Ketogenic diet: a good idea, rolling on fat?

Any athlete with even minimal experience knows that diet can play a major role in athletic performance. However, at a time when nutrition is a hot topic and everyone has an opinion on the best diet to follow, it can be difficult to know what to believe. It can even be stressful.

In this frenzy of information, certain diets are gaining popularity. Recently, some people have been swearing by the ketogenic diet, or keto diet. First proposed as a solution to epileptic seizures in children in the 1920s, this diet is characterized by a minimal intake of carbohydrates (cereal products, fruits, dairy products) and a high intake of lipids, or fats.

Its followers believe in its supposed virtues: weight loss, lower blood cholesterol, and prevention of certain cancers and type 2 diabetes. At first glance, it seems quite appealing, but it's important to keep in mind that strictly following this type of diet is difficult in the long term and not very compatible with a balanced lifestyle.

Do fat and endurance go well together?

In contrast to the high-carbohydrate, low-fat model, the ketogenic diet is attracting interest and selling a dream with a buttery taste... Increasingly popular within the sports community, is this trendy diet really compatible with endurance sports?

Let's see. According to this diet, 60 to 75% of the energy consumed during the day should be in the form of lipids (fats), only 10% in the form of carbohydrates, and the rest in proteins. So, for someone consuming 2,500 calories daily, that corresponds to 166 to 208 g of lipids and 62.5 g of carbohydrates. In other words, the maximum amount of carbohydrates allowed per day would correspond, in this example, to the intake required every hour during a high-endurance physical activity.

What's more, this drastic change in the intake of various macronutrients can cause physiological discomfort such as digestive problems, headaches, muscle cramps, general weakness, and deficiencies in several essential vitamins and minerals. 

However, the majority of the sports nutrition community recognizes that a significant intake of carbohydrates during exercise is important. It helps reduce glycogen depletion and supports vigorous athletic performance over a long period of time. However, some athletes claim that the body can adapt to a high-fat diet by gradually changing the way it uses available energy substrates.

Not great for anaerobic exercise

Recently, a randomized crossover study examined the effects of a ketogenic diet on anaerobic performance. The 16 participating athletes were required to follow a ketogenic diet for four days, then a high-carbohydrate diet, one week apart, and compare their performance. They first performed the Wingate test (on a stationary bike), which measures maximum anaerobic power. They then underwent a yo-yo recovery test, which involves running at high intensity for 20 meters and then walking for 10 seconds, alternating between the two, gradually increasing the running speed until the athlete is no longer able to continue. 

The results of this study showed that a high-fat diet reduced maximum power by 7% and average power by 6% during the cycling test. In terms of the running test, recovery time was affected by 15% with the ketogenic diet, compared to the high-carbohydrate diet.

Thus, it would appear that adhering to this diet for a short period (four days) impairs performance in sports that require the anaerobic system, i.e., high-intensity activities. 

The adaptation of the body

What seems well established, however, is that the ketogenic diet allows the body to make certain adjustments so that it primarily uses lipids as energy substrates during exercise instead of carbohydrates. It should be noted, however, that these adaptations mean that glycogen will be spared during exercise and less well regulated by our metabolism. Thus, a diet rich in fat and low in carbohydrates allows fat to be used as the primary energy source during exercise, but requires a greater amount of oxygen, which does not improve overall performance.

Other athletes argue that due to significant gastric discomfort associated with consuming large amounts of carbohydrates during exercise, they prefer to switch to a diet that promotes other energy substrates, such as lipids.

A restrictive diet

Furthermore, it appears that the protocol must be followed for at least six months before adaptive physiological changes can be observed. The downside? Adherence to a ketogenic diet, as prescribed, involves a great deal of dietary restrictions. And if it is not done properly and with close monitoring by a healthcare professional, it may lead to vitamin and mineral deficiencies. 

Not very compatible with a "normal" lifestyle, this diet can be part of a healthy diet, but only in specific cases where this daily routine is perfectly in line with the values and beliefs of the person following it. Because unfortunately, eating more fat isn't just about replacing fruit with bacon or maple syrup with oil. The foundations of a healthy diet are based on a perfect combination of foods, much more than on the nutrients they contain!

Furthermore, if you want to optimize your performance, keep in mind that carbohydrate periodization remains an interesting solution... but we'll come back to that in a future article! 

Foods to favor: ketogenic diet vs. balanced diet

Ketogenic (not very varied)

• Meat and meat substitutes (eggs, cheese, tofu, nuts)

• Butter, vegetable oil, avocados, olives

• 35% cream, fresh cream, mayonnaise

• Not much fruit

Balanced (very varied)

• Fruits and vegetables

• Grain products (especially whole grains)

• Dairy products

• Meat and meat substitutes (eggs, cheese, tofu, nuts)

Reference: 

MEDICA, E. M., "Low-carbohydrate, ketogenic diet impairs anaerobic exercise performance in exercise-trained women and men: a randomized-sequence crossover trial," inThe Journal of Sports Medicine and Physical Fitness, 2018.