LOW CARBOHYDRATE, HIGH FAT (LCHF) DIET – WHAT’S THE DEAL?
Low Carbohydrate, High Fat (LCHF) diets, otherwise known as ketogenic diets have been touted as the next big thing in endurance sports nutrition. The idea behind ketogenic diets seems simple enough: since glycogen (our carbohydrate storage in muscles and the liver used to fuel exercise) is in limited supply, whereas our fat stores are far more plentiful, is there some way to force our bodies to use fat as a primary fuel source, rather than carbohydrates?
Professor Louise Burke, a world renowned expert in sports nutrition, examined the merits and drawbacks of ketogenic diets for endurance sports performance in a review paper published in 2015. Going on a low carbohydrate (<25% of total calories, typically less than 50g) and high fat (>60% of total calories) diet has four main effects.
- Firstly, a shift from carbohydrate oxidation to fat oxidation as a primary fuel source for exercise can take place in as little as 5 days of eating a LCHF diet.
- Secondly, there is a downregulation in the body’s carbohydrate metabolising enzymes i.e. the body’s ability to metabolise carbohydrates as an energy source is impaired even when switched back to a normal carbohydrate diet.
- Thirdly, there may be some benefits to performance at a sub-maximal level (around 60% VO2 max).
- Fourthly, the ability to do high intensity work is adversely affected. Going on a LCHF/ketogenic diet also seems to have a favourable effect on reducing body fat levels; however, it comes at the cost of the ability to do high intensity work.
Athletes who plan to go on a LCHF/ketogenic diet in the long run should be aware of these affects and be prepared to change their training programme towards longer, sub-maximal exercise. Switching back to a normal carbohydrate intake is unlikely to result in a performance improvement for high intensity work, and may possibly lead to higher body fat levels. Ketogenic diets can thus be likened to a ‘one-way’ ticket for a change in substrate utilization for exercise – there’s no turning back!