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Nutrition for Marathon Swimming Events

Preparing for a 12-hour endurance swimming event, such as a channel swim or marathon swim, requires meticulous planning, especially regarding nutrition. The athlete’s diet plays a crucial role in optimising performance and ensuring they have the necessary energy to sustain such an extensive physical challenge. This blog outlines key nutritional strategies, supported by peer-reviewed research, to help athletes prepare effectively in the weeks leading up to their event and on the day itself.

Pre-Event Nutrition

Carbohydrates: The Primary Fuel Source

Carbohydrates are the primary fuel for endurance athletes. They are stored in the muscles and liver as glycogen, which is essential for prolonged physical activity. Research indicates that endurance athletes should aim to consume 5-12 grams of carbohydrates per kilogram of body weight per day in the days leading up to the event (Burke, L. M., et al., 2011).

Example: For an athlete weighing 70 kg, this translates to 350-840 grams of carbohydrates daily. The exact amount depends on the intensity and duration of training sessions.

Sources: Complex carbohydrates such as whole grains, fruits, vegetables, and legumes should form the bulk of the diet. Simple carbohydrates like sports drinks and gels can be used around training sessions to provide quick energy.

Proteins: For Recovery and Muscle Repair

Protein is vital for muscle repair and recovery. Endurance athletes should aim for 1.2-2.0 grams of protein per kilogram of body weight per day (Phillips, S. M., & Van Loon, L. J., 2011).

Example: A 70 kg athlete would need 84-140 grams of protein daily.

Sources: Lean meats, fish, eggs, dairy products, legumes, and plant-based proteins like tofu and tempeh are excellent sources.

Fats: The Secondary Fuel

While carbohydrates are the primary energy source, fats are also important, especially for long-duration events. Endurance athletes should aim to get 20-35% of their total daily calories from fat (Jeukendrup, A. E., & Gleeson, M., 2019).

Sources: Healthy fats from avocados, nuts, seeds, olive oil, and fatty fish like salmon are ideal.

Hydration: Staying Well-Hydrated

Hydration is crucial for endurance performance. Dehydration can significantly impair performance and increase the risk of heat-related illnesses. Athletes should aim to drink 0.5-1 ounce of water per pound of body weight per day (Sawka, M. N., et al., 2007).

Example: A 70 kg (154 lbs) athlete should drink approximately 77-154 ounces (about 2.3-4.5 liters) of water daily, with adjustments based on training intensity and environmental conditions.

Nutrition During Training

Carbohydrate Loading

In the week leading up to the event, athletes should consider carbohydrate loading to maximise glycogen stores. This involves increasing carbohydrate intake to 10-12 grams per kilogram of body weight per day while tapering training intensity (Burke, L. M., et al., 2011).

Pre-Training Meals

A balanced meal containing carbohydrates, protein, and fats 3-4 hours before training can help maintain energy levels. A smaller, high-carbohydrate snack about 30-60 minutes before training can provide an additional energy boost (Jeukendrup, A. E., & Gleeson, M., 2019).

During Training Nutrition

For training sessions longer than an hour, athletes should aim to consume 30-60 grams of carbohydrates per hour to maintain blood glucose levels (Stellingwerff, T., et al., 2011).

Sources: Sports drinks, gels, chews, and easily digestible foods like bananas or energy bars are good options.

Post-Training Recovery

Recovery nutrition is crucial to replenish glycogen stores and repair muscle tissue. A meal or snack containing a 3:1 ratio of carbohydrates to protein within 30 minutes of training is recommended (Phillips, S. M., & Van Loon, L. J., 2011).

Example: A recovery smoothie with 60 grams of carbohydrates and 20 grams of protein.

Nutrition on Event Day

Pre-Event Meal

The pre-event meal, eaten 3-4 hours before the start, should be rich in carbohydrates with moderate protein and low in fats and fiber to minimise gastrointestinal distress (Jeukendrup, A. E., & Gleeson, M., 2019).

Example: A breakfast of oatmeal with fruit and a side of scrambled eggs.

During the Event

Given the duration of the event, it’s crucial to maintain energy levels and hydration:

1. Carbohydrates: Aim to consume 60-90 grams of carbohydrates per hour. This can be achieved through a combination of sports drinks, gels, chews, and real food like bananas or energy bars (Stellingwerff, T., et al., 2011).

2. Fluids: Athletes should aim to drink 400-800 milliliters of fluids per hour, depending on sweat rate and environmental conditions (Sawka, M. N., et al., 2007).

3. Electrolytes: To prevent hyponatremia (low blood sodium), it’s important to consume electrolytes. Sports drinks containing sodium can help maintain electrolyte balance.

Example: A mix of sports drink, energy gel, and a banana every hour.

Post-Event Recovery

Post-event recovery is crucial for muscle repair and replenishment of glycogen stores:

1. Carbohydrates: Aim for 1.0-1.2 grams per kilogram of body weight in the first hour post-event and continue with regular meals containing carbohydrates every 2-3 hours (Phillips, S. M., & Van Loon, L. J., 2011).

2. Protein: Consume 20-30 grams of protein within the first hour to aid muscle repair.

3. Fluids: Rehydrate with water and electrolyte solutions, aiming to replace 150% of the fluid lost during the event (Sawka, M. N., et al., 2007).

Example: A recovery meal of a chicken and vegetable stir-fry with rice and a fruit smoothie.

Practical Tips for Athletes

1. Trial and Error: Practice your nutrition plan during training to see what works best for you and to avoid gastrointestinal issues on event day.

2. Personalisation: Adjust portion sizes and nutrient intake based on your individual needs, body weight, and training intensity.

3. Consistency: Maintain a consistent eating schedule to keep energy levels stable and avoid large fluctuations in blood glucose levels.


Proper nutrition is paramount for success in a 12-hour endurance swimming event. By focusing on carbohydrate loading, balanced macronutrient intake, adequate hydration, and strategic fuelling before, during, and after the event, athletes can optimise their performance and recovery. Adhering to these guidelines, and tailoring them to individual needs, can make a significant difference in the athlete’s endurance and overall performance.

By incorporating these strategies and ensuring that nutrition is personalised and tested during training, athletes can enhance their performance and endurance for a successful marathon swim.


• Burke, L. M., Hawley, J. A., Wong, S. H. S., & Jeukendrup, A. E. (2011). Carbohydrates for training and competition. Journal of Sports Sciences, 29(sup1), S17-S27.

• Phillips, S. M., & Van Loon, L. J. (2011). Dietary protein for athletes: From requirements to optimum adaptation. Journal of Sports Sciences, 29(sup1), S29-S38.

• Jeukendrup, A. E., & Gleeson, M. (2019). Sport Nutrition: An Introduction to Energy Production and Performance. Human Kinetics.

• 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.

• Stellingwerff, T., Spriet, L. L., Watt, M. J., Kimber, N. E., Hargreaves, M., Hawley, J. A., & Burke, L. M. (2011). Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. American Journal of Physiology-Endocrinology and Metabolism, 290(2), E380-E388.

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