The Mechanics of Metabolism

Or why we get fat

The Mechanics of Metabolism are a complex process.
But a 'working knowledge', will help us understand how we gain or lose weight.
I'll try to explain it as simply as I can...

When we eat, (and drink) our digestive system breaks it all down into chemical compounds, which, are absorbed into our bodies by our blood and lymphatic systems.

Some of these compounds are combined with oxygen from the air we breathe, and are used as fuel.
Thats Metabolism.

The processes of metabolism include...

  • Digesting food and nutrients
  • Eliminating waste through urine and feces
  • Breathing
  • Circulating blood
  • Controlling body temperature
  • Contracting muscles
  • Functioning of the brain and nerves

The digestive process

When we eat our food passes along our digestive tract and the process of digestion begins.
The food is broken down into various chemical compounds along the way,and absorbed in different parts and in different ways.

For example:
The Stomach
Starts absorbing fatty acids. It also absorbs 20% of the alcohol we ingest.

Your Small Intestine
Then takes over. This comprises of three parts...

The Duodenum
Which comes after the stomach, absorbs Sugars,Carbohydrate, Vitamins A and B1, iron, calcium, more fatty acids,and Protein.

Your Jejunum
Absorbs glucose, Carbohydrate, Proteins, copper, zinc, potassium, calcium, magnesium,phosphorus, iodine, iron, fat-soluble Vitamins D, E, and K, most of the B complex, Vitamin C, and the rest of the alcohol.

Then your Ileum
Absorbs Carbohydrates, sodium, potassium, chloride, calcium, magnesium, phosphorus, iodine,Vitamins C, D, E, K, B1, B2, B6, B12, and most of the water.

Finally what's left enters the Colon (large intestine)
Which absorbs sodium, potassium, water, acids, gases, some more fatty acidsfrom plant fibers and undigested starch, and vitamins synthesized by bacteria, such as Vitamin K.

mechanics of metabolism

Apart from the vitamins and minerals. We are mainly interested in three main compounds;

  • Carbohydrates
  • Proteins
  • Fats

Are basically fuel for the bodies processes.
During digestion they are converted into Glucose and transported round the body.
Where they are broken down to make a substance called Adenosine Tri-Phosphate or ATP as it is usually called.
ATP acts like a 'ready use' fuel which provides energy for processes such as muscle contractions.

Carbohydrates come in two types simple and complex;
Simple carbohydrates are basic sugars which are processed and used very quickly.
Complex carbohydrates are processed more slowly and their energy value is released over a longer period.

Are the building blocks of the body, used to build and repair cells.
They are made up from combinations of the 20 or so 'Amino Acids'.
Some proteins can also be processed down into sugars for fuel (as we will see a bit later)

Are the storage units in the body.
When we have taken on more fuel than we need, our bodies convert it into fatty molecules,which are sent round the body and stored in various places for later use, if the need arises.

Fats are pure fuel, and don't have any other nutritional value.

mechanics of metabolism
The body also uses fat to isolate some toxins that it can't excrete.
It 'wraps' them in new fat until they can be disposed of.

The speed at which our metabolism works, (knowm as our metabolic rate) and the amount of fuel, (food)we eat, along with the makeup of our bodies, determine how much fat we carry.

"If you were to measure the metabolism of two resting men, who weigh the same, but have different physiques,one being very muscular and one a bit flabby.
You would find that the metabolism of the muscular man was much faster than the flabby guy.

This is due to his higher concentration of muscle.

Muscle tissue just by existing burns around 50 calories per pound per day of energy.

A pound of fat on the other hand burns 2-3 calories.

Our big problem, is that our evolutionary default rate of metabolism is based on the requirements of a cave man who never knew where the next wooly mammoth was coming from!

So any fuel that wasn't burned by hunting, and just existing, got stored by the body as fat for later use.

mechanics of metabolism

Good for a caveman.

Not so good for modern man who knows all too well where the nearest fast food outlet is...

mechanics of metabolism
As Middle Aged Men we have also been undergoing various hormonal changes which result in loss of muscle tissue.

This loss of muscle means our metabolism is slowing down So the energy we don't use gets stored as fat
(just like the caveman).

A vicious circle.

This usually happens quite slowly,
(Too slow for us to notice)
and we start piling on the pounds.

I'll give you a demonstration
I did an online survey to check daily calorie requirement using the following details...

mechanics of metabolism

A guy, lets call him Dave, is 51 and he is 5'10" 155 pounds, reasonably fit and healthy, with a Body Mass Index of 28
(BMI or Body Mass Index is a ratio of your height to your weight)

Lets also say he doesn't take much in the way of exercise, so his metabolism isnt going to be that fast.

Dave's daily calorie intake to maintain his weight should be 2015 Calories per day.

That aint a lot, look...

Lets say Dave has for breakfast;2 slices of toast, washed down with a couple of cups of coffee with 1 spoon of sugar.

Total about 350 calories
Coffee time a couple of cups and a snickers bar
Total 400 calories
Lunch Cheeseburger med fries med cola
Total 1200 calories
Dinner 12oz sirloin 4oz fries salad with dressing bottle of Budweiser
total 1100 calories
Plus a couple more 'Buds' during the evening.
300 calories

Making Dave's total intake 3350 calories

3350-2015=1335 Times that by seven =9345
Surplus calories A WEEK!

Every 3500 surplus calories converts to a pound of fat.
That's 2.7 pounds of potential body fat per week

At this rate It wont be long before Dave's in trouble

mechanics of metabolism
Another evolutionary throwback is Survival mode.

When your body encounters a sudden loss of food intake it automatically goes into 'Survival Mode'

This is a state where the body goes into slow down as far as metabolic rate is concerned.

Because it doesn't know when its next meal is going to come; (Cave man again)
In order to stay alive, it stores as much fat as it can, and reduces metabolic rate.

If enough calories are not available from digestion of Carbohydrate, then the liver will break down Protein into glucose.
(Protein and Carbohydrate have the same calorific value 4 calories per gram.)

If this still isn't enough for its requirements. The body will then break down muscle tissue for energy.
Saving the energy it has stored as fat for last resorts.

During this time the calories your body is burning to stay alive can drop by over 25%.

So any weight loss due to starvation is likely to be water, muscle, and only a little fat.mechanics of metabolism

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