I have had many questions lately about how athletes can do low-sugar, no-carb, or Paleolithic diet. I have been researching this topic in depth in the last few months because of my interest in running longer distances. While I have been a runner all my life, running longer distances has never intrigued me (I prefer crazy races like 24 hour relay races or unmarked runs through the woods). This year, for some reason, I decided to run a marathon and that move made me hit the books to find the best way to fuel my athlete’s body.

What this article will show you is the state of the art about a no-sugar or no “food that act like sugars” (mostly grains) diet and how you can optimize your training and running (or cycling) by sticking to a no-carb diet most of the time. What you will learn is that (at least according to conventional wisdom) is that you have to include some sort of carbohydrate to keep your exercise intensity high.

Recovery

Let’s start at the end, your recovery. The most efficient way to recover from a long exercise bout is to first replace glycogen and then protein. Research has shown that muscles uptake of glycogen is most efficiently 20-30 minutes following exercise. In order to replace this glycogen, you need to eat some form of sugar. This can come in the form of fruits and fruit juices, but fructose (the sugar mostly found in fruit) is not as efficient as glucose so consider a recovery formula (I like the one from Vega).

After you have replaced the glycogen then you should move on to protein. During an hour-long training season, you have lost some protein and you should focus on eating protein to provide your muscles with the building blocks it needs for repair. There is good evidence that eating a diet without sugar or the foods that act like sugar most of the time is helpful at shortening recovery. So, 20 minutes following your exercise you should eat some form of protein like eggs or meat (I like Chili). What you are doing in this phase is giving your body what it needs to function well.

Exercise

In order to understand what you should be eating during exercise, you need to understand what your body considers fuel. When you are at rest, you body will generally use free-floating fats (fatty acids) as energy and this is true when you start to exercise as well. As you increase your exercise intensity, your body will switch from blood fats to using muscle fats called inter-muscular triglycerides (IMT). These are the main source of energy to run your muscles. As you further increase intensity, this is when your body will start to use glycogen (this is the form of quick sugar storage in your muscles and liver).

When you get to around 65 percent of your maximum intensity (VO2 max) this is when your body is using about 1/2 glycogen and 1/2 IMT. Things really change when you start exercising at 85 percent of your maximum or above, this is when glycogen becomes the dominant fuel. The body chooses glycogen at this point because it takes less oxygen to burn glycogen than those IMT.

You have probably experienced this if you have ever forgotten to take enough sugar during very intense exercise. As your glycogen depletes, you have to switch to burning body fat, this means you have to slow down because your body is using more oxygen. This isn’t quite bonking, but you feel like everything is uphill.

Review

So to review: if you are exercising slowly, then you don’t need glycogen or sugar; your body has enough fuel to get you around. You also don’t need sugar if you exercise intensely until you run out of glycogen (for most people this is around 1 hour of exercise). When you are exercising at a high intensity for a long time is when you need to keep a constant stream of sugar in your body. Most books will say that you need around 300 calories of sugar per hour for running something like a marathon or longer. If you run longer than a marathon, then you also need to think about consuming some protein.

There is also another trick you should know about that benefits the low-sugar athlete. Most athletes only focus on replacing glycogen, but you can improve your performance by increasing your inter-muscular

So while most athletes focus on replacing glycogen, you can increase your efficiency by storing more inter-muscular triglycerides (IMT) and this comes from eating low or no sugar and exercising at a high intensity. Yes, this means doing speed work.

I find that eating any sugars tends to make you crave more sugars (I call it the sugar magnet), but if you can focus on using sugar for recovery and using it for only the longest of your runs then being a low-sugar athlete has many benefits.

The last thing I want to say is that what you have read here is the conventional wisdom and researchers only look for what they believe to be normal. It may very well be that not using sugar right after exercise or during long runs may work, but it hasn’t been really tested.

For now, check out for more information about a low-glycemic diet for athletes.