The Significance of Excess Fat in Non-Obese Individuals

Regular readers will be well aware that excess body weight, or even excess body fat, is not always associated with health risks. In contrast, it is now increasingly recognised that excess body fat (especially visceral fat), may constitute an important health risk even in individuals well below the conventional BMI cutoffs for obesity.

Readers wishing to learn more about the nature of these so-called ‘lean-but-fat’ (LBF), ‘thin-on-the-outside fat-on-the-inside’ (TOFI) or ‘metabolically obese but normal-weight’ (MONW) individuals are directed to an excellent review article by Louise Thomas and colleagues from Imperial College London, UK published in Nutrition Research Reviews.

As the article stems from the Metabolic and Molecular Imaging Group at Hammersmith Hospital, it contains a nice selection of MRI images depicting these different phenotypes.

As the authors note, lean individuals with the typical metabolic phenotype more commonly associated with obesity

“…have been shown to have reduced insulin sensitivity, increased abdominal adiposity, a more atherogenic lipid profile, and raised blood pressure, accompanied by physical inactivity and a low VO2max. The combination of these factors is thought to predispose ‘metabolically obese but normal-weight’ subjects to an increased risk of type 2 diabetes and CVD.

This phenotype has been further refined using MRI to show disproportionate deposition of visceral adipose tissue, with many lean subjects having more visceral adipose tissue than overweight or obese subjects. This TOFI (thin-on-the-outside fat-on-the-inside) sub-phenotype has been observed in both male and female subjects, and increases an individual’s risk of metabolic disease.”

As they further note,

“Identifying subjects classified as TOFI may be important, since they may be at increased risk of metabolic disease compared with more obese subjects with less visceral fat. Incidence of ‘metabolically-obese but normal-weight’ has been reported to be between 13 and 18 %, which is similar to the incidence of TOFI (12 % women, 14 % men).”

Overall, these finding are in line with our own observations that EOSS Stage 0 overweight and obese individuals, which comprise about 5-10% of the obese population, do not appear to have an increased risk for cardiovascular mortality, while over 50% of individuals in the BMI 25-30 range can meet the criteria for EOSS Stage 2 and 3 and with the same risk of cardiovascular complications as their obese counterparts.

Unfortunately, despite the lower total amount of body fat, it appears that sustainably reducing body fatness is no less difficult in lean folks with excess body fat than in obese individuals. As I recently heard some one point out in a presentation (I forget who), losing and keeping off 5% of your body weight is as difficult (or easy) whether you are a 100 lbs or 300 lbs.

Edmonton, Alberta

ResearchBlogging.orgThomas EL, Frost G, Taylor-Robinson SD, & Bell JD (2012). Excess body fat in obese and normal-weight subjects. Nutrition research reviews, 1-12 PMID: 22625426