Should You Believe All diets?

With so many different ways of fuelling your body and many different options available to the athlete seeking to fuel their training, what actually works? Below we look at a few different methods that we have seen many athletes talking about recently. It is very much down to you to make your opinion of them but remember nutrition is the fourth discipline of triathlon, so you need to get it right!

High fat, Low Carbohydrate diet

Ketagenic is, in simple terms, a diet where you consume a higher proportion of fat and very little carbohydrates in the effort to use fat as your main energy system. The thinking behind this approach is that it is said the human body holds a virtually unlimited source of fat compared to about 2 hours worth of carbohydrate.

Studies on ultra-runners who followed a high fat diet compared to ultra-runners who followed a traditional high carbohydrate diet were able to burn fat at a greater rate than the high carbohydrate group. They were also able to run faster in a “fat burning” state as they were able to still burn fat at a higher percentage of their VO2 max. However, the high carbohydrate group were able to burn carbohydrates at a greater rate than the high fat group. Critically, this “fat burning” state doesn’t necessarily mean the quickest state. Equally, due to the limitations of training at intensity, the training stresses are significantly lower, and arguably performance is hampered.

A frequent guest of ours in Portugal decided to give this diet a go after deciding to enter the Marathon de Sables with the mindset that during the race carrying the minimum weight in your pack/vest becomes an advantage and that has an effect on the food you can eat and the amount of calories consumed during the 6 days racing. This meant they had to adapt their training by running to a strictly low heart rate – this meant walking up hills to reduce the increase of their heart rate too much. Over time, after the body had adapted, it meant they were able to go with a higher heart rate using fat as the main energy source. This has proven some positive results in multi day ultra endurance events though is always difficult to back with science as generally the results are subjective, “I felt better”, and the facts are inconclusive. 

This is a very specific example of a multi day event and that for most athletes, where speed and getting to the finish line first is the main objective, this method is flawed. In order to breakdown fat to adenosine triphosphate (ATP) more oxygen is required than the breakdown of carbohydrates to ATP, therefore less oxygen is being supplied to the working muscles - slowing your speed down. The toss up here could be described in a choice between a diesel or petrol engine. [See what our nutritionalist says



Fasted Training

Many endurance athletes use this concept purposefully or accidentally where they are restricting calorie intake before exercise, generally by training first thing in the morning where you have been fasting for an average of 10 hours over night since your last meal. The concept is to burn more fat during exercise. Fasted training is best done at a moderate to low intensity as you will struggle to train at a high intensity when fasted without going hypoglycaemic (or bonking)!

However, training at a higher intensity, using carbohydrates as the main energy source leads to more fat being burned post exercise. Therefore, if you are fasting before sessions for the purpose of losing weight then you are better off doing high intensity sessions . However, your body is usually very well suited to replacing what it has just burned, so burning more fat will mean creating more fat! [Read this


on weight loss.]

When it comes to a question of performance though, you have to ask yourself what is best suited to the race distance you are doing and the training sessions you are looking at. A more polarised training routine may be more suited to the less intense training sessions, but it certainly shouldn’t be a standard training procedure. In recent studies, there has been limited performance improvement for men and almost no performance increases for women. 

That being said it is not always possible to ensure you aren’t training while fasted. If you are doing a significant amount of training you are probably completing some training sessions in a semi fasted state as you haven’t had enough time between sessions to replenish your glycogen stores which is why post work out nutrition is so critical to get right. 


It is common knowledge that protein is used to rebuild muscle and frequently used as the significant focus in recovery fuel post workout. However, carbohydrate should also be included to help replenish our glycogen stores and the presence of carbohydrate is also required to synthesise protein and aid muscle rebuilding. Some good examples are yoghurt and honey or chocolate milk. It is especially important if you are training multiple times a day to refuel properly. A study of male swimmers on the same diet who trained for 1.5 hours in the morning then again for 1.5 hours in the afternoon compared to those who just trained for 1.5 hours in the afternoon showed that those just training in the afternoon showed a significant increase in sprint performance compared to those who trained twice a day. This surprise outcome was because the swimmers training just once a day where in a fully fuelled state, they did not have as much glycogen depletion and therefore could train harder, leading to greater performance. Clearly this didn’t look into overall performance for a season but shows the impact of multiple training sessions in a day and improper fuelling for recovery.

Never underestimate the importance of a rest day to allow for your muscles to replenish their glycogen stores and repair as it can take 24 hours or more to replenish depleted glycogen stores after a heavy training session. And if in doubt, when it comes to recovery, drink chocolate milk – protein, fluid and carbohydrates!

Do you want some help with your diet?

Are you tired of following a diet and not getting the response in the diet or training you were hoping for? Follow 

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to see how we can integrate your coaching package with your diet using our expert nutritionist and ensure that your training and fuelling experience is the best it can be. 

Will Munday

Will Munday

is a Tri Training Harder Coach and Guide and is based in Wales and Portugal. If you are interested in finding out more about how a coach could help your current training routine, please give us a shout on

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