Sports Science Monthly – January 2017

Welcome back to another monthly round up of recent research in the sports science world. This month we finally have some objective evidence on the use of high fat, low carbohydrate diets for elite athletes – perhaps this will lessen the debate, although I expect not. We also have a look at the training of elite endurance athletes, early versus late specialization in Olympic Athletes, sleep (as always), oxidative stress, and the use of hot baths after exercise, amongst others. Enjoy.

As always, the full Sports Science Monthly is available exclusively to HMMR Plus Members. The first overview below is free to everyone, but sign up now to read about all the research. To get an idea of what Sports Science Monthly is all about, our April and May editions are available in their entirety for free.

This Month’s Topics

Low Carb, High Fat Diets and Exercise

→ Quick Summary: In this group of athletes, a LCHF diet did not lead to performance improvements, whilst a diet higher in carbohydrates did.

Those of you who are regular readers of this round-up series might remember that I’ve discussed the low carb, high fat (LCHF) situation before. In what is fast becoming a semi-evangelical movement, supporters of LCHF (of which perhaps the most famous is Tim Noakes) believe that it is the Holy Grail of sports performance. Their theory is reasonably sound; at lower exercise intensities, fat is the preferred fuel of the body, and because you have essentially an unlimited supply of it in stored body fat, long-duration exercise becomes more efficient – much more so than needing to top up glucose/glycogen levels every hour or so during a race. However, there are some obvious flaws in this theory. The first being that athletics events typically aren’t won by those that can last the longest, but those that cover the distance in the shortest amount of time – meaning that exercise intensity, and not exercise longevity, is the perhaps the most important variable. Secondly, there is no evidence that high fat diets actually improve endurance performance; Tim Noakes knows this himself because he’s published research showing that. Instead, what the LCHF supporters are left with is a number of studies showing that fat oxidation is higher in athletes that eat a lot of fat, which is entirely unsurprising, and doesn’t even begin to hint that it might improve exercise performance.

Fortunately, more rigorous LCHF research is beginning to be conducted in elite sports people, which brings us to the first study of this edition, conducted at the Australian Institute of Sport (AIS). 21 elite race-walkers were recruited to this study, which was split across two different training camps; some race-walkers were at both camps, and therefore took part twice, resulting in 29 different “subjects” from a data analysis perspective. The race walkers were then placed onto one of three different diets. Usually how this would be done is via randomization; so subject one would be placed onto a diet at random, then subject 2, etc., until each diet had the same number of subjects. However, in this study, the authors had a very clever and novel research design; they educated the athletes as to the potential benefits and limitations of each of the different diets, and asked them to them to nominate their preferred diet of the three, information which was then used to place the athletes into the different diet groups. This is a smart design because it accounts for the placebo effect/expected outcome beliefs of the athletes. If, for example, athlete A believed that LCHF were terrible for performance, and then was placed into that diet group, he subconsciously might perform worse due to his lack of belief in the intervention, which could skew the results. The three different diet types were LCHF, comprised of less than 50g of carbohydrate per day and 75-80% of calories from fat; a high carbohydrate diet comprised of 60-65% of calories from carbohydrate spread across meals; and a periodized carbohydrate diet, also with 60-65% of calories from carbohydrate, but spaced differently throughout the day – sometimes the athletes trained with a high amount of carbohydrates available, and at other times they had fewer carbohydrates available (which has been shown to increase aerobic adaptations). All diets had the same amount of calories, and foods were weighed by AIS staff to ensure compliance. The dietary intervention took place over a three-week training block, with pre- and post-tests to monitor adaptations, including a 10km race walk event with prize money to incentivise the athletes.

The results make for interesting reading. The athletes on the LCHF found training harder than normal, sometimes being unable to complete sessions as planned; this effect was not seen in the other dietary groups. The LCHF group also reported a higher rate of perceived exertion (RPE) and had higher heart rates during a treadmill test of economy, and also required more oxygen to exercise at a prescribed workload, indicating a loss of economy compared to the other two dietary groups. In the 10km race, the carbohydrate groups were significantly faster in the post-intervention race than the pre-intervention race; the LCHF group were more or less the same.

Is a LCHF diet better for endurance athletes? @craig100m outlines new research saying no. Click To Tweet

The main findings of this study from a LCHF perspective, then, are two-fold; firstly, following a LCHF diet increases how much oxygen an athlete needs for a given work rate, and following a diet that is primarily carbohydrate based improves performance, a result which is not seen in athletes following a LCHF diet. Whilst all the athletes improved their aerobic capacity, this didn’t translate to performance improvements in the LCHF group only, and these athletes also reported an increased perception of effort during training. Overall, then, this seems like a nail in the coffin for LCHF diets and elite endurance performance. This study is of exceptionally high quality and it is seriously well designed, such that it’s difficult to see how LCHF proponents will be able to support their viewpoint that LCHF is superior for elite endurance performance. One potential argument point is that three-weeks is insufficient time to become “fat adapted”, i.e. used to using fat as the main source of fuel. The authors of this study recognise this, but maintain that according to prior research, three weeks is ample time for adaptation to occur. Hopefully, more research will be done in the future to further examine this, and LCHF and exercise performance, enabling a consensus to be formed.

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