Most people, especially those in endurance sports would say that no, they cannot perform off a high fat diet. And, for many years this would have been thought true as it was believed that competitive athletes should, and must in some cases, consume a diet rich in carbohydrates to fuel their training. Further to this, it was often professed that athletes, especially those of the endurance variety, should avoid fatty foods because they were thought to be an inefficient fuel source and could lead to unwanted weight gain. Although there is some truth to these things, there may be alternative fuel sources out there.
Recently, the belief that carbohydrates are the best fuel source has been questioned by scientists and athletes. This has been particularly the case amongst the ultra-endurance community, and it has recently been found that there are actually many ultra-endurance athletes who consume high-fat diets as a means to improve their performance.
A recent announcement from the Dietary Guidelines Advisory Committee that suggests cutting back on the starchy carbohydrates that are staples in many athletes’ high-carbohydrate diets, and instead consume more nuts and other fat-rich foods, in order to improve metabolic health, is likely to add fuel to the debate about carbohydrates and fats.
However, metabolic health is not the primary focus of serious athletes, and instead they are far more concerned with training and racing harder, faster and more frequently. They want their diets to make them better athletes.
In theory, a high-fat diet should allow athletes to do this, because after all, humans have a large amount of fat stored in their bodies. The European Journal of Sport Sciences recently published: “Rethinking Fat as a Fuel for Endurance Exercise,” and this stated that even the leanest marathon runner harbors “in excess of 30,000 kilocalories of adipose tissue reserves,” which is “an order of magnitude greater than maximum carbohydrates stores in the body.” So this suggests that we all carry enough fuel in the form of body fat to get us through multiple marathons- so surely we could use fat to fuel us in our sports?
However, it should be argued that dietary fat is not as readily available as carbohydrates, which are stored in muscles in a form known as glycogen. Muscles can take up and burn glycogen without many intermediate metabolic steps. Glycogen provides a fast sugar buzz and that buzz can fuel most exercise just fine. However, fat, must first be broken down into fatty acids and other components before it can be used by the muscles, an intermediate step that makes dietary fat less immediately available and efficient as a fuel, especially during intense exercise.
However, with training endurance training allows athletes to become better able to use fat as a fuel. And that metabolic adaptation led people to ponder what might happen if you extended that ability to its farthest extreme and trained an athlete’s body to rely almost exclusively on fat, by removing almost all carbohydrates from the diet and instead increasing the amount of fat in the diet.
Evolutionary, a high-fat performance diet makes sense, because early humans, who were quite physically active, primarily ate fat- and as such fat has been the main fuel for active humans far longer than carbohydrates have been. But the modern science to support the benefits of extremely high-fat/low-carbohydrate diets for sports performance is lacking.
Firstly, there is no formal definition for what constitutes a high-performance, high-fat diet for active people. Many athletes believe that reducing carbohydrates to less than 20 percent of their diet, while increasing fat to at least 65 percent, with the remainder being protein, represents the kind of high-fat diet that will allow them to subsist almost exclusively on fat during exertion and therefore almost never tire.
However, the ideal high-fat diet for sports performance would consist of closer to 85 percent fat and almost no carbohydrates. This extremely fatty diet leads to a condition known as ketosis, during which the body creates molecules called ketones that result from the breakdown of fat into fatty acids. The body and brain will burn ketones as fuel when the blood does not contain much sugar. Ketones also are believed to aid in the reduction of inflammation throughout the body. So, theoretically, ketones and fatty acids would fuel even the most prolonged and strenuous exercise in people following a very high-fat diet and aid in their recovery from that exercise by reducing inflammation and muscle damage.
However, there is no study to date that has shown that extremely high-fat, ketogenic diets actually “enhance sports performance,” only that they make endurance athletes better able to use fat as a fuel. And the same studies generally show that high-fat diets blunt performance during high-intensity sprints, which, even in fat-adapted athletes, demand fast-burning sugar stores.
There are still reasons for some athletes to experiment with higher-fat/lower-carbohydrate diets because sports performance requires metabolic versatility, and burning fat better can be part of that. Additionally, it has been found that very high-fat diets can result in weight loss, which can improve performance by itself.
But it should be noted that should you decide to try increasing your fat intake, please bear in mind that the switch is likely to disrupt your training. Performance actually declines dramatically during the first several weeks, especially if you are attempting to induce ketosis. The reason for this is because the body runs low on glycogen before it becomes well-adapted to using fat, and people tend to feel fatigued, heavy-legged, nauseated and ill for up to a month- so don’t change now if you are planning on doing a marathon in March!
Furthermore, please realize that the logistics and mechanics of such a diet also are difficult and daunting. While heaping servings of butter, cream and bacon may sound enticing, “it is really tricky to construct” an appetizing, sustainable diet consisting of at least 80 percent fat, and it is also important to still get enough nutrients from other food groups such as vegetables and fruits.
To conclude, although the evidence and research is sketchy, it seems that a high-fat, low-carbohydrate diet could conceivably be useful for some athletes, especially if they participate in prolonged, endurance-based activities- and so such a diet should not be disregarded just yet. But for the rest of us mere mortals, a balanced diet, with less sugar and perhaps a few more pats of butter (and other healthy fat sources such as nuts, seeds, avocado and fish), should improve our health and in that way allow us to perform better on the trails and at the gym.
So if you like, give a higher fat diet a go, and let us know what you think!