More prevalent than these two dangerous trends is loss of muscle mass (also loss of flexibility). It is unlikely that you can avoid it. What we can do is to slow it down. Muscle mass maintenance entails some amount of BMI increase.

— trend of growing overweight

Majority of elderly Chinese are seen to put on weight as they age.

For me, I observed myself for decades — tendency to put on weight.

Consequence of overwright is well-known, esp. for my heart condition.

— trend of growing underweight

I feel I might lose muscle mass as I age. I think this probability is more than 50%.