Indonesia mengalami peningkatan obesitas yaitu 12,2% (2007) menjadi 14% (2010). Indeks massa tubuh (IMT) tidak membedakan massa lemak dan massa bukan lemak.Tujuan: Mengetahui obesitas dan korelasi antara massa lemak tubuh dan IMT pada anak 7-12 tahun di Jakarta Pusat.Metode: Penelitian potong lintang analitik cluster random sampling antara Jan-Mar 2016.Hasil: Total subjek adalah 1.333 anak. Obesitas menurut massa lemak subyek lelaki sebesar 21,3%, subyek perempuan sebesar 13,1%. Median massa lemak lelaki 7-12 tahun berturut-turut 18,8,18,6,18,1,18,4,18,6,16,1%. Median massa lemak perempuan 7-12 tahun berturut-turut 23,6,24,23,8,23,7,24,4,25,4%. Korelasi IMT dan massa lemak subyek lelaki r=0,848-0,903, p<0,05, korelasi pada subyek perempuan r=0,717-0,846, p<0,05. Sensitivitas IMT terhadap massa lemak subyek lelaki 90,5%, spesifisitas 96,6%, kappa 0,879, sensitivitas IMT terhadap massa lemak subyek perempuan 88,2%, spesifisitas 92,4%, kappa 0,787 menggunakan P85 dan P95 hasil penelitian.Simpulan: Obesitas menurut massa lemak lelaki adalah 21,3% dan perempuan 13,1%, korelasi IMT dan massa lemak lelaki sangat kuat dan kuat pada subyek perempuan.

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Background: Obesity in Indonesia has increased in number from 12.2% (2007) to 14% (2010). Body mass index does not differentiate between fat mass and non-fat mass.

Aim: To determine the obesity profile and correlation between fat mass and body mass index in children aged 7-12 years old in Central Jakarta.

Methods: A cross sectional analytic study. Subjects were recruited from Jan - March 2016 through cluster random sampling.

Result: A total of 1,333 children were recruited. Obesity by fat mass in male was 21.3% and 13.1% in female. Fat mass median in male aged 7,8,9,10,11,and 12 years consecutively were 18.8,18.6,18.1,18.4,18.6, 16.1%. Fat mass median in female aged 7,8,9,10,11,and 12 years consecutively were 23.6,24, 23.8,23.7,24.4,25.4%. Correlation between BMI and fat mass in male r=0.848-0.903, p<0.05, females r=0.717-0.846, p<0.05. Body mass index sensitivity for fat mass in male was 90,5% and 96.6% specificity with kappa value 0,879, in female sensitivity was 88.2% and 92.4% specificity with kappa value 0.787 using new reference percentile generate from this study (P85 and P95 BMI).

Conclusion: The obesity profile determined by fat mass is 21.3% in males and 13.1% in females and with very strong correlation between BMI and fat mass for males and strong correlation in females.