Endurance and low-carb diet, a dilemma or a winning strategy?

Recently, the elite athletes of endurance sports finally decided to “break” the myth in their nutrition plans. The overflow of available information and scientific studies changed the game - we used to pay excessive attention to carbs when we talked about endurance sports, but this new approach to dieting started turning heads and drawing attention from sports scientists and nutritionists around the globe.

Energy brings results, better performance and, of course, new records. So, what is this new diet?

Main source of energy

By reducing carbohydrate intake, your primary energy source switches to fat. Some might argue high-intensity workouts are better performed with the use of simple sugars. Not necessarily! A chronic ingestion of simple sugars definitely has an effect on your insulin levels, blood sugar levels and gut health.

According to a study conducted by Achten and Jeukendrup, it was found that at a 63% VO2 max intensity, we have the maximum use of fat as fuel, while the minimum use of fat (and maximum glycogen use) is 83% VO2 max. We can easily adjust these tensions to our pulse rate. Here is an example:

If the athlete's age is 30, then half is 15

Maximum heart rate beats: 205 - 15 = 190

Heart rate for maximum fat burning and minimal use of glycogen (63% of VO2 max):

0.63 x 190 = near 120

Heart rate for minimum percentage of burning fat and maximum use of glycogen (83% VO2 max):

0.83 x 190 = near 160

The word "percentage" is not used because athletes often misinterpret this point. The absolute and relative (percentages) for fat burning differ slightly. When you pass the 63% of VO2 max intensity, the use of fat as a fuel remains constant as an absolute value, because overall burned calories increase, the percentage of fat intake decreases.

Let's put it down with numbers to make it easier:

Exercise at continuous low-intensity (30% of VO2 max) for some time:

Burned calories: 150

Calories from fat: 75 (50%)

Calories from glycogen: 75 (50%)

Exercise at a continuous moderate-intensity (63% of VO2 max, max fat burn) for some time:

Calories burned: 300

Calories from fat: 200 (75%)

Calories from glycogen: 100 (25%)

Exercise at a continuous high-intensity (83%, max glycogen burn) over the same time period:

Burning calories: 500

Calories from fat: 200 (40%)

Calories from glycogen: 300 (60%)

An increase in intensity does not equal to burning less fat. For someone who wants to focus on losing fat, the constant high intensity actually burns more calories than glycogen (which would be replenished after the food consumption). The calories from fat in our example remain 200, but the percentage of participation decreases, as greater intensity means greater energy need (500 vs. 300 calories in our example). "Plateau" is close to 60-65% of the volume.

So, how does fasted cardio apply?

Fasted cardio is another applied strategy which, in combination with the low-carb diet, can bring extremely positive results. Of course, fasted cardio is an essential part of an overall fat loss routine. To understand the definition of "fasted state" we need to have a complete picture of the food breakdown in our body. The meal which we consumed will be digested in a way that the proteins, carbs and fats are transformed into molecules, amino acids, glucose and fatty acids respectively. The small intestine absorbs all these nutrients into the bloodstream where they come in contact with insulin. Insulin transfers the nutrients straight into the cells for immediate use. When your body is processing the food (the "fed state"), your insulin levels are high. Once the process is finished, the body enters the "fasted state" in which the insulin levels are low. The body enters these states several times a day.

Many athletes start feeling as if their stomachs are empty for approximately an hour after eating - but they are not in a "fasted state" yet. We should always think "fasted" or "fed", rather than "empty" or "full". Basically, a fasted cardio is a cardio session done when our body is not processing food during our training. The best example of a fasted state is immediately after you wake up. Your body has surely been in a fasted state during the night and, most of the times, it has entered the natural ketosis.

Evidence that fasted cardio can give better results

When we talk about endurance sports, there is indicative evidence that fasted state training is in fact superior to fed state training. A diet rich in fats is very important because it gives us the ability to be insulin resistant. Of course, exercising in the fasted state gives the advantage to stimulate energy via fat oxidation. The human body stores large amounts of body fat in the form of triglycerides in both the fatty tissue and in between the muscle fibres. These reserves must be mobilised into free fatty acids and transferred to muscle mitochondria for oxidation during exercise. As exercise intensity increases from low (25% VO2max) to moderate (65% VO2max) and high (85% VO2max), the mobilisation of free fatty acids in plasma decreases. However, total fat oxidation increases as exercise intensity also increases from 25% to 65% of VO2max, due to the oxidation of intramuscular triglycerides, which provides nearly half of the fat for oxidation.

Endurance training increases fat oxidation during moderate-intensity exercise, increasing oxidation of intramuscular triglycerides without increasing mobilisation or oxidation of free fatty acids in the plasma. Similarly, during low-intensity exercise with low intramuscular triglyceride oxidation, increased fat oxidation in trained individuals does not appear to be due to an increase in free fatty acid mobilisation in plasma. The reason lays in higher percentage of free fatty acid oxidation.

A well-known fact is that the most successful endurance athletes follow a low-carb, high-fat diet. A recent study has been applied to Ironman distance triathletes and marathoners. They have been divided into two groups and the first group followed the classic high-carb diet and the second group the low-carb diet for approximately 20 months. The results have been fascinating! The peak of fat oxidation was 2.3 times higher on the low-carb diet which means fat oxidation was 59% higher in the low-carb diet.

Fat adaptation and performance

For years all the experts told us that science proves that carbohydrates are the ultimate tool for performance and fat can only be utilised in low-intensity and moderate-intensity exercises. These experts ignored the laws of nature. Our bodies always had limited glycogen storage capacity, while the fat stores are, in essence, "unlimited". These fat stores are more than enough even for a super lean athlete to finish an Ironman or even to ride a Double century. Our ancestors were eating carbohydrates approximately 5 times per year. Today, the whole humanity is basing our nutrition on carbs -even 5 times per day. This wrong approach is leading to health hazard and for the very same reason you should consider nutritional ketosis.

When do we need carbs?

With all due respect to sports people, top-notch or recreational, most of them often train/run at relatively low speed/intensity. We train at maximum load only for a small percentage of our time. This maximum load training might require carbs or glucose (sugar) as a source of energy. Train Low Compete High highlights this and says: any load except the maximum, can be very productive with only ketones. The problem arises when we put sugar on each training, constantly, and when we train with light intensity. That's 99% of the time for most people. In hypothesis, training low animates the body to indicate unconventional pathways that maintain energy metabolism. Training in a glycogen-depleted environment can encourage the body to be more effective at employing fat and conceivably spare glycogen during the endurance training. Basically, it is to generate a valuable dynamo for endurance sports.

So, what about Ketosis?

Ketosis is not omnipotent and is not a solution to all problems and may be a powerful weapon in your arsenal. To be fat adoptive, one needs a time of 4 days to 2 weeks until carbs withdraw. After this first stage, there is a second stage between 6-8 weeks of hormonal regulation.

My subjective prospective on a low-carb diet and fasted state training:

For many years I have been running and racing, running is so natural to me and has become a big part of my life. Racing was just a direct consequence of my addiction to run. In my early running career I managed to achieve great results with a very de-structured running plan and a very peculiar nutrition regime. In essence: I used to wake up in the morning, have a big coffee and off I go...most of my runs were under one or more of these conditions:

  • Zone 1 or 2 (basically 180 minus age minus extra 5/10)

  • Fasted

  • Mood based (means that, if I feel good I run more if I feel bad I run less)

  • Daily – rarely skip a day of training, to me it was like brushing my teeth or pooping, if I skip it I would have consequences all day long ☺

What happened in the last 6 months?

I read a nice book (the trigger was Tim “bloody” Ferris) and started thinking about low-carbs diet etc. Soon I realized that it was pretty much what I was always doing. Since my "change" wasn't so dramatic, I was able to test out some "extreme" measures:

  • Triathlon and long triathlon distances training in a fasted state

  • Intermitting fasting

  • Ketogenic diet 3 weeks before racing

  • Kept my primal lifestyle by making a cut on rice and grains, but keeping vegetable and 3/4 portion of fruits per day as my primary source of carbs (em...yes, I do at least 2-3 glasses of red per night, sorry Atkins but I need them).

The results in a nutshell:

  • Ran 2.30 marathon on hilly course just training for triathlon distances (the best in 5 years for me)

  • Qualified for 70.3 and 140.6 Ironman Worlds in the first year

  • No muscle pain day after big races

  • Kept a reduced carbo-loading only on the day before the race but based mostly on starchy vegetables (approximately 6.5 grams of carbs per kg so for me in the 400 range)

  • During competitions:

1) I barely ate during marathons, just drank water

2) At the 70.3 I had 2 bottles of coconut water, 2 bottles of water and a 50 grams of my chocolate bars (88% pure chocolate with marine salt and caffeine)

3) At the Ironman I ate like a pig but mostly organic-nuts based bars offered at the stops (I was a bit intimidated by the distance and didn’t want to risk). Next time I will try to avoid the bars and bring my own fueling

If science wasn't enough to convince you, I also ran the fastest age-group in the field in Kona, as a first-timer of the Ironman World Championship.

If you want to improve your race results, choose ketosis diet to be your first step - top-athletes around the planet have proven that this is the healthiest and most efficient way to achieve best times. If this works for them, there is no reason why it shouldn't work for you too.

Happy training!

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Maximal fat oxidation during exercise in trained men

Ketogenic diets and physical performance

by Stephen D. Phinney

Train Low, Compete High – Food for Thought

Endurance Planet - Faster Study

Modified Ketogenic Diet for Endurance Athletes

by Breanne Nalder

Body composition changes associated with fasted versus non-fasted aerobic exercise

The Paleo Diet for Athletes

by Loren Cordain

by Stefano Passarello

The Kapuhala Project Founder


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