Fat as a fuel

Increasing the reliance on fat as fuel during sport has certainly taken the sports nutrition world by storm in recent years, and this has forced many athletes to question if their current nutritional beliefs and practices are correct. Celebrity endorsements, television shows and some elite athletes praising the Low Carbohydrate, High Fat (LCHF) approach have driven this, in relation to improving athletic performance and long-term health. So which method is the best for athletes going forward? Research indicates fat can predominantly be used as a primary fuel source for exercise at lower intensities, however the conjecture seems to be which fuel source is favoured during periods of higher intensity exercise. Advice to athletes used to be: consume large amounts of carbohydrate throughout the whole day. This was in the days before the LCHF argument came to prominence. The LCHF approach poses an interesting question: if we can use fat as a fuel (as we have enough fat stores to fuel us for days) during higher intensities, does this conserve our glycogen stores (which are quite limited)? This reliance on fat during higher intensities can be achieved through maximising the exercise stimulus and changing the diet to consume high amounts of fat, moderate amounts of protein and low amounts of carbohydrate. A period of 4-10 weeks must be dedicated to “fat adapt” an athlete fully, which may mean significant compromises being made to the training program, as the athlete will feel fatigued and perform at a reduced capacity during this time. Sports dietitians may have previously taken a low fat, high carbohydrate approach in the past; however presently, we tend to take a “smart carb” approach. This means periodising the carbohydrate intake around an athlete’s training program and selecting lighter intensity, non-performance based sessions to reduce carbohydrate or “train low” in the lead up to that session, where over a period of 3-4 weeks, the athlete can achieve the same metabolic adaptations to the LCHF approach without compromising their training program. This additionally allows the athlete to be “metabolically flexible” in switching efficiently between their two fuel tanks dependent on the exercise intensity, as opposed to the LCHF diet which can impair the ability to use glycogen as a fuel source during bouts of high intensity exercise (sprint to the line or surge up the hill). No matter which camp you sit in, we all agree that our reliance on refined carbohydrate needs to decrease. However there are less restrictive approaches which can allow athletes to learn how to strategically use food to benefit their sporting performance, rather then forcing them to restrict themselves to the point where they mentally cannot cope, feel fatigued and may potentially compromise not only their training, but also their overall immunity and health. Stellingwerff T, Cox GR. 2014. Systematic review: Carbohydrate supplementation on exercise performance or capacity of varying durations. Appl. Physiol. Nutr. Metab. 39(9): 998-1011 Stellingwerff T, Spriet LL, Watt MJ, Kimber NE, Hargreaves M, Hawley JA, Burke LM. 2006. Decreased PDH activation and glycogenolysis during exercise following fat adaptation with carbohydrate restoration. Am. J. Physiol. Endocrinol. Metab. 290(2): E380-E388 Burke LM, Hawley JA. 2002. Effects of short-term fat adaptation on metabolism and performance of prolonged exercise. Med. Sci. Sports Exerc. 34(9): 1492-1498