The fats Vs carbs debate – some good evidence at last

At last we have some good evidence from research on the High Fat Low Carb Vs High Carb diet debate. These are some of my thoughts on the issue.

The emphasis on the ‘Low-Carb-High-Fat’ (LCHF) approach to nutrition has been going on for a number of years now, along with the related and more specific Paleo and Ketogenic diets. Concepts such as ‘fat adaptation’ and ‘fasted rides’ are now common in coaching and training terminology.

I have found all of this very interesting over the years and followed the progress of some endurance athletes – a few into their 70s – who seemed to be getting amazing performances from these approaches, along with effective weight control and good health.

While there are lots of angles to this as usual, the arguments are basically simple and seem appealing: the LCHF and Paleo-type diets are more ‘natural’ for our physiology and evolutionary background, and we have huge reserves of energy stored in the form of fat which we should draw from primarily in endurance events. Therefore, if we train the body to use that fat as the primary energy source, rather than carbohydrates (‘fat adapted’), we will have greater endurance potential because carbohydrate is limited to what is stored in the muscles and liver in the form of glycogen.

As is often the case, the science on the subject has been mixed and not very convincing either way* but, as I said, anecdotal evidence from endurance athletes seemed to validate the approach in some cases. However, the same anecdotal evidence also seemed to suggest that top-end performance might be diminished somewhat.

In other words, and as a simple conclusion which I had come to, the LCHF approach may be good for long, low-output events such as long-distance triathlons, but not so suitable where intensity is involved.

I would have liked to experiment with the full Paleo approach myself but, from a practical point of view, keeping to a true Paleo diet was just more trouble than I was prepared to take on. Also, as I mentioned, I wasn’t convinced that it was suitable for the high-intensity type of racing that I still dabble in.

Nevertheless, over the years, my diet has definitely drifted in that direction and I now consume little of the traditional carbs in the Irish diet – potatoes, bread and so on – but I’m not dogmatic about it and I’ll eat them moderately if put in front of me. However, I’d always be sure to have adequate low- glycemic ‘good carbs’ on the morning of a hard workout and I only use sugary-type carbs (gels and energy drinks) in competition or for unusually long and hard training days.

In other words, I’d come to ‘periodize’ my diet – to lean toward a high-fat-low-carb approach in general, but to bring on the carbs in various ways when needed (not forgetting about the important proteins of course, but they are not part of this discussion**).

I’m also a believer in the ‘fat adaptation’ approach to some extent and, in the off-season I do easy fasted rides of up to two hours without any difficulty and I encourage other riders to do likewise. I find it amazing that, initially, some riders find it hard to operate at all without some kind of sugar-hit first thing in the morning, and also by the amount of sugary-gels downed by riders on ‘leisure’ spins and such like. Clearly, the body can become very dependent on easily available carbs in the form of sugars if allowed to do so and, equally clearly, it can be weaned off that dependence relatively easily.

A convincing study on the matter has recently been published and I think it helps a lot on the debate.*** It was carried out by Australian Institute of Sport and published in the Journal of Physiology – which are both very credible – and finally seems to provide some definitive evidence.

It concluded that fat burning for energy was indeed increased by the LCHF diet, but there were no associated performance gains. Also, the diet led to reduced efficiency because more oxygen was needed for metabolism and to do the same amount of work, and the diet therefore “negated performance benefits in elite endurance athletes”.

While the study acknowledged that there is still a lot research needed, it suggested that athletes seeking performance should indeed periodize their carb intake, depending on training and performance demands (however, one detail to be cautious about in this particular study was that the LCHF diet used contained less than 50gms of carb per day which is extremely low and bordering on Ketogenic, which is another issue yet again).

As with all things, you make up your own mind on the topic using a mixture of science, experience and common sense.

My own summary is that the LCHF approach is very good in general, especially for good health and weight control, but that it needs to be supplemented with more good carbs when needed for intensity and performance. And, don’t forget those all-important proteins!

Thanks for reading, and get in touch if you have any queries.


* If interested, see the article I wrote on ‘Science Vs Wisdom in Training: Finding the Balance

** See my article ‘Additional Protein Needs for Older Athletes’ if interested.

*** Burke, L. M., Ross, M. L., Garvican-Lewis, L. A., Welvaert, M., Heikura, I. A., Forbes, S. G., Mirtschin, J. G., Cato, L. E., Strobel, N., Sharma, A. P. and Hawley, J. A. (2016), Low Carbohydrate, High Fat diet impairs exercise economy and negates the performance benefit from intensified training in elite race walkers. J Physiol. Accepted Author Manuscript. doi:10.1113/JP273230.

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