The Good, the Carbs and the Fat: Low Carb-High Fat Diets

To the disbelief of most, a lot of people, especially endurance athletes, are switching to diets high in fat (saturated and unsaturated) and low in carbs, completely going against the idea that fat and cholesterol is bad for you and that you need carbohydrates for energy. Before a long training or a race, instead of eating pasta or rice the ‘low carb-high fat’ (LCHF) athletes would be eating eggs, coconut milk, butter, nuts, seeds, fish and cream! It’s the complete opposite to what you would expect, but why are they doing it?

Firstly, your body has limited glycogen stores from carbohydrates but a relatively unlimited ability to store fat so once you teach your body to crack into these unlimited fat stores your endurance will hypothetically be enhanced. Plus, fat produces 9kcal per gram whereas carbs only produce 4kcal so your body requires less weight to produce energy, improving an athlete’s power to weight ratio.

Secondly, you have no nutritional requirements for carbohydrates. There are no diseases associated with a lack of carbohydrates yet there are illnesses associated with a lack of fats such as liver and kidney degeneration.

Thirdly, high carbohydrate diets have been known to lead to diabetes and cardiovascular diseases (But haven’t high fat diets been linked to heart diseases too? Well, keep reading) whereas a high fat diet regulates insulin and is ‘better’ for your heart.

Evidence Behind the Health Theories

Dr Jeff Volek conducted a study which was very interesting because he took athletes who had trained and adapted to high fat and high carb diets to compare the differences. Most other studies don’t give the participants sufficient time to fully adapt to the different diets so this study is a lot more accurate in that sense.

One of the significant findings was the amount of fat oxidation in the LCHF athletes compared to the high carb athletes. At a given intensity over 180mins, the LCHF athletes were getting about 85% of their energy and a mere 15% from carbs whereas the high carb athletes were only getting about 55% of their energy from fat and about 45% from carbs. It goes to show that the change in diet really did help to enhance the body to start using fat for energy, a much larger energy source than carbs. It was then noted in other studies that the adaption, or partial adaption, significantly improved participant’s exercise time to exhaustion despite having a lower muscle glycogen concentration. An interesting comparison to Volek’s study was that he found that the high fat athletes had the same muscle glycogen as the high carb athletes, so maybe if the participants had more time to adapt their muscle glycogen would have been the same too.

Volek also found that when the high fat athletes were given a high fat drink after exercise, their muscle glycogen restored at the same rate as the high carb athletes who had a high carb recovery drink after exercise.

There are also many studies and reports finding that people’s VO2 max and their “top gears” drop but Volek found that there was no significant difference in the VO2 max but this can also be because the athletes had spent time fine tuning their diets, perhaps implementing few, but sufficient carbs where necessary to keep their top gear.

Cholesterol: the cause of heart disease?

It has been admitted that the US Dietary Advisory Guidelines Committee came up with this theory but had no sufficient evidence behind it and have recently given cholesterol a “pardon” saying that it’s no longer a nutrient concern. These days we know that cholesterol isn’t bad, it’s only if the cholesterol oxidises that it becomes bad and will contribute to plaque in the arteries. High density lipoproteins (HDL cholesterol) and antioxidants have been found to stop the oxidation process so as long as there is a sufficient intake of unsaturated fats and antioxidants, enough HDL is produced to prevent the oxidation process.

In fact, it has actually been found that carbohydrates are worse for you than saturated fat in terms of heart disease as they contribute more to arterial clogging and, if there is not unsaturated fat in the diet, there are not so many HDL, increasing the risk of cardiovascular heart disease. Note, however, that trans fat (fries, donuts, margarine) has been found to cause arterial clogging along with omega 6’s so you should try to avoid them and balance them out with sufficient omega 3’s and other unsaturated fats.

A LCHF diet uses less carbs so less insulin is required. Insulin is a hormone that promotes the transfer of blood glucose to glycogen which is energy that can be used by the muscles. Fat still requires insulin in order to be converted into useable energy, but nowhere near as much as carbohydrates or sugar so for someone who is insulin resistant or has an insulin deficiency (especially a diabetic), a LCHF diet takes stress off their insulin requirements. Volek also found that the high fat adapted athletes had a much lower and constant insulin level than the high carb athletes which is a very important finding in modern society with such a large population of athletes and non-athletes suffering insulin related diseases.

It’s also worthwhile being aware that low carbs doesn’t mean no carbs…fruit and vegetables are essential because they are full of vitamins, minerals and antioxidants. Rather the diet suggests substituting rice, bread or pasta for foods high in fat.

The Negative Side

It almost sounds too good to be true, right? Well there are a few things that need to be considered. First of all, as we mentioned, a lot of people find that they miss their “top gear” on a LCHF diet. When you are performing at your VO2 max, fat is no longer the energy source so it is definitely something worth considering. Majority of the athletes following a LCHF diet are doing Ironman or ultra-marathons where you sit at a steady state most of the day. Cyclists, on the other hand, are constantly having to crack into anaerobic zones so there is question as to whether it would pay off for a cyclist.

There is also a lack of long term research. We don’t know of any long term effects yet because there aren’t a significant enough number of people who have been on the diet for their whole life. So whether it leads to different problems (or benefits), we don’t yet know.

Then there’s the practical side. Once you commit you will have problems if you are travelling or going out and about with friends and family because the majority of society is high carb, not high fat. You will really stick out like a sore thumb and will also have to find an alternative to taking pre-made, pre-packaged gels and bars to races or training because they are almost all high carb. Implementing the diet will take a lot of commitment and self-discipline.

LCHF diets may help enhance endurance and be better for you but they can also affect your top gear and be really hard to implement in modern western society. Perhaps the world should change towards a diet higher in fat because of the research supporting the health effects, an interesting idea to consider, but it’s a bit strange to suddenly hear the complete opposite to what you’ve been hearing your whole life about fat, right? Food for thought.

For more info check these links out:



Abbott, W.G.H., Howard, B.V., Swinburn, B.A. (1991). Evaluation of Metabolic Effects of Substitution of Carbohydrates for Saturated Fat in Individuals with Obesity and NIDDM

Booyens, J., Louwrens, CC., Katzeff, IE. (1998). The role of unnatural dietary trans and cis unsaturated fatty acids in the epidemiology of coronary artery disease, Med Hypotheses; 25:175-182.

Christiansen, M.P., Hellerstein, M.K., Krauss, R.M., Neese, R.A., Parks, E.J. (1999) Effects of a low fat-high carbohydrate diet on VLDL-triglycerides assembly, production and clearance, Journal of Clinical Investigation 1999, 104(8)

Christie, C., Dennis, S. C., Goedecke, J. H., Hopkins, W. G., Lambert, E. V., Noakes, T. D., Wilson, G. (1999). Metabolic adaptations to a high-fat diet in endurance cyclists, Metabolism Clinical and Experimental 1999, Volume 48, Issue 12

Dennis, S. C., Lambert, E. V., Noakes, T. D., Speechly, D. P. (1994). Enhanced Endurance in Trained Cyclists During Moderate Intensity Exercise Following 2 Weeks Adaption to a High Fat Diet, European Journal of Applied Physiology and Occupational Physiology 1994, Issue 4 Volume 69

Hu, F.B., Krauss, R.M., Siri-Tarino, P.W., Sun, Q. (2010). Saturated Fat, Carbohydrate and Cardiovascular Disease, The American Journal of Clinical Nutrition 2010, Volume 93, Issue 3

Noakes, T. (2014). Prof. Tim Noakes – ‘LCHF for Elite Athletes’,

Noakes, T. (2014). Prof. Tim Noakes – ‘Medical Aspects of the low carbohydrate lifestyle,

Volek, J. (2015). Prof. Jeff Volek – ‘Nutrition for Optimising Athletic Performance’,

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