How to Protect Your Knees Every Day

[flamingdem]

10. I have a question about this whole idea of weight bearing

Now when I walk carrying groceries, my improvised weight bearing exercise, isn't that good for my knees and bones?

Then why do they get on overweight as being extra weight on the bones, for every pound of weight it's four on the knees or somethng..
I would think extra body weight would then condition the knees -- make them grow more cartilidge or whatever weight bearing does?