Who is obese?
To put obesity studies on a scientific footing, researchers define who is overweight using the body mass index (BMI), which compares height to weight. You can calculate your body mass below.

A BMI of 25 or greater is overweight, and an index of 30 or above is obese. In general, anyone who is overweight or obese faces an increased risk of coronary heart disease.

BMI Category	Health Risk Based Solely On BMI	Risk Adjusted for the Presence of Comorbid Conditions and/or Risk Factors
19-24	Minimal	Low
25-26	Low	Moderate
27-29	Moderate	High
30-34	High	Very High
35-39	Very High	Extremely High
40+	Extremely High	Extremely High

Example:	For a person who is 5 feet 5 inches tall weighing 149 lbs.
Step 1.	Multiply weight (in pounds) by 703 149 x 703 = 104747
Step 2.	Multiply height (in inches) by height (in inches) 65 x 65 = 4225
Step 3.	Divide the answer in step 1 by the answer in step 2 to get your BMI. 104747 divided by 4225 = 24.8 BMI = 25 (rounded off)

Source: Shape Up America.

But don't let the neat and tidy BMI numbers fool you. Because muscle is denser than fat, muscular people may have an "overweight" BMI, but still have a normal risk of disease. Furthermore, your exact risk of heart disease depends on the presence or absence of other risk factors. Overweight, non-obese people may want to examine other risk factors, such as smoking, family history of disease, and inactivity before deciding whether to try to lose weight.

Why is obesity unhealthy?
By branding obesity an independent risk factor, the American Heart Association said that obesity, by itself, increases your risk of heart disease. Oddly, it turns out that nobody can explain this connection.

The key problem is that obese people often have other risk factors for heart disease, like high blood pressure, high blood cholesterol, and an inactive lifestyle. "Obesity is related to all these risk factors," says James Hill, who studies obesity at the University of Colorado Health Sciences Center. "If you are obese, you get elevated LDL [bad] cholesterol, elevated triglycerides [another harmful blood fat], and insulin resistance [which can lead to adult-onset diabetes]. The answer to what happens when you separate all these things out is not entirely clear."

Given these confounders, the question of the direct effects of obesity is "unanswerable," says Robert Eckel, an endocrinologist who helped sound the alarm for the American Heart Association. Obesity research, he argues, is in its infancy -- where cholesterol research was 20 years ago.

It's still possible that obesity causes harm that's unrelated to the known risk factors. For example, the need to pump blood through a larger, obese body could enlarge the heart, perhaps interfering with its critical pumping rhythm or leading to congestive heart failure. Some people, Eckel says, speculate that fat may produce hormones like angiotensin that harm the heart. Belly fat may release fatty acids that help grease the skids for diabetes.

Yet scientists like Hill suspect that simple obesity, something that can be seen with the naked eye, may be causing the well-known risk factors that can only be detected with laboratory tests. Thus, curiously enough, in terms of improving health, it may be more important to cure the "symptom" -- obesity -- rather than single out blood pressure or blood cholesterol for attack. "If you prevent obesity," Hill says, "you go a long way to preventing harmful fat content in the blood, high blood pressure and insulin resistance, all of which tie into heart disease."

I'm convinced that it's not healthy to be overweight. But will it help to lose weight?