitochondrial tangent of the carbs-make-you-fat crowd.  It's a clever gimick:  If you're burning more fat for energy, that means you're burning body fat, and if you're not, those evil carbs are "locking your fat away" in your fat tissue.   It doesn't take but a little common sense to see through this nonsense folks.  With the possible exception of super-extreme diets, as has been demonstrated in metabolic ward studies, varying the 85% or so non-protein intake between fat and carbs has little if any difference on total energy expenditure.  Also, within a fairly wide middle range of carb/fat balance in the diet, which substrate is preferred or used at higher levels for energy is something that is relatively constant though the major intake macro is used preferentially at some point. 


But so what.  The whole bank account analogy some find so "wrong" works quite well here.  If something costs me $20.00, it matters not if I buy it with 20 dollar bills or 40 half-dollar coins.  Our metabolisms are geared to burn predominantly dietary carb and stored fat.  By that I mean that we burn these preferentially to dietary fat and stored carb.  Stored carb, glycogen,  is burned mostly for (a) maintaining blood glucose levels and (b) to fuel acute energy needs (e.g. running to catch the bus), while most dietary fat is deposited in fat cells.  By contrast, most dietary carb is disposed of into muscle cells, a good portion of which is burned immediately while some goes to refill stores.  The fatty acids delivered to your cells are mostly released from your fat tissue and the levels are supposed to be regulated by said fat tissue.  Even someone with single digit body fat has plenty of fat available to provide a steady stream of fatty acids at all times.  Which is not to say that some fat burned doesn't come directly from dietary fat, even a greater amount with a high fat low carb diet ... but that's that much less that gets emptied from fat stores.

As even Taubes tells us, fatty acids are continually being cycled in and out of fat cells.  The percentage returning for another stay at the Hotel Adiposia is lower in the fasted state, higher in the fed state.  We've been through the calculations before but if a person requires 2000 calories of energy per day, if they consume 1500 as fat and 500 as carbs, then the carbs are pretty much oxidized when eaten (and some stored as glycogen, and some converted to fat by de novo lipogenesis, DNL, more if the carbs are delivered in an acute dose), the fat goes to the fat cells ... only later on, fat comes out to be burned.  In this scenario, the fat gets burned sooner, but the 1500 cals of fat that are burned throughout the day if you consume 500 cals as carbs, isn't NET coming from your fat tissue if you're eating 1500 cals as fat.  On the other extreme, if you eat 1500 cals carb and 500 cals fat, sure, those fat cals will be "trapped" in your fat cells for most of the day as your body metabolizes the carb.  Likely you have a little more DNL going on, but there is little evidence that these few grams of fat lead to body fat.  We've discussed this here before, as well as the evidence that muscle cells can convert carb to fat and burn it "onboard" in the lean tissue.  Bottom line, you may be burning more fat than you think, and even if you're not, if your energy requirements are such, that you require all the carb calories you consume, you'll burn them, and burn the 500 cals of fat at some time. 

If you're eating an 80% fat diet -- OK! -- Uncle! -- I concede that you are a superior "fat burner" to me.  Whatta ya want, a parade?  Because what does that mean??  Nothing.  If you're eating your needs in dietary fat you're not burning OFF any body fat.  And guess what?  If you are eating more than your needs in fat, you will not only store body fat, but you'll actually store a little more than had your excesses been carbs.  

So what's all the whoop dee doo over fat burning?  Mostly it's a catchy gimmick.  And I raise her name from time to time, but it's not all that much different from The Beverly Hills Diet "Science" from the early eighties.  The woman went on a fruit diet and lost a bunch of weight.  Somehow she managed to maintain that loss, and wrote a book.  Having no real knowledge she did some research and came up with the lipases in certain fruits increased your "fat burning".  One problem ... those are not the lipases involved in fat burning metabolism, they are the ones involved in fat absorption.  If anything, improved digestion of fats would lead to weight gain!  (Finding this on the WAPF website is disconcerting too.)  So too now, we have this "fat burning metabolism".  If I may ask ... nothing gets you "fat burning" like that much maligned cardio ... so if just switching to a fat burning metabolism was all you needed to melt body fat away, remind me ... Why is exercise (good for health, muscle tone, mood, skin, hair, nails, penis size, boob augmentation, moob reduction, tear production, ...) so useless for weight loss? 

Look ... if you're an elite performance athlete or body builder, there may well be things you can manipulate dietarily to get the most out of your metabolism.  And if your body loves ketosis and you feel like you can fast better being LC or that your BG's are more stable, etc., more power to you.  I'm not here to advocate how you should eat nor to discourage you from enjoying what you're doing.  But don't kid yourself and others with this fat burning metabolism nonsense.  Because that's what it is.  And knowledge of ketosis has been around for a very very long time.  So me, personally, I'm skeptical that it offers an advantage for endurance athletes.  Because surely if it did, it would be the norm for endurance training. 

What is the ultimate body fat burning metabolism and diet?  Whatever puts your bad ass into energy deficit.  That's what.