I think the problem is that the human body tries to resist gradual change, so adapts to such schemes and adjusts for them.
Compare this to the radical approach to diabetes, in which, hospitalized for their own protection, diabetics were put on 600 calorie a day diets for eight weeks.
It was too fast for the body to adapt, so they shed a lot of weight quickly, including the fat that had been inhibiting their insulin production.
Get back to me in a couple years. Those people will be even fatter than before. Starvation diets only work on a temporary basis. A successful diet entails a PERMANENT change in behavior.
And the numbers went down, but were they any healthier? Such a drastic diet (starvation) is very hard on the heart, but I imagine if any of these poor souls keeled over of a heart attack in the months after this regimen, the death was blamed on the diabetes.
I doubt, too, that many of them were able to keep the weight off for long. Our bodies see diets, especially ones that drastic, as starvation and become that much more efficient at putting on fat stores and keeping them in case there’s another “famine”.