The role of nutrition in endurance sports

South Africa is proud host of some of the world’s most renowned ultra-distance and stage races: Comrades, Two Oceans Marathon, Sani2Sea, the Cape Town Cycle Tour, Cape Epic, and the Wild Run multi-day trail running events altogether draw around hundred thousand athletes from all over South Africa and overseas to participate in often unique settings. What does it take in terms of training, and particularly with respect to nutrition to prepare optimally for such endurance events? 



Lisa is OmniBlend’s Sales & Marketing manager, and avid runner. In this series she’s sharing what she learned about training for an endurance event, specifically in terms of nutrition.


Trail runners flock to races held in Africa's most rural areas. One event on the Wild Run calendar is the Wild Coast Wild Run, and this is such a race that offers a unique course. Along the pristine coastline of the Eastern Cape, it allows trail runners to get onto the cattle tracks entering the grasslands of the Nguni cattle. You're crossing rugged cliffs, and running alongside the beaches of the Indian Ocean. It takes runners into rural South Africa, passing just a few rondavels, running from hotel to hotel with incredible views over the ocean.


No wonder when I heard about that race, I wanted to be part of it (read more about my history with running here), so I entered the 11thedition of the Wild Coast Wild Run, taking place 1-3 September 2019. After signing up for the Wild Run, and realising that this type of endurance stage race requires you to train your metabolism, I met with Adrian Penzhorn, qualified sports scientist with a Medical Honours degree in Nutrition and Dietetics from the University of Cape Town.

Adrian is a registered dietician specialized in sports dietetics, and through his work at The Performance Kitchen as a sports nutrition coach developing meal plans for athletes that are customised for their training plans, he’s got a wealth of knowledge and experience. The perfect guy to explain the concept of running efficiency in a bit more detail!

As a sports nutrition coach Adrian is used to explaining the concept: “To understand how your body fuels you during your run, you firstly need to understand the difference between your aerobic and anaerobic zones. When you’re running a comfortable easy pace, and you’re able to talk with your running buddy, you’re in your aerobiczone: for most people, the body is usingprimarily fat for energy, and there’s sufficient oxygen in your blood that is used by the muscles to process that energy on a cell level. Your body wants to use fat to spare glucose and glycogen, but it takes time. When you’re running a bit faster, and feel like you’re getting slightly out of breath, you’re moving into your anaerobiczone. This is where the muscles have too little oxygen to be able to keep up with the energy needs (it needs to create energy quicker), and need to shift from the most efficient fuel source (fat) to using glycogen (sugar) for fuel.”

Adrian adds on: “The key to this is that aerobic metabolism of fat is a slower process, your body wants to use it and spare glucose and glycogen but it takes time – so when the demand for energy and rate it is required is low you can use fat. At higher intensities the demand for energy is higher, you need to create it quicker and carbs are the chosen fuel for this.”

Adrian is taking a breath as he notices my desire to connect the dots about what I’ve heard Dr Bob Seebohar talking about in the Run to the Top podcast. He explains: “You notice that the ratio of fat versus carbohydrate burning changes constantly with increasing (or decreasing) intensity, and this is the crossover concept that Dr Bob Seebohar is referring to. The crossover point is where we move from predominantly fat to predominantly carbohydrate metabolism. Seebohar talks about the Metabolic Efficiency as the body’s ability to optimally use fat (vs carbs) as burning fat doesn’t have the waste products that develop on a cell level in the anaerobic zone, and more important: the body is able to store much more fat than carbs, or glycogen.”

Now that’s interesting: the body is able to store about 1600 calories in glycogen (carbs), and a relatively unlimited supply of calories from fat. For endurance events, when you need fuel for a good couple of hours, you want to make sure you’re using your fat reserves as much as possible as the supply is basically endless (even for the leanest of runners).

Adrian continues to explain how nutrition supports to improve your body’s ability to use fat as the main fuel source: “It’s actually quite simple, but still often overlooked, that to make sure your body shifts the ratio of fat vs carbohydrate burning, you’ll want to make sure that your food intake is also shifting that ratio. You’ll want to restrict your carbs intake to prevent your body from having immediate access to glycogen and glucose. When you do this, your body needs to turn to fat for fuel.”

He looks at his hands to explain the concept using Seebohars ‘Hand Model’: “Seebohar’s Metabolic Efficiency Training is aimed at managing your blood sugar level. When you’re consuming predominantly carbs, they are readily available either as simple sugars from the meal you’ve just eaten or the glycogen you have stored in your muscle and liver. You want to train your body to start using fat for fuel, and you do this by changing the carbohydrate to protein ratio. The aim is to consume carbohydrates and protein in a 1:1 or 2:1 ratio, depending on your energy needs as part of your training intensity. To keep things simple, when you want to determine the right ratio for your meal, you want to use 1 palm for protein, and the other palm for carbohydrates.”

The analytical brain in me wants to understand the why and how of this concept, so I ask Adrian to explain further: “With a lower carbohydrate intake your body is less reliant on using them as a fuel source. On a cellular level, the mitochondria (the energy producers in your cells) are starting to use fat as fuel turning this into energy. This is an adaptation on cell level that is required to become more energy efficient in the long run. Once your body, or actually the mitochondria have adapted to burn fat they will be more efficient at continuing to do so at rest and lower exercise intensities.

The beauty of this adaptation process, for overall health and well-being, is that once you’re able to effectively burn fat, you’re likely able to use both fuels, fat and carbs. It’s called ‘metabolic flexibility’, and it basically means that your body is able to burn carbs when you’re eating carbs or need carbs for high-intensity exercise to perform. Then you’re able to move back to fat for fuel when you’re eating fat, not eating at all or don’t have a high energy need. This type of flexibility ensures that you can effectively use a wider variety of nutrients, and tap into either fat or carbs to fuel different activities. Your body doesn’t rely on a constant supply of food and snacks as it can burn fat in between meals to keep your energy levels up. It’s also able to manage blood sugar levels (as your insulin sensitivity is better) so you don’t crash an hour after lunch as it can effectively metabolise carbs too.

Adrian adds that for exercise performance you don't want to completely remove carbs from your diet: "Through a removal of carbs as a substrate all the enzymes and processes involved in absorbing and metabolising them are blunted such that when you return to consuming them the processes for handling and fueling are worse off and high intensity exercise will suffer. A nice way of explaining this that I have come across is losing the 4th and 5th gear of your your car."

As long as you stick to mostly wholefoods your body is able to effectively use the nutrients for fuel. Your carb intake should be tailored to your activity levels, so eat more carbs when you’re exercising hard (2:1), and go easy when you’re not. The mitochondria play a key role in this process, and that’s why it’s so important that they function well. Aside from the fat-adaptation mentioned before, exercise is key to create and improve mitochondrial function. Long slow runs and interval training are both excellent to support the body to create new (and better) mitochondria.

Now understanding the theory behind metabolic efficiency, I want to get started. First thing is to establish my current fat oxidation level, which can be determined by taking a Fat Max test at the Sports Science Institute of South Africa. At the same time Adrian asks me to keep a food diary for a week, recording all my meals & snacks for him to get a view of my current nutrition, and give recommendations on where improvements can be made.


Next: The Fat Max test and relevance of keeping a food diary

Previous: What I didn't know about training for an endurance event



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