Individual Body Tissue Distribution Varies Considerably within and between Adjacent Body Mass Index Classifications in the Elderly

The body mass index (BMI) is an indicator of body composition (BC) and adiposity in particular. This status is the result of good correlations with indirect two- and three-component models predicting adiposity. The BMI has become the most widely used measure to diagnose obesity and yet no accepted ranges of fat percentage exist. Although being overweight or obese is strongly associated to excess mortality in large cohorts, the accuracy of BMI in detecting excess body adiposity in individuals is largely unknown. Moreover its direct relationship with anatomical tissues in general and subcutaneous, intra-peritoneal and intra-muscular adiposity in particular is not established. Concurrently emerging evidence indicates that health-related assessment of BC in the elderly is more appropriate if muscle mass and adiposity are considered jointly, instead of separately. However it remains unclear how BMI (weight/height²) and/or waist circumference (WC) relate to body tissue distribution in the elderly. Therefore the relationship of BMI and WC with body tissue masses, with muscle/adipose tissue mass ratios and with trunk adipose tissue distribution was explored by direct cadaver dissection. For this purpose post-mortem whole BC and segmental adipose tissue composition of twenty-nine Belgian elderly persons (17 females and 12 males, aged 78.1 +6.9 years) was determined at the anatomical tissue-system level: i.e. skin, muscle, adipose tissue, viscera and bones. Results indicate that BMI and WC are significantly related to adipose and non-adipose tissue masses in both sexes. Whole body muscle mass, and whole body and segmental adipose tissue masses corelated better with BMI (r-values between 0.61 and 0.90) than with WC (r-values between 0.49 and 0.83) BMI was also significantly and inversely related with various muscle/adipose tissue ratios in both sexes (r-values between -0.54 and -0.68), and was positively related with trunk adipose tissue distribution (i.e. ratio of internal/total body adipose tissue and ratio of internal/subcutaneous trunk adipose tissue) in elderly females (r-values between 0.50 and 0.54), but not in males. Although BMI and WC are significantly related with muscle/adipose tissue mass ratios in elderly subjects, persons with similar tissue mass proportions do not necessarily fit within the same BMI of WC risk-category. The use of BMI and/or WC for the comparison of individual BC is therefore limited, particularly in the intermediate ranges. Since individual body tissue distribution varies considerably future research should focus on adjusting BMI and WC, or on developing more valid anthropometric parameters for clinical decision making in elderly persons.