Food dialogue: The case for fats

Professor Tim Noakes OMS, MBChB, MD, DSc, PhD (hc), FACSM, (hon) FFSEM (UK), (hon) FFSEM (Ire)

Had you asked me that question (Should athletes ingest fat or carbohydrate before and during exercise?) a decade ago, I would have had no doubt about my answer. Carbohydrates before, during and after exercise – as much as you can stomach. Simple. That is what I wrote in my book Lore of Running. Now I am rather less certain.

The reason why I was so certain a decade ago was because that is what I had been taught. I started my academic career in 1969, in the decade that the muscle biopsy technique was introduced into exercise physiology by Swedish scientists, especially Drs Bergstrom, Hultman and Saltin. These three became iconic for their discovery that muscle glycogen appeared to them to be THE critical factor determining human endurance exercise performance. In retrospect these fine scientists did exercise science a disservice for they were guilty of reducing exercise performance to a single variable – the one they could most easily measure with their new technique – muscle glycogen content. Forty years earlier, AV Hill and Frederick Hopkins has made the same error by reducing maximal exercise performance to two simple variables – oxygen and lactate.


So when I entered my professional training, I was immediately introduced to the concept that all of human endurance performance could be reduced to that one single variable – how much glycogen the athlete had stored in his or her muscles before the start of exercise. For many years nothing else mattered. But then in 1986 a US study by Dr Ed Coyle, funded by the US sports drink industry, apparently showed that by ingesting glucose during exercise, the athlete could further enhance his or her performance.

This was a godsend to people like myself and Fred Brouns because now we could leverage these commercial companies to provide us with the funds to do research that would advance this certainty. So we tested multiple different combinations and concentrations of carbohydrates with the goal of maximizing the rate at which athletes could ingest, absorb and oxidize the carbohydrates contained in our fabulous concoctions. A key goal for us was never to come to a final conclusion – always we assumed that next year, with more of industry’s money, we would be able to come up with an even more potent concoctions that would turn our exceptional athletes into world-beaters.

Of course at no time could we ever have considered that we were simply a tiny part of industry’s grand plan to sell ever more products to gullible athletes who really should not have been so stupid to believe that drinking sugar water before and during exercise was really the key determinant of their athletic performances. (Don’t you think training and proper peaking might just be more important?) But to insure that we would all remain gullible, industry went one step further and bought the compliance of major sports science organizations like the American and European Colleges of Sports Medicine. As a result, exercise scientists attending the meetings of those organizations only ever heard one message: Carbohydrates are the key determinant of exercise performance. So that if you wish to perform optimally, it is essential that you eat as much carbohydrate as possible before exercise (carbohydrate-loading) and then during exercise you ingest preferably 100g of carbohydrate every hour that you compete.

That then is the state of advice that athletes are given by those exercise scientists who attend only those academic meetings funded by the big industry players and who listen only to those key opinion makers who are themselves funded by that industry.


My own epiphany occurred in December 2010 when I realized that all the carbohydrates that I had eaten for the previous 33 years (since I had first adopted a high carbohydrate diet) had seriously harmed my health by causing me to develop type 2 diabetes (I have a very strong family history of diabetes).

Realizing that continuing on the same nutritional pathway would simply cause my early death, I decide to do the polar opposite to what I had advocated in my book Lore of Running. So I converted within a few days to eating a carbohydrate-restricted higher fat diet. The results to my health were utterly miraculous. This then set me on the path of trying to understand where does a high fat diet fit in athletic performance and long term health.

My conclusions of my personal experiment and the intensive reading on the topic that I have done in the past 5 years are the following:

  1. Humans differ in the degree to which they express the metabolic state of insulin resistance. Those of us who are the most insulin resistant will benefit the most by following a very low carbohydrate diet. This is because we will retain our optimal health for longer. Also because we have an impaired capacity to utilize carbohydrates as a fuel we are essentially “metabolically-crippled” when we try to exercise on very high carbohydrate diets. In contrast we have an inordinate capacity to oxidize fat when adapted to a high fat diet.
  2. Humans have a much greater capacity to oxidize fat during exercise than is currently recognized, especially when fat adapted. The idea that during high intensity exercise (>80%VO2max) all the energy comes from carbohydrate is false. In fact new research shows that the best athletes are able to acquire considerable amounts of energy from fat even at 100% VO2max. In fact the best performers during high intensity sprinting exercise are those who generate the most energy from fat.
  3. High carbohydrate diets especially if full of sugar and refined carbohydrates produces a gut biome (gut bacterial population) that favours a whole-body inflammatory state. This will delay recovery from high intensity exercise.

Thus the possibility not foreseen by those Swedish exercise scientists who introduced the muscle biopsy needle, is that the high carbohydrate diet they promoted may on occasion produce a superior one-off endurance performance. But by promoting a state of whole body inflammation, the high carbohydrate diet might reduce the capacity to train hard and to recover quickly, leading ultimately to sub-optimal athletic performances.

The future of our understanding of the optimum diet for training must include an analysis of the effects of that diet on training intensity and recovery and on long term health and risk of developing medical conditions like type 2 diabetes. And not simply the effects of different diets on single one-off laboratory exercise test (under artificial laboratory conditions).

It is time to retire the bias that we learn from our tutors. Specifically that exercise performance can be reduced to a single variable, specifically the amount of carbohydrate in the diet.

We should by now be too sophisticated to accept that too-simple explanation.

Brouns guest blog



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