Dietary composition and fat to sugar ratios in relation to obesity

The aim of this work was to investigate the relationship between dietary composition and prevalent overweight and obesity in a middle-aged Scottish population. An age and sex stratified cross-sectional study was carried out of coronary risk factors and diet. This was based on a personal health and food frequency questionnaire with a clinic attendance for body measurements which included weight and height. The subjects were 11,626 men and women aged 25-64 who participated in the baseline Scottish Heart Health and MONICA studies. Those reporting to be on slimming diets were excluded. The subjects were contacted via ten general practitioners surgeries from each of 22 Scottish districts (12 Mainland Health Boards) surveyed during 1984-1986. The following were measured: (1) the prevalence of overweight (BMI 25-28.6 for women and 25-30 for men) and obesity (BMI > 28.6 for women, and > 30 for men) according to intake fifths of carbohydrates (starch, total, extrinsic, intrinsic and milk sugars) and fat to carbohydrate ratios; (2) the percentage of the variance in BMI explained by multivariate analysis models which included each of the sugar variables and total energy intake. The overall prevalence of overweight and obesity in the Scottish population were 43 and 11% for men and 38 and 14% for women respectively. Their prevalence increased from the lowest to the highest fifth of Fat:ES intake, respectively for men and women, from 5 to 18.5% and from 13 to 26%. The prevalence of overweight and obesity declined from the lowest to the highest fifth of total carbohydrate, total (TS) and extrinsic (ES) sugar intake. For ES as a percentage of energy, overweight fell from 55 to 40% for men and from 43 to 33% for women, whilst obesity declined four-fold for men (18-4.4%) and nearly two-fold for women (23-13%). On multiple regression analysis the model which explained the most variation in BMI for men (43.3%) included the variable FAT: ES, whilst FAT: TS explained 38.3%. For women, the variables Fat: TS and FAT: ES explained virtually the same percentage of variation in BMI, 28.0 and 28.3 respectively. Extrinsic sugar and the Fat:TS and FAT:ES ratios are significant predictors of BMI, independent of total energy intake. These data support the concept that the composition of the diet has a significant effect on relative weight and the prevalence of obesity, independent of total energy intake. Health advice to concomitantly reduce fat and sugar intake may not be practical.