what is a diet but just another name for a healthy lifestyle or not? It's how one determines the route of that diet whatever it may be and any given time, what is and isn't healthy seems to change at a drop of a hat. Some people like my elders lived into their hundreds without a care, lots of butter on the menu others would drop dead at the sight of it, but namely because of what they combined it with lots of other things that evidently didn't suit their chemical make up.
Diabetes too runs in my family, I don't have it am not pre- diabetic as of yet, hope not to be. If one were to do some serious research we would see some of the major culprits. I've worked in the health field and saw how the prescribed healthy ways of eating did nothing good for many of my patients over time, I was actually responsible for overseeing their entire day and during those times there wasn't a way for them to be cheating or altering the prescribed menu.. This isn't to say whomever made up those systems of eating, are wrong, they just don't work as planned for everyone. Just as they completely keep altering the food pyramids and now started saying how fat free foods are bad for you.
It is how several of you have said, it's the poor food choices and overeating that are the main culprits for what doesn't work in most cases when people put the weight back on. As we get older, our metabolism slows down, so, even what worked in our 30's food wise just isn't going to work for us when we're trying to lose weight past the age of 50, so either we accept our new poundage within reason or we adjust our plan and up the ante some how. Not necessarily by doing what some might consider a fad diet, but, by finding what is working for you, but, if it ain't working for you then, you need to adjust your thinking and or your method depending on what you hope to accomplish.
Some doctors are for and against my way of eating most of my doctors give it high five because, they are always impressed with my results and numbers while I'm on it. Many weight lost specialist agree it's a good way to go within moderation, even the diabetes association recommends restricting carbs to a degree or at least being smart about the choices when consuming them.
Again, fruit and vegetables aren't restricted and vegetables are a big part of my food plan for lunch and dinner always.
See this picture, this is what my plate looks like most days.
http://www.diabetes.org/food-and-fitness/food/planning-meals/
BTW, I don't follow Atkins, I follow low carb but my own plan similar in ways to Atkins, but not exactly.