Are low carbohydrate diets the 29-inch wheels of the mountain bike world?

Are low carbohydrate diets the 29-inch wheels of the mountain bike world?

I’ve learnt to recognise that contemplative look on people’s faces when they find out I work with Prof Tim Noakes and conduct research on low carbohydrate diets. I smile to myself as they recollect controversial snippets of news about the infamous professor, and then formulate questions like: “So is Tim right?” or “So should I also be following a low carbohydrate diet?”. To give myself the slightest chance of keeping a lid on the Noakes can of worms, I’ll just concentrate on the second question here. My quick answer is: “Well, it depends, but you could try out a well-formulated low carb diet to see if you like it”. My preferred answer is a little more complex and involves bicycles.

I’m going to shift gears quite dramatically now to share an analogy that developed over numerous mountain bike rides as I tried to illustrate the complexity of this second question to my cycling buddies. Put simply, diets are like mountain bikes, and choosing to go on a low carbohydrate diet is like choosing to buy a bike with 29-inch wheels, commonly known as a 29er. Don’t worry if you’ve never used inch and wheel in the same sentence, I’ll give you a quick explanation to bring you up to speed. Mountain bikes originally came standard with smaller 26-inch wheels. This wasn’t because of any solid research at the time to determine the optimal wheel size, but rather because tyre manufactures produced 26-inch tyres, so bike manufactures designed 26-inch wheel bikes, and that is what the public bought and rode for many decades without questioning it. In the early 2000’s, bicycles with bigger 29-inch wheels started appearing on the scene. There were a few ardent fans who raved about how fast these wheels were but these bikes were too niche and expensive, and the geometry wasn’t quite right for them to gain mainstream traction. Then in the last decade there has been a wheel size revolution as 29ers exploded onto the scene. This is where the diet-bicycle analogy starts.

Low fat (high carbohydrate) diets are a bit like the smaller wheel 26ers. Since the 1970s, most national dietary guidelines advised against eating much fat (especially saturated fat from meat) and promoted foods that were high in carbohydrate, despite very little scientific evidence to support these recommendations at the time (1). This coincided with a commercial market full of foods that were processed to be low in fat and high in refined grains and sugar. This was what we were told was healthy, this is what food manufacturers produced, so this is what we ate, largely without questioning it.  During this time, a few low carbohydrate diets (the early 29ers) emerged in the public sphere, most notably the one made famous by Dr Atkins. However, the Atkins diet was considered too unorthodox and dangerous to be taken seriously, so the low-fat dogma prevailed. In the past decade however, there has been the makings of a low carbohydrate revolution with very low (less than 10 %), low (10 – 26 %) and moderate (26 – 45 %) carbohydrate diets becoming much more popular. Low carbohydrate diets have now also been extensively researched both in athletic and clinical populations, however it is worth noting that the well-controlled studies are relatively short term (5 days to 2 years). While still very informative, the long-term safety of these diets can only be extrapolated from these short-term studies. Recently the American Diabetes Association (ADA) even acknowledged that there is merit for carbohydrate restriction in certain therapeutic applications, which is a pretty big step in the right direction.


Diets are similar to bicycles in other ways. Just like the food we eat is made up of macro- and micronutrients, bicycles are made up of macro components – the wheels, frame and fork (front suspension), and micro components – the nuts, bolts, brake pads, bearings etc. The presence and quality of each one these components or nutrients is important and will affect how the bike handles or diet affects us. Just like diet, it is very difficult to significantly change just one of the macro components of a bicycle without changing the others. You can’t just put 29-inch wheels on a 26er because they won’t fit into the frame and front fork. You would need to buy a different frame and fork, both of which would probably be lighter and better quality because they are newer. And since you are spending so much money anyway, you may as well upgrade the brakes, gears, saddle etc. So now ask yourself the question: Are you going faster just because you have bigger wheels or because you have an entirely new bicycle? The point of this digression is that we do the same when we experiment with cutting out carbohydrate. We call it a low carbohydrate diet for convenience, but we invariably eat more fat and protein, eat fewer total calories, choose heathier types of fat, spend a bit more money on the grass-fed and cold-pressed options, do away with ultra-processed grains, oils and E numbers, drink a bit less alcohol, smoke less, exercise more, reduce stress etc. etc.  So, are you now experiencing these wonderful health improvements because you reduced dietary carbohydrate per se, or because you have generally adopted a much healthier lifestyle?  Chances are it’s a bit of both, but this will vary depending on who you are.

Back to the actual question of whether a person should go on a low carbohydrate diet. I try to get the person to answer this for themselves by explaining that it depends on:

  • The person and what they want to achieve with carbohydrate restriction
  • What their low carbohydrate diet will look like
  • What their current diet looks like
  • Whether they are prepared to deal with the challenges of following a low carbohydrate diet.

In the same way that different bicycles are suited to different riders and disciplines, different diets are suited to different people and their unique goals. A marathon racer doing the Cape Epic (an 8-day ultra-endurance mountain bike race) would almost certainly perform better on a 29er, because the bigger wheels carry more momentum over rough ground, so the bikes are faster over this type of terrain. A dirt jumper on the other hand would never consider a 29er, because 26ers are much better for doing triple back flips on a smooth jump track. Then there is a grey area discipline: fast, steep, technical downhill racing, where choice of wheel size comes down to personal preference. Some riders, like myself, prefer the agility of smaller 27.5-inch wheels while others prefer the raw speed of 29-inch wheels. Overall race times are not that different between the two but the bikes will feel very different to ride. For others who are more interested in cruising around town, wheel size per se won’t be that important, as long as the bike fits them, looks cool and the components are decent quality.

This fits with the carbohydrate restriction analogy. In the same way that 29ers are faster for marathons, low carbohydrate diets are particularly effective for improving certain metabolic and neurological conditions, most notably type 2 diabetes and epilepsy, but also obesity and markers of cardiovascular disease (2). In fact, it’s becoming increasingly common for patients with type 2 diabetes to be able to normalise their blood sugar and stop taking diabetes medication while following a low or very low carbohydrate ‘lifestyle’ (3-5). In other words, they can put their diabetes into complete remission with relative ease. Previously, remission was only considered possible with bariatric surgery or severe calorie restriction. On the other hand, carbohydrate restriction is probably detrimental for elite performance in high-intensity endurance events. I say ‘probably’ because that is the direction that the current scientific literature is pointing (6), but the definitive study has not yet been done to confirm this. So far, the studies have been too short for athletes to properly adapt to the diet, which would disadvantage the low carbohydrate arm. Sub-elite endurance performance is perhaps a grey area for low carbohydrate diets, like downhill racing is for wheel size. Some endurance athletes appear to perform better on a low carbohydrate high fat diet or just prefer the feeling of having sustained energy, without necessarily having to eat before and during exercise (7,8). Others do much better on a high carbohydrate diet and feel that they need carbohydrate before and during exercise in order to perform well. Overall though, the research suggests that most athletes should be able to maintain endurance performance after adapting to a low carbohydrate diet (9-11), but exercising will feel very different between the two diets and will require different fuelling strategies. Finally, for people who are recreationally active, normal weight and apparently healthy, the amount of dietary carbohydrate per se (within reason) will be less important for health and well-being, compared to other factors like food and macro- and micronutrient quality.

Whether someone would experience a benefit from restricting carbohydrate would also depend on the quality and composition of their current and planned diets. Just like bicycles, low carbohydrate diets can vary considerably in type and quality. A low carbohydrate diet full of industrially refined vegetable oils that are laden with omega-6 polyunsaturated fats, and without a variety of nutritious foods, is a bit like a R500 29er bought from a supermarket. It may be fine for now, but a few years down the line, or as soon as you push it on rough terrain, it will fail. A diet of bacon and bullet proof coffee which became synonymous with a low carb diet in the media, is not much better. On the other hand, a diet consisting of minimally-processed whole foods such as grass-fed meat and full cream dairy, fish, free range eggs, a large variety of non-starchy vegetables, nuts, seeds, berries, moderate amounts of cold pressed olive and coconut oils, and a small amount of starchy vegetables and legumes would be the low carb equivalent of a high-end carbon fibre racing 29er. This type of diet would likely fit into the low carbohydrate category (10-26 % of calories). I believe that anyone can safely try this diet out for at least a month or so to see if it suits them with the possible exception of those with the following contraindications: pyruvate carboxylase deficiency, porphyria or inborn errors in fat metabolism. I would particularly encourage anyone with a family history of diabetes to give this diet a go, and to monitor how it makes them feel. For people with metabolic conditions, especially those taking chronic medication, it is strongly advisable that they do so with the help of a physician because some medications may need to be reduced with carbohydrate restriction. It is worth choosing a physician who is accepting of, and has experience treating patients on a low carbohydrate diet because blood tests will need to be interpreted differently. If a person can overcome the challenges of adapting to the diet, which may include a few weeks of low energy and constipation, and they don’t mind the inconvenience, expense and social awkwardness of following it, then I see no reason why they shouldn’t stick with it, if they prefer how it makes them feel.

Increasing the cold pressed oils and animal fat, moderating the amount of dairy and nuts, and cutting out all fruit, legumes and starchy vegetables would put this low carbohydrate diet firmly into the very low or ketogenic category. This type of diet is mainly worth considering if you want to treat an advanced metabolic or neurological condition like diabetes, obesity or epilepsy (for which there is considerable supporting clinical evidence (2) ) or for competing in an ultra-endurance event (for which there is mainly anecdotal evidence (8)). While the ketogenic diet may be overkill for most healthy people, it is not likely to be harmful as long as a variety of nutrient dense foods are eaten. An extreme version of a ketogenic diet that is becoming increasingly popular is the carnivore diet which does away with the nuts, seeds and vegetables and only includes a variety of animal products. This is perhaps a bit like a fixie bicycle, which does away with useful things like gears and brakes. I’m not mocking either the carnivore diet or the fixie (much), but both seem like an acquired taste.  Adding a moderate amount of fruit, starchy vegetables, legumes and maybe some rice to a low carbohydrate diet, while taking away a bit of the fat, would bump it up to a moderate carbohydrate diet. This is the way that I prefer to eat, because I like the way these foods make me feel. Cutting back on the added fats slightly more and adding more fruit, legumes, starchy vegetables and unrefined grains would then shift it to a good quality high carbohydrate (moderate fat) diet. Essentially, this would be the equivalent of a top-end 26er jump bike capable of pulling triple back flips. This is the type of diet that would suit many endurance athletes, but they would need to supplement with carbohydrate during prolonged exercise (12). It is also one that most healthy active normal weight people could safely follow if they wanted to, provided they kept an eye on their waistlines. Deep frying the potatoes in vegetable oil and adding refined grains, sugars, and other processed foods would drop the quality of this high carbohydrate diet to the status of an old rusty supermarket 26er. And no one wants to attempt a back flip on one of those.

For those of you who skipped to the end to find a summary, here are some key take away points:

  • It is absolutely essential to get sufficient fat, protein and a host of micronutrients in our diets. I believe this is best achieved by eating a variety of good quality whole foods that have not been heavily processed and do not contain significant amounts of artificial additives, sugar, refined grains and industrially produced vegetable oils. Get this right first, then start experimenting with carbohydrate restriction.
  • Dietary carbohydrate is not actually an essential macronutrient for humans and there is no strong evidence that eating a lot of fat, including saturated fat from meat, will increase a person’s risk for mortality and cardiovascular disease (as is commonly believed).
  • This means that most people can safely go on a well-formulated low carbohydrate diet to see how it makes them feel.
  • Different people can tolerate different amounts of carbohydrate so they will experience very different effects when removing it from their diets.
  • For those who are very intolerant of carbohydrate, it is toxic to them, and removing it from their diets will be literally life changing.
  • Carbohydrate tolerant people will likely notice less of an effect of carbohydrate restriction because their metabolism can easily switch between burning fat and carbohydrate for energy, depending on what they have eaten.

About the author:

Jamie is a scientist at the University of Cape Town’s Research Unit for Exercise Science and Sports Medicine. He completed his doctorate in Exercise Science in 2008 when he studied muscle adaptations that occur with regular exercise training and how these can improve glucose control in those with diabetes. Since 2011, Jamie has worked closely with Prof. Noakes on various projects related to a low-carbohydrate high-fat (LCHF) diet.

His first project investigated exercise metabolism and physiology (including liver glucose production) in well-trained cyclists who had followed a long term LCHF diet. He then shifted focus towards clinical populations where he studied diet and health in type 2 diabetes patients who had followed a long term LCHF diet. He is currently establishing a technique to measure liver glucose production in these  patients. He is also working on a collaborative project with Eat Better South Africa to evaluate their nutrition eduction program scientifically.

An avid sportsman, Jamie has competed in running marathons in the past, and is currently a passionate rock climber and mountain biker. Not one to shy from a challenge, he has personally tested out a range of low and high carbohydrate diets and has settled somewhere in the middle: a moderately low-carbohydrate, relatively high-fat, and whole food diet.



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