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.


Harry said…
Great piece Evelyn!

So often people get caught up in the acute response to a certain dietary or exercise manipulation, while forgetting that it is the net response (at the end of the day/week/month/year) that matters.

In exercise science we see this quite a bit when certain studies show that a supplement X increases post-workout protein synthesis by 400%. Holy Moly - 400% - that must be better than steroids! Well, no. Given the short time horizon, the studies fail to capture the fact that protein synthesis falls below baseline later down the track due to diurnal fluctuations, with the net result being no gain in muscle whatsoever.

Ditto with fat metabolism studies. It's all very well to show that a high fat ketogenic diet increases fat 'burning' relative to an isocaloric mixed diet, but as you say - so what! What we're after as dieters is net fat loss "at the end of the day", not some abstraction like "rate of fat burning increase"!

Thanks again, Evelyn.

But as you've mentioned before, the question isn't what happens wrt fatty acids in the fat cells, it's what happens as far as oxidation goes. So I wonder if there is something to LCing initially to help up-regulate that process. After all, the trick isn't putting your bad ass into energy deficit, it's *staying* there sufficiently long enough!

For me, whatever being a "good" fat burner means, at a minimum it's that you aren't ravenous every 2-3 hours because of blood sugar swings etc related to the body perpetually dealing with a heavy carb load.

Doesn't the concept of metabolic flexibility imply that some experience inflexibility? If that's true, then at least initially changing macronutrient ratio (and probably some resistance training or HIIT) may help folks be better fat burners (the mistake may be thinking you have to remain in LC land).

Up-regulating fat burning? As Martha would say, it's a good thing!
bentleyj74 said…

Speaking as a relatively lean person I think it's totally absurd to attempt a perpetual calorie deficit and I think that's where a lot of people fall off the horse. Too regimented and restricted and just...hard. If I had a lot of weight to lose I'd pick one or two days to create a fairly deep deficit and then just not compensate [but eat to non deficit calories] the rest of the time. I can be hungry for a few hours once or twice without any hand wringing but ALL of the time? No way. My comeuppance would be in the mail.
Sue said…
It would be difficult not to compensate for some. I like the idea of staggering calories through the week - some days higher, some days lower.
Well, there's just my n=1, but my experience on my version of PHD (I do a planned cheat once a week) is that I'm not hungry all the time. In fact, quite the opposite.

I'm not sure what exactly is going on, but if I had to guess, I'd bet it's the combination of sufficient protein, moderate carbs, and lack of NADs that perhaps are letting my presumably raging levels of leptin register!

Whatever is going on, I consider it a pretty good sign that I can skip a meal or two without major league hunger.
TWJS said…
Beth: "I'm not sure what exactly is going on"

Do you take any of the mineral supplements recommended on PHD? I'd also wondered if this addition may not be responsible for some of the ease of that diet. I've been doing this for a couple of weeks and see a marked decrease in my hunger. Just wondering if that may play a role.
Lerner said…
To add a little to Harry's very applicable comment, I'll point out one of the few audio interviews I'd found with any researchers on "Muscle Protein Synthesis", if anyone would like a brief (20 minute) intro to the field. This one is from Dave Gunderman:

The interview and also Gunderman's comments there explain why these types of investigations are done, and the shortcomings.
Lerner said…
Beth, did you also happen to change your exercising?

Oh, and speaking of hunger, I stumbled on this book: "The Beck Diet Solution: Train Your Brain to Think Like a Thin Person" http://www.amazon.com/Beck-Diet-Solution-Train-Person/dp/0848731735

Here is part of one review:
"Some of my favorite concepts from the book:
-That hunger is normal, and not an emergency. The idea that you can diet and lose weight and never be hungry is prevalent, and it sets up ridiculous expectations.

-That your strength of resolve is like a muscle- the more you make good decisions, the easier they get."

and another:

"When someone says 'it's just a case of eating less and exercising more' - this book helps you actually do that, without tears!"
Amy said…
I thought this would be of some interest. In mice weight gain caused gut changes which caused diabetes. http://www.sciencedaily.com/releases/2012/02/120215123352.htm

I have fructose mild malabsorption and based on this I would be nervous about getting diabetes. But, none of my relatives that have fructose malabsorption, who are in their early 80"s have any signs of getting diabetes.
Galina L. said…
This comment has been removed by the author.
Galina L. said…
I found out that developed physiological IR makes wonders for my endurance, in a process liver produces too much sugar,of course. I am not an endurance athlete, probably being pretty much IR is not optional, and my BS after 2 hours of exercise in a fasted state every time is higher than 120. Also, it takes a long time to be adopted to such regiment. I didn't aim for such result, it is what happened when I experimented with fasting. Due to injured knees I don't do 2 hours long sessions often, but it is a wonderful sense of freedom from fatigue I never experienced before. I now know I wouldn't get a migraine from overextending myself. My guess, some people may be interested to know about such option of rising an endurance. I want then to be aware about all setbacks before they consider it. Another guess, somebody may decide PIR is a better option than unstable BS. It is all about choices, picking battles and understanding that everything comes for a price. Also, according to my impression,the more I am adapted to fast and exercising in a fasted state, the less it is effective for a weight-loss. Body doesn't think it is something special any more. I don't want to push my experience on everybody, many of mine life-style decisions are based on the avoidance of migraines. It is not a wide-spread concern.

Here is a guy who incorporates LC eating into his training regime http://thatpaleoguy.com/2012/02/13/more-on-carbohydrate-and-endurance-sports/. Somewhere in his blog there are posts about training on a high-fat diet, but using carbs on a racing day.
TWJS, I supplement with magnesium every day since that's hard for me to get via food (I don't eat nuts). I also eat 4oz of liver and at least 6 pastured eggs each week. Before the holidays, I started with eating mussels once a week and am planning to start alternating oysters fairly soon. I do think that boosting micronutrients (especially the fat soluble ones) help lots!

Lerner, I didn't change my exercise early on. I have some real mobility issues as a result of a meniscus tear a few years back and a major league back spasm in August after AHS11 (at the time, the ortho wanted to fuse nearly my entire lower lumbar spine ... yikes!).

I was able to do some Body By Science before the back flared up, and after a month or so of back therapy I've started doing HIIT twice a week in the pool. I do very little cardio (and only recently have been able to start getting more than 5 minute walks in).
CarbSane said…
Thanks Harry! And I'm thinking more and more, for many, "at the end of the week" may well be a better timeframe to work with. Witness that 2 day/week VLCalCarb diet -- not major weight loss, but I am willing to bet those folks felt far less like they were "on a diet" than the day-in-day-out steady "dieters". To me the notion of one meal per week of "anything goes" (NOT binge, that is where folks go off the rails!) or alternating high and low calorie days, or whatever works best for a person is better than the constant eating X cals/day.

This notion of burning more fat for energy at any given time is indeed meaningless. It actually would seem to favor a lower energy expenditure over time ....
CarbSane said…
Hi Beth, I've only read the abstract, but that paper is an awesome find. Note, however what the problem is with metabolic flexibility (or inflexibility as it was) -- it's not fat burning that's the problem (as the lower RQ's of the obese shows), it's carb burning and fat storing that are the problem! I'm definitely going to be blogging on this one! Nice catch.

Burn off the backlog of choking fat stored in your muscle cells that doesn't belong there (as opposed to trained endurance athletes where it does b/c they are going to be using it in short order) and you become a better carb burner.
CarbSane said…
@Lerner: That hunger is normal, and not an emergency. The idea that you can diet and lose weight and never be hungry is prevalent, and it sets up ridiculous expectations.

Yes! Not only that, we're conditioned and cautioned and conditioned some more to believe that hunger will lead to OVEReating, and sometimes, I think, that hunger almost gives one license to overeat. The whole "never skip" thing is absurd and probably THE single worst advice every given!
CarbSane said…
Just a note on comments: I'm a bit backlogged on them due to spending many many hours in waiting rooms yesterday and blogger acting up a bit. I'll try to get to more as I can.
BTW, this paper is also interesting.

Maybe it's not so much that a LC diet increases one's fat burning metabolism per se as much as it improves the SAD state of affairs: high carbs, high fat, and sedentary behavior that really muck up the works. Since LC flu implies that gluconeogenesis can be downregulated, maybe that's what's useful in LCing to start. Add a little HIIT to that and maybe hello flexibility!
Keenan said…
Wouldn't being a fat burner mean you have high blood levels of free fatty acids? Which basically would make you diabetic?
Keenan said…
Maybe I don't understand your post entirely but fasting to achieve IR so you can have more endurance is by far the dumbest thing I've ever heard. It's a good way to screw yourself over for life when your body breaks down to the point where its not able to rebuild back up(the sugar your body produces is coming from your organs and tissue).
Nigel Kinbrum said…
To me, "Fat-burning Metabolism" means RER -> 0.7. This is achieved by depleting glycogen stores and by being sedentary. See Everyone is Different.

People on LC diets expend more energy through activity due to having less (but not none) hyperinsulinaemic grogginess and also from having a higher adrenaline level.

This increases Eout on one side of the energy balance equation.
Galina L. said…
My post was about reporting results of my n=1. I don't exercise in a fasted state often or even regularly. I tried to get adopted to fasting and found out that it creates physiological IR . It is not a permanent state, with eating more carbs such adaptation disappears. My guess my experience may be interesting if somebody has an unstable BS. Others may use it as a warning.
miro said…
Listen to the voice of reason
CarbSane said…
Welcome miro! I'm going to cry BS at around the 3 minute mark. I lost roughly 100 lbs doing VLC with planned cheats -- including a few longer vacations -- and they did not cause me to feel like crap or stop losing weight b/c my fat got locked back away when I went out of nutritional ketosis. It's Atkins "bite of potatoes" crap all over again. The sort of gimmicky garbage that has folks going on carb benders when they break their LC diets because it's all over once the insulin is spiked.

Interestingly, long term ketosis favors fuel partitioning to fat stores. Yep! It does!
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