The Ketogenic Diet and Sport: A Possible Marriage?

Antonio Paoli; Antonino Bianco; Keith A. Grimaldi


Exerc Sport Sci Rev. 2015;43(3):153-162. 

In This Article

Abstract and Introduction


The ketogenic diet (KD) is used widely as a weight loss strategy and, more rarely, as therapy for some diseases. In many sports, weight control is often necessary (boxing, weightlifting, wrestling, etc.), but the KD usually is not considered. Our hypothesis is that KD might be used to achieve fat loss without affecting strength/power performance negatively.


The ketogenic diet (KD) is a nutritional approach consisting of high-fat and adequate protein content but insufficient levels of carbohydrates for metabolic needs (<20 g d−1 or 5% of total daily energy intake[28]), thus forcing the body primarily to use fat as a fuel source. The original KD was designed as a 4:1 lipid:nonlipid ratio, with 80% of daily energy intake from fat, 15% protein, and 5% carbohydrate. Many modifications subsequently have been introduced to the original KD, for example, lowering the lipid:nonlipid ratio or no restrictions in daily energy (in kilojoules) intake with ab libitum protein and fat. The main knowledge on the metabolic aspects of KD comes from the pioneering studies on fasting from the Cahill group;[17,18] as a matter of fact, fasting (ingesting no or minimal amounts of food and caloric beverages for periods that typically range from 12 h to 3 wk[16]) induces a particular metabolic state called ketosis. Fasting is a practice that is spread widely throughout different religions, even though religious fasts are conceived mainly for spiritual health, they also have the potential to improve physical health. One example of a positive effect on health by fasting may be found in the Gospel of Matthew, in the episode of the epileptic (demoniac) boy: "And Jesus said unto them, 'Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you. How be it this kind goeth not out but by prayer and fasting '" (Matthew 17:14–21). Fasts are indeed present in the three principal fasting periods of Greek Orthodox Christianity (Nativity, Lent, and the Assumption), in the Bible-based Daniel Fast, and in the well-studied Islamic Ramadan. In recent years, many studies have investigated the effects of the daily fasting used during Ramadan that requires a total abstention from food and drink from sunrise to sunset for 1 month. Although such ritual intermittent fasting has only minor effects on the sedentary population, its observance may have important consequences for the training and performance of the athlete. These effects could be of greater importance when the competition is performed in summer when daylight hours are long. In general, studies have found that, in athletes observing Ramadan, the glycemia and tissue hydration decrease progressively from sunrise to sunset. However, overall performance seems to be unaffected if athletes are able to maintain an adequate total energy and macronutrient intake and a correct sleep length and quality and to adjust the timing of the training load, although with many interindividual differences.[5,35]

Ramadan fasting is an interesting model for intermittent fasting but is too short to induce ketosis; instead, a good model for prolonged ketosis is the Inuit case, in which the first well-documented fasting was reported by the Schwatka expedition. Lt. Frederick Schwatka was a graduate of West Point and Bellevue Hospital Medical College and he was the leader of an expedition that set out to find the missing Royal Navy "Franklin Expedition." On June 1878 when the schooner Eothen sailed from New York, Schwatka and the other participants (including Henry Gilder, a scientific reporter from the New York Herald) set up a winter base camp near Daly Bay. The following spring, accompanied by 12 Inuit (indigenous circumpolar people), they began a more than 5000-km sled journey eventually returning to Camp Daly on March 4, 1880, almost 1 yr later.[8] Regarding physiological issues, it is worth to underline that, once they finished their initial provisions, the expedition's only source of food was hunting and fishing because there were no other sources of supply along their route. Lt. Schwatka reported in his diary this often-cited sentence: When first thrown wholly on the diet of reindeer meat, it seems inadequate to properly nourish the system, and there is an apparent weakness and inability to perform severe, exertive, fatiguing journeys. But this soon passes away in the course of 2 to 3 wk.[34] This is the first documented description of the so-called keto-adaptation.

Years later, an anthropologist named Vilhajalmur Stefansson set out to travel throughout the Arctic mainland to study the Inuit language and culture. During his journeys, Stefansson experimented on himself with the typical Inuit's diet, consisting of about 80% to 85% of energy from fat and 15% to 20% from protein, and he reported no observed problems.[36] Pressed by the controversy raised from his reports, Stefansson agreed to recreate the Inuit diet under the scientific supervision of Dr. DuBois at the Bellavue Hospital, he confirmed his earlier observations that the adoption of a fat/protein diet was without any impairment or signs of nutrition deficiency. After these earlier reports, however, the study of KD seems to have sunk into oblivion until the 1920s when it experienced a "renaissance" as a therapy for epilepsy. Interest against waned with the introduction of pharmaceutical therapy for epilepsy, but it has been reawakened recently because of the severe side effects of pharmacological treatments.[11] It also has been reassessed as having utility in other pathologies such as obesity, polycystic ovary syndrome, cancer, diabetes, neurological diseases, and others.[20,21,26] In more recent years, KD mostly have been studied from a weight/fat loss point of view.[4] Interestingly, up until now, only a few studies have investigated the relationship between KD and sports performance. There are two main possible applications, in our opinion, of KD in sport: one is the more intuitive weight reduction for sports divided into weight categories[37] and the second is the surprising (based on some studies in the early 1980s) possibility of a positive influence of KD on endurance performance.[28]