Nutrition for Endurance

By: Jeremy Partl, RD

Heading out for a run or riding your bike isn’t going to build your strength, but it does wonders for your aerobic capacity and general fitness. Most content at Barbell Logic is geared toward training for strength, and while this article may seem to veer from that audience, some lifters also have an interest in endurance sports. Regardless, it can be insightful to explore the differences and similarities between nutrition strategies for endurance and strength training.

Fuel Usage

The best place to start is to understand how your body uses food energy during exercise.

Rapoport, B. I. (2010). Metabolic factors limiting performance in marathon runners. PLoS Comput Biol, 6(10), e1000960.

At rest, the body primarily uses fat for fuel. As we start to exercise, the body increases its reliance on carbohydrates, as carbohydrate metabolism can provide energy to the working muscles at a much quicker pace and with a less immediate need for oxygen.

Fat utilization is highest during low-intensity aerobic exercises like casual cycling, jogging, and swimming. Higher intensity activities like sprinting and resistance training rely heavily on carbohydrates.

Endurance exercise (lower intensity activity) uses more calories than high-intensity exercise, as you can see in the table below.

Adapted from AceFitness.org

In practice, this is probably due to the fact that lower intensity activity can be sustained for longer periods of time, resulting in more cumulative caloric expenditure.

What to Eat

This simple explanation of fuel usage and caloric expenditure during various activities will help us when discussing nutrition strategies.

As a side note, a lot of the recommendations are based on kilograms. To determine what it is in terms of pounds, just multiply the number of kilograms by 2.2. (100 kg x 2.2 = 220 lbs.)

Carbohydrates

A large source of heated debate among the fitness and medical communities on ideal food intake centers around carbohydrates. There is a large variation in recommendations for endurance athletes:

• “The joint position stand of the Academy of Nutrition and Dietetics (AND), Dietitians of Canada (DC), and the American College of Sports Medicine (ACSM) recommends that moderate exercise (1 h/day (h/day)) requires 5–7 g per kilogram of bodyweight per day (g/kg/day) of CHO, while moderate to high intensity exercise (1–3 h/day) mandates 6–10 g/kg/day.” ^[1]
• “Ultra-endurance athletes with extreme levels of commitment to daily activity (4-5 hr of moderate to high intensity exercise every day) may need up to 8–12 g/kg/day.” ^[2]
• “The International Society of Sports Nutrition (ISSN) recommends that athletes should employ an 8–12 g/kg/day high CHO diet to maximize glycogen stores.”^[3]

An often-described feeling by athletes of “hitting the wall” or “bonking” (associated with fatigue, reduced work, and impaired concentration) can be caused by depletion of liver and muscle carbohydrate stores. There are a number of strategies that can minimize this likelihood.

Carbohydrate Loading

In the past, it was pretty common to see athletes loading up on carbohydrates. Anybody remember pasta nights before track or swim meets? If the event is to last less than 90 minutes, it has been recommended to top off glycogen stores with at least 6 g/kg and up to 7–12 g/kg in the 24-48 hours before the event.^[4]

Critical thinking and experimentation come into play here as well. A lot of these recommendations are for elite athletes and are likely over the top for the general population. Is this necessary if you are only going to go for a 60-minute run? Not at all. By meeting adequate carbohydrate requirements the days prior, there is no need to make sure that you go above and beyond before an event.

For most people, a meal consisting of complex carbohydrates (35-60g), a full serving of easily digestible protein (20-40g), and a moderate amount of fat (8-15g) two to three hours before a session would be more than adequate. If you are pressed for time, reducing the portions and simplifying them is recommended (e.g., banana and a tablespoon of peanut butter).

Fueling During an Event

I can only imagine how much money sports nutrition companies have made off of their gels, bars, and products designed to give you a quick shot of energy. Many people have been fooled into believing they needed one of these products to get through their aerobic sessions.

If your activity is less than an hour, there is no need for additional carbohydrates. However, for activities longer than an hour, active fueling strategies may be recommended to maintain carbohydrate stores.^[5]

For events lasting one to two and a half hours, 30-60 g/hr is commonly recommended, ideally consumed every 10-15 minutes. For events lasting longer than two and a half hours, higher CHO intakes of 60–70 g/hr and up to 90 g/hr are associated with improved performance.^[6]

Again, common sense rules. If you do choose to consume something, make sure it is an easily digestible carbohydrate like a sports drink, dried fruit, a gel, or a bar.

Low Carbohydrate Fueling

Recently, interest in using a “train low” strategy involving lower intakes of carbohydrates and higher intakes of fat has been proposed to burn more fat, spare glycogen stores, and prolong time to exhaustion.^[7],^[8]

Physiologically, the basis for this rationale is actually pretty solid. Instead of relying on a small bank of glycogen stores and incoming carbohydrates, tapping into a much more vast energy supply (fat stores) could, in theory, keep energy levels stable and provide a much larger reserve. Most of the current research suggests that this train low strategy “may help improve an athlete’s ‘low gears’ (maximizing fat oxidation) for prolonged exercise at lower intensities, but at the expense of losing the athlete’s ‘high gear’ (maximal glucose oxidation) often needed during race situations.”^[9] Therefore, this strategy should likely not be employed in high-intensity training or race situations until further research is done.

Protein

Unlike many strength training enthusiasts, endurance athletes don’t put as much emphasis on protein intake. In addition, you will likely find a larger percentage of plant-based endurance athletes.

Regardless of who you are, protein is essential for the growth, repair, and recovery of muscles.

A total of ~1.2–2.0 g/kg/day (spread across 3-5 meals of high-quality animal protein) “may promote positive nitrogen balance and optimally benefit endurance athletes.”[10] For those who are plant-based, aiming toward the higher end of this range is surely recommended due to the reduced amount of essential amino acids being ingested.

Fat

Endurance athletes tend to ignore fat intake as an energy source—at least as compared to how much focus goes into carbohydrate intake—but fats are a worthy source of energy:

“Fats are fundamental components of cell membranes, playing roles in signaling and transport, nerve function, providing insulation and vital organ protection, and are the source of essential dietary fatty acids.”^[11]

Fat intake is recommended to fall between ~25-35% of your daily calories, mirroring most public health guidelines, as research has shown that chronic restriction to less than 20% of total energy puts individuals at risk of a low intake of fat-soluble vitamins and essential fatty acids. ^[12]

Consider limiting fat intake before and during events if there are GI comfort concerns.

Recovery Nutrition

While it’s often overblown, taking advantage of enhanced nutrient uptake post-exercise presents a window of opportunity to facilitate efficient recovery.

Aggressive carbohydrate refeeding at 1.2 g/kg/hr with high glycemic index foods for the first few hours post-exercise is recommended if glycogen repletion is needed quickly for another event with 4 hours of recovery time.^[13],^[14] However, it’s highly unlikely that you are going to be training again so soon.

Most people don’t know that eating a combination of carbohydrates that use different intestinal transporters for absorption (such as fructose and glucose, or pairing a grain with a fruit) can enhance carbohydrate delivery.^[15]

The addition of protein to carbohydrates can help to increase muscle glycogen repletion, helping to stimulate protein synthesis and recovery.^[16] Aiming for 0.2–0.4 g/kg/hour within the first 2 hours is recommended.

To make it simple, for most people, a solid post-workout meal may be fairly carb-heavy (40-60g) with a full serving of protein (20-40g) and moderate fat (8-15g). Obviously, this may differ for caloric needs and goals, but it is a pretty good recommendation.

Hydration

Interestingly, hydration recommendations have actually evolved over the years. While dehydration can certainly impair exercise performance and contribute to heat illness, exercise-associated hyponatremia (too much water) can produce acute illness or even death.

The recommendations from the ACSM suggest athletes drink ad libitum in the suggested range of 400–800 mL/hr.^[17] It’s important to tune into your body’s thirst mechanism, monitoring “bodily parameters such as body weight, urine color, race pace, body temperature, and environmental temperature to fine tune [your] individual hydration needs and avoid the complications of [over-hydrating].”[18]

It is recommended that you replace fluid at a rate of 150% of the fluid lost to the environment.^[19] For example, if you lost 1 kg (1000mL), you will need to drink roughly 1500mL to fully rehydrate.

Comparison to Strength Training

I previously wrote an extensive article on nutrition needs to optimize strength training. Below, I will compare the recommendations for these different training modalities.

As you can see, there is a lot of overlap between the two approaches. The main difference is carbohydrate intake, specifically during and around training sessions.

Because there is more of a likelihood for glycogen depletion with endurance training, optimizing adequate carbohydrate intake before, during, and after sessions is a big focus of related nutrition plans. Otherwise, basic sports nutrition principles for protein and fat generally are the same.

Protein intake recommendations for resistance/strength training may be a bit higher due to the increased likelihood of muscle damage with training.

In general, hydration recommendations tend to be less precise for strength training since sweat rates are less of a factor, and dehydration is not as big of a concern. Proper hydration throughout the day should be enough to ensure that you are coming into training sessions hydrated and staying hydrated for optimal performance and health.

Caloric needs for endurance activities tend to be higher than strength training due to the caloric cost of the longer sessions and perhaps more metabolically demanding activity. This is surely an area where the library of evidence could be improved.

Common Sense Thinking

For 90+% of our readers, specific fueling strategies are going to be a more advanced consideration, one that should be placed after focusing on overall nutrition habits. If you are aiming to optimize performance, then you may pay more attention to your pre- and intra-event nutrition strategies.

There is more of a likelihood with endurance training that you may reach a point of glycogen depletion. If you don’t consider overall energy expenditure, you may end up losing more weight and mass than you want to. But if you are planning on loading up on energy gels for your spin class or even a 5k, you really don’t need to focus on the advanced recommendations.

Focus on nailing the foundational principles, and let things like nutrient timing be factored in when you have the other considerations dialed in.

My goal with this article was to introduce the concepts of fueling for endurance activities and contrast them with the previous article I wrote on strength and resistance training. There are some differences and some similarities. The most important thing is that you put this information into a context that aligns with your individual goals.

^[1] Vitale, K., & Getzin, A. (2019). Nutrition and Supplement Update for the Endurance Athlete: Review and Recommendations. Nutrients, 11(6), 1289.

^[2] Vitale et al., “Nutrition and Supplement Update.”

^[3] Vitale et al., “Nutrition and Supplement Update.”

^[4] Getzin, A. R., Milner, C., & Harkins, M. (2017). Fueling the triathlete: evidence-based practical advice for athletes of all levels. Current Sports Medicine Reports, 16(4), 240-246.

^[5] Burke, L. M., Hawley, J. A., Wong, S. H., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of sports sciences, 29(sup1), S17-S27.

^[6] Burke et al., “Carbohydrates,” S17-S27.

^[7] Getzin et al., “Fueling the triathlete,” 240-246.

^[8] Getzin, A. R., Milner, C., & LaFace, K. M. (2011). Nutrition update for the ultraendurance athlete. Current sports medicine reports, 10(6), 330-339.

^[9] Vitale et al., “Nutrition and Supplement Update.”

[10] Vitale et al., “Nutrition and Supplement Update.”

^[11] Vitale et al., “Nutrition and Supplement Update.” (citing Institute of Medicine, Food and Nutrition Board. Total fat and fatty acids. In Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids; Institute of Medicine (U.S.), Ed.; National Academies Press: Washington, DC, USA, 2005).

^[12] Campbell et al., “International Society of Sports Nutrition position stand,” 8.

^[13] Jeukendrup, A. E., Jentjens, R. L., & Moseley, L. (2005). Nutritional considerations in triathlon. Sports Medicine, 35(2), 163-181.

^[14] Kerksick, C., Harvey, T., Stout, J., Campbell, B., Wilborn, C., Kreider, R., … & Antonio, J. (2008). International Society of Sports Nutrition position stand: nutrient timing. Journal of the International Society of Sports Nutrition, 5(1), 1-12.

^[15] https://www.gssiweb.org/sports-science-exchange/article/sse-108-multiple-transportable-carbohydrates-and-their-benefits

^[16] Kerksick et al., “International Society of Sports Nutrition position stand,” 1-12.

^[17] Sawka, M. N., Burke, L. M., Eichner, E. R., Maughan, R. J., Montain, S. J., & Stachenfeld, N. S. (2007). American College of Sports Medicine position stand. Exercise and fluid replacement. Medicine and science in sports and exercise, 39(2), 377-390.

[18] Vitale et al., “Nutrition and Supplement Update,” 1289.

^[19] Vitale et al., “Nutrition and Supplement Update,” 1289.