Triponderal Mass Index Not Superior to BMI in Estimating Obesity Outcomes

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BMI in youth had a better or equal association with adult outcomes vs TMI and SST.
BMI in youth had a better or equal association with adult outcomes vs TMI and SST.

Triponderal mass index (TMI) alone and in combination with body mass index (BMI) or subscapular skinfold thickness (SST) was not superior to BMI alone for estimating obesity-related outcomes in adulthood, reported a research letter published in JAMA Pediatrics.

Recent evidence suggests that TMI, a measure calculated as weight in kilograms/height in meters3, may be more accurate for estimating body fat levels in youth compared with BMI. However, the clinical importance of TMI in estimating outcomes in adulthood has not yet been evaluated. In this study, researchers compared youth TMI alone and in combination with BMI or SST against BMI alone as estimates of adult obesity-related outcomes. Participants age 3 to 18 years (N = 3596) were randomly selected from the national register in the Cardiovascular Risk in Young Finns Study.

Findings indicated that youth TMI, BMI, and SST were all significantly associated with the following adult outcomes:

  • Type 2 diabetes (TMI: odds ratio [OR], 1.22; 95% CI, 1.03-1.44; BMI: OR, 1.78; 95% CI, 1.54-2.07; and SST: OR, 1.52; 95% CI, 1.34 -1.72)
  • Obesity (TMI: OR, 1.61; 95% CI, 1.46-1.77; BMI: OR, 2.09; 95% CI, 1.89-2.32; and SST: OR, 1.80; 95% CI, 1.64-1.98)
  •  High carotid intima-media thickness (TMI: OR, 1.18; 95% CI, 1.06-1.33; BMI: OR, 1.19; 95% CI, 1.06-1.34; and SST: OR, 1.17; 95% CI, 1.06-1.31)
  • Level of high low-density lipoprotein cholesterol (TMI: OR, 0.85; 95% CI, 0.76-0.95; BMI: OR, 1.32; 95% CI, 1.20-1.46; and SST: OR, 1.11; 95% CI, 1.01-1.23)

Of note, BMI in youth had a better or equal association with adult outcomes vs TMI and SST, and combining TMI or SST with BMI did not improve or only marginally improved the association compared with BMI alone.

The investigators suggested the results may be because TMI does not account for fat distribution, which has been associated with higher risk for type 2 diabetes.

“TMI [also] does not distinguish fat mass from muscle mass, although low muscle mass has been associated with an increased risk [for] incident [type 2 diabetes], independent of general obesity. Future studies should determine whether youth muscle mass is associated with adult obesity-related outcomes,” wrote the researchers.

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Reference

Wu F, Buscot MJ, Juonala M, et al. Association of youth triponderal mass index vs body mass index with obesity-related outcomes in adulthood [published online October 15, 2018]. JAMA Pediatr. doi:10.1001/jamapediatrics.2018.3034

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