July 15, 2024


The early part of the year is an active one for all the distance runners, cyclists and triathletes. We have the local running marathons coming up in which many are participating in order to qualify for events like the Two Oceans Marathon or the Comrades Marathon. Swimmers are training for the Midmar Mile and the Troutbeck Mile Open Water Swim whilst triathletes are gearing up for the Troutbeck Triathlon in mid-February.

The “traditional” dietary recommendations for sport and exercise hinge around a relatively high carbohydrate intake to meet the energy demands of training and performance. So begs the question: is there a role for low-carb high-fat diets (LCHFD) for exercise, training and sports performance?

It is the topic of numerous anecdotal reports by athletes in many disciplines who have been using a LCHFD successfully, even at the top level of sporting performance including the New Zealand All Blacks rugby team, Tour de France champion cyclist, Chris Froome, and swimming world record holder, Adam Peaty. The research evidence is also growing and although it is not yet overwhelming, it is certainly enough to challenge the traditional facts, dogmas and doctrines regarding optimal sports nutrition for athletes. A low-carb nutrition program may offer significant benefits to athletes in training and sports performance over the traditional high-carb athlete diet.

Traditional high-carb diets in athletes have several potential drawbacks such as:

  • “hitting the wall” in prolonged exercise which describes the fatigue that results from liver and muscle glycogen depletion and insufficient glucose for the muscles and brain.
  • gastrointestinal upset from the sugary goos and gels ingested during long events.
  • increased body weight from carb-loading strategies.
  • reduced use of fat for energy since a high-carb intake blocks the utilisation of our more efficient and longer-lasting fat stores for exercise.
  • an increased long-term risk of adverse health outcomes like diabetes, heart disease and dental problems.

Click here to check out Callie Ann’s recipe for Peri peri prawns for a quick low carb meal

Our body fat stores are considerably larger (20 – 40 times larger in calorie terms) than our carbohydrate reserves. Fat is a very efficient fuel that supplies 9 kcal of energy per gram, which is more than double that of carbs. Utilisation of fat-derived ketone bodies creates more energy than glucose because of greater muscle energy production from ketone bodies.

A low-carb, high-fat program promotes fat adaptation and physiologically increases the capacity of the body to utilise fat for fuel to provide energy for exercise. There is a wide individual variance in time and degree with respect to fat adaptation. Upon starting a low-carb, higher-fat program, an athlete takes about 7 days to show early fat adaptation, and up to 2 weeks to resume effective training, after experiencing a period of fatigue and weariness during this early fat adaptation phase. It can take 2 – 4 weeks to exercise at previous endurance performance levels or to resume hard training. It can take 2 – 6 months for full fat adaptation to occur on a level commensurate with high performance in ultra-distance sport.

Fat adaptation results in markedly reduced rates of muscle glycogen (sugar) utilisation, effectively sparing muscle glycogen stores for the finishing sprint. Significantly high rates of fat utilisation can be achieved sufficiently enough to allow an athlete to cover their fuel requirements during an Ironman Triathlon event without the need for extra fuel!

Fat adapted athletes experience less muscle soreness and faster recovery from prolonged exercise. A LCHFD is associated with improved health biomarker levels of blood sugar, insulin and cholesterol lipoproteins.
An in-between option is the “train-low-race-high” strategy, which may benefit athletes doing shorter-distance, higher-intensity races like middle distance run events. This involves a low-carb, higher-fat diet during training, and then an increased carb intake immediately before and/or during an event. Sports scientists in Australia have done some great research on this model of sports nutrition and found that it suits some athletes extremely well.

In summary, alternative nutrition strategies such as a lower-carb diet may have significant advantages for athletes. Expert advice is recommended before one makes dramatic switches and each and every person will need to see what does and does not work for them when it comes to personal sports nutrition strategies.

Also read Dr Jeans article Cholestrol 101 for more healthy living advice

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