I'm damn sure granny and 99.9% of those criticising women within the officially healthy BMI range have not read any meta-studies suggesting the lower end of this range is healthiest.
They just feel entitled to police other women's behaviour - like a few posters here.
I could stand over every woman having a single glass of wine and discuss research strongly indicating the increased risk increase of breast cancer outweighs the reduction in heart disease.
But I don't, because I'm not an arse.
Leading public health researchers like Walter Willets originally tried to prevent publication of the paper that indicated higher BMi might be healthier - the grounds for this censorship were that it would discourage people from dieting to slim, i.e. censorship in our own interests, because we are too silly to hear different evidence.
Actually, like many scientists, I could see the possible weaknesses in the study and was certainly not convinced by any one paper contradicting the orthodoxy.
There have in fact been several studies suggesting that higher BMi may be beneficial at age 40+.
It just means we needed more evidence, not that we should censor any we have - totally against the scientific ethos.
So, I'm also not convinced by a single metastudy, when the subject is so controversial, the authors so eager to prove a particular point and the public health establishment so desperate to rescue their policies.
Unfortunately, scientific politics (oh yes, they exist !) means such studies can be skewed, the authors not being dishonest, but making a series of decisions leaning in favour of their preferred outcome.
Results are very dependent on what statistical measures they use, how they weight confounding factors etc.
So, not "proof" either way. We should examine a fuller body of peer-reviewed papers and decide where the preponderence of the evidence lies.
And definitely stop criticising women and policing their eating like they are toddlers - outrageous 
Those who are overweight because of several extra lb of muscle are likely to be far healthier than those of lower BMi who have low muscle mass.