For decades we’ve been told to avoid eggs, butter, whole milk, and red meat.

Then eggs were declared acceptable again. Butter quietly returned to many breakfast tables. Researchers questioned whether whole milk was really worse than skim milk. Even the evidence surrounding red meat proved to be less certain than many people had assumed.

No wonder people throw up their hands and ask, “How can the experts keep changing their minds?”

The answer is actually reassuring. Science is supposed to change.

Yesterday’s certainty

When I was growing up, breakfast meant bacon, eggs, buttered toast, and a glass of whole milk. Few people questioned whether those foods were healthy.

Beginning in the 1960s, however, nutrition advice shifted dramatically. Saturated fat became the villain. We were encouraged to choose skim milk instead of whole milk, margarine instead of butter, and carbohydrates instead of fats. Red meat became something to limit. Eggs were viewed with suspicion. Millions of us faithfully changed our eating habits because we believed the science was settled. But science is rarely settled.

Looking more closely at the evidence

Over the past decade, researchers have reexamined many of the studies that shaped dietary recommendations. Several respected investigators concluded that the evidence supporting three daily servings of low-fat dairy was much weaker than most people realized. Likewise, convincing evidence that whole milk increases the risk of heart disease compared with reduced-fat milk has been difficult to demonstrate.

Researchers also questioned the assumption that whole-fat dairy inevitably promotes obesity. Some studies found just the opposite: because full-fat dairy is more satisfying, people may actually consume fewer total calories during the day.

And eggs got a reprieve on life a few years ago.

Red meat has generated similar debate. Several comprehensive reviews concluded that the evidence linking moderate red meat consumption with heart disease, cancer, or early death was less convincing than previously believed. These conclusions generated enormous controversy — not because researchers recommended eating more meat, but because they emphasized how uncertain the evidence actually was.

That distinction matters.

Nutrition studies are notoriously difficult to perform. Most rely on observing what people choose to eat over many years rather than randomly assigning thousands of people to follow a single diet for decades. Such observational studies can identify associations but cannot prove cause and effect.

That is why nutrition recommendations often evolve as new evidence accumulates.

What we know with greater confidence

Although individual foods continue to be debated, the overall picture has become much clearer. The healthiest diets around the world have remarkably similar characteristics. They emphasize vegetables, fruits, legumes, nuts, whole grains, and healthy oils. They include adequate protein from meat, fish, or high-proteinvegetables.

They minimize highly processed foods loaded with refined starches, added sugars, and excess sodium, what we now lump together as ultraprocessed foods. They avoid excessive calories.

Whether someone includes modest amounts of dairy or red meat appears to be far less important than the overall quality of the diet.

In other words, arguing over whole milk versus skim milk while drinking sugar-sweetened beverages and eating highly processed snack foods misses the bigger picture.

The real dietary villain

Perhaps the greatest nutritional lesson of the past several decades is that our attention was often directed toward the wrong target. We became preoccupied with individual nutrients — fat, cholesterol, carbohydrates — while the food environment around us changed dramatically.

Today’s supermarkets are filled with ultra-processed foods specifically engineered to be inexpensive, convenient, and difficult to resist. These products often contain combinations of refined flour, sugars, unhealthy fats, salt, and additives that encourage overeating. And they are cheaper relative to whole foods on a calorie for calorie basis, making them the choice of those with limited funds.

Meanwhile, consumption of vegetables, fruits, beans, nuts, and other minimally processed foods remains lower than recommended for most Americans.

That imbalance likely contributes far more to obesity, diabetes, and cardiovascular disease than whether someone occasionally enjoys a steak or drinks whole milk.

Humility is part of good science

One lesson extends beyond nutrition. Medicine constantly evolves. Here is a good example.

For many years physicians believed stomach ulcers resulted primarily from stress and excess stomach acid. Then two Australian physicians demonstrated that most ulcers were actually caused by the bacterium Helicobacter pylori. Their discovery transformed treatment and eventually earned them the Nobel Prize.

Progress occurred not because science failed, but because science corrected itself. Nutrition science works the same way. As better studies become available, recommendations should change. That is a strength, not a weakness.

So, what should we eat?

Fortunately, the answer is much simpler than many headlines suggest. Eat mostly real food. Fill your plate with vegetables and fruit. Choose beans, whole grains, nuts, seeds, and healthy oils, and first cold pressed extra virgin olive oil. Include fin fish often. If you enjoy dairy, modest amounts are fine, especially live culture unsweetened Greek yogurt. Eggs are healthy and poultry is a good protein source. If you enjoy red meat, have it occasionally rather than making it the centerpiece of every meal. The Mediterranean diet is essentially these choices.

Limit processed meats. Most importantly, avoid making ultra-processed foods the foundation of your diet.

Michael Pollan in his book In Defense of Food, summarized this approach beautifully: “Eat food. Not too much. Mostly plants.” That advice has aged remarkably well.

Another way to look at it

Instead of looking at one diet or another, a Harvard study published in 2025 analyzed what people actually ate in data from 30 years of the Nurses’ Health Study and the Health Professionals Followup Study. They asked the question: what did the people who lived to age 70 and were healthy in body and mind eat? Less than ten per cent of the 105,015 participants were alive and met that criterion at age 70. Here is what they ate during midlife. It turns out that they were eating mostly real foods with an emphasis on fruit, whole grains, vegetables with special attention to green leafies, more unsaturated than saturated fats, beans, soy products, yogurt, low-fat dairy, and berries. They tended to avoid trans-fats, processed meats, high-sodium foods, and sugary drinks. Sound familiar?

The authors concluded,“Our findings suggest that dietary patterns rich in plant-based foods, with moderate inclusion of healthy animal-based foods, may enhance overall healthy aging, guiding future dietary guidelines.

The bottom line

Nutrition headlines will continue to change. Future studies will challenge old assumptions, and some recommendations will inevitably be revised. But the fundamentals have remained surprisingly consistent.

The healthiest diet is not built around eliminating one food or glorifying another. It is built around balance, moderation, and eating foods as close as possible to how nature produced them. To carry it a bit further, “Don’t eat anything your grandmother would not recognize.”

Healthy aging is not built on finding the perfect food. It is built on consistently choosing better foods, staying physically active, maintaining a healthy weight, and letting good habits — not dietary fads — shape your future. This is what will assure you of many healthy years, a longer healthspan, not just lifespan.

Perhaps the greatest lesson is not that everything we once believed was wrong. It is that science is always learning — and so should we.