Low Carb with sports and fitness? What you should know


Low carb with sports and fitness?

More and more athletes are advocates of the low carb diet and reduce the percentage of carbohydrates they eat to improve their athletic performance. The assumption of low carb advocates is that the reduced carbohydrate intake and increased fat intake improves fat oxidation. This improvement in lipid metabolism should ultimately serve to increase performance and endurance. But is the benefit of low carb diet in terms of performance enhancement real? Or is low carb in combination with fitness and sports rather counterproductive? In order to provide you the best answer, we have reviewed this question in light of the most recent scientific knowledge on the subject.

What exactly is a low carb diet?

The low carb diet is a carbohydrate-reduced diet thats higher in fats and proteins. Typically, less than 20% of your daily calorie needs are met by carbohydrates. The remaining demand is balanced out via proteins and fats. Important in the low carb diet is that it’s not primarily about the reduction of calories, but rather about a different composition of macronutrients. This diet may be implemented for weight loss, weight stabilization, or weight gain – depending on your goals. In addition to determining your optimal body weight, our BMI calculator also helps you to calculate your personal nutrient distribution.

Background of the low carb diet

Stephen Phinney, Jeff Volek, and Tim Noakes are three major figures advocating a low carb diet for fitness, criticizing athletes for being too dependent on carbohydrate metabolism for their main source of energy. When following a high carbohydrate-reduced diet, the body can improve fat oxidation and thus rely more on the body’s fat reserves. The advantage of the fat reserves compared to the glycogen stores in the muscles and liver, is the size of the fat reserves and amount of stored energy. These reserves empty considerably slower than the glycogen stores.

Above all, the three advocates of the low carb diet point to human evolutionary history. In the time of hunters and gatherers, fat was the most important source of energy. The initial fatigue and weakness that some people experience during the adjustment phase is temporary and generally lasts 2-3 weeks. Low carb diets could therefore also be a strategy for endurance athletes to increase performance and recovery. It is undisputed that the low carb diet leads to an improvement in oxidative capacity and increased formation of fatty acid transporters, as well as mitochondria (power plants of the cells – the mitochondria is in charge of aerobic energy production).

Forms of energy production

It’s important to distinguish between the different forms of energy production in order to understand in which situations which macronutrient is important in respect to the energy metabolism. Your body can gain energy both under aerobic conditions and under anaerobic conditions. Both terms are derived from the ancient Greek word “ἀήρ” (= aer), which means “air”. Aerobic means that oxygen is involved in energy production, so our breathing and the pulmonary circulation play their part, while the anaerobic metabolism gets by without oxygen.

As the metabolism slows, more energy processes become involved. The aerobic energy supply is slower than the anaerobic one and requires additional oxygen. In short, the more our heart rate and breathing speeds up, the faster we need energy. This causes the body to pump oxygen into the blood faster. If the oxygen is insufficient, additional energy without oxygen participation must be provided.

Both our fitness levels and our diet have a strong influence on when we are in which metabolic area. While some are gasping for breath when walking down the stairs and are in anaerobic metabolism, others have to do an Ironman triathlon to enter into anaerobic metabolism.

What happens during energy generation?

Muscles don’t just move on their own, but rather rely on some kind of fuel to contract. This fuel is called ATP (adenosine triphosphate) and is stored in the muscles in very small amounts. Splitting of a phosphate residue gives rise to energy, as well as to the decay products ADP (adenosine diphosphate) and organic phosphate. If we could only access the ATP stores in our muscles, we would only have energy that lasts for about 2 seconds. The body must therefore constantly produce new ATP during activity. In the first instance, the metabolism accesses the stored KP (creatine phosphate), with which we can bridge for about another 10 seconds. But even before these reservoirs are empty, our body constantly restores both substances to ensure a sustainable energy supply. This production, the resynthesis of ATP and KP is done by the aerobic and anaerobic energy metabolism.

Aerobic energy metabolism

During the aerobic metabolic process, carbohydrates and fats are burned with the consumption of oxygen, providing energy. Aerobic energy generation plays an increasingly dominant role after 1 minute of intense activity, with the body initially accessing carbohydrates (glycolysis), and fat burning (fatty acid oxidation) starting after about 15-30 minutes. However, this also depends on the form of exercise. It is important to understand that the aerobic metabolic process, as well as the anaerobic, is constantly active, as it also provides us with energy during rest periods. The circulating glucose in our blood constantly supplies us with a little energy.

The higher the intensity of the exercise, the more quickly the aerobic metabolism reaches its limits. This means that the more you intensely you work out, for example when sprinting as opposed to slowly jogging (here you will find our free Running Plans), the more energy your body needs in a very short time, and the lower the proportion that the aerobic metabolism can cover. Here, the aerobic glycolysis (carbohydrate combustion) works a little faster than the fatty acid oxidation. The reason why we cannot maintain a fast jogging tempo as long as a slow one is the size of our energy stores. When we run faster, most of the energy has to come from aerobic glycolysis, but the storage of glycogen only lasts for about 45-90 minutes, depending on your training condition. But then we do not break down completely, but can move on, more slowly, thanks to the lipid metabolism, which can supply us with energy much longer, but not so fast.

Anaerobic energy metabolism

If you’d like to do intense workouts (such as sprinting or muscle building with heavy weights), the rate of aerobic glycolysis is not enough. The oxygen must be removed from the energy to make it faster. We need our anaerobic metabolism, but that will not be without consequences. Anaerobic energy production differentiates between anaerobic aldactazide and anaerobic lactic acid. In anaerobic alactic energy production at the beginning of an intense exercise, the body uses its stores of high-energy phosphates ATP (adenosine triphosphate) and KP (creatine phosphate). As mentioned above, these stores are very small and must be constantly refilled. If the body needs energy very quickly, it resorts to anaerobic glycolysis. This anaerobic laktazide energy production represents the primary energy recovery process in all intensive activity where insufficient oxygen is available. It is not quite as fast as the anaerobic alactacid energy, but much faster than both aerobic ways.

This mechanism provides the power for very intense performances for another 20 – 40 seconds. In this case, the glucose originating from the blood and then the muscle glycogen (storage form of glucose in the muscle) is incompletely burned. This produces lactate (salt of lactic acid). This lactate is then recycled in the aerobic metabolism, as mentioned, this is slower, which accumulates in the stressed muscles with progressive higher activity. It comes to a metabolic acidosis (metabolic acidity). After all, this acidosis is performance-limiting, as it inhibits enzymes of the glycolytic metabolism, which in turn stops them. Consequently, we can no longer gain more energy from glucose and our metabolism is correspondingly slower, our performance decreases significantly. In extreme case, your body acidifies so much that vomiting can occur.

Benefits of carbohydrates over fats

Understanding the different energy recovery processes highlights two major benefits of carbohydrates over fats in stress metabolism. At first, carbohydrates can be released anaerobically about 5 times faster and aerobically 2 to 3 times faster than fats. They thus have a higher energy flow rate. In addition, carbohydrates provide on average 8.6% more energy per liter of oxygen absorbed than free fatty acid oxidation. It can be seen that the less oxygen available to the body and the higher the power to be delivered per unit time, the more important glucose or carbohydrates become, and even at low intensities these have two significant and functional advantages over the fats.

What happens if we do not have any carbohydrates available?

Athletes who want to perform intensely need carbohydrates, right? And isn’t it true that our brain cannot work without carbohydrates? In both cases, no. The human body is extremely adaptable, so there is another solution to these situations, so we are not not permanently at a disadvantage if we omit carbohydrates from our diets.

The riddle’s solution is called ketosis and describes a far-reaching change in our metabolism when we stop eating carbohydrates. In the initial adaptation phase, that lasts about two to three weeks, our body completely empties its carbohydrate stores, and then “learns” how to use so-called ketone bodies instead of carbohydrates as energy sources. These are produced under the influence of glucagon in the liver from fatty acids and can completely replace carbohydrates in the metabolism. The small amount of carbohydrates used for saliva production can be made from protein itself through a process called gluconeogenesis.

The performance of a ketogenic diet is comparable to that of a normal diet, as it compensates for the slightly slower metabolism with the slightly higher energy that ketones provide. From a medical point of view, ketogenic diets such as the Atkins diet can be carried out over a longer period of time without risks, even providing a solution to Alzheimer’s, diabetes, epilepsy, and other diseases where there is a “flaw” in our carbohydrate metabolism. In the implementation, a ketogenic diet is again difficult to classify, as you have to stay permanently below a limit of about 50g carbohydrates per day. Overall, a ketogenic diet requires a lot of discipline and is not suitable for everyday use.

Possible risks with low carb diets

When deciding on a low carb diet, it is very important to do it mindfully. A nutritionally inadequate low carb diet may impair performance, recovery, and immune function in the long term. Associated symptoms include general weakness, tiredness, fatigue, and increased susceptibility to injury and illness. In addition, there may be an impairment to your body’s signal systems, namely hormones and neurotransmitters.

Most important for the success of a low carb diet is getting the right amounts of nutrients at the right times – the first question must always be: “What does my body need now?”. The idea that your body needs full glycogen stores in the muscles and liver in the morning (i.e. needs carbohydrates in the morning) is long outdated. Due to the increase in blood sugar and the subsequent insulin response, lots of carbs in the morning actually makes your blood sugar levels go on a roller coaster ride throughout the day, which robs you of energy and affects your metabolism. Even the idea of not eating after a hard workout rarely makes sense: the energy stores are empty and want to be refilled, so that the body can regenerate faster and get powerful again as soon as possible. A proper low carb diet will not only tell you how much of a particular macronutrient you should eat, but also when, and from which sources you can best source the nutrients. If you’d like to know more, take a look at our Low Carb Guide.

Conclusion and recommendations regarding the low carb diet in fitness and sports

It is clear that the fat metabolism can be improved with a low carbohydrate diet. However, the performance-enhancing effect of a low carb diet with respect to sports and fitness depends primarily on how you implement it. Against the background of physiological laws, you should therefore measure and shape your diet according to the type of exercise you are doing.

Frequency and intensity of training are crucial parameters and factors that influence the best timing of your carbohydrate intake. If you exercise very often and intensively (activity level above 90 out of 100), with short recovery times, we advise against a rigid low carb diet and rather recommend that you adjust your carbohydrate intake – especially after the training sessions – to your needs. Otherwise, your performance will stagnate in the long run, and overtraining can lead to a performance slump. However, if you are physically active in the normal range (activity level below 90 out of 100), then a low carb diet, with occasional cheat meals, is perfect for you.

You do not have to worry about missing out on taste and flavor in this diet. Our nutrition experts have integrated the tastiest low carb recipes into your plans. Try out your own Low Carb Nutrition Plan now. What are you waiting for?


  • Burke, LM. (2015). Re-Examining High-Fat Diets for Sports Performance: Did We Call the Nail in the Coffin‘ Too Soon? Sports Med. S. 33-49.
  • Stackpole, EA. (1965). The long arctic search: The narrative of lieutenant Frederick Schwatka. New Bedford, MA: The Marine Historical Society. 1965.
  • Volek, JS., Noakes, T., Phinney, SD. (2014). Rethinking fat as a fuel for endurance exercise. Eur J Sport Science. S.79: 1-8.
    Weineck, J. (2010). Sportbiologie (10., überarbeitete und erweiterte Auflage). Balingen: Spitta Verlag GmbH & Co. KG. S.49-56.
  • Konopka, P. (2013). Sporternährung. Grundlagen – Ernährungsstrategien – Leistungsförderung (14. Auflage). BLV Buchverlag GmbH & Co. KG. S.55.
  • Gleeson, M. (2015). Immunological aspects of sport nutrition. Immunol Cell Biol. S.94: 117-123.
  • Andreas Hohmann, Martin Lames, Manfred Letzelter: Einführung in die Trainingswissenschaft. Limpert, Wiebelsheim 2007, ISBN 978-3-7853-1725-9
  • Stipanuk MH, Caudill MA. 2013. Biochemical Physiological and Molecular Aspects of Human Nutrition. Dritte Aufl. Philadelphia: Elsevier Saunders, 379-381.
  • Eric C Westman: Is dietary carbohydrate essential for human nutrition? American Journal of Clinical Nutrition. Band 75, Nr. 5, Mai 2005, S. 951–953
  • R. D. Feinman, W. K. Pogozelski, A. Astrup, R. K. Bernstein, E. J. Fine, E. C. Westman u. a.: Dietary carbohydrate restriction as the first approach in diabetes management: critical review and evidence base. In: Nutrition. Band 31, Nr. 1, 2015, S. 1–13

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