In fact, fat is our biggest and one might argue most versatile sources of fuel. It also makes up the shell of every cell in our body, and is part of a host of other essential for life processes that happen inside us. But the focus of this post is on how fat contributes to providing us with the fuel we need and use in every breath we take.
Fat is amazing. It's the most abundant fuel source in the
body.Every time we breath we're using fat to help take care of the energy needs of our bodies, whether thats muscular activity of lifting something, or the chemical activity of digesting something, or the transport activity of moving something from one cell to another.
In each of these cases, Fat contributes the lion's share of the energy to our physical processes. We couldn't live without it: adipose tissue affords protection to our body's various systems as well as immediate fuel storage sources; the membranes of cells are part fat and enable standard operations of the heart and lungs to get nutrients throughout our systems. And, it's also an energy reserve. Like having a bunch of batteries in the cupboard ready for when the smoke alarm or flashlight fails. Swap out the old cells put in the new.
Despite these great capacities, most of us want to shed some extra weight. Indeed, we know that it's our incredible ability to store fuel resources that works to our socio-cultural detriment in a society where fuel-as-food is readily and cheaply abundant. We put on extra weight. We carry reserves in excess of what we need given the ready abundance of fuel around us. And there are some pretty nasty health costs to carrying around that much surplus fuel, too. Type II diebetes, metabolic syndrome, additional load on joints, etc.
And so we look for ways to burn it off.
The goal of this article is to take a 50thousand foot view (ie really simplified view) at part of what's going on with that burn off, and why therefore fat is our super fuel and seemingly super nemesis.
What i mean by simplified view? Here's a map of the metabolic process:
A metabolic map, indicating the reactions of intermediary metabolism and the enzymes that catalyze them. Over 500 different chemical intermediates, or metabolites, and a greater number of enzymes are represented here. ((c) 1997 20th edition, designed by and courtesy of D. E. Nicholson, We're considering a wee fraction of this entire process, and only part of what's going on as illustrated below (source):
The three stages of catabolism. Stage I: Proteins, polysaccharides, and lipids are broken down into their component building blocks, which are relatively few in number. Stage II: The various building blocks are degraded into the common product, the acetyl groups of acetyl-CoA. Stage III: Catabolism converges to three principal end products: water, carbon dioxide, and ammoniaThese maps help to get that this is complex cool stuff. we are amazing. The above maps let us ask the question - how do we get the good stuff out of fat to use? and to appreciate how a little bit of fat goes a really really long way. To get to that, we need to consider what energy from fat means. And that means taking a look at ATP, the primal fuel block (what fat and other nutrients in large part become), and also situating fat a bit relative to other nutrients like carbs and protein in this fuel-making process (nothing shines out like a comparison). We'll take a wee look at what can increase the fat burn in cells (mitochondria) and finally, where this should lead: why fat, while it burns all the time, is still a challenge to shed.
Energy from Fat
Anyone who's spent time counting calories likely knows that the standard wisdom about calories is that carbs are 4kcal per gram and so is protein. Fat however is 9kcal per gram. Remember a calorie is a measurement of energy: the amount of energy to raise 1 g of water 1 degree.
Right from the outset, it looks like fat has the advantage in providing us with more energy than either carbs or protein. Looks like about twice as much. That's true. But what is really cool about fat is that it gives us more useable fuel for the body to do its lifting, chemical processing and transporting than we get from protein or carbs, and that's in terms of it's translation from a fat to ATP.
ATP
ATP or adenosine triphosphate. ATP is what powers all the energy in cells.
We hear a lot about ATP in the body building world and general strength training: in big lifts the point of that long recovery is to replenish phosphocreatine stores that can make a little bit of ATP available without the presence of oxygen - like when we hold our breath, or exhale out, to do that big dead lift, or keep our head under water for that 50m sprint to the end of the pool. 1 molecule of phosophocreatine when it's broken down into ATP yields only a few ATP molecules. That's not a lot for intense work, but it can re-synthesize quickly for short 30sec bursts.
But what about for efforts that last longer than 30secs? Then we start getting into carb and fat world. Protein is used for very little energy - 2-5% - it has other jobs. If no other source of fuel is available for energy - no carbs say after a workout and you use protein - a chunk of that protein will be used as fuel - transformed into carb-like fuel for replenishing energy stores. And when folks take on more protein than can be used for any current physical requirements, protein will be translated into fat.
Digression on Protein and Starvation
Here's the other thing about Protein as fuel: some folks find that when they're working out and dieting at the same time, it seems their fat loss stalls out. That's a well-studied phenomena that if the body has fat for fuel, and it feels like it's being starved (only recieving 50% or more of the needed cals for maintenance), it will horde fat for as long as possible, and will start to catabolize (break down) other sources in our bodies for fuel. Protein from muscle is a goody.
So often folks starting an exercise program after they've started dieting need to INCREASE their calories a bit to off set starvation.
Now if someone persists at starvation levels long enough, the weight will come off. The famous Minnesota experiment demonstrated this action.
So back to ATP - and ATP from our nutrients.
The body stores only 80-100g of ATP at a time. So it has to synthesize ATP all the time.
A huge point of taking in food is to convert these fuels into ATP. Without going into the detail here, here's where fat comes into its own: a molecule of glucose (stuff from carbs generally), depending on the source, produces 36 or 38 molecules of ATP. 1 fatty acid molecule (derived from fat sources) produces 460 molecules of ATP. That's considerably more than 10 times the amount of usable fuel for muscular, chemical and transport activities than carbs.
Why is this? Basically the way fat breaks down more of it can be translated into ATP than carbs. If you look at the second big map above, you'll see that carbs have to go through three intermediate steps before they get to acetlyCoA. Fat can go pretty much directly to that stage.
Fewer steps, less stuff used for other things than ATP...
The process of how these various translations of a food into a bundle of energy occurs is really cool. It's a testament to how adaptable we are. For instance if we don't have enough carbs in our bodies for the jobs carbs are used to do - like feed our brains and liver - the body will translate fat into carb substitute. This process is the subject of books like Lyle McDonald's excellent review called the Ketogenic Diet.
Why bother with carbs at all if Fat is so awesome? and is that the secret of these "low carb" diets?
Fat burns in the flame of carbohydrate.
One of the best ways to stoke fat to burn is in the presence of carbs - this has to do with stuff in the Citric Acid Cycle. When carbs aren't present and the body has to go ketogenic to use fats instead, well, it can do it, but it's not necessarily optimal. You can skip this next bit if you wish but some folks have asked for a bit more explanation of what this Flame means. So the following digression:
Always on, All the time - when possibleAnd just a note: that even diets that cut out grains and other what we might call fast carbs (fast to become avilable as fuel) to go ketogenic, even here one is encouraged to eat veggies. Lots of them. Why? carbs are part of our natural metabolic process. A third of our energy comes from carbs. Our brains like carbs. Our fat burning engine likes carbs; our muscles like carbs. In balance.
remember that all our energy systems are in play pretty much all the time. There's a little bit of glycolysis (carb burning) happening along with beta-oxidation (fat burning) even when we're at rest.
a by-product of the whole carb burning process is oxaloacetate (OOA). It connects with Acetyl-CoA to form citrate, and that gets processed in the citric acid cycle and ATP is produced.
Duel types of fat
Now here's the cool thing. Fat is so versatile it can get used as fuel a couple of ways. One of these - that produces the MOST ATP is via getting it into the citric acid cycle (see diagram above). This is what FFA's - free fatty acids do. Fat also becomes available as fuel as Glycerol. When you're low on carbs, it's glycerol that gets used as carbs (via gluconeogenisis) - whether you're doing a heavy workout or doing a ketogenic diet. BUT a molecule of glycerol only produces 19 ATP molecules.
FFA's Rock
Compare this rate of ATP availability with what FFA's do when they can enter the krebs cycle. Without getting into the Krebs cycle, fat conversion is also a relatively slow process so that pathway won't get energy to the muscles super quick. Which partially explains why even if you're on a ketogenic diet, most folks recommend getting some carbs into your system prior to a workout in particular for better available energy - and fat utilization. Now this is not to say that we don't adapt in a ketogenic situation to get the turnover of fat into carb substitute happening faster, and when loads are reasonable, all could feel ok. But even so, that rate can't compete with FFA going through the citric acid cycle.
Fuel from FFA is FFA going into Citric Acid Cycle (burning in the flame of carb)
first step is beta-oxidation of a FFA: cleaving off a couple of carbons from the fat (see first image by the battery) and we get products NADH and FADH2 which can form up into acetylCoA which can hook up with OOA to do the citric acid dance. This cycle in turn breaks down the acetylCoA into co2 and H. The H come out of the citric acid cycle to oxidize via something called phosphorylation. The result is 460 ATP from FFA conversion to energy.
SO this is why fat burns and really BURNS up in the flame of carbohydrate.
And fat in something called "slow glycolosis" (part of the Krebs Cycle, pictured as the ring in the second figure above) loves carbs to let it burn baby burn. Now before anyone jumps on me, no Fat does not REQUIRE carbs to help it break down into the stuff that enters the KC to become ATP but it is sort of the path of least resistance, perhaps, if i can put it that way.
And just to repeat what may well be obvious to all:
fat burns as fuel via the happily fairly constant activity of breathing. Fat is "oxidized" to break
down into fuel. This oxidation takes place in the mitochondria of the cell. Hence it's important to have rather a lot of it as we breath so much.Aside: Fat Burners. We may also recall that the discussion last week about super intense low volume 6min. workouts a week created as many new mitochondrias (ie fat burners) as did 1-2 hours a week of steady state cardio. Want to enhance fat burning? combined with diet, enhancing mitochondira helps.
I dunno, just thinking about all the things a bit of fat does it once again strikes me how incredibly amazing we are. So versatile. We can fuel ourselves up with just about anything we ingest. Our systems have preferences but can adapt to circumstances. Wild.
And fat is wild because it does so much for us.
Losing/Burning Fat - Hard Homeostatic or Hard Habit?
But you may be asking if we're burning fat (converting it into ATP pretty much constantly), why are we Fat? Why is fat hard to lose?
I guess the question might be reframed as is fat hard to lose?
What is hard, it seems, when food is so easily available to us, in ways historically unprecedented, we follow our ancient wiring and we eat. We want to load up for the lean times. But we don't live in scarcity. Access to ready prepared food continues to increase. Our need for these responses to horde up are less appropriate.
see
Hays NP and Roberts SB. Aspects of Eating Behaviors "Disinhibition" and "Restraint" Are Related to Weight Gain and BMI in Women. Obesity 2008:16, 52–58. doi:10.1038/oby.2007.12.
So perhaps what's hard is the habits around caloric restriction: being patient enough with ourselves to learn new habits to support some caloric restriction to lose weight. To be patient with ourselves that fat loss takes time. While the inital excess fat may come off faster, those last ten pounds are killers, and there are reasons for this too that i've discussed elsewhere.
And without habits to support ongoing lean attitudes, then how do we keep the weight coming off? and then how do we maintain our goal weight?
I've said it before, its this need for habits around food rather than specific diets that i like precision nutrition. It supports habits.
Rewiring for Fat: Love your Fat; Burn your Fat; Respect the Fat
So while we are wired to grab store and horde fuel, we can adapt our behaviours to be lean in the face of abundance. Once we start turning on those habits, we do need to tune them to optimize fat burning. The basic part of fat burning is to get the balance of eat less right with whatever activity one is at, so one stays productively above starvation level.
Being patient with ourselves to learn what that sweet spot mix of caloric restriction and workout effort to optimize fat burning - if that's the priority - takes time, patience, and a strategy to be able to assess if what's being tried works. Again, i'll say i like precision nutrition becuase it has a method called an Individualization Guide to support exactly that process.
Calorie Note: Why only 3500kcals to drop a Pound of Fat?
Some folks have noticed a seeming discrepancy between cals in a pound of fat and that there are fewer calories to burn a pound of "fat"
I'm still looking for sources on this, but here's the argument: let's start with the basics.
1g of fat = 9kcal
so 1kg of fat =9000kcal
9000/2.2 = 4091kcal / pound of fat (1kg/2.2=1lb)
Apparently a pound of human fat is made up of 10% water + 5% other materials that aren't digested - i need sources to support this, but if we go with that for a moment
4091 -15%= 3477.35
That's approx 3500kcals.
One other frequently quoted statement on the web is "Human fat tissue contains about 87% lipids, so that 1 kg of body-fat tissue has roughly the caloric energy of 870 g of pure fat, or 7800 kcal."
- just put that quote into google and it will show up on a dozen sites - but no primary source for it. - still that conveniently gets to the well cited 3500kcal/lb of (human) fat.
The closest i have to a real source for such info is
Adipose tissue contains 82-88% fat, 2-2.6% protein, and 10-14% water. The energy yield of adipose tissue is 8000-9000 kcal (34-38 MJ) per kg or 3600-4000 kcal (15.1-16.8 MJ) per pound.and that's at Answers.com, and i've no idea who writes this stuff for them or from where they get it.
Higher Up and Further In
if you're intersted in going deeper into the physiology here, may i recommend
Exercise Physiology: Energy, Nutrition, and Human Performance, 6th Ed.
McArdle, Katch & Katch (US| UK)
There's a 7th ed coming in November 09.
If you get really intrigued, for after the above, there's Brook's bioenergetics, referenced in the side bar book recommendations
Related Posts
- getting off diets and onto better eating habits. change is pain: reduce the pain :)
- becoming a better burner: 6mins a week to trigger mitochondrial growth = to 4.5 hours cardio
- cardio with kettlebells
- vo2max effort training
Great Info! I learned more from that article than I did in a full semester of a college nutrition class.
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