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J. David Schnatz, M.D.
Director, Lipid Education Service
Saint Francis Hospital and Medical Center
114 Woodland Street, Hartford, CT 06105
Telephone: (860) 714-5555
December 1999
So many of our patients with CHD and lipid disorders are obese, that it behooves us to look at the relationship between CHD, obesity and dyslipidemia. A common measurement of overweight is to account for the patient's height in the so called body mass index (BMI). BMI is calculated as follows: weight (kg)/[height (m) squared] or weight (lb.)/[height (in) squared] x703.
A 1996 analysis of the Framingham Offspring Study showed that the data "indicate that a high prevalence of adult Americans are overweight and support the concept that increased BMI is associated with an adverse effect on all major CHD risk factors" (1). One thousand, five hundred sixty-six men, 23-76 years and 1,627 women, 19-78 years were included in the study. Seventy-two percent of men and 42% of women were overweight (BMI> =25). In non-smokers, BMI was associated, significantly, with Chol, TG, LDL, LDL particle size, glucose and blood pressure in a linear manner. It was associated inversely with HDL. HDL levels and hypertension were the factors correlated most significantly with BMI in men and women. The strong relation between HDL and BMI was documented further in over 11,000 subjects in a Belgium study (2).
BMI does not account for differences in android (abdominal) vs gynoid (hip) distribution of fat. For this, the waist/hip ratio is helpful, using 0.85 as the dividing line between the two. Abnormal post prandial lipids, particularly triglyceride rich lipoproteins, were correlated with obesity of the android type, waist/hip ratio=0.91 (3). The five-year risk of death in 41,837 women, ages 55-69 years, followed in the Iowa Women's Health Study Cohort, correlated with measurements of obesity (4). However, the waist/hip ratio was a better marker for risk of death than BMI.
On the other hand, using self reported data from 19,297 male Harvard University alumni with a mean age of 46.6 years, the relation between BMI and mortality was positive and linear in those who had never smoked (5). Two published studies from the American Cancer Society's Cancer Prevention Study correlated mortality and BMI (6, 7). A 1998 publication based on 62,116 men and 262,019 women associated higher mortality with higher BMI up to age 75, but the risk decreased with age. A 1999 publication based on 457,785 men and 588,369 women showed a relative risk of death of 2.58 and 2.0 for men and women with high BMI, respectively, compared to a low BMI. Black men and women had a lower risk.
A 1998 publication outlines evidence based guidelines on overweight and obesity from the NIH Expert Panel on the Identification, Evaluation and Treatment of Overweight and Obesity in Adults (8). The following were among the points made:
Overweight is defined as a BMI of 25 to 29.9 and obesity 30 or greater.
All overweight and obese adults are at risk to develop CHD, Type II diabetes mellitus, hypertension, hypercholesterolemia and other diseases.
Increased morbidity and mortality are associated with obesity.
Weight loss reduces risk for CHD and diabetes. Further, weight loss reduces blood pressure, glucose, HgbA1C, and to some extent, CHOL and LDL while increasing HDL.
Waist circumference correlates positively with abdominal fat content. Excess abdominal fat, out of proportion to total body fat, predicts risk factors and morbidity, independently.
In patients with a BMI of 25 to 34.9, high risk is associated with a waist measurement of greater than 40 inches in men and greater than 35 inches in women. With BMI of 35 or greater, these measurements lose predictive power.
In weight loss, the initial goal should be to reduce body weight approximately 10% in 6 months. For patients with BMI of 27-35, a decrease of 300-500 calories per day will result in 0.5-1 lb. lost per week and roughly 10% in 6 months. When the BMI is greater than 35, a 500-1000 calorie per day decrease will result in a loss of 1-2 lbs. per week and roughly 10% in 6 months.
In general, women will consume a diet of 1000-1200 calories per day and men 1200-1500. These diets should be consistent with NCEP guidelines.
Regular and sustained physical activity is helpful in the prevention of regaining weight. The goal should be for at least 30 minutes of moderately intense physical activity on most, if not all days.
Despite the importance of weight loss, smoking cessation is paramount.
In the August 1999 issue of the New England Journal of Medicine, "Guidelines for healthy weight" were published (9). In this article, measurements of body fat are critiqued, noting that BMI does not distinguish fat mass from lean mass. Accordingly, in older adults who have lost an increased proportion of lean mass, it may not reflect body fatness as well as in others. The article depicts a graph that correlates relative risk of death in women increasing linearly from a BMI of 19-21.9 in those over 64 years of age, and from 22-24.9 in those 65-74 years of age. Those from 75-84 years of age did not have an increase above 1 up to BMI of 29-31.9. In men, the results were similar except there was some increase in risk in the 75-84 year range, as well. The relative risk of Type II diabetes, hypertension, CHD, and cholelithiasis was demonstrated to increase from a BMI of 21-22 in both men and women, with the risk of diabetes mellitus increasing 5 fold with a BMI of 25 in women and 27 in men. Insufficient data exists for a BMI less than 19.
In a 28 day study, energy restriction of 50% (2300 vs 1100 calories) produced significant decreases of BMI (31.7 to 29.6, p=0.0001), waist circumference (98.3 to 92.6 cm, p=0.0001), waist/hip ratio (0.88 to 0.86, p=0.002) and abdominal fat (2700 to 2400g, p=0.0001) (10). In association with abdominal fat loss, there was significant lowering of blood lipids; Chol (p<0.001), LDL (p<0.0005), TG (p<0.01) and an increase in LDL particle size (p<0.0005). HDL did not change, probably due to the divergent effects of decreased dietary fat and body weight loss.
Overweight and obesity are extremely prevalent in our society, leading to an increase in risk of CHD, elevated blood lipids and other diseases. Weight reduction will make a significant difference in serum lipids as well as the risk of CHD and other diseases. BMI and waist/hip measurements are good clinical tools for assessing the need and monitoring the result of weight loss.
References
1. Arterioscler Thromb Vasc Biol. 16:1509-1515, 1996
2. Atherosclerosis 137 (Suppl): S1-S6, 1998
3. J. Clin Endocrinol Metab 84:184-191, 1999
4. JAMA 269: 483-487, 1993
5. JAMA 270: 2823-2828, 1993
6. NEJ Med. 338: 1-7, 1998
7. NEJ Med. 341: 1097-1105, 1999
8. Arch Int Med 158:1855-1867, 1998
9. NEJ Med. 341: 427-434, 1999
10. Diabetes Care 21: 695-700, 1998
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