BY DR. BAYNE FRENCH
In Part 1, I detailed the specifics of the FASTER study, so the antithesis of high sugar fueling may be understood. With knowledge of the extremes, perhaps a healthy and enjoyably sustainable fueling method could be developed for your own endurance demands.
Biochemistry and Metabolism:
I do believe the best decisions are made in an educated state, free of bias. Becoming educated and shucking bias are truly transcendent human attributes, thus exceedingly rare.
I think it critical to have a basic understanding about what happens chemically when your blood stream is flooded with sugar. With this knowledge you may choose to stick with the status quo because it is working for you, or you may choose to go a different direction entirely.
I have written about metabolism many times. I feel that most diseases, most of what we will all die of, is a result of distorted metabolism. A sick metabolism leads to unwanted weight gain, type 2 diabetes, stroke, heart attack, Alzheimer’s disease, and cancers. Having an efficient metabolism reduces disease, medication, ass-time in doctor’s offices, and enhances health span and lifespan in a remarkable way.
My entire perspective on health and wellness, including athletic fueling, is viewed through the metabolic lens.
Metabolism involves the conversion of food particles to energy, and the storage of these particles for future energy. The overview is this:
Food + Oxygen = Carbon dioxide, water, and energy.
Food contains a lot of stuff, like fiber, vitamins, minerals, pigments and other nutrients. For metabolic purposes whether it is protein, carbohydrate, or fat, food consists of carbon, hydrogen, and oxygen. Protein also contains nitrogen. Just 4 basic elements.
This is not an exhaustive discussion of biochemical reactions. The topic of this article is a discussion of high carbohydrate fueling for exercise and its resultant harms. Consequently, the focus will be on blood sugar.
Sugar is sucrose. It consists of one molecule of glucose and one molecule of fructose linked together. Most carbohydrate, whether sucrose or a slice of bread, is broken down in the intestine to single molecules of glucose and fructose.
Glucose is absorbed into the blood stream by its own transporter complex called SGLT1. Fructose has its own transporter called GLUT5. These are the transporters that Dr. Jeukendrup, discussed earlier, showed could be increased in number and efficiency with “gut training”.
Enzymes are proteins that help a chemical reaction move forward. There are enzymes that specifically metabolize glucose. When glucose builds up and is in excess, these enzymes are shut down. This is called feed-back inhibition.
Despite huge amount of sugar consumption, and heightened sugar absorption from the gut from “gut training”, there are still bottlenecks with how much glucose can be converted to energy, ATP.
And THIS is what we’re really trying to do…make lots of ATP because this is what makes muscles move.
Insulin:
Insulin is a hormone that is made in the pancreas. Like all hormones it travels by the blood stream and exerts effects far removed from its organ of origin. There is no more potent modulator of metabolism than insulin.
When there is an increase in blood sugar, insulin is released. All of our 40 trillion cells have a docking port on their surface for insulin. This allows sugar to go from the blood and into the cell. Insulin is potently anabolic. Meaning it builds things. It builds muscle, glycogen (storage form of carb), and is particularly good at building fat.
First of all, with heavy exertion, it does not make a lot of chemical sense to have a hormone spike that is responsible for building things, when we really need to break things down to provide fuel. However, insulin is very good and in fact vital and allowing the entry of glucose into the cell. Glucose then undergoes a chemical process called glycolysis, and a little bit of energy is made in the form of ATP. After glycolysis, glucose remnants then enter the citric acid cycle, and eventually oxidative phosphorylation. This last set of reactions results in the majority of ATP formation.
ATP is directly responsible for the movement of our muscles. And this is what endurance athlete’s really care about…repetitive, prolonged muscle movement under a load, preferably performed better than everyone else in the race. Some athletes want this so badly, metabolic consequences be damned.
As mentioned, insulin is the most potent metabolic hormone. It is so powerful that to counteract its effects requires 3 other hormones: Glucagon, epinephrine, and cortisol. We already discussed that insulin is what allows glucose (blood sugar) to enter the cell. Inside the cell is where glucose is converted to energy, ATP.
Insulin has many other effects:
- Formation of glycogen, our form of carbohydrate storage.
- Prevents the breakdown of glycogen.
- Causes the conversion of carbohydrate to fat.
- Increases percent body fat.
- Prevents the breakdown of fat.
- Helps convert protein into muscle tissue.
- Stimulates glycolysis, the first step of glucose metabolism inside the cell.
- Prevents gluconeogenesis, the formation of new glucose.
- Prevents the conversion of lactic acid into glucose.
- Results in cellular proliferation, increasing the risk of heart disease and cancer.
Metabolic Consequences of Elevated Insulin:
When blood sugar is elevated and insulin levels high, you are a One Trick Pony. You cannot use protein and fat to create new glucose in a process called gluconeogenesis.
More importantly, you are unable to access fat for fuel. Fat tissue is broken down in a process called lipolysis. Insulin directly inhibits this. After fat is broken down it is metabolized in a process called beta-oxidation. Insulin further inhibits this reaction. Consequently, the dramatic amounts of energy (ATP) that fat is capable of providing is completely unrealized in a high insulin environment.
Lactic acid is normally made in the process of glycolysis. Much more is produced with strenuous exercise. High-level athletes recognize this chemical as causing soreness and being basically a nuisance. Lactic acid can however be a source of energy. It can be taken up from the blood stream by the liver and converted into more glucose. Insulin interferes with this process.
Heart muscle preferentially burns fat for fuel. Heart cells are very adept at performing beta-oxidation, breaking down fat into smaller pieces that then enter the citric acid cycle, and eventually oxidative phosphorylation to yield a huge amount of ATP.
Insulin directly interferes with the breakdown of fat and the heart’s ability to create energy. I could be wrong but I think most endurance activity requires a well-functioning heart and high insulin levels from a blood stream flooded with sugar directly impairs the hearts’ ability to burn fat.
Mentioned in the section above is that insulin stimulates proliferation, or growth, of cells. Fu et al. (Mol Metab. 2021) reports how insulin directly and indirectly affects arteries “exacerbating the development of endothelial dysfunction, atherosclerosis, restenosis, poor wound healing and even myocardial dysfunction”. These abnormalities are independent of blood sugar levels.
Patil et al. (Mo Med. 2012.) details the myriad cardiovascular complications that can afflict endurance athletes. These problems occur at a higher incidence, and at an earlier age in endurance athletes. Insulin is a primary driver of this.
Leitner et al. (Biochem J. 2022) in a fascinating article titled Insulin and cancer: a tangled web details the chemical reasons behind how insulin can drive cancer formation. Thirteen cancer types are found to occur with much higher incidence in individuals with obesity. A primary driver for the vast majority of individuals with obesity is chronic hyperinsulinemia (ongoing and prolonged elevated insulin blood levels).
Although Patil et al. above reported on cardiovascular diseases in endurance athletes, there is no compelling evidence to date that endurance athletes incur a higher risk of cancer. There is however, a mechanism of heightened risk associated with high insulin levels. Recommendations of 60-90 grams of carbohydrate per hour results in extreme insulin formation from the pancreas.
Muscle Types:
Maybe you have heard about white and red muscle types. It is as true in your Thanksgiving turkey as it is in us.
White muscle is lighter in color. It is considered a fast-twitch muscle type, capable of burst contraction. The turkey breast possesses this type of muscle. Sprinters and weightlifters also have a disproportionate amount of white muscle. White muscle is most efficient at burning glucose to create ATP.
Red muscle is a slower-twitch muscle fiber, capable of prolonged, sustained and repetitive contraction. Sounds a lot like endurance movement. Here is where high carb fueling recommendations becomes incongruous with efficient movement. Red muscle is most efficient at burning fat as its primary fuel to form of ATP. High carbohydrate fueling flies in the face of this. Thus the advice from Dr. Jeukendrup and Andy Blow is made further questionable.
A Bit More Biochemistry:
I detail how sugar detrimentally affects performance in an article Sugar. The Antithetic Performance Enhancer. A couple (of the hundreds) of highlights from the article:
- Nitric oxide is a potent chemical produced by the body that increases blood flow to tissues. It also allows entry of glucose into muscle tissue. It is a performance enhancer. Sugar directly interferes with the formation of nitric oxide.
- Sugar drives the formation of antidiuretic hormone (ADH). This means you urinate less, holding onto more fluid, further interfering with your power to weight ratio. Furthermore, ADH is a vasoconstrictor, meaning it constricts blood vessels to muscle. None of this is helpful for performance.
Recall that half of sugar is fructose. Fructose is a potent driver of uric acid which is associated with multiple chronic diseases. Although uric acid is most known for causing gout its metabolic effects are wide reaching. Here is an excerpt from that article I wrote Uric Acid and Its Metabolic Effects:
Whether you are afflicted with gout or not, elevated uric acid drives the formation of insulin resistance, elevated blood sugar, type 2 diabetes, elevated blood pressure, distorted cholesterol, systemic inflammation and weight gain. It is directly implicated in a large percentage of all-cause mortality and especially cardiovascular disease (Chen et al. Arthritis & Rheumatology Feb 2009).
The evidence between elevated uric acid and metabolic mayhem is strong enough that it is considered an independent risk factor. This means that on its own, elevated uric acid corresponds with disease.
An average adult human mammal has about 400 grams (14 ounces) of stored carbohydrate in the form of glycogen. This corresponds with less than 2000 calories. This amount could singularly provide enough ATP for 90-120 minutes of vigorous exercise.
A lean adult human mammal can have 10 kilograms (over 20 pounds) of fat providing upwards of 100,000 calories.
With excessive sugar fueling, blood sugar levels spike. Glycogen stores may stay replete but there is a lot of blood sugar left over. It will invariably spillover into fat formation. The stress hormone cortisol is elevated with heavy exertion. Cortisol will preferentially direct fat storage into the midsection, creating visceral fat. This type of fat is different from fat stores under our skin, called subcutaneous fat. Visceral fat releases hundreds of unfavorable chemicals that drive organ dysfunction over time.
High sugar consumption > Elevated blood sugar > Elevated insulin > Insulin resistance
Further elevated insulin > Increased cardiovascular disease and cancer risk > Fat formation and inability to burn fat
Exercise and relative reduction in calories (as in lower carbohydrate endurance fueling) triggers the formation of a protein called AMP-activated protein kinase (AMPK).
Stay with me here. AMPK does so many good things. Two of which are:
- AMPK stimulates mitochondrial biogenesis. This is the formation of NEW mitochondria, and mitochondria are what make ATP that fuels your performance.
- AMPK stimulates the process of autophagy. This is the removal of damaged and old cellular components. It’s like cellular housecleaning. Poor autophagy is a driver of several diseases.
Let’s End This Thing:
I have absolutely no use for high carbohydrate fueling during exercise and no respect for it being recommended. I view it to be health harming on many levels. There are no disputing myriad metabolic effects of sugar, none of which are favorable. If you try to dispute them you are either ignorant, mired in dogma and the status quo, or on the payroll of some sugar-touting entity.
There are so many metabolic flaws to the recommendation for high carbohydrate fueling during exercise. With inane practices of sugar-gorging, it is not biochemically possible to create a huge amount of energy from fat; perform mitochondrial biogenesis, and autophagy. Furthermore high insulin results, driving visceral fat formation, cardiovascular disease and numerous cancers.
I’ve put myself through physical suffrage that I wouldn’t wish on people I dislike. And that’s a lot of people. Exertion and discomfort that sometimes went on for days in pursuit of things with points and full curls. I’m all about seeking an edge, and investigating that which could confer an advantage over other mammals of my own species or different. Stuffing myself with a known toxin and a primary perturber of a healthy and efficient metabolism is not an “edge” at all, regardless of the resume of the pontiffs recommending it.
It is a leap of faith in a way, to undergo a complete metabolic change in how you generate fuel. It takes time, perhaps upwards of a year, to be truly “fat adapted” meaning able to extract vast amounts of energy from the burning of fat. It is the rare high-level endurance athlete that will change a behavior that seems to be working well for them. Especially given that their window of optimal performance is relatively short. I am not writing for these people.
If you are not of this extreme performance persuasion, I would urge you to buck this metabolically flawed trend. Do not be a One Trick Pony, completely dependent on sugar to generate ATP. Lower amounts of carbohydrate consumption per hour results in lower amounts of insulin. Fat stores are then accessible which lead to an amazing amount of ATP for muscle contraction. Importantly is that lower insulin level over time that confers a much lower risk of disease.
Always be your own advocate. The willingness to follow deeply flawed and unhealthy guidelines has a lot to do with psychology. Observing influential people doing something with good results drives a similar behavior. Break free from this. Ask yourselves difficult questions. Understanding basic mechanisms is a platform from which you can embark on a different and much healthier exercise fueling strategy. I hope this article provides that for you.
