Is a low-carb diet also suitable for endurance sports?

Paolo Colombani 26. July 2018

Mankind’s earliest ancestors lived on earth a few million years ago. Their intake of carbohydrates at that time was rather modest and only increased with the advent of farming about 10 000 years ago. What does this mean for us? Should we all switch to a low-carb diet?

Despite the highly propagated Paleo diets, we still do not know for certain what a Stone Age diet consisted of. We can also assume that there was not one single Paleo diet. The Stone Age lasted about 2.5 million years and there were certainly a lot of different diets during this time. However, the best present-day assumptions are: carbohydrates made up 20 to 30% of the energy supply and fats as well as proteins each made up 25 to 60%. More precise values cannot be scientifically determined. 

Low-carb diet for inactive people

The recommended percentage of energy from carbohydrates for the general adult population today, however, is around 40 to 50%, and for athletes it is much higher. Both these recommendations for carbohydrates are thus much higher than what humans have eaten throughout their entire history of evolution. What should we make of this?

The latest scientific evidence spells it out clearly. High intakes of carbohydrates increase the risk of common lifestyle diseases, such as diabetes or cardiovascular diseases. It therefore makes sense for adults to reduce their intake of carbohydrates, provided that their physical activity is modest to low. This is because regular physical activity offsets the negative effects.

Low-carb diet in sports

Between 1985 and 2005, sports scientists conducted a whole series of studies on high-fat diets in endurance sports. A high-fat and thus low-carb diet is supposed to maximise the lipid metabolism and in doing so, preserve the glycogen stores and lead to a better performance.

Following a high-fat diet for a few days actually increases fat burning during endurance training. And the corresponding cellular adaptations even last for one day after starting carbo-loading again. However, this does not lead to a better endurance performance as compared to a conventional carbohydrate-based diet. And since many find their training considerably more strenuous during a high-fat and low-carb diet, such a diet is discouraged when doing endurance sports.

Carbohydrates for intensive endurance performances

Despite the odd few athletes who have proclaimed to improve their endurance performance on a high-fat diet, the scientific evidence available paints a different picture. Most endurance athletes are only able to exploit their maximum potential with a sufficient intake of carbohydrates. In any case, carbohydrates are a limiting source of energy for intensive performances of up to 3 hours. Accordingly, classic, carbohydrate-rich diets are recommended and not high-fat and low-carb diets. And also in the case of longer events, general recommendations continue to promote a diet rich in carbohydrates for both the training and the competition.

A low-carb diet is good now and again

While permanently following a low-carb diet is undoubtedly the wrong choice for many endurance athletes, isolated phases or training units with a low intake of carbohydrates are an interesting idea. The ulterior motive here is to let the biochemical reactions that training initiates in the cells run a little longer to achieve improved training effects. However, there is an obvious problem: if there are too many low-carb phases, sooner or later you will slide into over-training due to the low carbohydrate intake. Such low-carb phases are therefore only generally recommended for adults who are already well-trained in endurance sports and then only once rather than two times a week. Such a phase can be one training unit on low carbohydrate reserves (no more than a low intake of carbohydrates after the previous training unit) or a longer recovery period with no more than a low carbohydrate intake (e.g. training in the afternoon and then hardly eating any carbohydrates the next morning at breakfast).

Summed up for use in practice

  • For those who are rarely physically active, a reduced intake of carbohydrates makes the most sense in order to stay healthy.
  • Instead of eating a serving of grain products, such as bread, pasta, or rice at each main meal, it’s much better to only eat them at two – and this can occasionally be reduced to just one meal without any problem.
  • In contrast, performance-focused endurance athletes require ample carbohydrates: in many situations, 6-8 g of carbohydrates per kg body weight is a sensible quantity (the food pyramid for athletes provides specific recommendations here)
  • In high-intensive training phases and directly before a competition, the quantity of carbohydrates should be increased somewhat and correspondingly reduced in quieter phases. A few low-carb phases bring variety to everyday life.