D.B.
The problem with "just eating healthy" is that there's no agreement on what that means. The food pyramid that many of us grew up with was thrown out some years ago because it was wrong and outdated, not representative of our current food supply.
The other problem is that our food supply has changed so drastically in the last 40 years, and our demands have changed along with it. We no longer eat seasonally at all - we want strawberries in January and apples in March, we expect certain foods to be available year-round. We import them from all over the world, and even if they are "local", they are grown in depleted soils with fertilizers that spur fast growth but don't allow them to absorb the nutrients and trace elements in the soil. That apple in March or July was picked last October and kept in storage, exposed to gas to prevent rotting. That kiwi was picked 3 weeks ago in Australia.
Even the American Medical Association doesn't think we can get what we need from food. Panels of food scientists have tested the nutrient content of today's food, and found it substantially lacking, to the point that you'd need to consume something like 6000 calories a day to get the vitamins, minerals, and phytonutrients your grandmother got. Then there are the arguments that the plants we eat, either through genetic modification or substitution of faster-growing species/varieties, "ain't what they used to be."
We went through low fat for years, but heart disease and obesity rates are through the ceiling. We're starving, in part because of the nutrient deficiency. So we crave things because we aren't getting what satisfies us and what our bodies need. Then we went high carb (everything was pasta and grains, instead of it being a side dish). Then we went to no-carb, with South Beach and Atkins. Then Paleo emerged, with additional changes and prohibitions. But we still have a heart disease and obesity problems. And we're eating corn-fed livestock loaded with antibiotics because they are raised in CAFOs. There's no agreement on what "free range" and "cage free" mean either. Those meats you eat on those diets aren't the same ones primitive humans ate. So it's not really Paleo anyway. And we have huge increases in problems with gluten, dairy, peanut and tree nut allergies, and more - so we are less and less able to process foods. We're overfed and undernourished.
The thing that doesn't seem to go out of style - at least so far - is the Mediterranean diet, with an emphasis on healthy fats (vs. no fats) and carbs offset by larger amounts of fruits and vegetables (vs. a big plate of white wheat pasta and a few tomatoes thrown in the sauce). But, of course, those fruits and veggies aren't nutrient-dense.
Because our health continues to decline and life expectancy is starting to reverse after many decades and even centuries of it going up(today's kids will not live longer than their parents), food scientists, researchers, and now the medical profession are re-examining things that we've taken as a "given" for years. Truthfully, you just can't "eat healthy" - not enough to meet your needs. You can make better choices or poorer choices, for sure, but until we face the realities, we're not going to see improved health overall.