We are constantly being urged to keep healthy, and one of the quickest ways of calculating how healthy you are is your BMI - your body mass index.

It is a crude way of telling whether you are overweight.

But over the years the BMI has come in for some criticism for not telling the whole story.

The next step is calculating their body fat using Massey's new research tool - the 'bod pod'.

Dr Kruger is using it to conduct a study comparing how a woman's BMI stacks up against her body fat reading, and she has been inundated with volunteers.