miércoles, 11 de mayo de 2016

LCHF & Endurance Exercise: Summary of Evidence

It is hard to read about low-carb diets without either getting lost in a world of anecdotes or worse, getting involved in a Twitter fight! There are few topics in the world of nutrition that are so hotly debated. My personal interest in Low Carb - High Fat (LCHF) diets is their application in endurance sport. Finding a way to use more of the 100,000 kcal of fat we have stored in our body is a dream come true. But as with nearly all things nutrition related it just isn't as simple as we'd like!

Before we delve into the evidence I want to point out that I am not looking at LCHF in terms of health, body composition or insulin sensitivity. This is simply looking at whether a LCHF diet will make you a better cyclist/runner/triathlete.

To discuss the current evidence I will be summarising an article by Louise Burke titled "Re-examining High-Fat Diets for Sports Performance: Did We Call the "Nail in the Coffin" Too Soon?" The original article can be found Here. I highly recommend that you read it. 

It is pretty well accepted that a short term (less than 3 days) LCHF diet is detrimental to performance due to the depletion of muscle and liver glycogen without producing an increase in fat oxidation. However following one of these diets over the long term has produced interesting findings. The key questions is, what happens to performance?

After an extensive literature review of studies from 1980 – 2006 the author’s key findings were.
  • ·         Exposure to a LCHF diet without ketosis causes key adaptations to the muscle in as little as 5 days. Adaptations include an increase in intramuscular triglyceride (IMTG) stores and an increase in the activity of hormone-sensitive-lipase (HSL) enzyme. This enzyme mobilises triglycerides in muscle and adipose tissue. These adaptations increase the athlete’s ability to oxidise fat.
  • ·         These adaptations still persist in the face of 1-3 days of aggressive carb-loading. Although the carb-loading reduces the rate of fat utilisation compared to LCHF alone, they still remain higher than those who follow a high carb diet.
  • ·         Exposure to a LCHF diet downregulates carbohydrate utilisation during exercise. Changes in utilisation of muscle glycogen as opposed to blood glucose have been shown to account for this downregulation. This downregulation has been shown to persist in high intensity exercise even in the trials with the carb-load after following a LCHF diet.
  • ·         Despite the increased capacity to use this enormous fuel source, fat-adaption strategies do not appear to enhance exercise capacity or performance. Benefits have been limited to protocols of prolonged sub-maximal exercise which do not reflect a true endurance sporting competitive scenario.
  • ·         Fat –adaption strategies may impair exercise performance, especially exercise involving shorter high intensity efforts. This is likely due to the impairment of muscle glycogen utilisation.

The author stated that due to the recent boom in the popularity of LCHF she revisited the literature. She found that the sudden re-emergence was not matched by a wealth of new studies that support the use of LCHF for endurance sport. In fact she found only 2 studies on athletes since 2006 and neither showed a performance benefit. They did however show a small but favourable change in body composition through a reduction in body fat.
The author makes the observation that the majority of support for LCHF diets is carried out in the lay and social media and mostly by (and for) non-elite athletes.
She concludes that instead of “black & white” thinking, researchers and practitioners should move towards personalised and individualised approaches when working with athletes.

My Thoughts 

I wanted to give you the take home message from what I think is a balanced view of the LCHF diet and endurance performance. If you want more info on the individual studies that the author mentioned then please consult the reference list of the original article.

I think Louise summed it up perfectly when she said we need to move away from black & white thinking. In the past very high carbohydrate diets were thought to be the only diet to follow if you wanted to partake in endurance sport. It now appears that a number of people have gone from one extreme to another stating that you simply have to follow a LCHF lifestyle.
While I see the benefits of sometimes limiting carbohydrate intake, especially if you want to reduce body fat, the fact remains that the evidence strongly suggests that if you want to perform well at higher intensities following a strict low-carb diet will be detrimental.

That is why here at GDRB we will offer you a personalised nutrition plan where we will modify the amount, timing, type of carbohydrate, fat and protein depending on your training goals and at what point you are in your training programme.  For more info please email wayne@gabinetederueda.es

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