Nutrition for Endurance – How to Boost Performance
Summary: Nutrition can be a game changer between simply training and truly maximizing the benefits of your workouts. This article summarizes insights from a new review on energy intake, carbohydrates, fats, ketones, protein, fluids, vitamins, and minerals for endurance athletes. The main question is how you should eat and drink to enhance performance, both over time and leading up to competitions. The conclusion is that adequate energy intake and the right amount of carbohydrates form the foundation, while fats, proteins, and fluids should be smartly planned based on distance and workload. Currently, there is no support for ketones, and micronutrients are primarily relevant if you're at risk of deficiency.
Why nutrition is critical for endurance
Nutrition is always crucial. What to eat, how to eat, and when to eat are discussed year-round. For sedentary individuals, the focus is often on weight stability, weight loss, or health, while athletes focus more on the connection between food and training.
For athletes—especially endurance athletes who burn a lot of energy—nutrition is key. Training remains the top priority, but right after that comes nutrition: the fuel for your engine. Following are sleep, stress, medication, and equipment. In this text, we focus on nutrition, based on a new review published this past summer in the journal Current Sports Medicine Reports. The study, a review article, is titled: Energy Availability, Macronutrient Intake, and Nutritional Supplementation for Improving Exercise Performance in Endurance Athletes.
Study basis – review article and setup
The study (review) is titled: Energy Availability, Macronutrient Intake, and Nutritional Supplementation for Improving Exercise Performance in Endurance Athletes.
The studies included in the review were published in 2017 and focused on nutrition for athletic performance.
The researchers analyzed the evidence for energy intake (kcal), macronutrient distribution (fats, carbohydrates, protein), micronutrient intake (vitamins, minerals), and fluid intake. We go through each section individually in this article. In a forthcoming article, we will also delve into supplements for athletic performance.
But first, the basics—let’s dive in.
Energy intake – the foundation for performance
Energy intake is priority number one for a sustainable athletic effort over time, as well as for immediate performance. A common guideline for energy balance is 45 kilocalories per kilogram of fat-free mass per day (45 kcal/kg/day). This guideline is a good starting point but requires knowledge of your body fat percentage.
Unfortunately, not all athletes maintain adequate energy intake over time. Many also fail with timing—periods of energy deficit at the wrong time hit hard. In a study published this past summer, researchers showed that 37% of female long-distance athletes and walkers had such low energy intake that their menstruation ceased during a high-volume block ahead of the competition season. Males were also affected: 40% had reduced/low testosterone levels during the same training block due to low energy intake.
Both males and women had 4.5 times as many fractures/injuries during this training block compared to training periods with calorie balance. Both males and women showed reduced metabolism, and the women also had significantly lower bone density.
These effects are obviously negative for anyone aiming to maximize training effect from a high-volume block. The recommendation is to maintain calorie balance or a calorie surplus during high-volume training and competition season to maximize training benefits and well-being. If you still want to lose a few kilos during this period, the calorie deficit should be a maximum of 250–500 kcal/day to maintain performance.
Carbohydrates – the fuel that controls intensity
Here are the recommended daily intakes for an endurance athlete. As a reference value at the population level (i.e., not specifically for athletes), the recommendation is 250–300 g of carbohydrates per day, with a maximum of 50 g coming from added sugar. This corresponds to about 4 g/kg of body weight for a 75 kg person — but based on a daily energy intake of only 2000 kcal, which is low for most endurance athletes. As an athlete, your normal diet likely exceeds 5 g of carbohydrates per kilo of body weight.
Daily intake depending on training load
Recommendations:
- Light training – 3–5 g of carbohydrates/kg body weight per day.
- Moderate training – 5–7 g of carbohydrates/kg body weight per day.
- Intense training with high volume – 6–12 g of carbohydrates/kg body weight per day.
In addition to the above, you gain extra benefits from proper carbohydrate loading with 8–12 g of carbohydrates per kilo of body weight per day 36–48 hours before competition.
Carbohydrate loading and the last meal
Carbohydrate loading is part of classic peak performance preparation. The last meal before competition should contain 1–4 g of carbohydrates/kg of body weight and be consumed 1–4 hours before start. Imagine consuming 4 g/kg of body weight if you eat 4 hours before, 3 g/kg if you eat 3 hours before, and so on. Example: a breakfast three hours before the start for a 75 kg male should contain about 200 g of carbohydrates — and keep it simple. No spinach leaves, celery, or fiber-rich oats right before the start (who even eats celery before a competition?) — you get the point. 😉 Keep it simple.
Under 60 minutes — mouth rinse and effect
A competition duration of less than 60 minutes does not require carbohydrate intake for performance. Here, mouth rinsing with concentrated sports drink or gel is often sufficient. This has been shown to increase performance by 7–14% in 60-minute time trials on a bike.
James et al. (16) examined competitive male cyclists after an overnight fast who were randomly assigned three trials where they mouth rinsed for 5 s with either a 7% or 14% maltodextrin solution, or a taste-matched placebo, every 12.5% of total exercise duration. Cyclists completed the time trial faster (P G 0.001) during the 7% (57.3 T 4.5 min) and 14% (57.4 T 4.1 min) carbohydrate rinsing treatments, compared with placebo (59.5 T 4.9 min).
Over 60 minutes — mixed carbohydrates
For performances over 60 minutes, carbohydrate intake with mixed carbohydrate types, such as glucose and fructose, provides the greatest performance benefits. More about carbohydrates and sports drinks can be found in the following articles:
Fat — timing is rarely the bottleneck
At least 20% of the energy in your diet should come from fat. It's a good guideline to achieve the energy intake required over a day for an endurance athlete. Furthermore, there are few specific guidelines as fat isn't a "deficient" fuel that needs to be timed with training.
Increasing fat intake and/or reducing carbohydrate intake, fasting, or doing long sessions with low carbohydrate intake are different methods to boost the body's ability to use fat as fuel. This is called metabolic flexibility, the ability to switch between fats and carbohydrates as fuel, and is useful if you are competing in distances over approximately 2.5 hours. Avoid or reduce carbohydrates on easier sessions where the aim is to rack up miles — that's when you train fat adaptation.
There is no evidence that fat intake during activity increases performance compared to an equivalent energy amount from carbohydrates or protein. In ultra distances (24–96 hours) where energy stations are missing, energy-dense, fat and carbohydrate-rich foods can be practical.
Metabolic flexibility and greater use of fat as an energy source to spare limited glycogen stores can improve exercise performance in ultra-endurance events (93 h) (23). Improved fat oxidation can be achieved through training (e.g., long, slow duration exercise) or through dietary manipulation such as fasting, acute pre-exercise intake of fat/ketones, and by high-fat, low-carbohydrate diets (1).
If you want to geek out more specifically about MCT fat and potential performance benefits, you can find info here.
Ketones — no support currently
Currently, there is no support that ketosis or ketone supplements enhance performance regardless of distance.
Pinckaers et al. (26) published a review on ketone supplementation and concluded that there is currently no evidence to support the use of ketone bodies as an ergogenic aid.
More info on ketones and performance can be found here and here.
Protein – for recovery rather than immediate effect
Protein intake should range from 1.4–2.0 g/kg body weight per day for an athlete. For our 75 kg reference person, this corresponds to approximately 100–150 g of protein per day. A small amount of protein, either as a complete protein or in the form of amino acids during activity, does not immediately enhance performance but can facilitate recovery.
Adding protein to a carbohydrate beverage/gel during exhaustive endurance exercise suppresses markers of muscle damage 12 to 24 hours post-exercise and decreases muscular soreness. Therefore, the position statement recommends 0.25g of protein/kg/h along with 30 to 60g/h carbohydrate for endurance activities longer than 1 hour.
More info about protein here.
Hydration – a plan beats thirst during longer sessions
Hydration is extremely important, and clear guidelines are needed here too. Thirst often serves as a good indicator, but drinking ad libitum (according to thirst) is not as optimal as following a planned hydration schedule when the activity time becomes longer.
In a study on cyclists who rode 3×5 km at 50% of maximum power (max watts) followed by a 5 km time trial with a 3% incline, participants either drank according to thirst or in a structured manner with intake every kilometer that matched sweat loss. Those who drank in a structured way were better hydrated when the time trial started. Those who drank in a structured way averaged 30.2 km/h, while those who drank according to thirst averaged 28.8 km/h — about a 4.5% performance difference in favor of the structured intake.
The conclusion is that during race-like training sessions, you should weigh yourself before and after to understand how much fluid you lose. When preparing the nutrition plan for a race, include hydration and try to compensate for fluid loss through sports drinks or water plus electrolytes.
More info on hydration here.
Micronutrients / Vitamins & Minerals – mainly important in case of deficiency
In summary, a balanced diet usually covers the micronutrient needs. Vegetarians and vegans are recommended to supplement with vitamin B12, iron, calcium, D‑vitamin, riboflavin, and zinc. These vitamins and minerals are important for optimal health, but intake above reference values has not been shown to increase performance — more is therefore not always better. Focus on avoiding deficiency.
More on, for example, D‑vitamin for us northerners is here.