top of page


Biochemist and exercise scientist Kirsten Flanagan, a former surfski champion turned triathlete and mountain biker, presents a guide to endurance athlete nutrition.

Kirsten Flanagan has a BSc Human Physiology & Biochemistry and Medical Honours in

Exercise Science. She is a Business Development Manager at TAILORBLEND with a mission to bring the benefits of personalised nutrition to people globally. With a passion for health

optimisation and high performance, Kirsten leverages her athletic career and scientific background to help individuals tailor their nutrition and supplementation strategies to

achieve health and performance goals.

As an endurance athlete, it’s vital to understand the significance of proper nutrition in enhancing performance.

Despite investing ample time, resources and effort into our training, coaching and equipment, we put little energy into the fuel that drives our athletic pursuits. Good nutrition not only benefits athletic performance but also contributes to overall health.

In this article, we’ll delve into the essentials of an endurance athlete’s diet, covering aspects such as caloric intake, macronutrient balance and the appropriate timing of these nutrients.

Overall calorie intake

Before we get into the three macronutrients (protein, carbohydrates and fat), one of the most important aspects when considering one’s diet is the overall calorie intake – how many calories are consumed in a day. Exercise causes a temporary stress response, leading to adaptations within the body that result in improved fitness and resilience. Adequate recovery and adaptation after training sessions require sufficient energy resources. If you’re in a caloric deficit, your body may resort to breaking down muscle tissue to fuel repair processes, hindering proper recovery.

The ideal caloric intake depends on various factors such as the type, intensity, duration and

frequency of physical activity, as well as body composition goals. Although online calculators

can provide a starting point, determining your specific caloric needs may require some self experimentation. Total intakes can range from 2 500 up to 6 000+ calories a day. Ultimately,

it is crucial to make sure you have enough raw materials to support your athletic demands.

While we might be following the same training program, it should come with no surprise that

our response to foods is extremely individualised. We can, however, follow some basic guidelines as athletes: protein should remain stable and a priority, and carbs and fats should be levers; adjusting them up and down strategically, depending on performance goals and training intensity.

Let’s dive into each macronutrient to understand its role in the diet.


Endurance athletes tend to focus solely on carbohydrates for performance enhancement, but protein plays a crucial role too. Protein requirements vary based on several factors such as weight, body composition goal (maintaining weight, building muscle, or reducing fat) and level of physical activity. Athletes training 10 or more hours per week in particular have higher protein needs.

Throughout the day, the body continuously undergoes periods of muscle protein breakdown

(MPB) and muscle protein synthesis (MPS), together called muscle protein turnover. Muscle

protein synthesis is the process of building new muscle tissue. When MPS chronically exceeds MPB, resulting in a positive net protein balance, we can expect muscle growth over the long term. Every meal not only represents an opportunity to build and repair muscle tissue by activating MPS, but also to prevent muscle loss.

After training, your muscles are more receptive to the muscle-building effects of protein and are undergoing more MPB. If you have exercised on an empty stomach, your body is in a negative protein balance making it important to consume protein as soon as possible. If not, aim to consume it within a couple of hours. The specific time frame for optimal protein intake depends on the amount of protein still being digested from previous meals.

Even if you’re not a powerlifter, eating adequate protein is crucial as it helps build body tissues and organs, regulates glucose and fat metabolism, strengthens the immune system, and contributes to faster injury recovery, increased strength and mobility, and reduced risk of falls and injuries. Muscle health impacts your quality of life – seems like a no brainer to focus on maintaining muscle mass, right?

Protein quantity

The recommended daily allowance (RDA) for protein, 0.8g/kg body weight, only represents the minimum amount required to prevent malnutrition, not the ideal intake for athletes. Endurance athletes in particular, have a higher protein requirement, and should consume between 1.4g to 2g of protein per kilogram of body weight (g/kg). For a 65kg athlete,

that’s 91-130g of protein per day. A simple formula to determine your daily protein

requirement is: your weight (kg) x 2.0 (g) = protein per day (g)

To ensure optimal muscle protein synthesis, aim to consume 30-40g of protein per meal, as this is the optimal range for muscle protein synthesis. A bowl of oats, or peanut butter on toast provides less than 15g of protein for breakfast – not enough to stimulate MPS.

As we age, our muscle mass decreases by 1-2% each year and is replaced by fat. This decline in muscle mass and strength is due to ‘anabolic resistance’ whereby older adults need to consume more protein and engage in more resistance exercise to maintain and build muscle. So, instead of thinking you should eat less protein than your children, consider increasing your protein intake as you age.

Protein quality

A food’s amino acid profile, leucine content and digestibility and absorption determine its protein quality. All proteins are made up of 20 amino acids, of which nine are essential amino acids (EAA) – those that need to be obtained through diet. All 20 amino acids are required to build muscle, but it is the level of EAA in the blood that triggers muscle protein synthesis, with leucine, in particular, being needed in amounts of 2.5g or more to trigger MPS. The minimum 30g per meal represents the average amount of protein required to obtain a minimum of 2.5g of leucine.

Animal proteins are typically high in all EAAs, making them ‘complete proteins’. On the other

hand, plant proteins are ‘incomplete proteins’ but this does not make them bad. To compensate for their lower quality, it is possible to include plantbased protein isolates such as rice or hemp protein powder, combine different protein sources to complement their amino acid profiles (eg, rice and hemp, or beans and quinoa), or supplement with leucine (2-3g) or essential amino acids to achieve the leucine threshold.

The key takeaway is ensuring a consistent supply of essential amino acids throughout the day, regardless of the protein source, be it plant or animal.


It is important to understand the types of carbs that should make up the majority of your diet. Complex carbs such as fibrous vegetables, starchy vegetables, fruit and whole grains should make up the bulk of your carb intake, while simple sugars such as bars, gummies and gels should only be consumed in small amounts, since they lack nutrients.

Training volume and intensity determine how many carbs you need. For the recreational athlete, a daily intake of 3-5g/kg of body weight is sufficient, while endurance athletes training for 1-3 hours per day need 5-8g/kg. Extreme endurance athletes training for 3-4 hours per day require 8-12g/kg.

While carbs are central to peak athletic performance, you want your ‘metabolic machinery’ to be able to burn both carbs and fats during training and racing. Metabolic flexibility refers to the ability of our cells to switch between carbohydrates (glucose) and fats (fatty acids) as needed during exercise. At low intensities, fat oxidation is the main energy source while at high intensities, carbohydrate oxidation increases to meet the body’s need for a faster energy source.

By understanding this, endurance athletes can periodise their carbohydrate intake to promote metabolic flexibility. This is called ‘fuelling for the work required’ by strategically placing your carbohydrates before, during and after more intense sessions when they’re needed most.

A strict low-carb diet has been shown to worsen athletic performance at high intensities.

While increasing fat oxidation through reducing carbohydrate intake and increasing fat intake can enhance the muscle’s ability to burn fat, it also decreases its capacity to burn carbohydrates, potentially impacting high-intensity performance like hill repeats or that sprint finish.


Once you’ve determined your daily protein and carb targets, the remaining calories should come from fat, which is typically 25-30% of total calories. For example, if your daily caloric intake is 3000kcal, that’s approximately 750-900kcal or 84-90g of fat.

Among the three macronutrients, fat is the most calorie-dense with 9kcal per gram, compared to 4kcal per gram for both carbohydrates and proteins. However, fats are oxidised (burned) slower than carbohydrates, which is why during low-intensity, steady-state exercises, fats play a crucial role.

Different types of fats, including polyunsaturated, monounsaturated and saturated, are all necessary for optimal health. However, polyunsaturated fats are relatively unstable and can oxidise and become damaged when processed, heated, or left to age, leading to inflammation and negative health effects. To avoid this, it’s important to watch out for seed oils, such as canola, soybean, rapeseed, and palm oil, which are commonly used in processed foods.

Instead, aim to get fats from whole foods that are nutrient-rich and of high quality, such as meat, fatty fish, nuts, seeds, eggs and avocado. When choosing oils, select pure olive

oil, avocado oil or coconut oil and avoid seed oils.

Balancing weight loss and performance

Weight loss is a common goal for many athletes, and there are a variety of tools that can be

used to achieve this all while still maintaining and sometimes improving performance. While

traditional weight loss strategies focus on simply reducing overall calorie intake, more specific and targeted methods are now being explored to enhance fat-metabolism and optimise fat burning during exercise. For example, fasted training involves having athletes do morning sessions without eating breakfast, and time-restricted feeding aims to reduce the number of hours over the day that someone is eating. Another tool, ‘lowglycogen

training’, is achieved by performing two sessions close together, with limited carbohydrate

intake in-between the sessions. The first is usually high intensity, the second lower intensity,

upregulating fat oxidation pathways.

However, it’s important to note that the focus should be on body composition rather than simply losing weight. This is achieved by increasing protein intake overall to 1.6-2.2g/kg. Building muscle mass and carrying out more load is the ultimate goal, as staying at a weight below what is best for one’s body can have negative health, physiological and psychological consequences. Thus, these tools should be used wisely and with caution, as overuse can result in low quality training.

Finally, it’s worth mentioning that high training loads coupled with constant eating is not exactly a longevity-promoting lifestyle. Emerging scientific evidence supports the notion that caloric restriction can increase lifespan. To maximise the benefits, consider incorporating intermittent fasting or longer fasting periods into your off season routine. This will activate the process of autophagy, which helps to cleanse the body of damaged and old cells, as well as cellular waste.

As an endurance athlete, you put extra demands on your body, from physical performance to

cognitive function. Optimal nutrition is key to meeting these demands and achieving your goals. Focus on eating enough, a diverse range of high quality foods, and ensuring adequate protein intake. Know what your macronutrient targets are based on your training and goals, and use them as a starting point to make adjustments. Don’t be afraid

to experiment to find what works best for you, as this is the only way to unlock your full potential.


bottom of page