We thank Dr. Kawada for his letter giving us the opportunity to comment further on our results. First, this report should be interpreted in the context of a considerable body of literature showing (1) the remarkable individual differences in accumulation of visceral/ectopic fat at any body mass index (BMI) value and (2) the added value of measuring waist circumference as it allows to identify those within a given BMI category who are likely to have more visceral adipose tissue (VAT), more liver fat, and an altered cardiometabolic profile. This report is only one piece of a large body of data linking excess visceral adiposity/ectopic fat to various clinical outcomes.
In addition, the multivariate analyses presented in Table 3 do show that adding waist circumference to BMI was statistically significant; however, these correlation coefficients do not give justice to the concept of the added value of measuring waist in clinical practice. Indeed, at the population level, there is obviously considerable variation in both the BMI and waist circumference (from very low to very high values). As a consequence, the correlation between waist and BMI was quite high in our study (r = 0.87 in men and r = 0.84 in women), as also previously reported in large cohorts. This is why we also used figures in our report to illustrate the considerable individual variation in waist circumference within each single BMI unit and the added value of measuring waist to identify those with more VAT, liver fat, and increased cardiometabolic risk (CMR).
Dr. Kawada also appropriately raised the issue of ethnicity, which was addressed in a previous report from our group that showed that Asian patients had more visceral and liver fat for a given level of BMI. However, at any given level of VAT and liver fat, we found that Asians essentially had the same CMR profile as the other ethnic groups examined in our study.
Finally, we were very careful not to conclude about cardiovascular disease or diabetes risk. Results of our study would essentially be the same had we considered each individual component of our CMR score or focused on the features of the metabolic syndrome. In this regard, we have shown in the past that metabolic syndrome as a binary diagnosis (present or absent) is certainly not adequate to properly quantify absolute cardiovascular disease risk.
Our report was just one more step in our journey to develop simple tools to identify the subgroup of overweight/obese subjects at an increased risk of chronic noncommunicable diseases. Although the BMI appears to be adequate to describe populations, this index has important limitations when comes the time to use it to assess individual risk in clinical practice.