Defining overweight

The first thing I'm going to do in this blog is to explain what causes overweight and obesity. I'll also explain what can be done about it. It will not be the old dogma of eating less and exercising more. It will be the truth this time. None of the theories described here are my own. I am merely passing on information acquired by others, although not without critical thinking.

Here is the first part of how to understand overweight using one definition and two questions:

If we are to understand overweight and obesity and all its related metabolic disorders, we need to have a clear understanding of what overweight actually is. Overweight is most often defined as above a specific body mass index. BMI tells us something about ones weight in relation to ones height. Although much criticized, BMI does have its use as an epidemiological tool, but must under no circumstances be used to define overweight at an individual level. The reason for this is simply that BMI does not differentiate between body tissues. I’ll come back to this.

Secondly, it is also important not to use the first law of thermodynamics as a definition of overweight. This law simply states that energy change equals energy gained minus energy spent. I might have to get back to the misuse of this law in discussions of overweight, but for a more thorough discussion here’s one in Norwegian:

http://www.forskning.no/artikler/2009/august/226860

For now it is enough to say that overweight cannot be defined by total body energy change, energy expenditure or energy intake.

After much thinking I have found that the simplest way to define overweight is to say that:

Overweight is excess storage of energy in fat tissue. (See, it's bold so this is definitely important.)

This definition might seem obvious, but it is of utmost importance for the scientific discussion of overweight to keep in mind that overweight is related to increase in fat tissue mass. Not muscle tissue, not nerve tissue, not bone tissue. Overweight is all about the size of the fat tissue. I think few would disagree with this, but as we will see, this definition brings us much closer to understanding overweight than most other definitions.

I guess many would have asked about the obvious by now. "How much is excess storage?" Well, while this is a perfectly reasonably question, it really cannot and should not be answered in general terms. In any individual an excess storage of energy must be defined by that person’s situation. We cannot keep making up numbers that puts some of us in the overweight category and some in the normal category. Remember also that overweight (excess fat tissue) is not necessarily harmful in itself, neither is it necessarily visible. A thin looking person might have a small fat free mass and a high fat percentage, and may thus be termed overweight.

So remember, overweight is all about fat tissue (adipose tissue). So if you want to know what you can do about it, you need to understand the fat tissue. Reed on and I’ll try to ease your understanding.