For a better understanding of the interrelationships in nutrition, it is worthwhile to familiarize yourself with some basics. At the end of the article, we will give you some specific triathlon diet recommendations.
When it comes to food, there are basically three types of energy sources: Carbohydrates, fats and proteins. While carbohydrates and fats are mainly used as energy sources by the body, proteins primarily serve as building materials, especially for the build-up and regeneration of the muscles.
Carbohydrates: Sugar, sweets, bread, pasta, potatoes, rice, fruits
Fats: Oil, bacon, sausage, eggs, butter, nuts, avocados
Proteins: Meat, fish, eggs, milk and dairy products, soy products, nuts and seeds
Energy sources in triathlon
In triathlon, carbohydrates and fats are the main sources of energy. Both are stored in the body after food intake and released again when needed.
A full carbohydrate store (glycogen store) lasts for approximately 1 - 1.5 hours of training activity, at very high training intensity even shorter. If the storage is used up, you will feel this as an unpleasant feeling of weakness (hitting the wall).
In contrast to carbohydrates, the fat reserves in the body provide an energy store that, even in lean individuals, is almost inexhaustible and can supply muscles with energy for many hours to days. The burning of fat is somewhat less efficient than that of carbohydrates. This means that less energy can be provided per unit of time.
While the burning of fats can provide a substantial portion of the required energy at moderate intensities, carbohydrates must be provided additionally at higher intensities. At very high intensities (e.g. a sprint), most of the energy comes from burning carbohydrates and fat burning only plays a minor role.
The burning of carbohydrates works all by itself and does not need to be specially trained. With fat burning it is different: If you do not pay attention to some important prerequisites, it remains completely inactive and you are dependent on the regular supply of carbohydrates during longer training sessions.
The role of insulin
The hormone insulin plays a central role in energy balance. If you eat a carbohydrate-rich meal, e.g. pasta, the carbohydrates are digested in the intestine and then absorbed into the blood as individual sugar molecules. From there, the sugar (glucose) is distributed throughout the body and either directly burned in the muscles and brain or stored for longer periods as glycogen in the liver and muscles.
The faster the ingested carbohydrates can be digested, the more the blood sugar level rises, because high amounts of sugar are absorbed in a short time. Sweets and white bread, for example, consist of very short-chain carbohydrates and therefore lead to a rapid and high rise in blood glucose levels. Whole-grain bread, on the other hand, contains mainly long-chain carbohydrates and consequently leads to a slower and lower rise in blood sugar.
As soon as the sugar concentration in the blood rises, the hormone insulin is released. The higher the sugar concentration, the more insulin is released. Insulin causes the circulating sugar molecules to be absorbed and stored in the muscles and liver. As a result, the blood glucose level drops again.
In addition to lowering blood sugar, insulin has another very important property: even small amounts of insulin completely block the burning of fat. In other words: After each carbohydrate-rich meal, fat burning is blocked for several hours.
An exception is the intake of carbohydrates during a training activity. Here, the sugar is burned immediately after ingestion. The blood sugar level hardly rises and no insulin is released.
Fat burning can be easily trained
In most people, fat burning runs at a very low level and provides little energy. Too little to supply the body sufficiently during a more intense workout or to prevent you from hitting the wall when the carb stores are empty. The main reason for many athletes is their carbohydrate-heavy diet. The permanent supply of carbohydrates leads to a constantly elevated insulin level, which in turn blocks fat burning. In extreme cases, the elevated insulin levels lead to diabetes over time (Diabetes mellitus Type 2).
The good news is: fat burning can be trained with relatively simple measures!
Reducing carbohydrate-containing foods prevents the release of insulin, which automatically activates fat burning. The absence of carbohydrates forces the body to draw energy from fatty tissue.
The longer fat burning is active each day, the more the body ramps it up and the more effective it becomes over time. This transition doesn’t happen overnight. For most athletes it takes 1 - 2 weeks to reach a certain basic effectiveness. Experiences show that the effectiveness of fat burning of triathletes with appropriate nutrition continues to improve even years after the change.
How to train fat burning?
Fat burning is automatically trained if you make sure that it is not blocked by insulin. This is where the low-carb high-fat diet comes into play.
Basically, the less carbohydrates you consume, the better. A daily carbohydrate amount of less than 150g is already very good. For a quick change, we recommend a target amount of under 100g of carbs. Some triathletes even set an upper limit of 50g per day as a goal (Keto diet).
Anyone who has ever tried to strictly reduce carbohydrates knows how difficult this can be. As with all dietary strategies, it is more effective to make moderate changes that can be maintained for years, rather than pursuing radical plans that must be abandoned after a short time.
If you do not want to completely abandon carbohydrates (e.g. bread or pasta), there are also other ways to train fat burning. With intermittent fasting you do not consume any (carbohydrate-rich) food during certain times of the day. The idea behind this is to activate fat burning by abstaining from carbohydrates for several hours.
You might have heard of the 16:8 diet where you only eat (carbohydrates) during 8 hours of the day (e.g. between 8 a.m. and 4 p.m.). The effect can be further enhanced by only consuming carbohydrates at breakfast or dinner. If you limit carbohydrates to the evening hours, e.g. between 6 and 9 p.m., the body has a carbohydrate-free window of 21 hours at a stretch and fat burning is effectively trained.
Even a small sweet snack can lead to an insulin release that puts fat burning out of action for 1 - 2 hours. That’s why it’s not a good idea to keep taking small carbohydrate-rich snacks throughout the day.
What exactly should you eat?
On the Internet you can find extensive lists of foods that are suitable for the low-carb high-fat diet. Here is a basic overview:
Often: Salad, vegetables, berries, eggs, meat, fish, cheese, high fat dairy products, various nuts (e.g. macadamia, almonds, hazelnuts, coconut), seeds (e.g. sesame seeds, pumpkin seeds), tea, water.
Sometimes: Sweet potatoes, cashew nuts, carrots, fruits, dark chocolate with 80% or more cocoa content.
Rarely: Sweet drinks, bread, pasta, potatoes, rice, peanuts, sweets, cereals, dried fruits.
Our recommendation for a moderate, everyday low-carb high-fat diet:
Breakfast: Greek yogurt with berries and sesame seeds.
Lunch: Meat / fish / egg / vegetarian protein source with salad or vegetables, garnished with sunflower and pumpkin seeds.
Dinner: Anything (don’t overdo it with the carbs)
In-between snacks: Nuts, dark chocolate, protein shakes, crackers with tahini.
We recommend avoiding carbohydrates as much as possible before low to moderate intensity workouts. Fasting workouts are great for fat burning and also lead to a higher VO2 max and larger glycogen stores in the muscles.
Before intense training sessions (intervals) we recommend to take fast absorbable carbohydrates 10 minutes before the start, e.g. dates, dried fruit, a banana or a cereal bar. During training, additional carbohydrates can be added as needed in the form of gels or drinks (e.g. with maltodextrin, 60g per hour).
In addition to carbohydrates, you should pay attention to a sufficient protein intake. For an optimal muscle build-up, a daily amount of 1.5g protein per kg body weight is recommended. This results in a daily requirement of 90g protein for a 60kg athlete, for example. The amount of protein should be taken throughout the day, consuming no more than 25g of protein per meal.
What are the benefits of a low-carb high-fat diet in triathlon?
It is obvious that triathletes with a well-trained fat burning system benefit from access to an almost inexhaustible energy store. Especially in longer competitions lasting over 2 hours, energy supply becomes an important factor. In triathlons over the middle and long distance (Ironman 70.3 and Ironman™), a well thought-out nutrition strategy is of central importance. Even for professional athletes, it is not uncommon to not be able to perform at full capacity due to nutritional issues.
Especially during running, the last discipline in triathlon, an inadequate energy supply quickly becomes noticeable and can lead to a real slump in performance. In fat-adapted athletes, a large proportion of energy comes from fat burning throughout the competition. This means that glycogen stores are retained for longer and can be used selectively during demanding passages. At the same time, the need for energy gels is reduced and with it the risk of stomach upsets.
However, a low-carb high-fat diet is not only worthwhile for long distance athletes, but for all triathletes:
- High fat-burning activity reduces the amount of fat in the body, resulting in an improved power-to-weight ratio. This will allow you to swim, bike and run faster.
- The low-carb diet prevents harmful blood sugar spikes, which cause a general inflammatory response. Recovery after training sessions and competitions is significantly accelerated.
- Many athletes report a more consistent training performance with high energy levels and fewer off-days after successfully making the switch.
- You become less dependent on a regular carbohydrate intake during longer training sessions.
A low-carb high-fat diet also has various benefits in everyday life and for your health:
- A rapid weight loss can be achieved through a LCHF diet.
- It is often reported that people with a LCHF diet can focus longer at work. In addition, avoiding large amounts of carbohydrates at lunch prevents afternoon fatigue.
- Many report better sleep when avoiding large amounts of carbohydrates in the evening hours.
- The risk of developing Diabetes mellitus Type 2 is significantly reduced. Patients with existing diabetes even have a good chance of getting off medication completely by changing their diet.
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