May 16, 2014

Fuel Partitioning 101: Hormones

Recall from the previous post in this series on fuel partitioning that we were talking about three things that determine which types of fuel our bodies use: 1) The type of activity being fueled; 2) The type of cells/tissue performing the activity; and 3) The hormonal milieu under which the activity is occurring.

We covered the first two last time, and because the post was getting long (shocker…), I decided to have mercy on people’s attention spans and save the third for a separate post. Well, here we are.

The hormonal milieu under which the activity is occurring

As I emphasized previously, this fuel stuff isn’t an all-or-nothing scenario. Thanks to the wonderful, elegant, infuriating, and fascinating complexity of the human body, we use a few different types of fuel concurrently. That being said, depending on what’s going on with our hormones, different biochemical pathways will predominate and others will take a backseat. (Kind of like how hormones made math homework take a backseat to the magazines you found in your father’s nightstand when you were 16…)

Even though our fuel usage system is not binary, hormones are powerful enough regulators of metabolic pathways that we can say, overall, you can be a “sugar burner” or a “fat burner.” Entire textbooks, books for laypeople, doctoral dissertations, magazine articles, and about a hundred gazillion blog posts have been written about what determines which one someone is. Forgive me for radically oversimplifying things, but if you’ve managed to find this humble little blog, I’ll assume you know at least a tiny bit about this stuff. At the most basic level, what governs an overarching use of fat for fuel versus an overarching use of carbohydrate (sugar) is insulin. We need only to look at untreated type-1 diabetics to understand that (barring any other wacky hormonal complication) it is darn near impossible to accumulate body fat in the absence of insulin. And we need only to look at an insulin-dependent type-2 diabetic with poorly managed blood glucose to understand that sustained, elevated insulin levels make it darn near impossible not to accumulate excess body fat. There is far more to this than just insulin, but insulin really is the biggest player here, and since I’m not writing a book about this stuff (yet…), I’m not going to get into all the rest of it. Just know that I’m using insulin as just one example of how hormones affect fuel partitioning, ’kay?

Let’s check out this nifty chart I got way back in biochem class:

*Chart courtesy of C. Saladino, PhD, Professor of Chemistry & Biochemistry, Misericordia University

What do we see? A quick glance at the right-hand column tells us we have at least three hormones (cortisol, epinephrine, and glucagon) that “stimulate fatty acid release from adipose tissue.” English translation: those hormones get fat out of our fat cells so some other cells (muscle, most likely) can burn it. Nice! I mean, fat burning is pretty much what we’re all after, right? (At this point, you might be a little confused about cortisol. We usually think of cortisol—our primary “stress hormone”—as a fattening little son of a gun, right? Look for the P.S. at the end of this post for an explanation. For now, let’s stick with the main story.)

So there are three hormones that help us get fat out of our fat stores. And there is one—ONE—whose job (among other things) is to “stimulate fatty acid synthesis and storage after a high carbohydrate meal.” SAY WHAT?! Do we need another translation here? Synthesize and store fat after a high-carb meal? That means: make fat and lock it away on your butt, belly, hips, and thighs. Gaaaah! Eff you, insulin! Imm’a drop kick you straight to the curb!

Not so fast, McGillicutty. Insulin gets a bad rap in ancestral health circles. A very bad rap. One that is richly deserved, but not that richly deserved. Yes, it can be a roadblock when it comes to fat loss, but it can also be your best friend when it comes to building muscle. (And you know what they say: “Losing weight will help you look good; building muscle will help you look good naked. So insulin is very much a double-edged sword. Like any good tool, used properly, it’s an asset. Used improperly, it’s a major obstacle to your physique enhancement goals.) If you don’t think insulin does anything good, I refer you to the aforementioned untreated type-1 diabetic, who is wasting away to death because, without insulin, he is in a constant and uncontrolled state of breaking down his fat stores, muscles, and organs for fuel (since he is unable to metabolize glucose in the total or near-total absence of insulin).

Okay. Hormones. Insulin. What’s the deal there? Well, the way that hormones sometimes work is that they affect expression of enzymes, and enzymes are what essentially govern the itty bitty, teeny tiny biochemical processes that go on inside us. As one example, in order to make fatty acids (usually from excess dietary carbohydrate—yes, you read that correctly—we make fat from carbs, some of us more efficiently than others [me, dammit]), the body uses an enzyme called acetyl CoA carboxylase (ACC, for short). According to the same smart people from the previous post, “Insulin stimulates fatty acid synthesis by activating the carboxylase, whereas glucagon and epinephrine have the reverse effect.” See? Insulin stimulates the enzyme we use to make fat. (And the other two hormones mentioned inhibit it.)

Also: “In starvation [or carbohydrate reduction, adds Amy], the level of free fatty acids (in the blood) rises because hormones such as epinephrine and glucagon stimulate adipose-cell lipase. Insulin, in contrast, inhibits lipolysis.” See that last sentence? Insulin inhibits lipolysis? That’s fancy science-speak for “insulin gets in the way of you burning your fat stores.” (Adipose-cell lipase is another one of those wacky enzymes I keep mentioning. It’s also known as hormone-sensitive lipase: as in, sensitive to hormones, like insulin, glucagon, and epinephrine. What HSL does is take fatty acids that are locked up tight inside your fat cells and break them down into small enough pieces that they can leave the cell, travel through the bloodstream, and be brought to other cells, where they can be burned. So if we want to lose body fat, we want this enzyme to be rockin’ and rollin’ all over the place. And when insulin levels are high, this lipase enzyme is inhibited [limited]; when insulin levels are low, it is not inhibited. Bottom line: want to get rid of some body fat? Keep insulin levels low. There are a couple of ways to do this, but the most effective, bar none, is to keep your carbohydrate intake low. (Not zero, just low enough to keep insulin relatively low. And maybe not all the time. There’s a strategic time and place for big boluses of carbs. More on that some other time.)

Again, from some smaht people: “Animals that have fasted and are then fed high-carbohydrate, low-fat diets show marked increases in their amounts of acetyl CoA carboxylase and fatty acid synthase within a few days.” (English: Even after fasting, when the body would theoretically have more “room” for carbohydrates, upon eating those carbohydrates, animals still have increases in the enzymes that make fat. Could this be why it's so darn easy to regain lost body fat when you [almost inevitably] binge on carbs after a prolonged period on a low-calorie diet? Hmmmm...)

Why would insulin do this to us? Does it hate us? Did we do something unsavory to insulin’s sister on prom night? Let’s think about it from an evolutionary perspective. High carb availability means it’s summer. (Because that’s when the majority of naturally sweet things: fruit and sweeter vegetables—would have been available in abundance, right?) And to our hard-wired brains, summer means that fall and winter are just around the corner—specifically, the winter famine, when everything’s frozen and there isn’t all that much food to be had. At the most basic level, lots of carbs (and the elevated insulin levels they trigger) are our body’s signal to store all that energy for the winter, when energy sources are scarce.

Want some jellybeans with your books? 
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They sell candy everywhere now.
That’s nice. Nicer than nice, actually. It’s fantastic. Without that mechanism, most of us wouldn’t be here right now, because our ancestors would have starved to death during periods of food scarcity. This super-duper ability to sock away carbs as fat in our adipose tissue is only a “problem” in the modern world, in which we encounter sweet foods everywhere, all the time. See, in 2014, the famine never comes. You can go to Whole Foods in Nebraska in January and buy papayas, for crissake. There’s no famine, no time when we have to tap into our fat stores—unless we impose one on ourselves by either fasting altogether; cutting total calories way back from all sources; or the most palatable, enjoyable, sustainable way (in my opinion): cut way back on carbs. High carbs + high insulin is our body’s protective mechanism – storing away all of those carbs as fat to get us through the winter. Like hibernating animals. Except we don’t hibernate. The long, dark, foodless winter never comes. We have endless summer: lights on all day and night, and high-carb foods all around us. (You can’t even go to Best Buy without being inundated with candy displays, just in case you wanted some gummy worms with your new hi-def TV.)
Earlier I said something about being a sugar burner vs a fat burner. Do we agree now that insulin is the main hormone that flips this switch?

Let's think about this in the context of breakfast. Typically, when you wake up in the morning, your blood glucose and insulin levels are both fairly low. Even if you ate a sugary late-night snack right before bed, by the time you wake up several hours later, your body has done what it needs to go with the glucose and your numbers are back to normal. So now it's time for breakfast. There are two ways to go: you can consume a breakfast that will fill you up and keep you satisfied for hours without raising your blood glucose or insulin all that much. This would be a meal of primarily protein and fat: eggs and bacon; sausages and cheese; ham; leftover meat loaf; full-fat plain yogurt with some cottage cheese for extra protein; leftover chicken & veg. (Coffee with tons of butter and coconut oil...) You get the point. could eat what we've been told for years is a more healthy breakfast: glass of orange juice; bowl of wheat & bran flakes with skim milk; fat-free blueberry muffin; granola bar; bagel with margarine or jam. 

While that first breakfast will keep you going for several hours both physically and mentally, this second one is a recipe for blood sugar and mood regulation disaster. Right here at the start of the day, the poor unsuspecting soul who eats this healthy, low-fat breakfast has set him/herself up on the blood sugar rollercoaster, and they'll be holding on for dear life all day. Do you see how misguided it is to the start the day with a huge bolus of carbohydrate? (Maybe not for everyone, but if you're trying to lose body fat and/or prevent hypoglycemia and even out your mood swings, oatmeal and fiber bars are not the way to go.) Like Dr. Robert Lustig said, "Breakfast is not the time for your sugar fix."

Let's see what just happened in terms of setting the body up to be a sugar burner or a fat burner. Upon waking, just when the body is best primed to remain in fat-burner mode (courtesy of the low insulin levels), this low-fat dieter has just ingested a few wallops of carbohydrate--be they from sugary cereal that is obviously problematic or even from a whole grain, complex carb" source, like multigrain bread. And with this, she has just  given her body the unmistakable signal to NOT burn fat. To NOT use fat as fuel (either dietary fat from her food or her stored body fat—precisely what she is so desperate to get rid of.) By consuming that large amount of carbohydrate and raising insulin, she has  essentially shut down the use of fat for fuel. So much for losing body fat with a low-fat diet. According to John Kiefer, Your body starts each day as a fat-burning machine, and the key to simultaneous fat loss and muscle gain is to avoid screwing that up.

This is what I mean when I say the hormonal milieu.” Fuel partitioning is NOT only about how many "calories" we eat. It's about how the types of food we eat affect our hormones. (And for the love of all that's holy, do NOT let anyone tell you different!)
Nutritious breakfasts, or blood sugar bombs?

Stay tuned for next time. If these more science-y posts have been putting you to sleep, hang on to your hat. The next one in this series will be much simpler, and it just might be the single most important and thought-provoking thing I've ever written on this blog.

P.S. About cortisol: according to the chart above, cortisol breaks down fat but also breaks down muscle. And it turns the amino acids it gets from breaking down that muscle into glucose. (One of cortisol's primary purposes is to raise blood glucose levels in response to a stressor. From an evolutionary perspective, this stressor would have been a real, no-bull emergency, and you would have needed a lot of glucose flooding your system to give you quick energy to either stay and fight or RUN FOR YOUR LIFE. [Hence fight or flight.] A lion chasing you, trying to make you its dinner. A lion chasing your friend, and you want to make sure he is dinner, and not you. Okay, so cortisol gets released, blood glucose goes up, and then what? Insulin levels go up, too, right? And what did we learn about insulin today? It inhibits fat burning. So we’ve broken down muscle tissue to get at the amino acids to turn them into glucose, and we can’t burn all that much fat. Eek! It’s a metabolic double whammy. This is why there is actually “stress-induced diabetes.” Indeed, if you are a stressed-out, stressy stressball, you can make yourself diabetic even if you eat a pretty good diet. Piece of advice: calm the _____ down. Now.

(As best you can, anyway.)

P.P.S. Cortisol flooding your body with glucose isn't necessarily a bad thing. It's what is biologically hard-wired to happen, and at its heart, it is a protective mechanism designed to keep us alive in a very threatening situation. Problems with cortisol arise when we are constantly stressed out and do not fight or flee. If glucose floods our bloodstream because our bodies perceive the traffic jam, work deadline, or argument with a significant other, as an "emergency," and then we just proceed to sit there stewing in our car, at our desk, or on the couch, we might as well have eaten a donut and then vegged out on the sofa. (Well, no, it's not quite as dramatic a glucose spike as that, but you can see what I mean.)

Remember: Amy Berger, M.S., NTP, is not a physician and Tuit Nutrition, LLC, is not a medical practice. The information contained on this site is not intended to diagnose, treat, cure, or prevent any medical condition.


  1. But if you have that bagel (Montreal not New York style, less doughy, and this has nothing to do with the NHL play-offs), well spread with cream cheese and smoked salmon, or generously dabbed those pancakes with butter (from grass-fed cows off course) with a side of bacon/ham/sausage (from that magical pastured pig to paraphrase Homer), will that balance things out to avoid the insulin spike?

    Thinking more along the lines of a "balanced" ancestral diet vs Paleo/Primal.


  2. NHL? You said the magic word! ;-) Mmmm...hoooockey. (Used to be a huge fan, but I think all the guys I followed are probably long since retired now.)

    On the other subject, yes, you're right -- having some fat and protein with the carbs will help moderate the BG/insulin rise. It'll still happen, but won't be quite as high (or peak as quickly) as with the carbs on their own. I still think people are better off with fewer grains at breakfast, though. If one wants some CHO in the morning, I'd stick with potatoes, possibly some fruit. (Your typical greasy spoon diner breakfast comes to mind: scrambled eggs w/bacon or sausage, [even better maybe a cheesy omelet], side of hash browns or home fries, but I'd skip the toast -- do the toast *or* the potatoes, but not both. Depending, of course, on body composition & overall health goals. And then, there's always room for just enjoying life and eating it all, unapologetically slathered in Heinz ketchup's HFCS goodness, as I am known to do once in a great while.)

  3. In the Eades book "Protein Power" they have a table that shows how much the different macronutrients and their combinations affect insulin and glucagon levels. They actually asserted that high carb plus protein elevates insulin the most giving it a 9, and then carbs alone are down around 5, and fat is at zero. So consuming carbs with protein may actually not be such a good idea. On the other hand my problem with this whole discussion is that we don't eat "carbs", "protein", and "fats" we eat plant parts and animal parts (and sometimes earth parts). So what happens when you're consuming a nice juicy hamburger with fries a coke and a milkshake to top it off? Which parts are additive or subtractive or multiplicative? The Eades would say the carbs plus the protein is the problem and the fat would only very slightly reduce the problem. But about those fats -- Do they really subtract from the equation? Or when used in particular combinations do they add or multiply into the equation? Sure having lots of fat with your sugar and starch will slow the digestion but will it really keep blood insulin down? [and according to the Eades it would keep the insulin down only by one point (dropping from 5 to 4)] And what about the metabolic process where excess sugar/starch + fat both get stored as fat? (The latter would imply that fat is safe to eat except in the presence of excessive starch/sugar)

    Here are my notes about what they wrote from p.37 of their book:
    Large amts carb and small amt protein elevates insulin the most, and quite significantly (9)
    Then carbs (5), and after that,
    carbs + fats (4)
    Protein, Protein + fat, Hi Protein + low carb (all 2)
    Fat – no change. Fat is invisible to insulin.

  4. The Third option for Breakfast of course is to have nothing and do not break your fast and carry on reducing glucose levels and switching to burning fat.

  5. Hi Amy,
    Really appreciate your blogs. Would love to know your thoughts on why insulin resistance occur? I mean as a teenager my energy expenditure was perfect, in fact, most of our energy systems run properly in the early years (unless something is broken in our metabolism). I'd give my kid a cup cake and cookie and she is bouncing off walls, right? So Leptin and SNS and all are working fine. Why is it that over a period of years (for some people it might happen early in their 20s for some later in 30s or 40s) we develop insulin resistance?
    The same kid (think me) at 37 is now thinking of cutting down on CHO to regulate insulin better. Is it because of regular wear and tear of cells / tissues that the insulin receptors don't work efficiently or is there a combination of reasons? If we know the root cause of insulin resistance we might be able to target that as opposed to taking care of it the hard way i.e. avoiding those delicious carbs. Is it because we were not meant to be taking so much carbs (think Sugar) in the first place (as designed by nature) and therefore the receptors are just rusty as they have performed so much all these years and now need servicing? I have read Dr. Jang's theory on this but I am not so convinced. See here -

    Would love to know what you think! Cheers!

    1. Why and how insulin resistance occurs is the million (KAJILLION) dollar question, and I can't day I have the answer.
      Have you read this post yet? Maybe some answers in here:

    2. I thought so! May be the next nobel price up for grabs for someone who figures it out :). I am going to read this post now. Thanks!

  6. Hi Amy,
    Some other questions that popped up as I was thinking about this, so generally speaking : -
    Q1 - Can we say that at the time of feeding/re-feeding our bodies fill up the glycogen stores first and fat stores once there is no more space in glycogen stores (in liver and muscles)? i.e. Fat is stored when there is no place for energy to go except for it to get stored as fat by insulin?
    Q2 - When we burn calories, do we follow the same sequence as above - i.e. burning glycogen most of the time and getting access to fat only when glycogen is depleted and insulin levels are low?
    PS: I know you mentioned about body not being a binary system but generally speaking would this sequence of storing & burning make sense? If so, then one can design work out schedules in a way where low intensity and high intensity are sequenced in a way where fat burning is at its best (for that specific body). There are too many ifs and buts, just that I am trying to connect the dots to understand my body better and see what will work best for me. Could you please provide some perspective here?
    Also, would be great to have your thoughts on : -
    Q3. What about people missing out on fiber (soluble and insoluble) if consuming LC or Keto diets or even intermittent fasting for that matter?
    Q4. What about latest research on having diversity in gut micro biome (which might be jeopardized by cutting down on a lot of ingredients / food sources for diets in like LC/Keto etc.)

    Many thanks in advance! You def have a serious follower here! Cheers!

    1. Hard to answer all these.
      I have ZERO concern about lack of fiber on keto, during fasting, or on carnivore diet. Many people do fantastically without any in their diet at all, but others do very well. Gut biome research is in is INFANCY and anyone who claims to know what an "optimal" biome is is out of their mind. What we eat influences the composition of bacteria in the gut. You can change this in a matter of days by changing the food you eat. The gut biome of someone who eats a lot of fiber is probably shifted to thrive with a a lot of fiber. A strict carnivore's gut biome probably thrives without much fiber. The biome stuff is interesting, but I'm more intrigued by the fact that so many people have reversals of very serious metabolic illnesses by removing sugar, starch, and seed oils from their diet, with zero specific focus on the biome, and not special interventions to address certain bacterial strains. No probiotics, no anti-candida protocol, just going keto, low-carb, or carnivore.

      I'm not an expert on the fuel partitioning and glycogen repletion during exercise. Sorry. I can speculate, but that would just be speculation and not hard and fast answers. Do you follow Ted Naiman on Twitter? He would be a better guy to ask.

    2. Thanks Amy, I have started to follow Ted now. Cheers!