Should I? Shouldn’t I?

messages Apr 13, 2009

Exercising on an empty stomach to burn fat sounds nice.You can create a scenario in your mind that if your body needs energy to exercise, it will take it from the fat cells.Unfortunately, this is not the case.I know the scenario sounds good.I know it may even "make sense" in your mind.You may have even read somewhere that you should workout on an empty stomach.It's a nice hypothesis, but it's NOT TRUE.

There's how we think the body should work,

and then there's how it actually works.

The need to eat before a workout can be difficult for clients to accept when they've bought in to exercising with no food in the system. I can use scientific data to explain it, yet people are still apprehensive to believe it. There have been several instances where they refuse to believe the science and I am forced to pull out the "Trust me - I'm a professional. I know what I'm talking about. I went to school for six years to learn how the body works, I'm a competitive athlete, and my body fat is exactly where I want it to be."  (Which then makes me feel like an ass.)

As I mentioned in my Sumo Wrestler Diet post, you need to put glucose in the system before you exercise. Today I'm going to explain why you should eat, when you should eat, what you should eat and how much you should eat before a workout.

WHY? If you are exercising with no glucose in the system, it sends your body in to Emergency Mode. Emergency Mode = hold on to body fat for as long as possible because it is valuable energy and will be necessary to survive. Instead of fat, your body will break down muscle tissue and use that as energy. It does this for two major reasons:

1) Muscle is metabolically active tissue - it takes approximately 10-20 calories of energy to sustain 1 pound of muscle in a 24-hour period. For this reason it's viewed as costly when there is not enough energy coming in. Your body is "doing you a favor" by getting rid of really needy, high maintenance cells. Emergency Mode is all about energy conservation:  Get rid of muscle, hold on to fat.

2) Losing muscle mass slows down your metabolism, which conserves energy. Which is your body's goal when there is no food in the system.

If you are working out - or even physically active - and there is no glucose in the system, your primary fuel source is muscle, not fat. Get your body out of Emergency Mode by making sure to keep adequate glucose in the system by eating several small meals and snacks throughout the day.

Here's another thing to think about: how much energy are you going to have for a great workout when there's no fuel in the system? It won't be your best performance and doesn't make any sense from a physiological perspective. Your intensity will be lower and you probably won't be able to go as long.

If you consistently put energy in to the body by eating several small meals and snacks throughout the day, your body never goes in to Emergency Mode. This means that if there is some glucose in the system, but not enough, your body will feel confident to take some of what it needs from the fat cells because you've trained your body to know there will be more food coming in a few hours.

WHEN? It can be a few minutes before you're about to workout all the way up to 2 hours before you workout, depending on what and how much you eat. The most important thing is to make sure there is glucose circulating in the system.

WHAT? To make the best decision about what to eat, use the glycemic index. The glycemic index is simply a measure of how quickly a food gets broken down in to glucose and released in to the system. All foods are classified as either low, moderate, or high glycemic. A low glycemic food gets broken down in to glucose and released in to the system more slowly over time. If it is closer to 2 hours before you workout, make sure you eat something that is low glycemic so that it will last you up to and into your workout. If it's about an hour before your workout you should choose either a low or moderate glycemic food.  If it's a few minutes before your workout, you could have either a low, moderate or high glycemic food.  Here's a very simple chart that shows where many popular foods fall.  There are 3 things that will make a food lower glycemic:  if it contains fat, fiber, and/or protein.  There are plenty of books and websites available if you want to learn more about where specific foods fall.


Glycemic Index table

Low glycemic: Low to moderate glycemic: Moderate to high glycemic: High glycemic:
  • barley
  • black beans
  • broccoli
  • cashews
  • cherries
  • chickpeas
  • grapefruit
  • green leafy vegetables
  • kidney beans
  • lentils
  • milk
  • peanuts
  • peanut butter
  • pears
  • plums
  • soybeans
  • strawberries
  • tomatoes
  • tomato soup
  • wild rice
  • plain yogurt
  • All-Bran
  • apples
  • brown rice
  • carrots
  • garbanzo beans
  • grapes
  • honey
  • ice cream
  • kidney beans
  • navy beans
  • oranges
  • peas
  • peaches
  • pears
  • pinto beans
  • potato chips
  • bananas
  • figs
  • mangos
  • potatoes (sweet and white)
  • pineapple
  • pita bread
  • oat bran
  • oat bread
  • white rice
  • raisins
  • carrots
  • brown rice
  • kidney beans
  • shredded wheat
  • bagels
  • beets
  • cakes
  • Cheerios
  • dates
  • corn flakes
  • pies
  • pretzels
  • refined durum wheat pasta
  • jelly beans
  • parsnips
  • puffed wheat
  • sweet corn
  • white bread
Chart is loosely based on Foster-Powell, K., S. Holt, & J. Brand-Miller. 2002. International table of glycemic index and glycemic load values. American Journal of Clinical Nutrition, 76 (1), 5-556. URL: (free full text; accessed 03.28.2007).

HOW MUCH? If it's literally a few minutes before you workout, you're not going to want to eat much. You could do a small glass of juice. You might function well after eating a small piece of fruit. You could also choose to have a small piece of toast or muffin. Eat just enough to fuel your body without upsetting your stomach.

If it's an hour before your workout, you're going to need to eat a larger amount to give you enough energy up to and through your workout.


You are going to have to experiment with what works best.


If you feel like you run out of energy after a bowl of cereal that you ate an hour before your workout, it either wasn't the right amount of food or the right combination of nutrients for you.If you had a stellar workout after having a banana with peanut butter, it was probably a good choice!Only you will know what type and amount works best for your body and your needs.


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