Carbohydrates or fats? What should you use as a fuel source?
Coach Kevin looks into the somewhat controversial topic of carbohydrates versus fat as a performance nutritional strategy. Kevin looks objectively into the science and information out there as well as bringing in some of his own personal experiences. The information may surprise you!
It seems like the subject of nutrition is often a polarising one – many people have a preferred way of doing things and can sometimes become quite blinkered to different viewpoints. In this article, I’d like to explore the two sides to a couple of very different approaches, the (typical) high carbohydrate-based diet and the (more left-field) ketogenic diet.
To give a little perspective, I’ve practised both types of approaches. I was moving into a very high carb diet when my training volume increased ten years ago, and then for the last four years with a ketogenic diet. I am easing off most recently to low carb (low carb is just a less extreme version of a ketogenic diet). I feel this has given me a good insight into the pro and cons of each – I’m certainly not against either approach, which unfortunately often seems to come through in a lot of the articles I’ve read around these subjects.
Let’s start with carbohydrates. You could go all the way back to the early ’70s when American dietary researcher Ancel Keys effectively started a ‘low fat’ movement by manipulating data for his study, which, while never fully published, suggested a link between heart disease and saturated fats. (This study takes the since found complete data and finds no link: Re-evaluation of the traditional diet-heart hypothesis: analysis of recovered data from Minnesota Coronary Experiment (1968-73) | The BMJ)
If you cut down on fat, they tend to be replaced with carbohydrates. A typical recommended ratio for a ‘modern western diet’ might be around 30% fat, 60% carbs and 10% protein. (it is interesting to note that fat gets a special ‘up to 30%’ limit in the linked NHS advice while the other macronutrients do not). There is more to food than just the macronutrient balance of course, but it’s an ideal way to categorise a diet (and some would argue this causes problems in itself!)
The ketogenic diet is the opposite extreme, where the majority of calories in your diet come from fat: up to 75 – 80%, and only 5 – 10% from carbs, with 10% protein being maintained. So from this point of view, quite a bit more ‘extreme’ in its macronutrient imbalance.
So it’s probably clear why the keto diet could be considered the black sheep here. I’m fairly sure that unless you are specifically trying to follow a ketogenic diet then your dietary macro breakdown is much more likely to be closer to the former example, and that should be most people’s approach unless they have got a good reason not to (I’ll get to that later!)
Let’s also consider sports nutrition – with an equally shaky scientific basis at the start, Gatorade was the birth of the carbohydrate fuelling during sport. Many scientific studies have since come along, however, and proven carbohydrate intake during sport to improve performance, without any doubt, especially if you are working in the higher intensity ranges.
The ketogenic diet, or supplementing with fat / or ketones for performance, has not really gained much traction in the scientific area. Nevertheless, some studies show improvements in specific situations but just as many show no effect, and some have negative outcomes.
So at this juncture, it seems like carbs are the clear way to proceed, and is there even any point in considering keto? The concise answer to that is ‘probably not’, but of course, there is more to it than that.
There is the fact that the anecdotal evidence has failed to go away, despite it perhaps becoming less of a popular ‘fad’. There is also a tremendous theoretical argument to a ketogenic diet that revolves around the fat ‘fuel tank size’ compared to the carbohydrate equivalent. A potential advantage that gets bigger the longer the duration of the sporting event you take part in. You can hear terms like ‘metabolic efficiency’ or perhaps the desire to become a ‘fat-burning machine’, a phrase often seen in the average keto blog. It’s undeniably good for weight loss – and here, the science does support it...if you can ensure compliance with the diet! Many of those who follow the diet (and are therefore likely to respond well to it otherwise, they probably would have given up) talk about more stable energy levels, an ability to skip meals if required, much less reliance on the need to fuel during long endurance efforts, and often an improved sense of well-being or lowered stress levels.
Another thing to keep in mind, which could explain the lack of scientific support, is the fact that sports studies are very hard to control, especially when:
You have to deal with people and control both their exercise regime and diet precisely.
Improvements in sporting performance are slow – meaning the above controls need to be applied for a long time, making the study even more challenging to control
Despite some physiological changes being apparent in 3 – 4 weeks (already a long time for a tightly controlled study), many individuals on a keto diet report that their full range of performance can take many months to return outside of the low-intensity endurance improvements – studies just don’t typically last this long.
Carbs are fairly addictive! (compliance to ketogenic diets is low)
So, where does this leave us? I believe that the critical consideration with dietary choice is individuality. Responses to particular diets can vary substantially between individuals (and sexes), especially in the more ‘extreme’ diets. If carbs are working for you, why change? If you are struggling with carbs (perhaps shown through digestive issues, energy swings through the day, difficulty with fuelling during longer/race efforts), then maybe you should consider trying out a ketogenic diet. After giving it a good chance, do you feel better? If the answer to this is no, switch back, and what have you lost? There is never any harm in a little self-experimentation if you do sufficient research, time it correctly, and keep an open mind.
In Kevin’s next article he discusses how to make the transition to a high-fat diet.
Kevin opened a B&B for cyclists in France in 2014, & then a year later decided to start a cycle coaching (level 3) qualification. This was mainly in order to be able to better support his guests (but also to make his own training more effective too). At the B&B he runs the odd training camp for cyclists but mainly offers coaching advice while guiding guests. An engineer by background, he happy diving into all sorts of training data, but also understanding that coaching is about much more than just the numbers!
After being introduced to triathlon by a good friend & then taking part in races for a couple of years he decided that a level 2 coaching course with British Triathlon was the way forward, completing this in 2019.
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