deep dive on bonking, glycogen stores, and the train low diet.
We’ve all done it — and we all dread it: bonking. That terrible feeling when you know you’ve not consumed enough calories and it’s going to be a slow, painful shuffle home or, worse yet, to the finish line. Yet understanding a little more about how bonking happens can go a long way to helping you prevent it.
Firstly, let’s start with glycogen. Glycogen is a collection of glucose molecules (or sugar in its simplest form) and the simplest form of carbohydrate. Glycogen particles come in two forms: proglycogen and macroglycogen. These two forms of glycogen particles are important to understand as they are both responsible for differing rates of glycogen particle repletion. The proglycogen acts quickly and is dependent on dietary intake of carbohydrates, thus allowing for rapid replenishment, while the macroglycogen are formed from collections of glucose units that build slowly and allow secondary glycogen particle repletion over a longer period of time to occur. Both are important phases and are described as the “biphasic nature” of glycogen repletion.
WHAT YOU HAVE
Before worrying about getting depleted and needing to refill your stores, you should know that your body has approximately 600g of glycogen particles in it, dependent on body mass, diet, overall fitness and your most recent bout of exercise. The majority of your glycogen particles are stored in your muscles (~300-700g), and the remainder in your liver (~80-160g) and brain (100 times less than the number of glycogen particles stored in your muscle cells). The liver glycogen particles are constantly used to replenish the small amount (~4g) of glucose in your bloodstream. This amount of glycogen is entirely adequate for a sedentary individual who is not performing bouts of short to long, low to high-intensity exercise most days of the week (that’s not you, endurance athletes!). For triathletes, understanding your glycogen stores and how they affect you—and how you can affect them—becomes a lot more important to understand.
In order to have muscular contractions, ATP (adenosine triphosphate) needs to be produced. This is the energy that powers you during exercise. It is (at the most basic level) the energy that allows cells to function. Without it, you do not perform. It is produced by organelles called mitochondria, which are the energy factories of your muscle cells. ATP is produced by the oxidation of fatty acids from the bloodstream and from intramuscular fat stores, along with glucose supplied by the liver into the bloodstream and the glycogen particles stored in your muscle cells and between the muscle cells. It is widely agreed upon that as exercise intensity increases, reliance on blood and muscular glycogen particles increases. In fact, as intensity approaches 60% VO2max, you will find that the predominant fuel source being oxidized through anaerobic and aerobic processes to produce ATP will be the glucose in your blood and muscle.1 This is in large part due to the type of muscle cells being recruited (i.e. Type II) in order to allow for the intensity and exercise to continue.
It's time to dispel a lot of the media hype currently associated with protein. Everyone out there seems to think there's a new brand of protein powder that is going to magically transform them into a super athlete with less than 10% body fat. That with no dedication, commitment, or awareness, anyone can achieve the ideal body shape they so desire. Sadly, protein in any form is not the “magic” macronutrient for body transformation. Protein is just one part of the nutritional requirements needed to achieve health goals. Following on from my article about sarcopenia and protein requirements for the ageing athlete, I thought it timely to discuss protein in a broader context: What protein is, what it’s not, what it does, and the practical application of its use.
What is Protein?
In its simplest form, protein is amino acids. There are twenty of these, and nine of them are considered essential amino acids (EAAs). EAAs are essential because the body does not produce them, so you need to consume them in liquid or food form to get them into your system. Now, of these nine EAAs, there are three branched chain amino acids (BCAAs). These are your most important amino acids as they are key regulators in muscle protein synthesis (MPS) They are dependent on the other 6 EAA's to make their magic happen so taking them alone really is not something you need to consider doing. One BCAA in particular, leucine, is viewed as the key amino acid for triggering muscle growth after exercise.1 Leucine will trigger MPS when ingested at sufficient levels (~2.5g) and can be found in higher levels of proteins derived from animals vs plants. If you are consuming plant proteins, it may be worth considering fortifying your proteins with EAAs, BCAAs or leucine on its own. This has been shown to be an effective method of improving a poor quality protein. Thus far, there is nothing magic about the mystical creature, protein - just some solid science.
What can protein do for you?
If you look at reviews and studies on protein and its effect on muscle building, improving body composition, and improving strength2-6, you will see clear evidence to support protein's use. While the World Health Organization has a recommendation of 0.8g per kg of bodyweight for individual protein intake, the International Society of Sports Nutrition has a position stand that recommends 1.4-2g per kg of bodyweight for physically active individuals.2 This difference in recommendation is because protein breakdown is higher in training individuals, and should be supported with an increased intake.
What can protein do for body composition?
Protein may have an effect on your body and your body composition5-7– but not a magical one. Firstly, protein may reduce the total amount of food you are eating due to its ability to keep you feeling fuller for longer. On a higher protein diet, you can go into a calorie deficit without knowing it. This is one of the great practical applications of a higher protein diet for a lot of clients. Have you ever tried eating 400g of chicken compared to 400g of bread? Big difference in difficulty. This is a huge part of why higher protein diets work. Not because of all the fancy science behind protein’s effect on the body, but simply because most people cannot eat large volumes of food.
With that said, protein does have a greater thermic effect called TEF, or the thermic effect of feeding. In other words, your body works harder to break protein down and thus uses more energy to digest it. Protein is an uneconomical fuel source, but beneficial when used in the right manner. Protein has a TEF of approximately 19–23% in both obese and lean individuals, whereas carbohydrate has a TEF of approximately 12–14%. Studies investigating higher protein diets support that the majority of individuals (~70 %) who consume a high protein diet (>2 g/kg/bodyweight daily) get an improvement in body composition. This method is not 100% foolproof, but it does often work.
Protein also assists muscle protein synthesis. This means if you’re in a calorie deficit, there is potential for the muscle mass to be maintained whilst fat stores are utilized for energy. The parts of your body that aid metabolism are therefore maintained. When protein is combined with quality resistance training, then protein consumption starts to have a very significant effect on lean mass growth and fat loss. Protein isn’t the key to muscle growth on its own. But without it, you won’t make significant strides in your pursuit of increased lean muscle and reduced body fat.
The information in this article is directed towards the slightly older population, so if retirement and old age are still decades away, you could be forgiven for thinking it isn’t relevant to you. But you’d be wrong. One day you’ll fall within that age bracket. And unless you came from a test tube, your parents and grandparents are likely to be there already. I cannot say it enough, if you care about your future health and theirs, read on.
This article was originally written for True Protein back in 2016 whilst I was working for Oracle Team USA and living in Bermuda. I stand by True Protein as the best supplements company I have ever worked alongside and as a result now work with them as the True Protein in-house Performance Nutritionist. I am responsible for Product Development and innovation along with ensuring we stay on point with relevant research and evidence based practice. Enjoy the read.
This article was originally written for Triathlete magazine in the USA and published on the 18th March 2020. It is an article written to assist with understanding if, when and how much carbohydrates eat for endurance athletes. Enjoy.