There are reasons for underweight. The answers are explained below.
Jan and Gene do have set points and basal metabolic rate. Due to this, it look as if Gene has a much higher set point and also higher basal metabolic rate than Jan but the fact is that his body is in a state of homeostasis
The external differences in terms of Jan and Gene is that the social -cultural affects Jan ability to fit in by holding on to a slim body is better and much stronger than on Gene.
Jan may suffer from sickness such as neophobia and Gene is said to be subjected to more food variety that boast his eating habits.
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