Carbohydrates: Evil or Essential?

athlete sugar junkieAny athlete who is concerned about their performance has questioned, if not thoroughly investigated, whether they should eat more carbs or less carbs to improve their fitness. Actually, with the current trend towards low-carb diets and a Paleo-lifestyle, and considering the world pandemic of obesity, you may be a conscientious-carb-counter. This topic is much more involved than just cutting carbs and going gluten-free with hopes of improved health and athletic performance.

There are important questions to be explored here. In regards to training, when is the best time to eat carbs – before, during, or after exercise? What type of carbs should you consume – sugary stuff like pure sucrose or honey, or do you go with complex carbs such as pasta and potatoes? And of course – how many carbs should you be eating? Ultimately the amount, type, and timing of carbohydrates doesn’t come down to who the NY Times asked for an interview and is now making headlines as a superior diet or performance enhancement, but what works for you with respect to your health, fitness level, activity level, and how you perform with any given food.

Fuel Your Athletic Body

Our bodies primarily run off of carbohydrates (glucose) and fat for energy. Though fat is the preferred fuel source in most instances, (unless you’re sprinting, for example), most people are actually burning more sugar (glucose) for fuel even when they train aerobically. Many are burning more than ideal glucose to get them through their daily tasks even if that includes sitting at desk most of their day. Relying on sugar as a primary fuel source results in a host of health and performance problems, both mental and physical.

You need to burn sugar at certain times – it’s essential for health and to some extent, athletic performance. For the most part you’re always using a combination of fat and sugar for energy. Less glucose isn’t always better, but you want to spare your sugar reserves and rely on them only when necessary. In other words, you want to use fat for fuel as much and as long as you can so the glucose is there when you need it – perhaps for a longer duration workout, a race, high intensity training, or just to keep you from being stupid. Yeah, that’s right – adequate glucose getting to your brain will keep you from being stupid. When your glucose levels are depleted, (you’re close to or have already hit the wall  or “bonked”), your brain will be starved of its preferred fuel source, so you won’t think straight, and maybe you’ll just be a moody pain in the ass. This is why so many athletes participating in endurance events, (which I define as at least roughly one hour duration – but hey, that’s just me), especially ultras or Ironman events, often don’t stick to their race plan in regards to eating, drinking, and pacing. When glucose levels in the blood drop the body is focusing on the muscles, including the heart, rather than the brain.

Insulin, Stress Hormones, and Blood Sugar

athletes carbsLet’s learn a bit of biochemistry relative to the subject as well as you – a hopefully efficient, or soon-to-be efficient – athlete.

Simply put, when you eat something that contains sugar, whether that’s fruit, bread, or something sweet, your body releases a hormone called insulin from your pancreas. This insulin causes your liver and muscles to take in glucose from the blood. If your liver and muscles don’t need to store this sugar, then the insulin will assist in delivering the sugar to your adipose tissue, so you store it as fat.

Hormones never work alone in the body; it’s never that simple. Although there are many complex biochemical pathways involved, one other to understand is the role of our major stress hormone, cortisol, with respect to insulin. When blood sugar goes up, (you just ate some carbs), insulin goes up, which helps bring blood sugar back down. But when you need more blood sugar your body often does so at the expense of cortisol, which is released from the adrenal glands. Glucagon from the pancreas also plays a part here to help elevate blood sugar, but for athletes who are training hard and for the average person under often considerable daily stress, they’re constantly in a tug-of-war between their pancreas (releasing insulin) and their adrenal glands (releasing cortisol), to stabilize their blood sugar.

boy crying wolfWe need insulin to survive; it’s not a bad hormone as many have made it out to be. But most people make too much, too often, and then their body stops paying attention to the high levels. The receptors that deal with the insulin eventually get tired of dealing with the hormone, and like the fable “The Boy Who Cried Wolf”, these receptors stop paying attention to the high insulin levels. This is what is called insulin resistance. With insulin resistance the body has lost its sensitivity to insulin; it’s not paying attention to it as well as it once did. So now the body has to make more and more of the hormone to achieve what it once only needed a little bit of to accomplish the job. It’s inefficient, and linked to pretty much all inflammatory diseases and a host of health problems from obesity to cardiovascular disease to cancer. Aside from diagnosable health problems, insulin resistance will give you a slew of other problems such as a low sex drive, premature aging, poor mental and physical concentration, and overall not feeling as good as you should be feeling.

When your body stores this glucose (sugar) it does so in the form of glycogen and it stores this glycogen in your liver and muscles. If it’s in the muscles, as most of it is, then it is going to be used by those muscles for energy. The liver will convert its stored glycogen to glucose to keep your blood sugar stable, (or as stable as possible), to use for energy and metabolic processes, as well as for your brain to function efficiently (hopefully).

The process of converting stored glycogen to glucose is called glycogenolysis (breaking down glycogen). Again, it’s not a bad thing to pull from the stores, as long as you don’t do it too much and deplete your stored sugar. This process though is promoted primarily by epinephrine, (adrenaline), which is one of the stress hormones secreted by your adrenal glands in response to stress. This is why when you’re under stress you make stress hormones and your body burns more sugar – it’s the preferred pathway to get your body out of trouble – that “fight or flight” system.

The average 150 lb endurance athlete can store roughly 400-450 grams of glycogen. This stored sugar is divided up between the liver (100-125g) and the muscles (300-350g), for when it is needed. When you need to pull from those stored glycogen levels depends on your exercise intensity, your exercise duration, and your overall health and fitness. It’s not a cut-and-dry number, and isn’t necessarily always dependent on your current heart rate you are training or racing at. Though heart rate can often be one of your best measurements of exercise intensity, you still may be burning more glucose than what is appropriate even if you feel you are training aerobically. Yeah, this is why some people don’t make gains when they train easy – their body is still burning too much glucose.

If your body is running too low in blood glucose and glycogen, then it body will want to make some. So it calls on a different part of your adrenal glands to secrete another stress hormone, this time cortisol, to help make glucose from another source. This process is called gluconeogenesis and occurs in the liver too. But this time the body is making sugar (-genesis) and most often it is doing so from amino acids, which are coming from protein, which is often coming from breaking down valuable muscle tissue. No, that’s not a good thing.

running on fat fuelEven if you’re burning mostly fat during training, after some time you will be pulling protein for fuel. Many say this occurs around three hours in a well conditioned athlete, and therefore for those not so well conditioned, it will occur much sooner.

Aside from breaking down muscle tissue and not using fat for energy, those stress hormones which are created to help provided the “necessary” glucose levels will wreak havoc on your health over time. Obviously, chronic stress is not a good thing. So if you’re always training hard and depleting your tanks, perhaps literally, then you’re a great candidate for illness, injury, and a variety of health problems.

In the future I will discuss how to train your body to burn fat as fuel, not just when you’re actually training, but the entire day.

Sock Doc Newsletter


  1. Clive Quinn says

    Thanks for this. I am still unsure though how to plan a race. Obviously on race day, one aims to run fast. I have followed the maffetone method and have managed to go from 9:30 mins per mile down to 7:30 mins per mile at my aerobic rate. Problem is I am running a half marathon this weekend and would like to race faster and I am sure I will be entering anaerobic hr levels during the race and I am not sure how to fuel my body for the faster speed. Any tips on how one who is used to the maffetone method sets oneself up for race day. For example my aerobic hr is 145 so at this level if I am doing it right then I am burning fat. So I am still burning a percentage of fat at hrs in the 160-170 zone

    • says

      This article is approximately 1500 words out of 9500 I have on the subject. I will post more the next couple weeks but it has come to the point on the Sock Doc site where the majority of info will be in the book – due out in 4-6 months.

  2. says

    That’s a good article and I’m interested to se the follow up. As a marathon runner who ate tons of pasta for 20 years and is now on a paleo diet, I can attest that, yes, the body runs mostly on fat when you are not sprinting and if you take a little time to adapt. IF also helps in that respect.

    For me the question is how far is it possible to go on the “fat burning adaptation” ? I’ve read the books of Phinney and Volek and i’m tempted to go on ketosis mode and see what happens. They claim that the keto adapted athlete can go up to 80% of VO2max on zero carbs, which is pretty much a marathon pace, but this claim seems to be disputed by others (Anthony Colpo for instance)

    One questions that stills nag at me is that I’m always surprised to see that my blood glucose never goes below 0,7 even after a 24 hour fast or a 2 hours running on an empty stomach. So I wonder if it means that I still have some glycogen stored somewhere and that’s enough to keep the level in the blood because the muscles are using fat for energy – or if the neoglucogenesis is on and this glucose comes from my muscles. But then what happens when someone is in ketosis mode ? For me ketosis means adaptation to very low carb intake, in this case does the blood sugar goes to hypoglycemia levels but as ketones are produced the brain think it’s OK or are we burning muscle at the same time to keep the glucose level around 1 ?

    Thanks and send the other posts !

    All the best,


  3. says

    Clarifying pieces of information. Thanks a lot, doc.
    Looking forward to reading a text about “burning more fat than sugar” as clear and intelligent as this one.
    Wish you could also talk a bit about the combos bodybuilders make putting together Whey Protein and a high glicemic index carb such as dextrose or maltodextrin and whether it is indeed a good combination for a pos workout diet or not. I’ve been doing it for four months, the muscle recovery seems great and my muscle mass has increased as well, but how bad is it to swallow down simply from 30g to 60g of such “insuline attention caller” sugar for the pancreas? Tottally good I bet my gains on cardio and muscle mass that it’s not.

  4. mike mcpherson says

    sock doc, great article. I’m 49 and over half of my calories come from sugar. I work in a factory for 12 hour shifts and the work is very physical. Every time I try to change my diet I fail. I run and lift and have this job. Can I get away from the sugar or due to my lifestyle I will need sugar in my diet. Thank you.

  5. Heather says

    Hi Doc,
    Your advice has already helped me in many ways (threw out my orthotics and have been feeling great). Not sure if you will address it in your book and I can’t seem to find any info online anywhere about my “problem”: I’m 38, female, 5’6″ and have weighed 100-105lbs since I was a teenager. I just have a naturally fast metabolism no matter what I eat. I started running two years ago, have done two marathons, but generally plan on sticking to 15k and half-marathons because they’re more fun. But despite eating as healthy as possible (eating vegan protein shakes, avoiding bread, dairy and gluten 75% of the time), I’m starting to lose weight and I need to eat a LOT when I run (gels, nuts, dried fruit, gummi bears, peanut M&Ms, even sandwiches) or I crash. Should I start eating pasta and rice? Any way I can bulk up without the added sugar or gluten? Thanks for your response!

    • says

      You’re a vegan or just eating vegan protein shakes? If you’re vegan the way you “bulk up” is to eat high quality protein (meat, eggs, whey).

      • Heather says

        I’m not a vegan, that’s just the protein shakes I’ve been drinking after long runs (Vega brand, FYI) because I can’t seem to find any other really good organic/high quality brands here in France. I have been eating eggs and duck and sushi and hamburgers, etc., should I just eat….more?


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