RE: Can I ask one more question......?
[font size="1" color="#FF0000"]LAST EDITED ON Aug-17-02 AT 11:31AM (Est)[/font][p]No matter what it is still calories out vs calories in that determines whether fat is lost. I'm a big fan of Covert Bailey's but I have never seen him advocate exercise on an empty stomach--I went back and checked my latest Covert book. Here's why.
When you exercise on an empty stomach--nothing to eat for at least 8 hours, the body will deplete its glycogen stores, then, because the body HAS to have glucose to function, will make it from other sources (gluconeogenesis)--this is a mini-starvation situation. While fat will contribute a small amount to this, the biggest source of substrate for gluconeogenesis comes from protein (~85 percent)--in an unfed state, the typical source is lean muscle mass. If you have adequate glycogen available during exercise, you can burn a significantly greater amount of fat to fuel the exercise than you will to build glucose. Additionally, when glycogen stores are low, endurance is low--you can't exercise as long or as intensely. For purposes of loss of body fat and/or lean muscle maintenance, exercise on an empty stomach is counterproductive.
In healthy people, blood sugar levels decrease during exercise, hitting a critical point about 20 minutes into the activity. Prior to this point, there is some fat fueling the exercise, but the primary fuel is blood glucose. At about the 20 minute point, as the blood sugar levels decrease to a certain point, hormones cause a surge of fatty acids to be released from the fat cells. In a glycogen depleted state, the blood sugar levels have to be build up first--through gluconeogenesis--and a whopping 85% of the substrate for gluconeogenesis will come from protein stores! In an unfed state (such as overnight), this is already happening before the exercise starts, but when the energy demands increase, so will the grams of protein contributing to the building of glucose--bye-bye, muscle! Blood glucose levels have to be maintained for the body to function normally--if they are low to start with due to not eating, or any other reason, for that matter, the body will make more glucose, but using primarily protein (~85%) to make it.
The "Better Butter Burner" Covert is talking about comes from developing the fat metabolizing enzymes through becoming fit. The fitter you are, the more your body will be able to utilize fat as a fuel for exercise at any intensity. It isn't a matter of having to deplete glycogen for this to happen--there's a difference in having blood sugar drop during exercise and being in a depleted state. Actually, fit people are glycogen sparers, not glycogen burners--they have enhanced capacity to store glycogen and enhanced capacity to utilize fat at all times, especially during exercise. Unfit people have poorly developed fat metabolizing enzymes because they burn few calories through activity. The fewer calories expended through exercise, the less well developed the body's fat metabolizing system needs to be--it's survival and "use it or lose it".
As for not eating immediately after exercise--again, it's calories out vs calories in. Immediately post exercise is a prime time to replenish glycogen stores, especially with simple carbs. And, the elevation in metabolic rate post exercise is enhanced by eating, meaning that a post exercise meal will result in more calories being burned than that meal will if you eat it several hours later.
When you read something where a specific product is touted, like Precision Protein, look very skeptically--regardless of the credentials of the person, there is financial motivation behind the article. And it makes no difference when you exercise during the day--other than if you have trouble sleeping after a workout. The mechanisms for exercise and recovery are the same.
Bottom line is that exercise on an empty stomach guarantees one thing--protein will be burned to a very significant degree. For long term metabolism maintenance and fat loss, this is a bad thing. Does it burn a few extra calories to force your body to have to make glucose--yes. Do you expend significantly less calories in the exercise process when you hit the wall or have to drop your intensity level--absolutely--particularly with strength training, which is highly dependent on glucose as fuel. Are the few extra calories expended to make glucose worth the loss of intensity and lean muscle mass--IMHO, no way!
Maribeth
