The use of low-carb high-fat diets (LCHF) for exercise, training and sports performance is the subject of increasing volumes of published research. It is the topic of numerous anecdotal reports by athletes in many disciplines who have been using a LCHF successfully for years, even at the top level of sporting performance.
The evidence is growing and although 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 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 risk of adverse health outcomes like diabetes, heart disease and dental problems.
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.
Utilization 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. Significantly high rates of fat utilisation can be achieved, which would be sufficient 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 LCHF is associated with improved health biomarker levels of blood sugar, insulin and cholesterol lipoproteins.
A ‘train-low-race-high’ strategy may benefit shorter-distance, higher-intensity athletes. This involves a low-carb, higher-fat diet during training, and then an increased carb intake immediately before and/or during an event.