On Weight Management

Healthy weight management is about controlling how much of the optional-extra body tissue you have. Your body is actually extremely malleable, and can produce extra tissue in many places - professional athletes sometimes have very large hearts or major arteries, and musicians who play wind instruments can have remarkable lungs.

However, there are three types of body tissue that ordinary people can relatively easily choose to control.

1. Muscle
   
2. Bone
   
3. Fat

As a general rule, if you need to gain weight, you should try to gain muscle and bone. If you need to lose weight, you should try to lose fat.
In an otherwise healthy body, gaining muscle and bone will also add enough supportive fat for the larger body (if it doesn't, see your doctor).
In a healthy body, significant loss of muscle or bone are signals of illness, starvation or inactivity, and generally indicates that you should see a doctor.

Muscle and Bone
Your body develops muscle by using it. As your body develops muscle, it also develops the supporting bone.

To develop muscle and bone, your body also requires building blocks, nutrients and energy - in other words, protein, vitamins and minerals, carbohydrates, fats and oils. The process of making muscle also requires plenty of water, so make sure you drink.

I never recommend intentionally losing muscle or bone. A healthy human body will regulate muscle and bone development based on how that body is used. If you think you need to lose muscle, bone or both, see your doctor.

Almost everything I have to say about developing muscle and bone is in my articles On Exercise and Nutrition and On Bodies.


Fat

WARNING
I am not a doctor. If you have a metabolic illness (an illness which affects how your body digests and uses energy), see your doctor and any specialists she refers you to. The information in this section of the post relies on rules of thumb which may or may not apply to you.

Energy digested > energy used = energy stored.
Energy used > energy digested = energy consumed.

That is the fundamental truth of managing your body fat. Nothing you can do changes that truth, the most you can do is tricks to modify what energy gets used or digested.

Your body stores extra energy as adipose tissue, more commonly known as fat. Fat has four purposes in the human body:

1. It stores energy.
2. It acts as 'packing peanuts' for many of your vital organs, cushioning them against damage and helping to hold them in place.
3. It insulates your vital organs against temperature variation.
4. It's a cushion. You have fat in places like the pads of your feet, the 'sitting' part of your buttocks, and your hands.
   

You must have the 'packing peanut', cushion and insulation fat - if you don't, you will get sick. Never try to lose weight so much that you lose that fat. If you have already lost this fat, see a doctor as soon as possible. The doctor will be able to help you regain it.

Estimating how much body fat you have is difficult. Wikipedia has an entry on body fat analysis. I also found a useful series at stumptuous.com on body fat.
(Note: the URLs at the base of the article are broken. Here are part 2, part 3 and part 4.)

Healthy fat management is about controlling how much of the energy-storing fat you have. You do this by manipulating two factors: what you use, and what you digest.

What you use
Muscle uses a lot of energy.

Muscle at rest uses some energy.
Muscle that has been used in the last day or two uses more energy.
Muscle that's active uses the most energy.

To use more energy, make and use muscle. It's as simple as that, and there are no shortcuts.

What you digest
There are few ways to manipulate your digestion that I consider to be smart and healthy: there are only two I'm comfortable with.
The first is painfully simple: only eat what you're willing to digest.
The second is a variation on the first, and uses the glycaemic index to manipulate the sugar-storage system of your body.

Here's an oversimplified version of how your body's sugar-storage system works:

• When you eat carbohydrates, your stomach and gut convert them to sugars and put it in your blood.
• When there is sugar in your blood, your pancreas puts out insulin based on the amount of sugar there is in your blood.
  
• Insulin does many things, but the relevant one is that it tells your body to store any extra sugar in your blood as fat.

If you eat carbohydrates that your stomach and gut convert to sugar quickly, they put it in your blood quickly. There's lots of extra sugar floating around that your body doesn't need right at that moment, so your body stores it as fat.

If you eat the same energy load in carbohydrates that are digested slowly, the pancreas puts out insulin more slowly. This gives your muscles more time to grab the sugar to use while you walk back to the office (or whatever you do), and the sugar never gets converted to fat.
If you're trying to put on weight, use the glycaemic index to find slow-digested carbohydrates anyway. Putting on muscle improves your whole-body health and metabolism, in ways which are too complex for me to explain here (ask your doctor). Your muscles need this sugar to develop.

The glycaemic index is a number that tells you how quickly the average human body digests any given foodstuff.

For more information about the glycaemic index, contact any reputable diabetes association or website, or check the GI homepage.

Diabetes is, in part, a disease of the insulin system. The glycaemic index is especially helpful for diabetics, but is useful to everyone.

There are other ways to control what you digest, such as using tablets which prevent you from digesting fats and oils. Fats and oils are necessary in themselves, and many contain useful vitamins, minerals and other essential elements. I don't like the idea of preventing the body from digesting them, but I admit that I may be biased. If you want to manipulate your digestion, talk to your doctor.

In summary

• Gain muscle and bone.
• Manage your fat stores.
• Energy in > energy out = more fat.
• Energy out > energy in = less fat.
• More exercise = more muscle.