Actually for a heart this might make some sense.  So say we have a subject A who is BMI 31 completely fat and Subject B who is BMI 41 also completely fat.  So at BMI ~30 the heart might actually be pumping at 100% and would not be able to sustain a larger body fully. As subject B's body might only have 80% or less proper circulation on the outer limits of its body.  This would make subject B have things like bruising and dead tissue around its body.  Which anyone on FPH would know actually happens.  So subject A and subject B actully have the same heart attack risk of "Soon", because they both are pushing the heart at 100% all day everyday.