A reminder on how the bodies digestive system works

The speed read: do you remember it all…?

Your digestion is a complex process that converts food into energy. Athletes, especially endurance athletes, require careful nutritional planning to fuel performance, maintain health, and aid recovery. Key areas include managing energy through carbohydrate ingestion, staying hydrated with proper electrolyte balance, and consuming the right proteins and fats to support muscle repair and prevent injury. Proper nutrition enhances performance, mental clarity, and overall well-being, while poor habits can negatively impact long-term health and reduce life expectancy. Supplements, when used wisely, can also enhance endurance and recovery.

The starting point: A complex system whose effectiveness varies a lot depending on what we eat

The digestive system is a complex network of organs that transforms the things you eat into energy and essential nutrients. A lot of transformation happens during this process and the system is complex and therefore somewhat fragile.

Let’s start with a primary school level reminder how our digestive system works. Yeah, maybe it’s a little basic but sometimes it is fun to recap these things and we need to start somewhere.

• Mouth: Digestion begins in the mouth. When you eat, your teeth break down food into smaller pieces. Salivary glands produce saliva, which contains enzymes like amylase that start breaking down carbohydrates even before swallowing.
• Oesophagus: Once you swallow, food travels down a muscular tube called the oesophagus. Muscles in the oesophagus contract in waves (peristalsis) to push the food toward the stomach.
• Stomach: Your stomach churns food, mixing it with gastric juices that contain acids and enzymes. This process turns food into a thick liquid called chyme. Here, proteins are primarily broken down by enzymes and acid.
• Small Intestine: Chyme moves into the small intestine, where most digestion occurs. Enzymes from the pancreas and bile from the liver help break down fats, proteins, and carbohydrates. Tiny finger-like projections called villi line the walls of the small intestine, absorbing nutrients into the bloodstream. These nutrients include sugars, amino acids, fatty acids, vitamins, and minerals.
• Large Intestine: Any remaining undigested food moves into the large intestine, where water is reabsorbed. The leftover material is compacted into faeces and stored until it is excreted

Conversion of food intake to energy

• Energy Extraction: As food is digested, nutrients are absorbed into the bloodstream.
• Energy Use: These nutrients are transported around the body and used for various processes:
  • Carbohydrates are converted into glucose
  • Fats are broken down into fatty acids.
  • Proteins are broken down to Amino Acids for building and repairing tissues or converted to energy when needed.
• Storage: Your excess energy is stored as glycogen in muscles and liver or as fat in adipose tissue for later use.

Besides macronutrients (carbohydrates, proteins, fats), your body requires:

• Vitamins and Minerals: Essential for various biochemical processes (e.g., vitamin D for bone health, iron for oxygen transport).
• Hydration: Water is crucial for digestion, nutrient transport, and temperature regulation.
• Fibre: Important for digestive health; it helps regulate bowel movements and can aid in nutrient absorption.

Now another reminder from the primary school days: Good nutrition significantly enhances quality of life by providing the body with essential nutrients that support physical health, mental clarity, and emotional well-being, leading to more energy, better mood, and stronger immunity. In contrast, poor nutrition can contribute to chronic diseases, fatigue, and mental health issues, reducing life expectancy and overall happiness. A well-balanced diet promotes longevity, vitality, and a greater sense of happiness, while unhealthy eating habits can lead to diminished quality of life and long-term health problems. Studies even suggest that unhealthy dietary habits, such as diets high in processed foods, sugar, and unhealthy fats, and low in fruits, vegetables, and whole grains, can shorten life by up to 10 years [1][2][3]. 10 years! Crazy, isn’t it? And with few tweaks and following some basic easy rules we can make our nutritional habits so much healthier…

The issue: What we put into our bodies determines the quality of life for everyone - but for us as athletes it is even more critical

You are an endurance athlete. You train hard and you regularly push your body to the extremes. It should be no surprise that you have unique nutritional needs. Proper planning of your food and drink intake is crucial for optimising performance, maintaining health, and promoting recovery. Here are the ten key reasons why it's especially important for you as an endurance athletes to carefully manage nutrition:

1. Energy Requirements

• High-Calorie Demands: You know you can burn thousands of calories. If you don’t replenish their energy adequately, you risk underperformance and fatigue.
• Fueling the Muscles: Carbohydrates are your primary energy source during endurance activities. Without sufficient stored glycogen (the storage form of carbohydrates in the muscles and liver) and carbohydrates eaten, athletes can “hit the wall" or experience a sudden drop in performance. Proper pre-race and during-race fueling strategies are essential to avoid this. Yes I am talking about sugar here! But not all sugars are created equal and sugar per se is not a bad substance, it just has gotten a real poor reputation during the past years! (read my blog post ‘is sugar really the enemy?’ on this topic to learn more)

2. Glycogen Management

• Preventing Glycogen Depletion: Your glycogen stores in muscles (and liver) are limited, and once depleted, athletes experience a severe reduction in energy and endurance. Planning carbohydrate intake before, during, and after exercise helps sustain these stores, allowing for prolonged performance.
• Glycogen Replenishment: After endurance exercise, it’s vital to replenish your glycogen through carbohydrates to prepare for future training sessions. Recovery nutrition also supports muscle repair and reduces soreness.

3. Hydration and Electrolyte Balance

• Maintaining Hydration: Endurance athletes lose significant amounts of fluids through sweat, which, if not replenished, can lead to dehydration. There is quite a lot of debate about how much dehydration we can sustain before performance is impacted but at a certain level it undoubtedly reduces endurance, and increases the risk of heat-related illnesses. [8]. And, over-hydration can be fatal in the form of hypernatremia, when too much fluid is replaced without the corresponding electrolytes. [9]
• Electrolyte Replacement: In addition to water, you lose electrolytes (especially sodium, potassium, and magnesium) through sweat. Electrolytes are essential for maintaining muscle function, nerve signaling, and fluid balance. Careful intake of fluids with electrolytes prevents cramps, dizziness, and fatigue.

4. Preventing Gastrointestinal Issues

• Choosing Digestible Foods: Eating the wrong types of food or consuming inappropriate gels, drinks, or snacks during an event can lead to gastrointestinal distress like bloating, cramps, nausea, or diarrhoea. You need to carefully plan what you eat to avoid foods that are hard to digest, especially before and during events.
• Timing of Intake: The timing of meals and snacks is critical. Eating too close to an event or not eating at all can cause digestive issues or lead to a lack of energy. Planning meals at the right times ensures food is digested properly and energy is available when needed.

5. Recovery and Muscle Repair

• Post-Exercise Nutrition: After intense exercise, your muscles undergo damage and need protein for repair. Additionally, carbohydrates help replenish depleted glycogen stores. Consuming a balance of protein and carbohydrates within a critical recovery window (30-60 minutes post-exercise) helps with faster recovery and reduces muscle soreness.
• Avoiding Catabolism: If your body doesn’t receive adequate nutrition post-exercise, it can start breaking down muscle for energy, leading to muscle loss and slower recovery.

6. Avoiding Energy Spikes and Crashes

• Steady Energy Supply: Consuming fast-acting sugars or foods with a high glycemic index can cause rapid spikes in blood sugar followed by crashes, which can lead to fatigue during endurance activities. Depending on the event length and individual needs athletes may need to plan for slower-releasing carbohydrates, along with a balance of protein and fats, to provide sustained energy.
• Managing Hunger and Satiety: Proper nutrition planning helps prevent you from feeling hungry or overly full during competition, both of which can negatively affect performance.

7. Enhancing Performance

• Optimizing Macronutrient Ratios: By strategically managing carbohydrates, proteins, and fats, you can optimize their energy levels, endurance, and strength. Carbohydrate loading before an event, for example, helps maximize glycogen stores.
• Minimizing Inflammation: Certain foods help reduce inflammation and promote faster recovery (e.g., antioxidants from fruits and vegetables, omega-3s from fish). Avoiding highly processed, inflammatory foods improves long-term performance and health.

8. Reducing the Risk of Injury and Illness

• Strengthening Immunity: Proper nutrition, rich in vitamins, minerals, and antioxidants, supports the immune system. We as endurance athletes often put a lot of stress on our bodies, making them more susceptible to illness. For example, vitamin C, zinc, and a well-rounded diet reduce the risk of infections.
• Supporting Joints and Muscles: Nutrients like calcium, vitamin D, and magnesium are essential for bone health and your muscle function. Proper intake helps reduce the risk of injury like stress fractures, muscle tears, and strains.

9. Psychological Impact

• Mental Endurance: You have noticed it probably. Nutrition also affects mood, concentration, and motivation. Low blood sugar levels can lead to irritability, lack of focus, and mental fatigue. A well-thought-out nutrition plan supports both physical and mental endurance during long-distance events.
• Confidence in Preparation: Knowing you’ve prepared your body with the right nutrients gives you a psychological edge, increasing confidence in your performance.

10. Avoiding Nutritional Deficiencies

• Meeting Micronutrient Needs: Endurance athletes, particularly those training at high volumes, need to ensure they’re getting sufficient vitamins and minerals. Deficiencies in key nutrients like iron (important for oxygen transport), magnesium (crucial for muscle function) or calcium (crucial for bone health) can impair your performance and recovery.
• Tailored Diets for Specific Needs: Depending on individual metabolism, food intolerances, or dietary preferences (e.g., vegetarianism), you may need to be more deliberate in planning to avoid deficiencies that could affect endurance.

The ‘so what’: Of course you knew that nutrition planning matters a lot, here are my 5 tricks how to do it

• Fuel with Carbohydrates Strategically
  • Recommendation: Focus on carbohydrate periodization, tailoring intake based on the intensity and duration of training or competition.
  • For more guideline read the next blog post [LINK] on carbohydrates
  • Why: Carbohydrates are the primary fuel source for endurance events, and strategic intake helps you to prevent glycogen depletion and sustain energy levels.
• Hydrate and Replace Electrolytes Regularly
  • Recommendation: Develop a personalised hydration strategy based on sweat rate and environmental conditions.
  • Guideline: for more guideline also read my blog post [LINK] on electrolytes
    • Daily: Aim for 35-50 ml of water per kilogram of body weight per day, adjusting for sweat losses during exercise.
    • During exercise: Replace 400-1500ml of fluids per hour during intense training or events, and add electrolytes (especially sodium) in hot, humid conditions. That is an enormous range and you only need to be over 800ml/hour if the conditions are warm, the exercise is intense and you are exercising for over two hours.
    • Electrolyte intake: Include 500-1000mg of sodium per liter of fluid, especially for activities over 2 hours. Again, you only need the higher levels of sodium replacement in hot conditions and if you have high concentrations of sodium in your sweat.
  • Why: Proper hydration prevents dehydration, maintains performance, and replenishes lost electrolytes, helping avoid cramps and fatigue.
• Optimise Protein Intake for Muscle Repair
  • Recommendation: Ensure adequate protein intake to support muscle recovery and repair, especially post-exercise.
  • Guideline:
    • Daily: 1.2-2.0 grams of protein per kilogram of body weight, depending on training intensity. There is debate about the type of protein you need to ingest post-exercise: Collagen-based? Whey protein? Remember any protein is broken down into individual amino acids, so a protein source with a wide spectrum of amino acids is probably best.
    • Post-exercise: Consume 20-30 grams of high-quality protein (e.g., whey, plant-based) within 30-60 minutes after training to stimulate muscle repair and recovery.
  • Why: Protein supports muscle maintenance, repair, and adaptation, preventing muscle breakdown and promoting recovery after endurance efforts.
• Incorporate Healthy Fats for Endurance and Recovery
  • Recommendation: Include healthy fats in the diet for sustained energy and anti-inflammatory benefits.
  • Guideline:
    • Daily: 20-35% of total caloric intake from fats, focusing on healthy fats like omega-3s from fatty fish (e.g., salmon), nuts, seeds, and olive oil.
    • Pre-exercise: Avoid large amounts of fat right before intense sessions, as fats take longer to digest and may impair performance.
  • Why: Fats provide a longer-lasting energy source for low- to moderate-intensity exercise and play a role in reducing inflammation and supporting recovery.
• Use Supplements Judiciously
  • Recommendation: Take only evidence-based supplements that have a proven impact on endurance performance.
    • Guideline:
      • Beetroot powder: Beetroot powder is an excellent natural supplement for you if you are looking to enhance endurance, oxygen efficiency, and muscle power. Most of these benefits are due to it beingg a powerful vasodilator (relaxes blood vessel walls, making them wider), Taking 5-10 grams daily, particularly before or during exercise, can provide optimal performance benefits.
      • Caffeine: 3-6 mg per kilogram of body weight 30-60 minutes before exercise for a performance boost, but monitor individual tolerance to avoid jitteriness or GI issues. It’s almost certainly the most well-researched supplement out there!
      • Beta-Alanine: 2-5 grams per day can help buffer lactic acid and delay muscle fatigue in longer, high-intensity events. It often causes GI distress, so use with causation. Sodium Bicarbonate works in the same way.
      • Creatine: Though primarily used for strength, 3-5 grams per day can aid in recovery for endurance athletes who also perform high-intensity efforts.
      • BCAAs or EAA (essential amino acids): 5-10 grams during exercise can reduce muscle breakdown, especially for events lasting over 3 hours.
      • Vitamin D: Ensure adequate levels (2000-4000 IU/day) if not exposed to enough sunlight, as vitamin D is crucial for bone health and immunity.
    • Why: Supplements like beetroot powder, caffeine, beta-alanine, and creatine have been shown to enhance performance and recovery when used appropriately, but it's essential to tailor supplement intake to individual needs and training loads.

Sources:

[1] Global Burden of Disease Study (GBD). The Lancet, 2019.

[2] British Medical Journal (BMJ). 2022 study.

[3] Harvard T.H. Chan School of Public Health. Nurses’ Health Study and the Health Professionals Follow-up Study.

[4] Nemours KidsHealth. Digestive System (for Teens). Available at: https://kidshealth.org/en/teens/digestive-system.html

[5] National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK). Your Digestive System & How it Works. Available at: https://www.niddk.nih.gov/health-information/digestive-diseases/digestive-system-how-it-works

[6] WebMD. Digestive System (Anatomy): How It Works. Available at: https://www.webmd.com/digestive-disorders/your-digestive-system

[7] Cleveland Clinic. Digestive System: Function, Organs & Anatomy. Available at: https://my.clevelandclinic.org/health/body/7041-digestive-system

[8] Gatorade Sports Science Institute. Does Dehydration Really Impair Endurance Performance? Recent Methodological Advances Helping to Clarify an Old Question. Available at: http://www.gssiweb.org/sports-science-exchange/article/does-dehydration-really-impair-endurance-performance-recent-methodological-advances-helping-to-clarify-an-old-question

[9] Hew-Butler, T. et al. Exertional Dysnatremia in Collapsed Marathon Runners: A Critical Role for Point-of-Care Testing to Guide Appropriate Therapy. American Journal of Clinical Pathology, 2009, 132(3), pp.336–340. Available at: https://academic.oup.com/ajcp/article/132/3/336/1765408