Your body has two sources for fuel: fat, and carbohydrate. One is abundant (Fat), one is not (carbohydrate). Based on the first sentence, which fuel source do you think your body should be better tuned to burning during an endurance event?

Let’s start with Fat. Fat is a very abundant energy source, both by the sheer amount of it in our bodies, and the number of calories per gram. Fat has 9 calories per gram, compared to 4 calories for a carbohydrate. Even for those people who are at a low body fat % (<9), they still have a near unlimited supply.

During periods of low level aerobic activity (walking), or very little aerobic activity (sitting), your body is burning fat as its primary fuel source. During these periods, there aren’t any huge energy demands on the system to render the need of carbohydrates, which we know are broken down easily into readily usable energy. The rate of burning calories can be met by breaking down fat into energy.

Carbohydrate (CHO) is stored in the form of glucose, and is stored in both your liver and muscles. Your body can only store roughly 500 grams of CHO between the liver and muscles. Because of this limited supply, we need to replenish our bodies with carbohydrates during exercise.

Based on everything above, we should train our bodies to burn more fat as an energy source, rather than CHO. To do this, we are required to do a few things:

1. Train at the right intensity
2. Eat the right % of Fat vs. CHO
3. Eat the right Fat

Training Intensity

Obviously, low level aerobic activity and “base building” efforts should be performed at the correct intensity to ensure the fat burning mechanism is utilized. Once your body is used to exercising at this intensity, it will learn that fat can be used as a major energy source.

But intensity doesn’t necessarily mean training at base building effort all the time. Studies have shown that short bursts of high intensity training (sprints, tabata training) have shown an increased rate of fat metabolism. I don’t know the physiological basis behind all of this, but there are plenty of studies documenting this – take their word for it.

% of Fat vs. CHO

Another way to teach the body to burn fat is to simply eat more of it, and less CHO!

One key way is to control the types of CHO ingested into the body. During exercise, complex CHO (maltodextrin, a common ingredient in sports consumables) should be utilized to help keep blood sugars regulated. When not exercising and especially during increased volume and demanding training blocks where glycogen needs to be replaced more rapidly, complex CHO like brown rice, potatoes, yams, etc (ie. more “naturally occurring” carbs) should consumed to keep glycogen stores at regulated levels. In general, try to avoid processed carbs like pasta’s and breads (Trust me, I like pasta and especially bread as much as the next guy, but you will feel better once you mostly/completely cut it out of your diet!)

Be careful not to eat too many carbs at once because that will throw your insulin levels out of whack, and eventually make you tired because your body isn’t used to having to deal with that much CHO when not exercising! Also, aside from fruit, simple sugars should be used sparingly and arguably, only during exercise.

Not all fats are created equal

Eating more fat doesn’t mean its okay to start eating fast food all the time! GOOD fats should be consumed when eating, and some common foods where good fats are found are:

• Nuts (cashews, almonds, nuts, nut butters)
• Oils (Olive, Palm)
• Avocados

Some may argue this, but I believe animal fat is a good fat as well. I believe this because humans have been consuming animal fat for thousands of years, and when eaten in moderation, it does not make you fat. I will even say that eating chicken breasts with meals are sometimes are just a little too lean for me, and recently opted for a thigh/leg combo at times.

However, I will argue that fat from dairy should used sparingly because 1. I am biased – I am lactose intolerant, and 2. We are the only beings on earth that consume milk past being very young. But again, this is just my opinion – different things work for different people. As an aside, I personally try to minimize eating food items that contain an ingredient list.

Does this work? Are you for real?

It did for me when I trained for my first Ironman in July. You would think that someone training for an Ironman would be consuming copious amounts of carbohydrates, but in fact, it was the opposite. At a health fair in early June, 6 weeks out from Ironman, I had my blood glucose level measured, and I came in at 91. For comparison, pre-diabetes starts at 150, and those that consume low carb diets are typically under 100. Although I ate quite often, I was never tired during the day due to food/calorie consumption, and owe that to my body’s ability to burn fat, and only consuming CHO when absolutely necessary.

Written by Ryan Denner