LCHF and Paleo: What does the science tell us?

The incredible uptake of social media has spawned an abundance of information and commentary on diet and exercise. This can make it difficult to differentiate the right advice from speculation, popular trends and hearsay. In this article, I’d like to touch on the reasons why the interpretation of scientific information is essential, explore the facts regarding the Low Carbohydrate/High Fat (LCHF) diet, touch on the Paleo trend, and explain the relevance of these diets to triathlon.

While reading a controversial sentence in a journal article abstract, or relying on one person’s statement and another’s anecdotal evidence may spark questions, this should not be relied on when developing an informed opinion. One of my favourite university lecturers taught me to always read research articles thoroughly and to understand how their methods may have influenced their results. Thorough reading can be time-consuming, but can also be rewarding if you want to understand a topic and the science behind it in depth.

LCHF 101

The concept of LCHF has been explored in waves over the past 50 years and has recently jumped back into life via expert opinion (Phinney, Noakes and Volek), social media and anecdotal evidence.

The focus of the current LCHF movement involves limiting carbohydrates (carbs) to <30g or <50g per day, and obtaining 75-80% of total energy from fat and 15-20% from protein. To consume these levels of fat usually means eating a significant amount of cheese, cream, nuts, grass-fed meat fat and oils. The aim of this diet is to achieve an increase in ketone levels to reach “ketosis” (not to be confused with ketoacidosis) – hence the ‘Keto diet’ or ‘Ketogenic diet’.

“Higher intensity exercise (85-90%) requires access to muscle glycogen, something that an LCHF diet resists.” (Burke, 2015)

To explain this further, and this is by no means a comprehensive or complete overview – for that you will need a Biochemistry textbook – when the body is deprived of glucose (low carb or starvation), blood glucose is initially maintained through gluconeogenesis (new glucose is made from breaking down protein). At the same time, the breakdown of fats into the molecule Acetyl CoA provides energy (ATP). Note: The brain can’t use Acetyl CoA directly, and Acetyl CoA can’t be converted to new glucose in this pathway.

After a certain period of time (two to three days in starvation) our bodies decide enough is enough and we need to conserve our protein. Fatty acids then become the dominant fuel source, causing an increase in Acetyl CoA. When levels of Acetyl CoA rise (due to a down-regulation of NADH), they are converted to ketones, which are released by the liver into the blood and used similarly to glucose (i.e. can be used by the brain). The time taken for this to occur in a non-starved state (on an LCHF diet) has been recently shown to occur within three weeks (Burke et al., 2016).

One of the alleged benefits of using ketones for fuel is the abundant store of ketones that even lean athletes have. As such, an athlete should be able to exercise for prolonged periods without having to refuel. While this process takes time to adapt to, it has been shown that glycogen utilisation (stored glucose) may be reduced four-fold, and blood glucose utilisation reduced three-fold during moderate intensity cycling (Phinney et al., 1983) post-adaptation. However, we simply don’t know how much energy can be derived/is available from ketones for use during exercise (Burke, 2015). 

LCHF Benefits vs. Detriments

There is no question that, in as short as five days of following a LCHF diet you will be able to oxidise (burn) more energy from fat in your muscles. Sounds good so far, right?


As detailed above within three weeks you can achieve ketosis, and reduce your reliance on carbohydrate for fuel – both Phinney et al. (1983) and Burke et al. (2016) found a fat oxidation rate of ~1.5g/min during moderate exercise. However, the ability to perform high-intensity exercise is compromised by not having the stores of carbohydrate, or ability to access these stores as readily. Furthermore, the body is more efficient at burning glucose than other substrates for energy.

How do we know this?

A recent Australian study put three groups of race walkers on either an LCHF, high carb or periodised high carb diet during a training camp for three weeks (Burke et al., 2016). They assessed both lab (walking economy) and field measures (1km, 10km and 25km time-trials) to compare the group’s pre- and post-training. Interestingly the LCHF group required more oxygen (VO2) to perform at the same 20km and 50km race speed pre vs. post, while the other groups had no change. We could say from this data that the economy of effort was worse on an LCHF diet.

Furthermore, the 10km time-trial performances were improved on both high carb diets, though no change was seen on the LCHF diet after training (Burke et al., 2016). The reason being that higher intensity exercise (85-90%) requires access to muscle glycogen, something that an LCHF diet resists (Burke, 2015). Furthermore, carbohydrate releases more energy for a given amount of oxygen, i.e. it is simply more efficient than using oxygen to burn fat. Finally, that difference in economy can be perceived, i.e. it will feel harder to perform a given intense workload, on an LCHF diet (Burke, 2015).

You may be thinking that, as a triathlete, most of your training is at lower intensities, however anytime we call upon a higher intensity – be it accelerating out of transition, running up a hill or battling a headwind – we will call upon higher energy states. Conversely, if you are performing ultra-distance training/racing at sub-maximal intensities, or if you’re competing in events where access to carbs or any food is an issue, then an LCHF approach may be of benefit to you.

For those looking to trial LCHF, I would question the long-term implications of a high fat, keto diet for your health. I would also be careful about ensuring adequate fruit and vegetable intake to tick-off vitamin and mineral requirements, along with making sure your fibre intake is adequate. Furthermore, due to some LCHF’ers reliance on cheese to make up their fat quota, salt intake is a consideration. Finally, initial side effects of the diet may include an upset stomach and constipation.

As a side note: A review article by Noakes, Volek and Phinney (2014) called for more research into the LCHF diet for athletes. Though I believe they were a little short sighted in their blanket approach, suggesting that dietary prescription for athletes is currently based on exclusively high-carbohydrate diets. The current sports nutrition recommendations are for an individualised dietary plan and periodising carbohydrate intake – using carbs where they will have the most benefit.

For a more in-depth look at LCHF for sports performance, I would thoroughly recommend Louise Burke’s excellent review article (2015). At this point, I would like to state I have a bias towards her work. However, she is extremely balanced in her approach and recommendations.

Paleo 101


The Paleo diet, as most readers will be aware, stems from the idea that we should eat like our distant ancestors or cavemen. There are different variations of this diet, though using one of the ‘developers’ as a source would suggest a reliance on meat, fish, fruit and vegetables while avoiding processed foods, dairy, grains, seed oils and legumes. This effectively makes it low carb, unless an individual chooses to eat potato/sweet potato and a significant amount of fruit. It is generally high protein and high fat though percentages aren’t set.

Paleo Benefits vs. Detriments

For some people, moving to a Paleo diet will mean they improve their diet quality, with a greater reliance on fresh veg, fruit and less processed foods. If you were an endurance athlete looking at this diet, you would need to be deriving most of your carbohydrate from sweet potato and fruit.

The detriments to Paleo include the exclusion of legumes, which is nonsensical. Also, on this diet, you will likely be getting way more protein than you need or can use, plus the long-term consequences of a very high protein diet aren’t clear (and it’s expensive). Removing grainy foods may result in reduced fibre intake. You may also be getting significant amounts of saturated fat. Furthermore, unless you are lactose intolerant, there isn’t valid evidence to limit dairy. Finally, with a Paleo diet, you are limiting your choices for event competition and easily digestible pre-race carbohydrates.

My suggestions for triathletes on a Paleo diet would be to limit their red meat/saturated fat intake and think about including legumes/beans and some whole grains for carbohydrate energy. This would actually bring you closer in line to the Australian Dietary Guidelines.

The Australian Dietary Guidelines

While on the topic of recommending carbohydrate intake, something that gets thrown around like an old set of training togs, is the Australian Dietary Guidelines (ADG). This is a document based on thousands of research articles and while it needs adapting for individual recommendations, particularly sports people – it is a great starting point for Australians. The suggested number of grainy products per day is six serves (18-51year olds), which equates to, at most, around 160g carbohydrates. If you added a medium spud (counting as two serves of vegetables) and two big pieces of fruit, you might get to around 240g carbs. For an endurance triathlete in heavy training, this is a relatively low intake of carbs. So, my suggestion would be for most triathletes thinking about trialling one of the above diets, is to take a look at the ADG’s first and use this as a guide for the minimum amount of carbohydrate you should be aiming for.

My Interpretation

Finally, while it is easy to get caught up in the hype, and it may sound great to try something new and exciting, sometimes we need to step back and look at the evidence clearly. While an LCHF approach may assist those participating in ultra-distance, low intensity events, for most triathletes there is no question that carbohydrate intake, individually prescribed, will facilitate faster times, better training responses, less perceived effort and better economy of effort – more on this in another edition when Alicia discusses ‘training low (carb)’.

Disclaimer: please discuss any drastic dietary change ideas with a sports physician or accredited sports dietitian first, as any underlying disease factors need to be addressed by a professional to ensure your safety.



Burke, L. M. (2015). Re-Examining High-Fat Diets for Sports Performance: Did We Call the ‘Nail in the Coffin’ Too Soon? Sports Med, 45 Suppl 1, S33-49. doi: 10.1007/s40279-015-0393-9 Burke, L. M., Ross, M. L., Garvican-Lewis, L. A., Welvaert, M., Heikura, I. A., Forbes, S. G., . . .

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. doi: 10.1113/jp273230

NHMRC. (2013). Australian Dietary Guidelines.  Canberra: National Health and Research Medical Council.

Noakes, T., Volek, J. S., & Phinney, S. D. (2014). Low-carbohydrate diets for athletes: what evidence? Br J Sports Med, 48 (14), 1077-1078. doi: 10.1136/bjsports-2014-093824

Phinney, S. D., Bistrian, B. R., Evans, W. J., Gervino, E., & Blackburn, G. L. (1983). The human metabolic response to chronic ketosis without caloric restriction: preservation of submaximal exercise capability with reduced carbohydrate oxidation. Metabolism, 32(8), 769-776.


Peter Herzig

Centred Nutrition was founded by Peter Herzig (APD). Peter is a qualified Dietitian and Accredited Sports Dietitian who also has a degree in Exercise Science. Peter set up Centred Nutrition in Brisbane and the Sunshine Coast to focus on a client centred approach; as there is no one solution in nutrition that will work for everyone.

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