Why You Need to Know about Nutrient Substrate Utilization

Doug Jackson, M.Ed.,CSCS

10/9/05

(Quick note: I am now accepting personal training clients in Weston, Florida. Limited spots available. Fill out the online application to apply.)

The science of fitness is an interesting thing to study. What do all of the weight loss and health experts say? Eat less and exercise more. And for many people, this advice lays at the heart of the matter. However, as you might imagine, there is more specific and more effective advice for people who want to optimize fat loss and their metabolism.

Getting into the intricacies of muscle building and fat loss is beyond the scope of this article, but suffice to say, it's more complicated than eating less and exercising more. One of the things we must examine to optimize conditioning programs is how exercise affects substrate utilization.

Just what is energy substrate utilization? It's the term we use to define how the body burns fats and carbohydrates.

When you hear someone say that cardio burns fat and weight training doesn't burn fat, substrate utilization is what they are referring to. Of course, the idea that "cardio burns fat and weight training doesn't" is a half-truth.

Here's the question and the point of the newsletter today. Do you do cardio and weight training on the same day? If so, do you perform cardio first or weight training first?

Compare your answer with this simple fact: You will burn a high percentage of fat performing cardio after weight training than if you do it before weight training or on another day.

Why?

Resistance training burns carbs (depletes glycogen stores). If you perform cardio after the weight training which has depleted your glycogen stores, you will burn a high percentage of fat during cardio.

If you are performing cardio with the primary goal of fat loss, you will find benefit in performing it after a session of resistance training.

If you do the reverse and perform cardio before weight training, you are hampering your results. Here's why. If you do cardio first, your body will preferentially burn carbs. When you begin your resistance training in a glycogen depleted state, your body will enter a catabolic state and convert your muscle tissue into glucose so you have the energy to perform the resistance exercise. Instead of building muscle and increasing metabolism, you will actually be breaking down muscle tissue and decreasing metabolism.

So is it as simple as eat less and exercise more? No. And instead of dumbing down the information, I'd rather give people the science they need to get measurable results. Both of the approaches above (cardio before weights or cardio after weights) will create weight loss, but one leads someone to a lean, tone look and the other will lead to a condition that trainers typically refer to as "skinny fat". "Skinny fat" defined is someone that looks good with clothes on, but underneath the clothes they have virtually no muscle and are at a moderate or high body fat level. Don’t be skinny fat.

Final word for the day. If the goal is fat loss and improving muscle tone, it's best to perform cardio after resistance exercise. Alternating days of cardio and resistance is good if the goal is general fitness, but not ideal for maximum fat loss. And performing your resistance training after cardio is a BAD idea unless you want to look like an emaciated long distance runner or be skinny fat (Results dependent on genetics and other variable factors. Consult a qualified trainer for further details).

By the way, for healthy meals delivered to your doorstep at a price you can't beat, check out:

Sign up for Doug's can't miss newsletter, Fitness Empowerment

Ask Doug your most pressing fitness-related question

Schedule a FREE phone consultation