Fueling Your Morning Swim
Guest blog by Scott Tindal, Co-founder of Fuelin
Key Takeaways:
- Swimming increases energy expenditure significantly due to the thermic effect of water, necessitating proper pre-fueling to maximise performance.
- Fuelin uses a structured approach to pre-session and in-session fueling to ensure athletes have the energy to sustain quality swim training.
- The Fuelin traffic light carb system helps athletes select the right snacks/meals for their specific swim session intensity and duration.
The Unique Energy Demands of Swimming
Swimming is often overlooked when it comes to fueling strategies. Many endurance athletes, particularly triathletes, are meticulous about fueling for their bike and run sessions but tend to under-fuel their swims. This is a significant mistake. Swimming presents unique physiological challenges that make proper pre-session fueling non-negotiable.
One key reason is the thermodynamic effect of water. Unlike running or cycling, where the body can effectively dissipate heat, swimming occurs in a cooler environment that forces the body to work harder to maintain core temperature. This significantly increases caloric expenditure. Additionally, because swimming is a non-weight-bearing activity, it can be deceptive in terms of effort—athletes may not feel as fatigued immediately. However, energy expenditure is often much higher than one expects.
Failing to fuel adequately before a swim session can lead to sluggish performance, early-onset fatigue, and poor adaptation to training. At Fuelin, we ensure that all morning swim sessions are pre-fueled appropriately, setting athletes up for success in the water and beyond.
Fueling Strategy for Morning Swim Sessions
Morning training sessions present a challenge since athletes often swim fasted after an overnight period of glycogen depletion. While some athletes may be tempted to train fasted for body composition goals, this approach usually backfires regarding performance and adaptation. The key is to consume the right balance of fuel in the appropriate amounts based on the session's intensity and duration.
Fuelin follows a structured approach based on the session’s demands:
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Easy Swim ZONE 1-2 (Technique, Low Intensity, <60 min):
A RED snack before the session is sufficient. -
Moderate Swim ZONE 2 (Aerobic, 60-90 min):
A YELLOW snack is recommended to ensure adequate carbohydrate availability. -
Intense or Long Swim ZONE 3+ (>90 min, Threshold, VO2 Max, Race-Specific):
A GREEN snack is required to ensure sufficient glycogen availability and sustained energy.
Additionally, hydration is critical. Swimming can lead to dehydration without athletes realising it, as sweat loss is not as noticeable. Electrolyte intake, especially sodium, may be necessary for maintaining fluid balance and preventing cramping. Fuelin has a fuel/hydration testing system built into it that allows athletes to track their sweat rate during training!
Fuelin’s In-Session Fueling Rules
NOTE: The specific meals/snacks that you would have prescribed in your Fuelin plan would relate specifically to your total training load (intensity and volume), the previous week's load, your body weight, and your body weight/composition goals).
While many swim sessions are 30-60 minutes and may not require in-session fueling, longer or high-intensity sets demand strategic carbohydrate intake. Fuelin utilises rules for in-session fueling. Athletes training in hot environments or at higher intensities should also consider additional sodium intake to maintain performance.
- For <60-minute sessions: Hydration (water + electrolytes) is the focus; additional calories are not required.
- For 60-90 minute sessions: 30-60g of carbohydrates per hour can be beneficial, usually as a sports drink.
- For 90-120-minute sessions: 50-70g of carbohydrates per hour are necessary to maintain energy levels and prevent glycogen depletion.
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For >120-minute sessions: 70g+ of carbohydrates per hour are necessary to maintain energy levels and prevent glycogen depletion.
Fuelin’s Pre-Swim Snack Recommendations
Fuelin uses a color-coded nutrition system to simplify fueling decisions. Here are examples of Red, Yellow, and Green pre-swim snacks, each designed to provide the optimal balance of macronutrients for different swim session intensities.
These pre-swim snacks ensure athletes have the fuel for peak performance while avoiding gastrointestinal distress. They should be simple, practised, and built into a pre-swim routine. Ideally eaten 30-60 minutes before the swim starts, they can be consumed in 10-15 minutes to practice gut training.
Red Snack (Protein 5-10g, Fat 5-10g, Carbs ~30g)
Best for: Short, low-intensity swim sessions (<60 min).
Option 1: One banana with 1 tbsp almond butter.
Option 2: Greek yogurt (150g) with a handful of berries.
Option 3: Two boiled eggs with a slice of whole wheat toast + tablespoon jelly/jam.
Yellow Snack (Protein 5-10g, Fat 5-10g, Carbs ~50g)
Best for: Moderate-intensity swim sessions (60-90 min).
Option 1: Oatmeal (½ cup) with a tablespoon of honey or maple syrup and a scoop of protein powder.
Option 2: Two slices of whole wheat toast with peanut butter and jelly/jam
Option 3: A smoothie with 1 cup almond/cow's milk, ½ banana, and ½ cup oats.
Green Snack (Protein 5-10g, Fat 5-10g, Carbs ~100g)
Best for: High-intensity or long swim sessions (>90 min).
Option 1: A large bowl of overnight oats (¾ cups oats, almond milk, banana, honey, chia seeds).
Option 2: Whole grain bagel with peanut butter and jam, plus a glass of orange juice.
Option 3: A large smoothie with 1 cup almond or cow's milk, 1 banana, ½ cups oats, and two tablespoons honey or maple syrup.
The Bottom Line
Under-fueling morning swim sessions is one of the most common mistakes endurance athletes make. Swimming requires increased energy due to the thermic effect of water and high-intensity intervals, so pre-session fueling is essential for optimizing performance, preventing fatigue, and supporting recovery.
At Fuelin, we use a science-backed fueling approach to ensure athletes consume the right fuel at the right time. By following our structured fueling guidelines and using our Red, Yellow, and Green snack recommendations, athletes can train smarter, recover faster, and perform better.
So, before your next early morning swim, don’t make the mistake of heading to the pool under-fueled. Grab the right snack, hydrate properly, and set yourself up for a strong, high-quality session in the water! 🚀 🏊♂️
