This is THE 2016 hot topic of sports nutrition. Indeed, like Christopher Froome, athletes wishing to practice the ketogenic diet are multiplying, seeing in this food model (not so new for that matter), an additional way to increase their energy performance. We are talking about a ketogenic diet, ketones or ketones in English, to be “keto-adapted”. But what is it really? What does this diet correspond to? Is it beneficial or, on the contrary, dangerous? Let’s take stock, because there is in all these words, to drink and to eat …
Once upon a time … ketogenesis
The ketogenic diet is a diet known for decades. It was widely publicized as part of therapeutic or low-calorie and high-protein diets in the late 1980s, before reappearing in the limelight with the Dukan diet more recently. The principle is relatively simple: when your body has all the nutrients it needs, in short when it is in a situation of food abundance, it uses different sources of energy, mainly fats and carbohydrates. It’s a bit like having a multi-tank car that can play with the fuel mix depending on how fast you ride. Some organs, like muscles, preferentially use glucose derived from carbohydrate foods or glycogen to cover their energy needs. Other organs, such as the brain and the heart, need them in an indispensable way.
So the question is: how do these organs do when we stop eating carbohydrates? Simple answer: they adapt, by sounding the alarm to activate an emergency route, the ketogenesis. The body is still well done …! It will thus allow the gluco-dependent organs to capture a source of energy other than glucose, producing itself compounds derived from fats: ketone bodies. It is your liver, again and again, that manages the story. This metabolic revolution, however, does not occur simply by snapping your fingers . Three daysare indeed necessary on average to fully activate this alternative energetic path and the condition – essential – that you strongly limit the intake of dietary carbohydrates, of the order of 30 to 50g per day. The production begins at the end of the first day of carbohydrate deprivation, but this average period of three days is necessary to allow the body to cover up to 40% of the energy needs thanks to the ketone bodies (1/3 of the energy required for the brain is covered after 3 days, 70% after 40 days), or a production of about 150g per day of ketone bodies by hepatic mitochondria, against about 35g after a night of fasting. If your body is fasting for at least 5 days, the quantities produced can reach up to 280g per day (7-10 mmol / L of blood),
In the meantime, both warning you, you will know a kind of “no man’s land” energy often resulting in fatigue, hunger can quickly become imperious, a loss of vitality, even discomfort. It will therefore be necessary to arm yourself with courage for 48 to 72 hours … To know then a true energy transformation resulting in a state of form and vitality, sometimes described as euphoric associated with a strong reduction, even a suppression of the feeling of hunger (anorectic effect). Your liver will produce acetone (eliminated by the lungs, which is the cause of characteristic bad breath) and acetylacetate in large quantities that can be converted into beta – hydroxybutyrate (β- OHB) . From a chemical point of view, beta-hydroxybutyrate is not really a ketone, but is considered physiologically speaking (4, 5). These ketonic bodies are then transported by the blood, they pass the membrane of the mitochondria to be transformed again into a molecule at the crossroads of energetic pathways, Acetyl-CoA, which will be able to be used preferentially by the heart, the brain and the muscles. You are armed for this period of hunger carbohydrate.
But the story is not over. These ketone bodies – or ketones – perform indeed other roles equally important during this particular period. They intervene in particular in the cellular signaling and represent significant therapeutic tracks in certain therapeutic frameworks such as cancer, epilepsy (the frequency of the crises can for example reduce up to 40% thanks to the ketosis) or the inflammatory chronic diseases . These ketone bodies also, and this is the heart of the subject that interests us today, ensure the regulation of the use of energy substrates by skeletal muscle(6).
How is the ketogenic diet on your plate?
The 80’s have allowed (and sometimes still today …) carbohydrates to know their hours of glory, especially through the research of nutritional protocols to optimize glycogen levels. Thus, the conventional recommendations in sports nutrition have focused their attention on carbohydrate intake because in fact, in case of total depletion of glycogen, point of continued muscular effort. They thus gave pride of place to carbohydrates, ideally representing at least 50% of the total energy intake, or even 55 to 60% for endurance athletes, 30 to 35% in the form of lipids and around 15% in the form of carbohydrates. of proteins. It’s a restricted, energetic vision of food that has a number of limitations, in particular to cover the need for quality fats, micronutrients and, above all, reduce the sensitivity of cells to insulin. Indeed, once again your body adapts: if you bring him permanently carbohydrates and in large quantity, he reacts by secreting insulin. As your cells become more resistant, your pancreas needs to secrete more and more insulin to achieve the same physiological effect. This is the beginning of a vicious circle that has led more than 2 million French people with type 2 diabetes and 6 million who are in a state of significant obesity … It then becomes legitimate to question the interest of use a diet that strongly limits the secretion of insulin, by by reducing the sensitivity of cells to insulin. Indeed, once again your body adapts: if you bring him permanently carbohydrates and in large quantity, he reacts by secreting insulin. As your cells become more resistant, your pancreas needs to secrete more and more insulin to achieve the same physiological effect. This is the beginning of a vicious circle that has led more than 2 million French people with type 2 diabetes and 6 million who are in a state of significant obesity … It then becomes legitimate to question the interest of use a diet that strongly limits the secretion of insulin, by by reducing the sensitivity of cells to insulin. Indeed, once again your body adapts: if you bring him permanently carbohydrates and in large quantity, he reacts by secreting insulin. As your cells become more resistant, your pancreas needs to secrete more and more insulin to achieve the same physiological effect. This is the beginning of a vicious circle that has led more than 2 million French people with type 2 diabetes and 6 million who are in a state of significant obesity … It then becomes legitimate to question the interest of use a diet that strongly limits the secretion of insulin, by he reacts by secreting insulin. As your cells become more resistant, your pancreas needs to secrete more and more insulin to achieve the same physiological effect. This is the beginning of a vicious circle that has led more than 2 million French people with type 2 diabetes and 6 million who are in a state of significant obesity … It then becomes legitimate to question the interest of use a diet that strongly limits the secretion of insulin, by he reacts by secreting insulin. As your cells become more resistant, your pancreas needs to secrete more and more insulin to achieve the same physiological effect. This is the beginning of a vicious circle that has led more than 2 million French people with type 2 diabetes and 6 million who are in a state of significant obesity … It then becomes legitimate to question the interest of use a diet that strongly limits the secretion of insulin, byfat and restricting the intake of carbohydrates, even excluding them completely. It is now that the ketogenic diet comes on the scene. This food model has a totally reversed distribution:
- Unlike fasting or a low-calorie diet using the principle of ketosis (see my article on fasting ), energy intake is still sufficient to meet daily needs and thus maintain a stable weight, protect muscle mass and avoid any decline in basal metabolism, which can reach 10% in the context of a poorly conducted caloric diet.
- Protein intake remains similar to a typical dietary distribution, in the order of 12 to 15% of total energy requirements , ie about 1.2g / kg body weight / day for a sedentary person and 1.5g / kg body weight / day for a regular sportsman. During the period of keto-adaptation of which we will speak again, it may be useful to increase the contributions temporarily to 2g / kg body weight / day to protect the muscular tissue (7, 8),
- The lipids see their needs increase to about 80% of the total energy contributions . You want to like fat …
- The amount of carbohydrates must it be strongly limited, of the order of 50g per day or 40g, or just 5 to 7% of the total energy intake of an athlete . Individual variations are important, however. The critical threshold can indeed be between 20 and 125g and the proportion of carbohydrates in the total energy supply can be reduced to 2%. The state of physical and psychic form, the stability of the weight or the feeling of hunger are all criteria allowing to evaluate in an individual way this critical threshold.
From a practical point of view, this ketogenic diet requires a small revolution in terms of food choices compared to conventional habits. Indeed, this critical threshold of carbohydrates per day is almost reached by the only consumption of vegetables (at will, except carrots and beets in the most stringent situations). This means excluding all sources of starch (cereal products, legumes, quinoa, etc.), sugars and fruits, except 50 to 100g of berries (such as blueberries or berries) for people enjoying a critical threshold high. Do you visualize the story better now? Regarding proteins no change so. On the other hand, for the lipids, it is a question of doing them the part-beautiful while making sure to promote as much as possible the fatty acids of quality (the famous onesomega 3 ). The consumption of saturated fatty acids in large quantities does not seem to increase cardiovascular risks, on the contrary the concentration of circulating saturated fatty acids is reduced in this type of diet, forcing the body to use them as an energy substrate. Thus your breakfast will be transformed from the model “bread / jam / orange juice” to “avocado / egg / oleaginous and tea” for example, or that the differences, such as the evening pizza, will have to be put in the closet at the risk of returning your body to an area of metabolic discomfort for one to two days.
If you want to move towards such a food model, it will inevitably ask you a time of adaptation, beyond the average 3 days related to the establishment of ketosis. This adaptation is twofold: food certainly, but also in the management of your training. In fact, a sportsman’s metabolism that has become accustomed to working with super, and who is asked to fuel diesel, risks coughing for a while … but the most important thing to remember is that he is capable of , unlike the engine of your car if you ever mistakenly pump at the gas station. Indeed, as you certainly know, the energy substrates in the effort are of several orders: carbohydrate certainly, but also lipid and to a lesser extent, protein. The share of lipids in the energy supply to the effort will then greatly increase to preserve the glycogen present, at the price nevertheless of a lesser capacity to support the efforts at high intensity, at least for a certain period. This is one of the goals of this diet from an energy point of view: to allow your body to effectively metabolize fat on exercise at the expense of carbohydrates, the reserves being much more important than those of glycogen, while using beta-hydroxybutyrate (β-OHB) as a complementary energy source.It is estimated that the time required for keto-adaptation in an endurance athlete varies from 3 to 6 weeks depending on the individual and that the long-term beneficial effects, especially on the performances, are fully expressed after several months at a year. For high-intensity sports, little data is available, but the delay is logical, more important. In addition, some athletes are (very) difficult to implement this adaptation because of a particularly recalcitrant metabolism. Having the opportunity to offer this food model to some athletes, I happened to face the impossibilities of maintaining it, lack of sufficient adaptation to the effort. Using a glucometer is a more relevant way to measure your ketone body production than urine strips. Soon devices directly measuring acetone by breathing should also be available on the market. But then, beyond a better sensitivity to insulin, what are the benefits to revolutionize its diet?
The benefits of the ketogenic diet
Faced with this question, the answer appears at two levels: health on the one hand and performance on the other. Regarding the first point, the ketogenic diet has shown many positive effects (9, 10), including:
- Better insulin sensitivity on all markers
- A decrease of more than 50% in blood glucose variations in patients with type 2 diabetes
- A reduction of oxidative stress
- A decrease in chronic inflammation
- An increase in antioxidant defenses
- Better cellular energy efficiency
- A reduction in oxygen consumption
- A reduction in blood pressure
- A loss of fat mass
- Better cardiovascular prevention
- Less plasma circulation of saturated fatty acids
A study published in Science in 2012 also showed that the ketone body concentration, following a ketogenic diet and such values as only such a diet allows in comparison with a simple low carb model, regulates many genes involved in the increase of antioxidant defenses, so in the regulation of low grade inflammation.
And on sports performances?
The improvement of these parameters naturally induces an optimization of the physiological capacities, and therefore of the performances. This is what physiologist Jeff Volek has been trying to demonstrate for several decades. Until recently, the studies conducted to analyze the effects of ketone bodies on metabolism were mainly conducted in the context of prolonged fasts, diabetes or the search for therapeutic solutions. Fascinated, Jeff Volek then began to study the effects of a ketogenic diet, or more generally a high-fat and low-carbohydrate diet (LCHF), on performance. He has also created a research center that he named for the occasion FASTER ( Fat Adapted Substrate Oxidation in Trained Elite Runners). The adoption of a ketogenic diet also allows, beyond the improvement of insulin sensitivity and the increase in the capacity to use exercise lipids, which represent two important aspects of energy performance, optimize other performance-enhancing mechanisms, including lactate reduction, lower membrane damage and increased defenses against infections.
And above all, a better control of the systemic inflammation, said of low grade, consecutive to the sport practice (even my article about here). The significant presence of ketones also appears to benefit mental abilities by reducing central fatigue during exercise and improving cognitive abilities.
But then you will tell me, if carbohydrates are almost absent from the plate, what about the famous glycogen? It seems that the organization demonstrates again its fabulous ability to adapt. Indeed not only glycogen is consumed at a much slower rate in a keto-adapted athlete, but the body is also able to use glycerol from triglycerides (the components of fats) and degrade certain amino acids to make glucose via gluconeogenesis. This results in a maintenance of the glycogen level at about 50% of its optimum value. This amount of glucose produced from the amino acids would also seem not to induce the risk of muscle wasting. On the contrary, blood levels of amino acids glucoformers, these famous BCAA, increase by 25 to 40% during a ketogenic diet with constant consumption of dietary protein, thus making it possible to compensate for the insulin decline caused by the elimination of carbohydrates. This adaptation is allowed thanks to the mitochondria then adapted to burn priority ketone bodies and fatty acids to provide energy, preserve its BCAA (12). Nature is well done, right?
Some moderation vis-à-vis this regime
Reading these lines, everything seems ideal in the best of worlds provided – and not least – to agree to reform in depth your diet. You can imagine that there is a Yes, but somewhere … Indeed.
From a health point of view above all. Indeed, the “true” ketogenic diet induces a state of deleterious metabolic acidosis in the long term, in particular on demineralization and on cellular exchanges (see my article on this here ). This state of acidosis therefore requires increasing water intake (at least 2 to 2.5 liters of water per day outside the requirements related to dehydration during training), minerals, in particular calcium, potassium (allowed by vegetables also providing alkalizing organic salts such as citrates), magnesium and certain vitamins, justifying frequent use of supplementation and medical monitoring of blood values. Sodium intake must also be controlled.
Levels high of ketone bodies (10 to 20 mmol / L) may also be the cause of renal failure or cerebral edema can lead to death, as part of diabetes in particular. Such toxic levels, however, relate to pathological conditions. As part of a prolonged effort or the practice of a ketogenic diet well controlled from a nutritional point of view in the context mentioned, circulating ketone body levels reach comparatively low values (about 0.5 mmol / L). and 4 to 5 mmol / L in prolonged fasting) and therefore do not cause metabolic acidosis.
The cardiovascular risks induced by the increased consumption of saturated fatty acids or of cholesterol sometimes mentioned are however not proven . On the contrary, as we have mentioned, the levels of saturated blood fatty acids decrease under a ketogenic diet (13).
From a performance point of view, the long-term adoption of a ketogenic diet does not seem necessary to see the first benefits. After just one night of fasting, the body stimulates the production of ketones during the endurance effort by more than 2 hours, resulting in a concentration of up to twice the initial value, including after the effort (14-21). Beyond the nutritional status, the concentration of ketone bodies also appears to be influenced by the intensity and duration of the effort (16, 22-24). As well as trained athletes have lower concentrations than those who are poor (18, 19, 20), presumably because of their ability to increase the use of free fatty acids (18,
The specific effect of ketone bodies on exercise energy metabolism therefore remains complex in the end,primarily because studies have been conducted with athletes who have been following a ketogenic diet for a long time (14, 27, 28, 29). In addition, the presence of ketones appears to reduce the oxidation of carbohydrates during exercise (6, 30-32), compromising performance especially in sports requiring large variations in intensity (33-37). that a high concentration of ketones further promotes muscle glycogen reconstitution after exercise (38). The question arises then of the interest that could be represented by the simultaneous presence of the two substrates, the carbohydrates and the ketone bodies. The use of these could then be increased without necessarily requiring a ketogenic diet, while preserving the body’s ability to effectively utilize carbohydrate during exercise (39, 40). It is from this observation that a somewhat original idea was born.
A small glass of ketone esters?
Kieran Clarke, a professor of biochemistry at Oxford University, has been studying the metabolism of ketone bodies for years and wanted to measure their impact on soldiers in operation. The latter can in fact regularly suffer from hypoglycaemia, with serious consequences when they are in operation or even subjected to fasting. In 2003, was born a drink bearing the code “DeltaG”. Imagine a situation where fasting is simulated by the supply of ketone bodies to an athlete in perfect health, without any caloric restriction, realizing an intense and prolonged effort. The result is a physiologically unprecedented situation, during which the body does not appear lacking in carbohydrates, while being provided with a new source of energy: ketones. In such conditions, their presence makes it possible to limit the consumption of glycogen while promoting its storage by virtue of the mimetic action of insulin. Indeed, in comparison with a fast or a ketogenic diet requiring several days of carbohydrate restriction to achieve a large production of ketone bodies, the direct consumption of ketone esters via a drink increases the concentration in 1 hour barely (40, 41). For example, values of 3 mmol / L were obtained after ingestion of 400 mg per kilogram of body weight of ketone esters during exercise (42-44), or even 6 mmo / l 45 min, due to the consumption of 600 mg / kg body weight after exercise (27). However, the tolerance of such a drink has been little studied.
The combination of carbohydrates with ketone esters also appears to improve cardiac capacities (45, 46, 50). The effect of these ketone esters, however, varies according to the nutritional status of the athlete. Indeed, the peak plasma concentration of beta-hydroxybutyrate appears 60% lower when they are consumed following a standard meal, compared to a keto-adapted state (47). On the other hand, when the consumption of ketone esters occurs after a night of fasting, the body uses them more than after only a few hours of carbohydrate deprivation (43). Other factors may further modify the use of ketone esters during exercise, in particular the type of muscle fibers required (17, 25, 26, 30), the training state (18, 19, 19). 21, 30, 48) or the circulating rate of ketone bodies (14, 30).
Several recent studies in 2016, however, highlight new data. When ketones are brought by a drink during a cycling effort, the performance increases by about 2% (50), the glucose availability increases by 33% and the glycogen reconstitution is increased by 50% in comparison a placebo drink (49, 51). The availability of glutamine appears to be greater after exercise, thus reflecting a better preservation of BCAA, which is also less oxidized. It should also be noted that the consumption of a ketone ester-based drink does not influence the insulin secretion on exercise (51). This same study also shows that the presence of ketone esters not only preserves the carbohydrate metabolism during exercise, even for efforts at high intensity (75% W max) but also to prioritize their oxidation on those of other sectors, by promoting the ability to use the carbons resulting from the oxidation of free fatty acids, therefore β-oxidation. Clearly, the ketone esters make it possible to optimize the oxidative energy yield. However, in the light of all these improvements, the increase in performance appears relatively low, thus highlighting – and this is an essential point – thatcellular performance is not only related to muscular energy availability but represents an integrated and complex response (52).
On the other hand, some arguments seem to work against the enrichment of ketone esters. Indeed, the ingestion of such a drink would seem to reduce the use of intramuscular triglycerides after 2 hours of high-intensity endurance sport (53), which is nevertheless a particularly important source of energy in the context of a diet. low in carbohydrates. In addition, the presence of ketone esters may exert a negative feedback on glycolysis, thereby reducing the expected benefits (46). The mediatization of the positive effect of this drink on performance is also closely linked to a specific sporting practice (rowing and cycling). In addition to the 2016 study, a first study in 2013 consisted in bringing 230 kcal by a ketone ester drink to 22 rowers under fasting conditions and making a 30-minute effort. Their performances have also proven to be better by an average of 1 to 2% (54), but studies demonstrating an improvement in performances in other sports lack or even moderate the interest of ketone bodies (14, 43, 27, 28, 29, 41).
What to think of this drink?
This drink, initially intended for the military, is now available and marketed as an energy drink in Great Britain, for the modest sum of …. 2000 pounds a liter! More and more used in the world of cycling, its access legitimately launches a debate on sports ethics, when it is found that this drink has a limited accessibility (the price), a potential toxicity (that of high-dose ketones.) To recall the harmlessness of the drink n ‘ has not been proven in the long term and under all conditions) and uses molecules naturally produced by the body (ketones) to increase performance (about 2%). It is therefore far from appearing as a product to trivialize, unequivocally ethical conclusions, even if the World Anti-Doping Agency has not positioned against today.
In conclusion: the ketogenic diet, good or not?
The ketogenic diet, the true, the pure and hard, namely imposing a maximum consumption of carbohydrates up to 40 to 50g per day, has many benefits on paper, including better sensitivity to insulin, better defense against -oxidative and consequently lower inflammation of low grade. In view of the habits of our Cro-Magnon ancestors, such a diet appears to be more in line with our genetic predisposition than a diet that is a part of cereals. However, three essential aspects are to be considered:
- The establishment of such a diet requires a significant change in eating habits , quite feasible, however, to consider before you want to embark on the adventure. Rigor and perseverance are essential in the light of current food conventions.
- The long-term consequences of such a dietary model remain controversial when it is nutritionally poorly conducted , even if a well-conducted ketogenic diet does not have a significant metabolic acidosis to the point of causing risks of renal insufficiency. cerebral edema, or even coma as may be the case in pathological situations such as diabetes.
- The ketogenic adaptation, the famous period of keto-adaptation on average of a duration of 3 to 6 weeks, remains very variable according to the individuals, even particularly trying and long to put in place. The effects on performance can only be fully measured from months to a year. Sports practice during this period must be followed and adapted according to the general condition. In the same way that the establishment of a ketogenic diet must be carried out with the accompaniment of a doctor trained in this food model .
- The practice of the ketogenic diet has an undeniable advantage, that of reducing the risks of digestive disorders in the race , in particular by strongly limiting the intake of carbohydrate foods during the effort, or even by suppressing them in athletes practicing the ketogenic diet. strict manner.
Beyond these elements, a central data deserves especially particular attention, namely the confusion that engenders the media coverage of this regime. Indeed, it is very common to confuse the ketogenic diet stricto-sensu, with low carb diets (low carbohydrate) or LCHF (Low Carb High Fat) for which the margins of maneuver in terms of carbohydrate intake are more important. The goal of these diet models is then to direct the body towards the same metabolic pathways, in order to benefit in part from their benefits, while providing a little more carbohydrates (around 100 to 150g of carbohydrates). , especially in recovery or during the effort by the intake of carbohydrates (drinks, gels or fruit pastes for example). Such a model, in particular allowing the maintenance of fruits and legumes, may represent a more flexible and long-term alternative for athletes, both on the practical and the social side. In addition, the maintenance of carbohydrate intake in long-term effort and in competition recovery (which is also done by most athletes on a ketogenic diet), for athletes who have put in place a low-calorie diet. carbohydrate intake,Glycemic index low and high fat quality , can optimize the induced adaptation while maintaining a healthy diet. So that’s my conclusion, far from any ketone ester drink!
A little parenthesis to finish. It is common to read that some professional runners adopt a ketogenic diet or are keto-adapted. However, it is not (or rarely) specified that these same runners have more recourse to a low-carb diet, interspersed with periods of carbohydrate abundance, it, far from the original state of mind of such a model .
Enjoy your meal !