Lower circulating FSTL1 levels in patients with severe obesity than in non‐obese adults and lower adipose FSTL1 expression levels in obese mice than in healthy mice have been observed (Horak et al., 2018; Prieto‐Echagüe et al., 2017). Here, FSTL1 is linked to obesity due to melanocortin 4 receptor deficiency.