My advice to them today is to go and jump out of a plane!
Here is another serious review of the options for treatment of diabetes and obesity.So long as you don't mind a little science then it provides a very powerful argument for why carbohydrate restriction should be the first port of call for medics treating these diseases. And in case you are wondering, no, it is not proof, just a long list of rather big observations. Anyone interested in public health should read this: http://www.nutritionjrnl.com/article/S0899-9007(14)00332-3/fulltext
For those wanting a slightly easier summary look here:
Apart from finding the report fascinating I love the reference to the blinkered approach taken by many who say that in the absence of conclusive scientific proof the diet should not be regarded as safe. .http://www.bmj.com/content/327/7429/1459
There is no rigorous scientific study that proves that using a parachute is a justifiable intervention to stop death by falling out of a plane. But hey, when you look at the options available it seems to work OK, so in general we do it, unless we are looking for some divine intervention.
The same is true for dietary restriction of carbohydrates.