Nutrition and health science is constantly evolving, and it often seems as if the latest study contradicts earlier ones. It's hard to know what to believe. But, over the last few decades, a wide array of independent studies has tended to confirm some conclusions about the relationship between excess body fat and associated health risks.

The basic conclusion is that anyone who is considerably overweight is at higher risk for a number of potential health problems. These include various forms of heart condition, high blood pressure, diabetes, colon cancer, liver damage, gallstones and others.

But what is 'considerably overweight'?

There's no static, ideal weight for any given individual, though there are various factors that provide a healthy range. One measurement that is a good starting point is BMI (Body Mass Index). To calculate it, just divide your weight (in kg) by your height (in m) squared. The following table is a rough classification:

Under 18.5 = Underweight

Between 18.5 and 24.99 = Normal Weight

Between 25 and 29.99 = Overweight

Between 30 and 34.99 = Obese (Class 1)

Between 35 and 39.99 = Obese (Class 2)

40 and above = Extreme Obesity

For those on the lower end of the BMI scale, health risks are no more (or at most only moderately higher) than for anyone. Genetic and other environmental factors will outweigh any body fat or weight issues. But for those nearer the higher range, there is strong evidence that health risks are higher.

For example, abdominal obesity (having large fat deposits around the stomach and abdomen) is associated with increased risk of cardiovascular disease and insulin resistance syndrome. For women, a waist circumference of 35 inches or more (40+ in men) is an indicator of abdominal obesity. Among other conditions, high blood pressure, high triglycerides and high cholesterol are all common factors associated with that condition.

Narrowing of the arteries, atherosclerosis, contributes to the possibility of a clot which can cause a stroke. Excessive body fat is one factor in producing that condition. At the same time, it plays a part in increased blood pressure (hypertension).

Rapid weight gain, from 10-20 lbs for the average person, increases the odds of developing Type 2 diabetes. Genetic factors are fundamental, but weight gain plays a role, according to most studies. The risk is double that of an individual who has not had a weight gain, when other factors are held constant.

Liver disease, apart from that associated with excessive alcohol consumption, can be caused by insulin resistance. That resistance is much more likely among those who are obese. There are many studies which have correlated BMI with the degree of liver damage. The higher the BMI, the greater the odds of liver trouble.

Gallstones are more likely to form in those who are obese, and may be correlated with a rapid rise in BMI. Sleep apnea (interruption of breathing during sleep) is another condition commonly linked to obesity.

In short, though no single study is definitive, and there are many genetic and other environmental elements, excessive body fat is a substantial factor in health issues. Being overweight is not merely an issue of acceptable appearance, it's a health risk.