Sunday, August 15, 2010

DO FAT PEOPLE DIE EARLIER THAN SKINNY PEOPLE?

Overweight and obese people are generally thought to be unhealthy and have more diseases and higher death rate than people of normal weight. However, such information is usually found in articles written by authors who have not examined the actual medical evidence which support these statements. The purpose of this paper is to take a close look at the evidence for some of these claims.



There is no agreement among epidemiologists concerning the increased risk of death in overweight and obese individuals. Some studies indicate that no relationship exist and some that the relationship is the reverse. Some studies agree that obese people are more likely to die than people of normal weight, but there is disagreement concerning overweight people and increased risk of death. Some say yes and others say no. These studies have been summarized by McGee (2005) who concluded that overweight people do not have a significantly higher rate of death than normal weight people.



A recent study claims that even overweight women or men are at a greater risk of dieing than people of normal weight (Adams et al 2006). In their study the relative and actual risks were elevated for under weight, obese men and surprisingly men and women in the normal weight categories 2 and 3 (Table 1). These conclusions are taken from relative risk ratio statistics in column 2. In this table I have added the relative risk as percent (column 3) and the actual risk as percent (column 4) for comparison. It is apparent that the actual risk of death is not great even for obese men in which the increase is only 1.9% greater than the normal reference body weight of 1.3%. Underweight men have an elevated actual risk (3.5%) which is similar to those who are overweight (3.2%). Similar risks were found for all women studied (results not shown).



TABLE 1 RELATIONSHIP BETWEEN BODY MASS INDEX BMI), RELATIVE RISKS AND ACTUAL RISK OF MORTALITY IN ALL MEN*




*Similar results were found for women. **BMI or Body Mass Index is
equal to the body weight in kg divided by height in meters squared.

A BMI calculator can be found at http://www.nhlbisupport.com/bmi/bmicalc.htm


The conclusions that can be drawn from Table 1 are:



1. Underweight and some low normal weight individuals are at an increased risk of death. This important point rarely gets a mention in the news media or fashion magazines.

2. Overweight people are not at an elevated risk of death.

3. Obese people have an elevated risk of death similar to underweight individuals.


INFLUENCE OFSMOKING AND BODY WEIGHT

In order to examine the effect of bodyweight on risk of death the influence of smoking was considered by Adams et al (2006). To do this data were grouped into the following groups: Never Smoked, Current Smoker and Former Smoker. For the sake of simplicity I have made a table which shows data from never smokers and current smokers (Table 2).


TABLE 2 RISK OF DEATH IN MEN WHO NEVER SMOKED AND CURRENT SMOKERS



* Actual risk was calculated by dividing the number of individual in each category by 100,000. Data were obtained from table 2 in Adams et al (2006).


If you look only at the results of relative risks and compare never smokers with current smokers you could draw the incorrect conclusions that it is better to be an obese smoker than an obese non-smoker. For example, in group 10 the relative risk for the never smoker is 159%, whereas for the current smoker in this group the risk is 42%. This is a good example of how relative risks can be misleading and why actual risks should be used in these kinds of studies. Comparing the actual risks in these two groups provides the correct answers. The actual risk of death in category 10 for the never smoker group is 2.6% compared to 5.0% for the current smoker group. So just as we suspected being obese and smoking is not good for you.



The reason for the reversal seen with relative risk analysis is that the reference category 4 is a lower number (0.78) in the never smoker group than that of the current smoker group (3.08). Since all weight categories are compared to these numbers the relative risk increases in the smoker groups are lower. For example: in the never smoker group the percent in category 10 is 2.6 compared to 0.78 in the reference group. Therefore the relative risk is 3.25 times as great as the reference value of 0,78 for never smokers and only 1.61 times as great for current smokers (5.0/3.08 = 1.61).



The influence of smoking on the actual risk of death is shown in figure 1. It is clear from these data that current smoking increases the actual risk of death in all BMI categories. The data for women are similar to men (data not shown). In this figure and in table 2 we see that men in the never smoked group show similar actual risks in all categories except the obese groups 9 and 10 and these are not great but they were judged to be significant by Adams et al (2006). The former smokers have a small actual increase in risk in categories 3 – 8 and elevated risks in the underweight, low normal and obese categories. There is no evidence from these data that being overweight increased your risk of death.


Figure 1 Actual risk of death as function of BMI groups in smokers and non-smokers.





STUDIES ANALYZED BY MCGEE 2005



My conclusion that being overweight does not increase the risk of death agrees with that of McGee (2005) who analyzed 26 large population studies which included 388,622 individuals.



TABLE 3 RELATIVE RISK OF DEATH DUE TO VARIOUS CAUSES IN OVERWEIGHT AND OBESE WOMEN AND MEN.




Data taken form McGee 2005. The data are expressed as relative risks and the 95% confidence interval in parentheses. All groups were compared to normal weight individual defined as having a BMI of 18.5 to 25. Over weight defined as BMI between 25 and 30 and obese as BMI of 30 or greater. Abbreviations: CHD, coronary heart disease; CVD, cardiovascular disease.



From table 3 it is clear that even the relative risks of death for overweight individuals is not different from those of normal weight. Actual risks could not be calculated because insufficient data. These data suggest that obese men and women are at a greater risk of death from all causes, CHD and CVD but not cancer. The lack of any increased risk of cancer in overweight women supports my contention that heavier women do not have higher risk of breast cancer.



CONCLUSIONS



1. Underweight and some low normal weight individuals are at an increased risk of death.

2. Overweight people are not at an elevated risk of death.

3. Obese people have an elevated risk of death similar to underweight individuals.

4. Current smoking in obese and under weight individuals increases their risk of death. This is also true for those in the former and never smokers but the risks are not as great.

5. Obesity increases the risk death from heart and vascular diseases but not cancer.



The finding that overweight men and women show no significant increased risk for heart and vascular diseases or death casts doubt on the continual bombardment from the news media, nutrition experts, many physicians, drug companies and food manufactures that being over weight will increase the incidence of many diseases.


REFERENCES


McGee DL (2005) Ann Epidemiol 15:87

Adams KF (2006) N Engl J Med 355:763


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