According to the National Research Council Committee on Diet and Health (1989), of the adult population of the United States, more than 25% of women and 31% of men are overweight or obese, based on use of the Body Mass Index (BMI; defined below)! That was in 1989; in the year 2000, the figures are fast approaching 50%.

To judge from the numbers of patients that actually do something about losing weight, most people are unaware that overweight, even if only slight, can kill. Statistics on how many people actually make an effort to lose weight are difficult to obtain, but a Gallup poll in 1985 indicated that anywhere from 2% to 7% of those asked had been told to lose weight by their doctors. The percentage who made a serious effort to follow that advice, in a supervised program, was insignificant! Since that survey, the availability of both commercial weight loss programs and hospital programs has increased substantially, but current estimates are still that less than 4% of those who must lose weight actually enrol in a suitable program, so there is much room for improvement!

The survey mentioned also revealed that a large proportion of the population claimed to follow diets of their own design, and that the main motivation for any sort of diet (even the "wishful thinking" type) was appearance; many of those surveyed who claimed to be on a diet did not even need to lose weight!

The relationship between diet, body weight and health is very complex, and is becoming even more so as science pushes the borders of our knowledge outwards. For example, few are aware that being underweight reduces life span more than being overweight, and that having too little body fat is associated with serious health risks. Again, not many realize that high-fat diets based on plant and fish products are associated with much lower incidences of some "diseases of civilization" than low-fat diets which include red meat products and margarine.

For body weight, the most important, and most general, observation is that mortality increases as body weight increases or decreases away from the mean defined as ideal weight. In other words, if you deviate from the mean, your chance of ending up dead before your time is greater. If you are fat, and want to stay alive, then lose weight. Conversely, if you are too thin, then gain weight.

The risk of death can be quantified, using the concepts of excess mortality or anticipated survival. Excess mortality is a definition of how much likelier death is for the person concerned, while anticipated survival expresses the shortening of the life span, in both cases using standard figures for persons of normal weight and the same age and sex to give a baseline for comparison. These approaches are based on statistics, so a few fat people do survive to ripe old ages. Most do not!

Many different figures have been published, but all are bad, in the sense of "ominous" and not of "faulty". As a guideline, life expectancy will be reduced by 2 - 3 years for every 10% over the ideal weight; for the average patient who still has 30 or more years to live, this probably has little impact. Telling such a patient that they are likely to drop dead will make them think about it! To illustrate, life insurance figures show that the chance of death is increased by 25% in people who are only 5% - 15% over their ideal weight, but is increased by more than 400% in people who are more than 25% over ideal weight. Data from life insurance companies is, of course, biased, since it relates only to those who applied for, and got, insurance, thus were probably healthier (in other respects) than those who either did not apply, or were turned down! Another study (Drenick et al., reported by National Research Council, 1989) followed the fates of 185 obese men (50% or more over ideal weight) and found that mortality increased by 1200% in younger subjects (25 - 34 years at start), by 500% in the group aged 35 - 44 years, but only doubled in the group aged 55 - 64 years.

A Norwegian study (Waaler, opus cit.) which covered the entire population (of 1.7 million) gave similar bad news, but also showed that short people were more likely to die early than tall people. This may tie in with the current consensus that though being fat is a serious risk factor, the distribution of the fat in the body is also important (risk increases with the ratio of waist to hip measurement).

The most important conclusion from all the reported studies is that being fat is going to kill you. The risk may be a little lower if you are not only fat, but also tall, old, and have big hips. Even if this is the case, losing weight will still add years to your life.

Being too fat in itself is rarely a direct cause of death, except in the most bizarre circumstances. Rather, the obesity is usually the cause of, or an aggravating factor for, other diseases which have the potential for early death, and which, if the weight problem disappears, will generally themselves disappear or at least become less serious.

Relationships that govern the consequences of obesity are too complex to explain in detail. For example, the observed increase in incidence of gallstones in obese persons not only relates to the obesity itself, but also to other factors, including dietary habits (the types of food eaten) and relative essential fatty acid deficiency.

For the serious (life-threatening or life-shortening) diseases, data from epidemiological studies (which show statistical relationships between degree of overweight and the incidence of the various diseases) confirms that being too fat increases the incidence of cardiovascular diseases, cancer, diabetes mellitus, hypertension, gallbladder disease and lung disorders. Obesity is thus a risk factor for these conditions, all of which, either directly or indirectly, can result in death. However, other risk factors also play a role, and the various risk factors can interact, which makes the situation very complicated, particularly with respect to calculating how matters would improve if obesity was eliminated as a risk factor.

In simple terms, even if we managed to get everyone in North America down to their ideal weight, there would still be some people (though fewer) who would have heart disease, cancer or gallbladder disease, because they are exposed to other risk factors. We also do not know how these other risk factors interact with obesity. In the case of heart disease, for example, a recent study (Willett et al., 1993) implicated consumption of trans fatty acids in partially hydrogenated domestic oils as the most important risk factor. It would be possible to hypothesize that fat people consume greater quantities of hydrogenated domestic oils, and this in turn could be one reason why being fat also predisposes to heart disease. There would also be some scientific basis for suggesting that trans fatty acids, since they interfere with some important metabolic functions, might also play a causative role in obesity, or could be implicated in the increased incidence of gallbladder disease (Jones, 1993).

Similar arguments could be found for any of the conditions listed, which serves to illustrate how epidemiological studies are good at identifying relationships, but poor at pinpointing the reasons for those relationships. Be that as it may, the diseases listed above include those that are the major causes of death in most of the civilized world, and it behooves us to take the role of obesity in these diseases very seriously indeed!

Though it should be the strongest of arguments to tell the fat patient that they are likely to have a heart attack, or get gallstones, most patients are likely to take the optimistic and misguided view that it cannot happen to them, and they feel quite all right, thank you! Unfortunately, until it is too late, there will probably be no symptoms, and the old adage "out of sight, out of mind" will be subconsciously applied.

The same is not true of some other, less serious, disorders that have been related to being too fat. These conditions, fortunately, impair the quality of life for the fat person, and thus can drive home the argument that being overweight is unhealthy.

One of the most obvious is hiatus hernia, which usually manifests as "heartburn", and is thus very apparent to the patient! The reason is simple; the diaphragm keeps the esophagus closed except when swallowing, and when the abdominal cavity gets larger because of fat deposits, the diaphragm has some difficulty keeping the tension high enough to stop reverse flow. Antacids will give temporary relief, but losing a few pounds usually makes the problem go away for good!

A second obvious condition is infection and irritation of the skin. The skin starts to crease and fold more as people get fatter, and these folds are more susceptible to infection and skin complaints. Provided the patient is not too old, and does not stay fat too long, the folds disappear again as weight is lost.

Obesity also predisposes to lower back pain, particularly in men, may precipitate gout attacks, aggravates arthritic joint problems, may cause flat feet,and can contribute to both circulatory problems (such as varicose veins) and respiratory problems (shortness of breath, possibly snoring). Being fat also increases risks associated with anesthesia (general anesthetics are soluble in fat) and complicates pregnancy and childbirth.

Weight problems can be associated with reduced libido in men and women, and with disorders of the menstrual cycle in women.