understanding fat metabolism
06-19-08, 02:40 PM
#27
Twincities MN
You think fat can be converted into carbohydrate?
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06-19-08, 04:38 PM
#28
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Fat is not converted to glycogen directly but it contributes to it. The glycerol backbone of a triglyceride is used to create glucose by supplying carbon molecules, which can be converted to glucose that will contribute to the regulation of blood glucose levels. Some of that glucose may get stored as glycogen. Up to 8% of blood glucose originates from glycerol. This pathway is called glycerol gluconeogenesis. So even though the amount of glucose supplied is not great it still is a significant amount.
"Glycerol, which is a part of all triacylglycerols, can also be used in gluconeogenesis. In organisms in which glycerol is derived from glucose (e.g., humans and other mammals), glycerol is sometimes not considered a true gluconeogenic substrate, as it cannot be used to generate new glucose."
TF
06-19-08, 05:40 PM
#29
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Try this link it is a good starting off on point that provides some good info, and it is published by a very reputable company and can explain it better than I can.
06-20-08, 01:10 PM
#30
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Try this link it is a good starting off on point that provides some good info, and it is published by a very reputable company and can explain it better than I can.
We cannot get glycerin through diet; it must be synthesized from glucose. The glycerin is then used to form triacylglycerols for fatty acid storage in the adipose tissue. When the body needs to use the stored fat for energy, the triacylglocerol is broken down, releasing the glycerol which can be used for glucose synthesis. So, you can get glucose from stored fat, but it is not enough to restore (or even maintain) the glycogen in the muscles.
TF
06-20-08, 01:24 PM
#31
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Ok, this is my unlearned take on what is being said.
We cannot get glycerin through diet; it must be synthesized from glucose. The glycerin is then used to form triacylglycerols for fatty acid storage in the adipose tissue. When the body needs to use the stored fat for energy, the triacylglocerol is broken down, releasing the glycerol which can be used for glucose synthesis. So, you can get glucose from stored fat, but it is not enough to restore (or even maintain) the glycogen in the muscles.
TF
We cannot get glycerin through diet; it must be synthesized from glucose. The glycerin is then used to form triacylglycerols for fatty acid storage in the adipose tissue. When the body needs to use the stored fat for energy, the triacylglocerol is broken down, releasing the glycerol which can be used for glucose synthesis. So, you can get glucose from stored fat, but it is not enough to restore (or even maintain) the glycogen in the muscles.
TF
I didn't read the link, but most dietary fats are a mixture of triglycerides, so they come with their own glycerol.
Last edited by Enthalpic; 06-20-08 at 03:49 PM.
06-20-08, 03:42 PM
#32
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06-20-08, 03:59 PM
#33
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The role of glycerol in carbohydrate metabolism is being exaggerated. Glycerol is only used as a “carbohydrate” during gluconeogenetic states (aka starvation).
Normally a triglyceride is broken down into free fatty acids and glycerol only to pass through a membrane; after which the fatty acid and glycerol recombine to form a trig.
Only during starvation or very low carb diets do side metabolic pathways begin to contribute significantly (protein gluconeogenisis, glycerol contribution to pyruvate, ketosis, etc). We should not assume that these pathways contribute significantly during fed states or during moderate exercise.
Normally a triglyceride is broken down into free fatty acids and glycerol only to pass through a membrane; after which the fatty acid and glycerol recombine to form a trig.
Only during starvation or very low carb diets do side metabolic pathways begin to contribute significantly (protein gluconeogenisis, glycerol contribution to pyruvate, ketosis, etc). We should not assume that these pathways contribute significantly during fed states or during moderate exercise.
Last edited by Enthalpic; 06-20-08 at 08:50 PM.
06-20-08, 08:15 PM
#34
Twincities MN
Uhm, I think you should reread mine and only read what I wrote and don't assume I don't know anything else about energy systems. Look, when you say that I'm wrong, it implies that you really do think that fats become some other kind of energy source such as carbohydrate... which really does not happen. What are you implying?
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06-24-08, 03:58 AM
#35
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So, I got into cycling (and running) to lose weight, more specifically to become lean. With that, here are some questions I'm trying to figure out:
1. How is adipose (fat) tissue decreased?
2. When is it burned... During or after exercise?
3. If it can be burned during exercise, what type of exercise burns it best?
I know that we all have a very personalized way of leaning up, what I'm afte are the fundamentals, things that I can wrap my brain around. So, feel free to discuss the Krebs cycle and all that jazz.
1. How is adipose (fat) tissue decreased?
2. When is it burned... During or after exercise?
3. If it can be burned during exercise, what type of exercise burns it best?
I know that we all have a very personalized way of leaning up, what I'm afte are the fundamentals, things that I can wrap my brain around. So, feel free to discuss the Krebs cycle and all that jazz.
To get practical: the key role is played by how high is your power output while remaining in an aerobic state. The graph with the 3 bars says it all.. the higher the intensity, the higher the absolute amount of fats that is being used.
But also the lower this is as a % of your VO2max the higher the % of fats is being used.
So, at one end you have a near 100% of fats being burned when asleep and at the other end nearly 0% of fats being used when you're at your HRmax.
A lot of people think they need to do interval training (HIIT) as this is what gives the best post exercise fat burning effect.. turns out this isn't really amounting to a lot over time. You can sustain a lower intensity effort for much longer and hence burn more calories of which more is fat.
The downside of it is that the body becomes very conservative over time when you exclusively do low-intensity rides (like lowering resting HR) and it does nothing to increase VO2max. So you need a combination of both.
Also, remember to also ingest both protein and carbs during your ride as a small % of energy is derived from protein. If you don't eat it.. then there's always the muscles to rob it from. Which is why a lot of cyclists have atrophied upper bodies.
The very best thing to do when you want to prevent your metabolism to go down is to lift weights and preserve muscle mass.
06-25-08, 11:45 AM
#36
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remember to also ingest both protein and carbs during your ride as a small % of energy is derived from protein. If you don't eat it.. then there's always the muscles to rob it from. Which is why a lot of cyclists have atrophied upper bodies.
The very best thing to do when you want to prevent your metabolism to go down is to lift weights and preserve muscle mass.
The very best thing to do when you want to prevent your metabolism to go down is to lift weights and preserve muscle mass.
Also, could you expand on how weight lifting helps to preserve muscle mass? I'm assuming that you were illuding to something like weight lifting prevents the body from breaking down its own protein sources (e.g. muscles) for fuel, yes/no?
06-25-08, 11:51 AM
#37
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Most people use protein powder made from whey.
Cycling is a way to get fit and burn calories .. but it won't build you muscles, with the exception of legs and behind. All other areas will suffer. Watch pro cyclists, most of them have scrawny arms and an atrophied UB.
Lifting weights will not give a strength edge but can also help in preventing that your UB muscle disappears when you're eating at a deficit.
Cycling is a way to get fit and burn calories .. but it won't build you muscles, with the exception of legs and behind. All other areas will suffer. Watch pro cyclists, most of them have scrawny arms and an atrophied UB.
Lifting weights will not give a strength edge but can also help in preventing that your UB muscle disappears when you're eating at a deficit.
07-23-08, 06:52 PM
#38
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Look at the charts that enthalpic posted to help you follow the discussion. The cells need glucose, the simplest sugar, for energy. But the body can metabolize or break down carbohydrates, fats and even protein to get that glucose. But the body seems to prefer to get the glucose in a certain order of preference, based on the speed of the different processes:
Now all of these occur together when you exercise. 1 - 4 happen more in vigorous exercise because they're fast processes. 5 happens more in moderate exercise, especially endurance activities like cycling. 6 happens when you're hungry or starving.
However, it doesn't matter which you do as far as losing weight goes. As others have said, this is because when you rest, your body goes back to a state of equilibrium: Blood glucose and triglycerides go back up. Glycogen is replenished in the muscle and liver cells. If protein was broken down in 6, it's built back up (anabolic steroids help here).
Where does the energy come from for restoring equilibrium? It usually comes from the big meal you want to eat after a hard ride. If you don't eat enough, your body will use adipose fat to restore equilibrium, just as it did back in 5. That's what people mean when they say that you continue to burn fat after you exercise. IOW, to lose weight you not only have to exercise, you also have to eat less after you exercise. Your body does not want to do that--it would rather have the meal--and that's one reason it's so hard for some people's bodies to lose fat.
- From glucose that's already in the cells--but that lasts only a few seconds of exercise.
- From glucose that's already floating around in the blood. This will last for a few minutes.
- From glycogen--a form of sugar stored in the muscle cells and in the liver. This will last for a couple hours or so.
- From triglycerides in the blood-->free fatty acids.
- From stored fat in adipose tissues. This can last for many hours or even days or weeks.
- From protein in the cells. This ordinarily is the body's last resort and leads to ketosis.
Now all of these occur together when you exercise. 1 - 4 happen more in vigorous exercise because they're fast processes. 5 happens more in moderate exercise, especially endurance activities like cycling. 6 happens when you're hungry or starving.
However, it doesn't matter which you do as far as losing weight goes. As others have said, this is because when you rest, your body goes back to a state of equilibrium: Blood glucose and triglycerides go back up. Glycogen is replenished in the muscle and liver cells. If protein was broken down in 6, it's built back up (anabolic steroids help here).
Where does the energy come from for restoring equilibrium? It usually comes from the big meal you want to eat after a hard ride. If you don't eat enough, your body will use adipose fat to restore equilibrium, just as it did back in 5. That's what people mean when they say that you continue to burn fat after you exercise. IOW, to lose weight you not only have to exercise, you also have to eat less after you exercise. Your body does not want to do that--it would rather have the meal--and that's one reason it's so hard for some people's bodies to lose fat.
Two organs in the body utilize glucose and glycogen strictly as energy sources, (the two most important organs) the brain and the heart. During times of prolonged fast the body protects their glucose supply by generating ketone bodies from fatty acids for consumption by the other organs to protect glucose levels for the two essential organs and this is the principle behind fat loss seen in low carbohydrate diets. The body reacts similarly during prolonged exercise, reserving glucose for essential organs and providing other substrates for muscles, liver and kidneys.
07-23-08, 09:43 PM
#39
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Also, if you consume a whey protein drink before your ride, your body will use more burn more fat cells for energy instead of instantly using your carbohydrate reserves.
