The fun bit about this pearl of wisdom is it is true. Marilyn (at her biggest) was a size 16. That is she was a 1950's 16.
To illustrate my point I have made the following collage of pictures taken from a vintage pattern I have from 1957.
As you can see the size 16 is clearly printed on the front of the envelope, the size chart clearly printed on the back which indicates that a size 16 has a 36 inch bust and a 28 inch waist, which in modern standards makes a size 10 Australian.
So why is it that Marilyn has those famous curves an the modern 10 often has a more "skinny" look. Well in my opinion a lot of that has to do with style of the time. I won't be the first person to tell you that cutting your body at its widest point will make you look wider (hello swimsuit picture above) and that the opposite is also true. So when fashion cut at the smallest waist it helped to emphasis bust and hips (when the full skirts weren't taking care of that emphasis) and that modern fashion by comparison cuts lower on the wider part of the hip giving a more rectangular and less curvaceous look.
This is all very important to remember when working with vintage patterns. Just because you are a size 10 doesn't mean a size 10 pattern from 1945 will fit you off the bat. In fact you will likely have to add anywhere up to 4-5inches on all dimensions.
It is also important when looking at body image in this world. When we let ourselves believe a falsehood like Marilyn Monroe was a size 16 we buy into a belief that we too can look like her in that swimsuit, which just leads to disappointment when we don't.
Now it is important to love yourself whatever your size and if you find you can't make the changes to get there. If you look back to 2011 you will see I made this pattern and wore it (once only) my goal for 2014 is to get back into these size 16's.
I am aware (and I think this illustrates it beautifully) that size is only a number - however in my reality size is also a wardrobe full of home made awesome dresses just wishing they could zip up.