Correction factors for the calculation of metabolic equivalents (MET) in overweight to extremely obese subjects.

Background/objectives: The metabolic equivalent (MET) is a construct that is commonly used to quantify physical activity as well as exercise performance. 'One MET' is equal to a resting oxygen uptake of 3.5 ml O2 kg(-1) min(-)(1). However, this assumption is unlikely valid in obese subjects. The aim of our study was to quantify the difference between calculated and measured METs in overweight to severely obese subjects and to provide body mass index (BMI)-specific MET correction factors.

Subjects/methods: Resting oxygen uptake (VO2-REE) was measured in 1331 patients with a BMI >25 kg m(-2) (72.0% women; age: 42.5 ± 13.0 years; BMI: 42.5 ± 7.0 kg m(-)(2)) by indirect calorimetry and MET-REE, that is, VO2-REE related to body weight was calculated. Six hundred and fifty-two subjects (70.9% women) additionally underwent a bicycle cardiopulmonary exercise test for measurement of maximal MET (MET peak).

Results: Mean MET-REE was 2.47 ± 0.33 ml O2 kg(-1) min(-1) in women and 2.62 ± 0.34 ml O2 kg(-1) min(-1) in men, that is, markedly lower than the expected 3.5 ml O2 kg(-1) min(-1). MET-REE decreased with increasing BMI (P<0.001 for both sexes). On this dataset, gender-specific MET correction factors were developed for distinct BMI groups. During the exercise test, women performed 4.4 ± 1.3 MET peak and men 4.7 ± 1.3. After applying our correction factors, MET peak increased to 6.2 ± 1.7 and 6.1 ± 1.6, respectively.

Conclusions: Data indicate that the commonly used 1-MET value of 3.5 ml O2 kg(-)(1) min(-)(1) largely overestimates values in overweight to severely obese subjects. Our correction factors can help to reduce this systematic error and thus appear to be valuable for clinical practice as well as research studies.