Bonk 2

[Kano]

Great information in the first thread, and now, after sharing with DH, he asked a new question: So when does the FAT he's been saving up for years and years until he started biking start burning?????

Karen in Boise

[Dogmama]

When he lights a fire under his butt & starts riding...?

[brok]

Actually, if I remember my physiology of exercise class correctly - during the first 20 minutes of exercise (aerobic), carbohydrates are the primary energy source. Fat is broken down and becomes the primary source after 20 minutes. The longer you exercise past 20 minutes, themore fat you burn. And on that happy little note I'm off for a 2 hour ride

[Dogmama]

If you exercise at a higher rate, e.g., doing intervals, you will burn more calories and that will burn more fat.

[Cassandra_Cain]

I don't remember all the details - or maybe I never knew them - but anyway...

To use fat as a primary source of fuel, I think you have to be going at a rather low pace. Everything I've read suggests that the body much, much prefers carbs as its chosen fuel. Once you bonk....

Either that or the light a fire under your backside theory may apply

[velogirl]

So many myths surrounding fat burning, ladies.

Remember, you have dietary fat (ie the fat you eat) and adipose (the fat you store around your middle). We do not use adipose for fuel during exercise.

We are always buring a combination of carb, fat, and protein. While fat is burned in a higher ratio during lower-intensity exercise, you're also burning fewer calories for the duration, so the logic that there is a "fat burning zone" or that you'll melt away your middle by exercising at a lower intensity is a myth. Our bodies are very inefficient using fat or protein as fuel. Carbohydrate/glycogen is the preferred fuel source (and our bodies are very good at utilizing it).

We lose weight/fat by increasing our caloric expenditure (burning more calories through activity) and/or decreasing our caloric intake (eating fewer pints of Ben & Jerry's). It's that simple. It really doesn't matter what intensity exercise you do. Move more and eat less.

If you want to lose fat (or you want your husband to lose fat), you're referring to adipose (the stored fat). The only way to lose that fat (besides liposuction) is to deficit yourself 500-1,000 calories/day. This equals a weight loss of approximately 1-2 pounds a week (3,500 calories = 1 pound). If you deficit yourself more than 1,000 calories/day, you will also lose muscle mass and/or your metabolism will respond by slowing down.

Weight gain was a gradual process -- you don't become overweight overnight. Weight loss is also a gradual process, so be patient.

[Kano]

So, Velogirl, what you're saying is that the answer to his question is "the rest of the day," yes? And then, when he wonders what's the point of the biking, the answer is "to build muscle and what all that will burn the fat," AND "to build strength to cart it all around while we're burning it!"

I was sharing the information about how we need to keep "carbing" while we ride -- run out and we're done for, and then he wanted to know about the fat thing. The idea that "we start burning fat" part way into the session, well, that makes sense to a point -- but then, there would be no such thing as bonk, at least not for a lot of us, because there's just no way I could ride long enough to run out of that fuel!!!

Karen in Boise

[thatonegal]

Your husband doesn't lose weight because he hasn't been using up the energy his body has on standby and so doesn't use the energy his body has stored in adipose tissue(fat). A more scientific and biochemical explanation below might help, but no guarantees that I explained it well.


A calorie is a simple measure of energy. Our bodies use ATP for energy so the calories in food are calculated according the how many ATP the food can allow our body to produce. Our bodies digest food and run it through biochemical cycles at the sole purpose of producing the energy rich ATP.
Carbs tend to contain glucose which is the direct ingredient in the glycolysis cycle which has a product that is then directly put into the citric acid cycle to make ATP. So carbs are easy to convert into energy. Fats are made of long chains of molecules which can be easily modified to go into the ATP producing citric acid cycle, but they take the longest to put through. Proteins are broken into small fragments that can be used to produce ATP but because the process to put protein into glycolysis and the citric acid cycle is longer and doesn't produce as much ATP protein is more often broken down to Urea or used to provide protein building blocks to the body.
High protein low carb diets allow the body to use up available glucose(carb) stores in the blood and then when the body looks to make more ATP and the easy to cycle glucose is unavailable it opts for the harder to cycle protein and the longer to cycle fats, but protein doesn't produce as much ATP so the body prefers to use stores of fat in the blood. The trick with high protein diets is that your body can't effectively use all the protein consumed either because of time constraints or there is too much protein in the blood stream so any extra amount of protein in the blood is excreted instead of being stored or used up like a fat or carb would be stored or used.
The steady level of fat in your blood at any time is where your body will first grab fat to produce ATP, and the adipose cells(fat cells) of the body release more fat to keep the blood stream at a constant level. So when you lose weight you have been using up the fat in your bloodstream and the cells that store fat along your stomach, butt, or wherever have been releasing fats so they lose their filling and shrink.
The problem using fat is fat takes time to be released into the blood stream and it takes time to be processed to the proper form. So if you use up most of the carbs and proteins in your blood your body will begin taking protein from your muscles and tissues to make up for the smaller amount in your bloodstream until it can use the fat to produce more ATP.

Everything in the body is about balance.

I am such a nerd. I hope that explanation makes sense.

[velogirl]

A more scientific and biochemical explanation below might help, but no guarantees that I explained it well.


A calorie is a simple measure of energy. .........

<snip>

Everything in the body is about balance.

I am such a nerd. I hope that explanation makes sense.

Any chance you could share your reference for this explanation?