Triathlon season is upon us and there are a growing number of endurance events to choose from. Triathlons incorporate three activities; swim, cycle and run. That’s the order of events with varying durations.

Short course triathlons such as Sprint and Olympic distance races take an average of one to three hours. Middle distance IRONMAN 70.3’s and T100 races last an average of six hours, while full distance IRONMAN races average 13-14 hours so there’s a huge range! Transitioning between distances is part of the race, so you need to be quick. A plan is required to ensure your body is correctly fuelled for the race duration.

Triathlon nutrition can be complex, as you may need separate nutrition plans for each discipline. If your event is a 13-hour IRONMAN, you will have increased nutrition needs as your race will continue over mealtimes and you’ll be burning off energy that needs replacing. Carbohydrate nutrition supplements are well known to have affects disrupting the gastrointestinal system and will need to have been practiced in your triathlon training.

Triathlon Nutrition Guide

Read further to explore each discipline and the key principles of triathlon nutrition during training. We’ll aid you through the whole triathlon diet, pre-race, race day, in race and post-race nutrition. We will also share hydration strategies, best and worst diets, supplements and common triathlon nutrition mistakes that should be avoided.

Triathlon nutrition for training

This section will look at the key triathlon nutrition principles during training and tips. Intense training sessions which mimic race day should be used to trial race-day nutrition plans.

Fuelling for swim training

Carbohydrates are the main macronutrient the body uses as a fuel source. The body can only store carbohydrate for 90-120 minutes’ worth of vigorous exercise. Carbohydrate is stored as glycogen, mainly in skeletal muscles and acts as the primary fuel source. muscles. If your planned session exceeds this you will need to plan a pre-training carbohydrate snack.

Give yourself sufficient time to have a snack before swimming, consider 1-3 hours before the session begins. Research suggests 60-90g of carbohydrate (CHO) is recommended for prolonged exercise. Some examples include:

  • 2 slices of bread (30g CHO) with a banana (~25g CHO)
  • Eight Medjool dates (40g CHO)
  • Bowl of granola (~30g), ½ cup blueberries (~10g) with glass of milk (~11g)
  • CLIF oat bar (~45g)

Amounts calculated are based on servings sizes and will vary across brands, check the ‘Carbohydrate’ section on food labels.

Fuelling for bike training

The body can tolerate taking on around 60-90g of carbohydrate per hour, but this varies person to person and the gut needs to be trained to manage this intake.

The bike section is easiest to take on nutrition compared to the swim and run. The gut is stable, periods of downhill mean you’re less out of breath and can chew and, you can carry a variety of carbohydrate foods.

Opt for fuel sources that work for you.  You’ll want to aim for 60-90g of carbohydrate per hour, though if you’re taking on a longer event like a full IRONMAN you will want to consider training your body to take on more than 100g of carbohydrate. Consuming more carbohydrates on the bike will help to maintain energy for the run.

Options to consider are carbohydrate premixed drinks, gels, chew blocks, energy bars, and bananas. There’s a host of brands to choose from, and different products work for different people. Some brands include SIS, precision fuel, GU, Veloforte, Hi5, Maurten and Clif to name a few! For longer event triathletes, consider bike accessories to ensure you can carry all your nutrition.

Those taking on longer endurance events like IRONMAN may find they struggle with taste fatigue and hunger levels, and therefore real food may be desirable. In this case, ensure the foods travel well, are easy to eat/open on the move and are rich in carbohydrates. Examples include bagels, crumpets and bananas.

Fuelling for run training

Gastrointestinal issues or ‘runners trots’ can occur in the run stage due to the increased gut jostling, so ensure to have trained with the brand and amounts of carbohydrate you intend to consume.  At this stage of your triathlon, fuel should be easy to consume and swallow such as gels or ready-made carbohydrate drinks. Timers on smartwatches might be useful to remind you when to take on nutrition.

Pre-race nutrition for triathletes

What to eat the night before a triathlon? This section will focus on nutrition up to the day of the triathlon.

Carbohydrate loading

Muscles can store carbohydrate as glycogen for up to 2 hours of vigorous exercise. Stores get depleted during triathlons, to ensure they are at capacity on race day it’s advised to increase their carbohydrate intake 2-3 days leading up to the race. Recommendations for athletes who exercise at a high – very high intensity require 6-12g/Kg of body weight per day. Examples include potatoes, pasta, grains, beans, fruits and vegetables. Opting for simple carbohydrates with less fibre will provide quick releasing energy needed for racing. You may also want to take electrolytes before race day to ensure adequate hydration. (Continue reading for more hydration tips!)

Carb loading meal and snack ideas
Jacket potato with tuna
Pasta bake
Jam and peanut butter sandwich
Porridge with toppings
Smoked salmon bagel with low fat cheese
Sweet potato with chicken


Foods to avoid:

  1. High fibre. In the lead up to the race, you want to ease up on fibre so that carbohydrates are easy to digest. Reduce the amount of fruit and vegetables and transition to simple carbs.
  2. Spicy. Generally, you want to stick to plainer foods, and those that are trialled and tested to avoid stomach disruption.
  3. High fat. Foods high in fat take longer to digest and can make you feel sluggish, so avoid high fat foods before race day!

Race day nutrition for triathletes

Give yourself enough time on the morning of the event, eat at least 2 hours before swimming. Considering what’s already been discussed, opt for a low fibre, high carbohydrate breakfast. If you usually take caffeine, do so as normal unless you have practiced an alternative caffeine plan (More on caffeine and hydration below!).

Race day breakfasts
Toasted white bread with jam/honey/ banana
Overnight oats with honey and banana
Bagels with jam/ banana/ honey
Crumpets with jam/ banana/ honey


In-race fuelling for triathletes

In short distance triathlon’s, your breakfast might suffice, but for those doing longer distances, a gel before starting can maintain glycogen stores. Unlike the other disciples, you won’t have a chance to take on nutrition during the swim for obvious reasons.

Within 15-20 minutes of settling into the cycle, start taking on nutrition. You may want to consume food such as an oat bar, a bagel or chew blocks. Depending on which fuel source you opt for, aim for 60-90g carbohydrate per hour. It’s more likely you can aim for the higher end while on the bike. This will look like 2-3 gels or 500ml ready-made carbohydrate drink per hour.

You might experience taste fatigue and want to swap from chew blocks to gels as you start running. Gels are easy to consume and are designed to deliver fast energy. If you have trained your gut to consume gels while running, continue to aim for 60-90g carbohydrate, however you may find at this point it’s more realistic to aim for the lower end of 60g/hour.

Hydration strategies in triathlon

Let’s not forget hydration as part of triathlon nutrition. Appropriate hydration is essential to maintain blood volume, solely drinking water can dilute sodium levels in the blood leading to low sodium. Sodium is important for muscle contraction, nerve impulses, cognitive function and nutrient absorption, so be sure to maintain levels.

Consider alternating between electrolytes and water or taking on some electrolyte tablets separately. Some gels include small quantities of electrolytes; however, you can also get electrolyte tabs & chews. It can be helpful to separate components to ensure you get enough of each.

Factor in the temperature on race day which may impact hydration levels, as well as how much you tend to sweat. If you are a sweaty person and often have white sweat marks on clothing, you will have higher hydration and electrolyte requirements. Monitoring thirst levels, mouth dryness, increased heart rate and twitching or cramping can alert to signs of dehydration.

Post-race nutrition for triathletes

Don’t let the excitement and fatigue take over your triathlon nutrition once you’ve finished! The body needs sufficient nutrition for ideal recovery, in the form of carbohydrate, protein and electrolytes.

Muscles are best able to take on nutrients 30-60 minutes post-race. Some examples include pasta or a sandwich with some protein, but if this isn’t feasible, you could carry a pre-made shake.  Including anti-inflammatory foods may also aid the body’s ability to recover, these include berries, oily fish, walnuts, almonds, bell peppers, tea and coffee.

Rehydrate your body sufficiently, and you may need more electrolytes post-race to replenish stores. You could add sea salt to your post-race meal to replenish sodium and aid recovery.

Daily nutrition for triathletes

Day to day triathlon nutrition enables the body to perform intense training sessions, avoid injury and recover adequately. The following is an example of a typical triathlete diet which you could adapt.

Breakfast Lunch Dinner Snacks
Wholemeal toast with banana, peanut butter and seeds Tuna niçoise salad with boiled eggs and couscous Chicken noodle stir-fry Chia pudding
Oats with fruit, honey and yogurt Tuna sandwich with whole meal bread and sweetcorn. Side salad Spaghetti bolognaise Oat flapjack
Smoothie: Protein powder, banana, spinach, oats and yogurt Jacket potato with beans and side of vegetables Salmon poke bowl with vegetables and rice Granola and natural yogurt
Scrambled egg on toast with avocado and tomatoes Chicken and quinoa salad Tuna, pasta bake Fruit salad
Target daily macronutrients:

·      Carbohydrates: 8-12g/kg of body weight, spread across the day

·      Protein: 2g/Kg of body weight every 3-4 hours

·      Fat: 20-35% of remaining calories


What are the best diets for a triathlon?

The Mediterranean diet is recommended as one of the healthiest diets to follow as it’s proven to reduce heart disease risk, metabolic risk and a whole host of other conditions. It focuses on increasing seasonal and minimally processed foods such as fruit, vegetables, pulses, grains and nuts. Researchers in the US found running performance in athletes increased 6% after four days of adapting the Mediterranean diet.

High carbohydrate vs low carbohydrate

Some research suggests that a low carbohydrate & high fat diet (LCHFD) will improve performance. The body has higher fat storing ability, whereas carbohydrate storage is limited and therefore why not utilise this fat capacity? Fat metabolism is slower hence why athletes have tended to rely on carbohydrates when carrying out intense exercise, however by following a LCHFD it has been demonstrated that athletes adapt their ability to utilise fat for energy. Currently there is not sufficient research to determine which method is best and therefore it is recommended to continue reliance on carbohydrates.

What are the worst diets for triathlon?

Ketogenic (‘Keto’) and carnivore diets

The keto diet is a low carbohydrate high fat diet (LCHFD), consisting of <50g carbohydrate. Diets that follow this genre include Atkins diet, Dukan, diet, and the Banting diet. There have been trends towards athletes trying keto diets to aid sport endurance over recent years, as it is believed that adapting a lower carbohydrate diet may train the fat storage fuel system to adapt when performing endurance sports. Considering the popular discussion of the topic, there has been limited research studies conducted. The study ‘Ketogenic and high carbohydrate diets in cyclists and triathletes’ and another ‘Low carbohydrate, high fat diet impairs exercise economy…’ both found no benefits for endurance athletes.

Carnivore diets eliminate plant-based foods and focus solely on animal-based products: meat, fish, eggs and small amounts of dairy. This eliminates carbohydrates, fruits and vegetables, and doesn’t provide a balance of macronutrients and lacks diversity for gut health. Due to the imbalance, it wouldn’t be recommended for a triathlete to follow this diet long term. ‘The Journal of Exercise and Nutrition’ suggests the carnivore diet could improve sprint speed, but research is preliminary and more is needed across different athletes.

Supplements for triathlon athletes

A healthy, balanced diet should provide the necessary vitamins and minerals through whole foods. People with specific deficiencies and symptoms should seek medical advice. There are some supplements on the market you could consider if you’re looking to achieve a personal best, we recommend consulting a sports dietitian to find out more:

  • Caffeine can be an easy way to elevate performance. Studies in the ‘Medicine and Science in Sports Exercise’ journal showed caffeine intake can increase Vo2max, meaning more oxygen can be utilised during a workout and fatigue was reduced. Be cautious taking caffeine later in the day as it stays in the system for up to 10 hours depending on intake, and may influence sleep quality.
  • Omega 3 fatty acids have anti-inflammatory effects and help muscles recover after repeated sessions, reduce delayed onset muscle soreness and reduce the perceived effort of a workout making it feel easier. Sources include salmon, mackerel, walnuts, flax and chia seeds. A supplement may help if you can’t achieve the recommended dose of 250-1000mg/day.
  • Creatinine monohydrate is one of the most researched performance supplements. ‘The Journal of the International Society of Sports Nutrition’ has shown creatinine increases power output in a high intensity capacity (sprint sessions), accelerates recovery and improves ability to hydrate and thermoregulate. Follow a specific creatine loading programme, and then supplement 3-5g per day to maintain stores.
  • Beta alanine can be taken to aid acid regulation as it increases carnosine production by 80%. This plays a role in reducing the build-up of lactic acid and fatigue during short sprint sessions. It hasn’t shown any benefits during swimming.
  • L-Carnitine supplements may increase fat burning and aid endurance by reducing the amount of glycogen used. The supplement therefore helps with recovery and performance over long distance races, as found in a systematic review article in ‘Nutrition’.
  • Nitric oxide is an essential component in metabolism. It is linked to athletic performance as it controls vasodilation, blood rate and mitochondrial respiration. Nitrates are found in foods such as beets, garlic, meat, dark chocolate and leafy greens to name a few. Nitrate needs can be met by consuming 250-500g of leafy greens. A study in ‘The Current Research in Physiology’ found oral beet supplementation enhanced cyclists’ ability to maintain high intensity intervals, and improve their recovery. Supplementation doses depend on the product, so check the labels recommendations.

It’s important to adhere to the recommended doses of each supplement and check the labels for health contraindications before consuming.

Common triathlon nutrition mistakes that should be avoided:

  1. Not practicing the nutrition plan! By not practising your triathlon nutrition plan, you risk overloading the gut with intolerable amounts of carbohydrate leading to gastrointestinal issues.
  2. Incorrectly racing with caffeine. Always proceed with caution using caffeine, practice with it during training, if you are hypersensitive you may end up spending more time in the toilet than desired.
  3. Insufficient electrolytes. Do a sweat test and work out how much salt you need during exercise. Insufficient electrolytes cause cramping, fatigue, nausea and vomiting. Overconsumption of electrolytes causes hypernatraemia and can lead to dizziness, vomiting and diarrhoea so read the labels and consume safe amounts.
  4. Not prioritising nutrition. Nutrition is known to be the fourth pillar in a triathlon and will enable your body to perform it’s best. Don’t underestimate how much you need and load up on carbohydrates prior to racing and training, but also afterwards to ensure your body recovers properly.

Having support from a dietitian can help with your triathlon training as well as ensuring that you are eating a balanced and well varied diet. Book a consultation with a Sports Dietitian here.

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