Can someone explain how excess fat in the body gets broken down?

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spicypumpkin

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So, I'm trying to understand the basic fundamentals of energy usage in the body. I understand the basic components of catabolic and anabolic processes in the body. When the body needs extra energy, it breaks down protein molecules into glucose. When there is an excess of sugar and protein, and the muscles have been stimulated, there is an anabolic process which results in the building of muscle. How does fat fit in to all of this? How does the body decide whether or not to break down fat versus protein for energy? Which is more efficient for your body to break down and why? What is the chemical process in which fat is broken down into a usable fuel for energy?

If anyone has any information or articles on this, it would be very helpful.
 
ok disregarding the first half of what you said, mainly because it is over simplified and not necessrily true.

1) Fat is more effecient. Not only is energy from protein a consuming process, requiring deamination and producing less energy, overall it is at the cost of what would have been providing a purpose to the body like transport or structure.

2)The process of which fatty acids are broken down is called fatty acid oxidation. Heres just a quick link that first popped up.



3)The body will always prefer fat over protein for energy which im sure you could find somewhere in google or ask someone that knows at your university.
 
See an article such as Extracted below :-

How Are Carbs, Protein And Fat Absorbed And Stored?

The human body needs energy to power muscles and to fuel the millions of chemical and biological reactions which take place throughout our system every day. This energy comes from the food we consume in our diet. Food consists mainly of water and three types of nutrient - protein, dietary fats and carbohydrate - which are found in varying proportions in most foods. These nutrients are broken down, digested and absorbed by the body in the gastrointestinal tract, running from the mouth to the anus. Each of these macronutrients is processed and absorbed by the digestive system in different ways.

How Are Surplus Carbs Used And Stored?

Carbohydrate is the major source of energy for the body. This is because, of all nutrients, it converts most readily to glucose which is the body's preferred fuel. When we eat carbohydrate, it is converted to glucose in the digestive tract and distributed via the liver to cells throughout the body for use as energy. Once our immediate energy needs are satisfied, the remaining carb glucose is handled in one of two ways. Either it is converted to liquid glycogen (a temporary source of readily available energy) and stored in the liver or muscles. Or, it is converted into fatty acids by the liver and stored in adipose cells (fat-cells) around the body.

How Is Surplus Protein Used And Stored?

Protein is broken down into amino acids in the stomach and small intestine, then distributed via the liver to cells throughout the body for a variety of uses included cell formation and repair. Some surplus protein amino acids are kept circulating in the bloodstream, the remainder is either converted into a type of simple sugar and used as energy, or (like carbohydrate) is converted to fatty acid and stored in adipose cells.

How Is Surplus Dietary Fat Used And Stored?

Dietary fat is broken down into fatty acids and glycerol by the stomach and small intestine. It is then distributed (in the form of triglycerides) via the lymphatic system and bloodstream to the cells for a variety of specialized uses or, in the absence of sufficient carbs, for energy. However, since dietary fat cannot be converted into protein and only about 5 percent (the glycerol part) is convertible into glucose, and because dietary fat is not the body's preferred choice of fuel, a significant amount ends up being stored as body fat in the adipose tissue.

Conversion Of Body Fat To Energy

If energy is required suddenly, the body first uses up its glycogen reserves. After this, it converts the body fat in the adipose cells into energy by a catabolic process called lipolysis. During lipolysis, triglycerides within the adipose cells are acted upon by a complex enzyme called hormone sensitive lipase (HSL). This converts the triglyceride into fatty acids and glycerol. The fatty acids are then transported via the bloodstream to tissues for use as energy, or (along with the glycerol) taken to the liver for further processing.
 
spicypumpkin said:
How does fat fit in to all of this? Which is more efficient for your body to break down and why?
Click to expand...

Great article...breaks it down nicely! :)

I've found that you can read several articles and they'll pretty much explain the same thing, but they differ in some ways. Same experience with speaking to doctors, trainers and other experts...info is generally consistent, but certain pieces vary. In the end, you just have to eat right, exercise and have faith that everything will fall into place. At the same time, us humans have an odd inclination towards wanting to be in control and having some semblance of understanding of what's involved....so we seek information; as if understanding the process will change it ;)

It's all so fascinating. A bunch of food goes in and is comprised of fat, carbs & proteins...it's all disassembled in our digestive system. Proteins primarly serve as building-blocks for our body. Indeed...protein is a very poor choice as a fuel, it takes a lot of energy to break down and it yields relatively little energy as a fuel, this's why I suspect many diets push protein. I've been told our actual need for protein is relatively small, yet many people consume excessive amounts each day erroneously believing it'll help build bigger muscles or promote a leaner body.

Fats & carbs are far more suited towards becoming fuel for the body. A lot of people mistakenly presume that fat becomes fat. Actually, fat also plays an important role in the building-blocks of the body and other bodily functions. From what I recall, fat breaks down a little slower then carbs so it's not the ideal fuel while you're on a long run/ride....but this is all on the digestive side. The fat more often referred to is the storage means of our body to store energy.

Back to the basics. So the body consumes carbs, fats & proteins....and as far as energy we burn a combination of fat, glycogen and Creatine-Phosphate/ATP.

spicypumpkin said:
How does the body decide whether or not to break down fat versus protein for energy?
Click to expand...

As the article indicates, we primarly burn the glycogen. The generally theory holds that after 20 minutes of exertion/exercise our blood-sugar starts to drop and the body starts breaking into the fat reserves to fuel our continued needs. My nutritionist told me recently that the 20-minute thing is just nonsense....but whatever. The bottom line is that any prolonged exertion will lead to the body resorting to it's reserves to fuel our needs....that's where the fat comes in.

When SpicyPumpkin referred to burning protein for energy, I presume she means catabolism. I'd like to think that if you keep a reasonable pace you'll stay within the glycogen/fat resources for fuel and not touch the muscle (catabolism). Catabolism is supposedly only going to happen when you're pretty much tapped-out or pushing so incredibly hard that your body turns to its own muscle as a means for nutrients/energy to continue fueling the muscles.

The guy I see is a nutritionist, dietician and trainer....he led me to believe that unless I do several many hours of intense work, I'd unlikely see any real catabolism. Only in extreme cases does this happen.

I used to be out there riding my bike or swimming and I'd be thinking to myself "I sure hope my body is burning the fat and I'm not just eating-up muscle". I think it was Karky or Phate who said it best....so long as you're eating right and not doing crazy-excessive amounts of intense exercise, catabolism isn't an issue.

The last thing I'll toss in is that I've read and been repeatedly told that by taking some Branch Chain Amino Acids (BCAA's) before and during and even after your workout (most protein drinks have this already)....you're less likely to see any catabolism. I really don't believe the body turns to it's own muscle/protin as a source of energy except in extreme cases.
 
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Right, the body indeed does not turn to protein unless like you said in extreme cases - such as running for hours which would produce cortisol in significant quantities to begin protein utilisation for energy.

Just a thing i find a tad annoying is the term catabolism consistantly refering to muscle degradation. But in fact, anabolism and catablism are continously happenning simultaneoulsy at a great amount at each point of time..

:)
 
matt182 said:
Just a thing i find a tad annoying is the term catabolism consistantly refering to muscle degradation. But in fact, anabolism and catablism are continously happenning simultaneoulsy at a great amount at each point of time..

:)
Click to expand...

Very true. I think the OP and general fitness public generally regard "catabolism" in the sense of the body turning to it's own muscle to use as fuel. You are correct, the scope of catabolism is quite broader then the sense in which we typically refer to it:



Spicy....did any of this help?
 
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