High Fat, Low Carb diets for athletes' - what's all the fuss?

Why is it that every triathlon/athlete Q+A session ends up with nutrition taking up at least 50% of the conversation. As such a big part of an athletes overall performance, most of us find it hard to distinguish (1) What is the right information to listen to (2) How to use that information to make performance gains?Now I'm no dietician, I don't have a specific degree in sports nutrition, but through a background in sport and exercise science, teaching, training, racing and coaching I've found that sports nutrition is very individual, differs for everyone and more importantly, is continuing to develop and pose new ideas.

The latest and most talked about nutritional development is the trend of endurance athletes experimenting with high fat, low carb (HFLC) diet. Although this is not really a development as the Atkins diet from the 70's started a trend of low CHO to reduce weight, the addition of higher fat intake has been geared towards potential benefits for endurance athletes   - without going into too much specific nutritional detail, here is my brief take on it all and why I choose to stick to what I know!

The basic idea behind the diet, is that fat as an energy source yields more energy than carbohydrates, therefore prolonging our aerobic performance level. The drawback and often less detailed part is that this needs to be achieved at a lower intensity of exercise (due to the need for oxidation), limiting the use to specific types of athletes/events. While research is being done, and numerous well-known athletes attest to the benefits of the diet, the science is not conclusive (opposed to a higher CHO diet).


Now you may think that as an Ironman or marathon runner all of your primary work is done at a lower intensity? This is true to an extent, but what this diet (in my opinion) does is sends athletes the wrong message about the types of training we should be doing in conjunction with HFLC. I find these athletes often then become very driven by volume and reduce the quality, higher intensity training that we all need to improve specific aspects of our performance. Would you advise a group of elite Kenyan marathon runners to strip their daily diet in favour of HFLC?

Here are some of my main thoughts:

The Perceived Benefits of High fat, Low carb

  • Increased energy
  • Prolonged performance
  • Potential weight loss
  • Control blood sugar

The Drawbacks

  • Less fuel for higher intensity training
  • Weight loss
  • Loss of concentration with lower CHO intake
  • Muscle recovery potentially compromised
  • High fat a risk factor for heart disease
  • Incline towards increased volume of training
  • Time consuming to prepare appropriate and varied meals/snacks

How I stack all this up

  • Quality high intensity training requires higher CHO intake (although endurance events are primarily aerobic, there will always be periods of the race completed at higher intensity, and also high intensity performance gains in training will require CHO), for this I would and always advise the main component of the diet to be CHO.
  • Take it from a man in the know, check out Asker Jeukendrup's article about the importance of CHO intake during exercise http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4008807/
  • Use reduced intake of CHO for lower intensity, higher volume sessions to promote fat adaptation (longer run/ride), but refuel properly after with adequate CHO to back up for training the next day and don't make all of your training based around these types of sessions.
  • While weight loss may be a factor in determining some level of performance gain, this should not be the primary goal of training and a balanced diet met with regularly prescribed exercise is more beneficial for the body.
  • Also check out the article by nutritionist Matt Fitzgerald about his thoughts on the HFLC diet and athletes, and what he calls 'sour grapes syndrome' http://racingweight.com/blog/sour-grapes-syndrome/
  • Also read between the lines in some HFLC articles, a lot of athletes who are claimed to use HFLC diet have often made alterations to their diet to become more efficient at utilising fat, or moving towards cleaner more refined form of carbohydrates. Not all of them follow a strict HFLC diet.
  • Ultimatelyperformance gains should be driven by training and adaptations to progressively challenging loads, diet should be used to support this, not the other way around.

Either way, as research continues to delve into this diet you will findarticles to support it, and for every one probably more to oppose it. All I can say istalk to the people you trust,don't make big changes too quickly. Look after your body and make sure training and diet are planned to support the specific changes you need to make in performance.