Putting the High Fat Diet to the Test
The High Fat Diet has been debated by endurance athletes since the 1980s, and is commonly supported with a cult-like following by many, notably mountain runners and ultra-marathoners. But just like many diets and fads, there is only anecdotal evidence to support the claims that it is an effective, sustainable, and ideal diet for endurance athletes.
The theory is that by limiting carbohydrates as an energy source and providing the body with a large amount of fat, the body can learn to use this fat more efficiently. Fat is used as an energy source in the body under low intensity, aerobic conditions (ex: while you're sitting here reading this article), and is ideal because of the high yield of energy produced when it is metabolized by the body (good "bang for your buck"). But the catch is that fat is metabolized much slower than carbohydrates, and therefore, the body struggles to use it when energy is required at a faster rate, such as during intense exercise. In these cases, the body typically switches from burning fats (even if they are more plentiful) to carbohydrates. With the high fat diet, the thought is that the body will be depleted of carbohydrates, and will have to learn to metabolize the fats at a faster rate during intense exercise to compensate.
Nutritionists at the Australian Institute of Sport have long been sceptical of this diet choice for endurance athletes. Race walkers were the subject of choice due to Australia's predilection for the event, as well as the race distances and the largely aerobic nature of the event with multiple anaerobic components during tactical surges. 13 elite, Olympic-calibre male race walkers from a number of different countries were recruited to participate in the first stage of the Australian lead study. Evan Dunfee, UBC Human Kinetics alumnus and Canadian record holder in the 50km, was excited and keen to participate, both to satisfy his own scientific curiosity on the subject (partial credit: UBC HKIN), as well as for the prospect of high-level training with a much larger group of walkers than his training group at home. He had few reservations over making such drastic changes going into an Olympic year, as he felt that the advantages of the training environment far outweighed the potential risks.
The study period began in November, and consisted of 3 weeks on a 80% fat, 20% protein, and minimal (<1% carbohydrate) based diet. To put this in perspective, based on their daily caloric intake, the maximum carbohydrate allotment equals approximately one piece of white toast with jam; all remaining food was entirely fat or protein. All the study participants stayed on site, where every meal was prepared for them to ensure proper rationing. The meal portions were calculated based on the individual athletes' estimated energy requirements for that day, taking into account their individual resting energy requirements plus their estimated energy requirements for the day's workouts (AKA lots of math). They had three prepared meals per day, and were given daily snack rations in the morning. At meals, the participants were allowed to ask for seconds if they were still hungry, but were denied seconds if it was just because it was tasty. Typical meals included breakfasts of muslei, cream, bacon, and eggs; lunches with low-carb bread and lots of avocado; and dinners with almond satay, zucchini pasta, curry, salad, tacos, pizza, and burgers. Base-line athletic testing was completed on arrival prior to starting the test diet, then regular season training for the 3 weeks on the specified high fat diet, then post-study athletic testing on the last day to compare results.
The results of the study are not yet available as there is still testing being done with other groups of athletes, as well as other break-downs of the diet. Most scientific studies take ages to publish, which is often why these studies appear so far behind the new nutrition trends. However, we do have Dunfee's experience and opinions to shed some light on the subject. Please bear in mind that these are just one athletes' (although in the author's opinion, a very reliable and awesome one) experiences, thus rendering the report is anecdotal at this point, and cannot yet be extrapolated to any general population.
In Evan's opinion, it was really hard to get used to the small portion sizes and he was always hungry (fat has twice the calories of carbohydrates, so you need to eat less volume), his iron levels plummeted, and he felt terrible during training with a high heart rate and slower paces. Other athletes in the study struggled with gastrointestinal upset as they tried to adjust to the high fat content, but otherwise reported similar experiences. Despite feeling rough, they were all able to complete the workouts and training, and pre and post-10km walk times were equivalent. Long easy walks were decent, but speed workouts were compromised. On the plus side, Dunfee lost 5kg of weight over the 3 week trial (3kg of fat, moving from 12% lean to 9% lean) and improved his VO2max. Two weeks after finishing the diet trial, he had his best race to date and smashed the Canadian record by 4 minutes in the 50km race walk. All of the participants reported great races and excellent training over the weeks after being on the diet trial.
In Dunfee's perspective, he would never want to race on the high fat diet. His theory is that the high fat diet is an effective training diet, either due to the adaptation of burning fat more efficiently, or because of the added stress using this fuel source provides during training. He feels that he would consider using this diet during base training season, and then transition back onto a high carbohydrate diet for competition season. To quote another interview with Alex Hutchinson that Dunfee gave on the topic:
"I’ve been left pondering whether the future direction of this conversation isn’t so much a which diet is better approach, but when to utilize each diet to maximize adaptation and performance. I know a lot is being done right now looking at a periodized approach on a microcycle level (i.e. being carb restricted for a couple of workouts each week). But it would be interesting to research the application of a perdiodized high fat low carb diet throughout an entire season. Where the base training (mostly LSD training anyways) could be done on high fat low carb to get the fat metabolism adapted and as you enter pre-competition builds you re-introduce carbs and consciously try to adapt that system to its full potential, probably still keeping a few workouts a week carbohydrate depleted to maintain the gains made earlier. Obviously these adaptations would be time limited, much like altitude, and I could not fathom a guess as to how long the adaptations would last, but I think it is a perfect direction for future study.
Evan is currently in preparing for the IAAF World Race Walking Team Championships on May 7 and 8th in Rome. You can follow Evan Dunfee on his Road to Rio with his blog: http://dunfeewalks.weebly.com/.
Dr. Brittany Imlach BHK 2012 | Human Kinetics & Biology
DVM 2016 | Veterinary Medicine XC, 800m, 1500m
