Traditionally peasant workers would thrive on diets full of potatoes (Ireland), pasta (Italy) and other similar foods. Shouldn't that mean we should be really healthy on those diets today? Only if we actually had the workload they labored under as well.
In regions of the world where people poured in 20 hours of hard work each day, they had to eat hearty meals. If they did not fill their body with energy, they would collapse before they got halfway through their tasks. Yes, they had great bodies and healthy lungs. That is because their "exercise plan" was to push, pull, dig and walk for many, many hours a day. I'm sure if any of us in modern times did even a quarter of the work they did that we would be in awesome shape.
My grandmother grew up in Ukraine, living on potato pancakes, potato-filled pirogies and many other carby delights. She also would walk 4 hours just to get to town to sell or buy goods, and then 4 hours to get home again. That was in addition to her normal chores.
In modern times our energy needs are simpler in most cases. We have everything done "for us". We have elevators! We have cars! I think sometimes we really don't appreciate how much easier our lives are than even our grandparents.
Let's think about potatoes, for example. Potatoes were explicitly grown in markets (like Ireland) where farmers worked 20 hour hard days and needed high sugar foods to get them to survive with that workload. The average modern office worker barely has to walk up and down stairs. They honestly don't need that high sugar intake.
It's the same with pasta in Italy. Pasta was SUPER for hard working farmers who worked in the fields all day long. They needed that energy to power their bodies. Modern office workers don't need that same energy load.
So in general, as much as we might idolize the diets of our hard-working ancestors, it doesn't make sense for a person with low energy needs to eat a diet of high-energy, that was designed for a full day laborer. It makes sense for a person with low energy needs to eat a balanced low energy diet that matches their daily energy expenditures.
Of course the other alternative is to get a fun hard working career like the crab fishermen in Alaska. I bet they could eat any food they wanted and still end up skinny and muscular, with the incredibly hard work they put in every day!
Lisa Shea's Library of Low Carb Books