Conclusion:
The healthiest BMI was 22.

STUDY

1. Prospective study entered over 7500 men aged 40-59 from general practices in 24 British towns.
2. Included men with preexisting cardiovascular disease and those taking regular medication.
3. Mean follow-up = 15 years.

RESULTS

1. Mean BMI = 25.5.
2. There were 1271 deaths during follow-up: 643 cardiovascular; 432 cancer.
3. There were 974 heart attacks; 290 strokes; 245 new cases of diabetes.
4. All cause mortality was increased in men with a BMI less than 20 and over 30.
5. Risk of cardiovascular death, heart attack, and diabetes increased progressively from BMI of less than 20 (after adjusting age, smoking, social class, alcohol consumption, and physical activity.)
6. For the combined end points the lowest risks were seen at an index of 20-24.
7. In never smokers and former smokers deaths from any cause rose progressively from a BMI of 20-22.
8. BMI was strongly and inversely associated with cigarette smoking and physical activity and positively associated with social class and alcohol intake.
9. Exclusion of deaths which occurred within the first 5 years of follow-up did not greatly affect the patterns of risk.
10. Coronary heart disease: incidence increased progressively with increasing BMI. The risk increased significantly at an index of 24 and above.
11. Stroke: the lowest risks were seen in those with an index 20-22. Risk tended to increase thereafter.
12. Diabetes: for those without diabetes at entry, risk increased significantly at 26 and above.
13. Combined endpoints (heart attack, stroke, or diabetes): lowest risks were seen at BMI 20-24 —significantly increasing at over 26.
14. Effect of smoking:

1. Current smokers had higher overall mortality rates than former smokers and never smokers at all BMIs. Deaths from any cause were higher in those with BMI < 20 fell to a nadir at 20-22 and then rose to high levels at BMI 30 (figure 2). (Ie, if you are a smoker and very thin or very overweight prognosis is especially poor.)
2. Risk of combined end points rose dramatically in smokers at BMI over 30.

15. Systolic and diastolic BP, total cholesterol, glucose, triglyceride, urate, packed cell volume, and insulin levels were lowest in those with BMI under 20 and rose progressively to high levels in those with BMI over 30.

DISCUSSION

1. "In this study the well established U shaped relation between mortality and body weight was confirmed, with excess deaths in very lean men largely due to cancer and other non-cardiovascular causes."
2. Excess deaths in the heaviest men were due predominantly to cardiovascular disease.
3. The relative risk of diabetes increased progressively from an index below 20.
4. The lowest risk of stroke was in those with a BMI 20-24.
5. "These findings strongly suggest that the healthy, biologically normal, or optimum weight in these middle aged men was towards the low end of the range which is currently regarded as acceptable."
6. In this study an increase in 1 BMI unit from 20-22 onwards was associated with an approximately 10% increase in the combined end points of death, coronary heart disease, stroke, and diabetes.
7. There is considerable evidence that weight reduction reduces risk factors for cardiovascular disease and diabetes.

CONCLUSION

Increasing BMI is closely related to an increase in factors intimately involved in the development of coronary heart disease.
"The importance of maintaining a healthy weight throughout life as a major primary preventive measure against cardiovascular disease and diabetes seems incontrovertible."
Within the normal range of body mass index (20-27) it is better to be leaner. The optimal healthy body mass index for adults is about 22.
The rising tide of obesity in the industrialized world deserves to be treated with some urgency.
BMJ May 3, 1997;314:1311-17 Original study from Royal Free Hospital, London

Comment:

If you are an adult and not sick and do not smoke being thin confers the best prognosis.
To put BMI into perspective—a 6 foot man with a BMI of 22 weighs 162 pounds. I believe primary care physicians can perform a most valuable service by regularly calculating and charting patient’s BMI and advising then accordingly.
Charts are available to convert weight in pounds and height in inches to kg/m2. RTJ