The Health Claims Against Saturated Fats Were Based on Bad Science

For decades, Americans were told that foods like butter, steak, and full-fat milk belonged on a blacklist — dietary villains blamed for clogged arteries and early death. Grocery aisles filled with margarine, low-fat dairy, and seed oils, all marketed as safer choices for the heart.

But as those recommendations took hold, something unexpected happened. Rates of obesity, diabetes, and chronic illness climbed steadily. Despite widespread compliance with low-fat advice, the nation did not grow healthier — it grew sicker.

Now, the scientific foundation of that advice is unraveling. A growing body of research suggests the fear of saturated fat was never backed by strong evidence. And soon, federal nutrition policy may finally reflect that reality.

The Hypothesis That Shaped a Nation’s Diet

The campaign against saturated fat traces back to the 1950s, when scientist Ancel Keys proposed a link between animal fat and heart disease. His theory gained global influence after the publication of the Seven Countries Study, which appeared to show higher heart disease rates in nations consuming more saturated fat.

But the study had a critical flaw. Keys selected countries that supported his theory and excluded others — including France and Germany — where people consumed butter and meat regularly yet experienced lower rates of heart disease.

The missing data mattered. In the decades that followed, researchers launched rigorous randomized controlled trials to test Keys’ claims. These studies — involving roughly 67,000 participants worldwide — replaced animal fats with vegetable oils like corn and soy in experimental groups.

The outcome was clear: lowering saturated fat did not reduce deaths from heart disease — or deaths overall.

When Cholesterol Fell — But Death Rates Didn’t

The trials did confirm one thing: diets lower in saturated fat reduced LDL cholesterol, often labeled “bad cholesterol.” But that biochemical change failed to translate into longer lives or fewer heart attacks.

In one recovered study, researchers found something even more unsettling — participants who lowered their cholesterol the most were actually more likely to die from heart disease. The cholesterol story turned out to be more complicated.

Saturated fat also raises HDL, or “good cholesterol,” which helps protect the heart. It may also increase a type of LDL particle that is large and buoyant — a form not strongly linked to cardiovascular disease. In short, the numbers improved on paper, but real-world outcomes did not.

Evidence Points in an Unexpected Direction

Some data even suggest potential benefits. The largest observational nutrition study ever conducted — tracking 135,000 people — found that higher intake of saturated fat was associated with lower rates of stroke. Meanwhile, the push to reduce fat replaced traditional foods with refined carbohydrates and ultra-processed products — now strongly linked to obesity, diabetes, and early mortality.

The results speak for themselves. When the first Dietary Guidelines for Americans were released in 1980, just 15 percent of adults were obese. Today, that number is closer to 40 percent. Three-quarters of Americans live with at least one chronic condition, and heart disease remains the leading cause of death.