David S. Gray

Diagnosis and Prevalence of Obesity

Obesity is a condition of increased adipose tissue mass. Many techniques are available for measurement of body fat, but none is available widely for clinical purposes. The new technique of bioelectrical impedance may change this in the future. For now, relative weight and BMI are used as indices of obesity, which may be defined as a BMI greater than 30 kg per m2. This corresponds to a relative weight approximately 120 per cent above desirable. According to this definition, obesity exists in 10 to 12 per cent of adult men and women in the United States and Canada.

Use of relative weight and body mass index for the determination of adiposity

Relative weight and Body Mass Index (BMI) are commonly used as measures of body fatness in epidemiologic and clinical studies. In order to determine their accuracy, they were compared to body fat measured by underwater weighting and total body water determination in 29 males and 75 females who varied widely in body composition. Relative weights calculated from the Metropolitan Life Insurance Tables correlated so highly with BMI that these measures can be considered to be identical (R2 = 0.992 to 0.999). Linear regression analysis showed a significant correlation between BMI and percentage body fat in men (R2 = 0.68, %fat = 0.99 X BMI -1.32, p less than 0.001) and women (R2 = 0.74, %fat = 0.94 X BMI + 10.77, p less than 0.001). We conclude that relative weight and BMI are nearly identical, and that they are reasonable estimates of body fatness.

Effect of carbohydrate refeeding on free fatty acids after a fast in obese diabetic and obese non-diabetic females☆

The metabolic effects of refeeding with oral or intravenous carbohydrate were studied in obese women after ten or 14 days of fasting. Seven patients were refed with protein-free fruit juice for a total of 250 g of carbohydrate (1,000 kcal) over ten hours. The juice was sipped continuously throughout this time, causing a drop in free fatty acids (FFA) from 1.07 +/- 0.08 to 0.61 +/- 0.05 mmol/L (P less than .01) over the first four hours. Over the next four hours, despite continuous ingestion of the carbohydrate and elevated plasma glucose (132 +/- 9 mg/dL) and insulin (2.81 +/- 0.86 ng/mL) (1 ng/mL = 25 microU/mL), FFA rose to 0.99 mmol/L (P less than .01). Similar results were obtained in five patients refed with similar amounts of oral glucose and four patients who received an equivalent amount of glucose intravenously (IV). Refeeding with carbohydrate of obese diabetic and non-diabetic women after a two-week fast caused an abrupt decrease in FFA that was followed after four hours by an increase in FFA and glycerol, despite continued ingestion of carbohydrate glucose and insulin.