Introduction: The Fat We Were Told to Fear

For the better part of 60 years, the message from doctors and public health officials has been clear and consistent: to protect your heart, you must avoid saturated fat. Foods like butter, red meat, and cheese were cast as dietary villains, directly responsible for clogging arteries and causing heart disease. This advice became a cornerstone of modern nutrition, shaping how billions of people eat.

But the scientific story behind this advice is far more complex than most people realize. It’s a history filled with surprising twists, questionable data, influential personalities, and crucial studies that were buried for decades. The seemingly solid consensus was, in fact, built on a foundation that is now being challenged by re-discovered evidence. Here are five surprising takeaways from the convoluted history of saturated fat.

1. The “Diet-Heart Hypothesis” Has a Surprisingly Flawed Origin Story

The idea that saturated fat causes heart disease by raising cholesterol, known as the “diet-heart hypothesis,” was first proposed in the 1950s by physiologist Ancel Keys. The bedrock evidence used to support this theory was Keys’s influential Seven Countries Study, which for decades was cited as definitive proof of the link.

However, a closer look at the study reveals major shortcomings. Critics have long pointed out that Keys used a “nonrandom approach” to select the countries, leading to accusations that he “cherry picked” nations likely to confirm his hypothesis. For example, he did not include countries like France or Switzerland, where people ate a great deal of saturated fat but had low rates of heart disease.

The problems went deeper than just country selection:

• Flawed Dietary Data: Dietary information was sampled from only 3.9% of the men in the study, totaling fewer than 500 participants.

• The Lent Omission: The data collection on the Greek island of Crete suffered from what later researchers called a “remarkable and troublesome omission.” The dietary sample was taken during Lent, a period when the Greek Orthodox church banned “all animal foods.” This meant saturated fat consumption was almost certainly undercounted, yet this skewed data became a cornerstone of the argument that the famously healthy “Cretan diet” was low in saturated fat.

2. Major Studies That Contradicted the Hypothesis Were Left Unpublished

While the diet-heart hypothesis was gaining widespread acceptance, several large and rigorous clinical trials were conducted to test it. Shockingly, when the results contradicted the prevailing theory, they were often ignored or simply not published.

Two critical examples stand out:

• The Minnesota Coronary Experiment (MCE): Conducted between 1968 and 1973, this was the largest test of the diet-heart hypothesis ever performed, involving over 9,000 men and women in one nursing home and six state mental hospitals. Despite successfully lowering participants’ cholesterol, the study found no reduction in cardiovascular events, cardiovascular deaths, or total mortality. The results went unpublished for 16 years.

• The Framingham Heart Study: This landmark study is one of the most famous health investigations in history. Yet, a detailed dietary investigation completed in 1960 concluded there was “No relationship” between saturated fat consumption and heart disease. This crucial finding was not publicly acknowledged by a study director, William P. Castelli, until 1992.

Why would the results of such a major trial like the MCE be withheld for so long? The study’s principal investigator, Ivan Frantz, reportedly explained his decision with a simple, telling admission:

“We were just disappointed in the way it came out.”

3. Swapping Saturated Fat for Vegetable Oil Lowered Cholesterol—But Was Linked to a Higher Risk of Death

When the long-lost data from the Minnesota Coronary Experiment (MCE) was finally recovered and re-analyzed decades later, it revealed a stunning and deeply counter-intuitive finding. The study’s intervention, which replaced saturated fats with vegetable oils rich in linoleic acid (like corn oil), was successful in its primary biochemical goal: it lowered participants’ serum cholesterol by an average of 13.8% compared to the control group.

According to the diet-heart hypothesis, this should have led to fewer deaths. Instead, the opposite happened. The re-analysis showed no mortality benefit at all. More strikingly, it uncovered a dangerous paradox: for each 30 mg/dL reduction in serum cholesterol, there was a 22% higher risk of death.

This finding is monumental because it directly challenges the core assumption that lowering cholesterol through this specific dietary change—swapping saturated fat for vegetable oils high in linoleic acid—automatically translates to better health and a longer life.

4. Major Conflicts of Interest May Have Shaped the Official Advice

The official dietary advice to limit saturated fat wasn’t just shaped by flawed science; it was also influenced by powerful financial interests.

In 1961, the American Heart Association (AHA) became the first major organization to recommend that Americans limit saturated fat. What is less known is that in 1948, the AHA received a transformative donation of $1.7 million (about $20 million in today’s dollars) from Procter & Gamble, the makers of Crisco oil. This product, made from polyunsaturated vegetable oil, benefited directly from advice to avoid traditional animal fats. According to the AHA’s own official history, this donation was the “bang of big bucks” that launched the group into a national powerhouse.

This pattern of potential conflicts has persisted. An analysis of the 2020 U.S. Dietary Guidelines for Americans (DGA) advisory committee found numerous conflicts, including members with extensive funding from the soy and tree nut industries—which benefit from recommendations favoring polyunsaturated fats—and members who were openly plant-based advocates.

This raises serious questions about the objectivity of the guidelines, especially for specific numerical caps. In a private email obtained through a Freedom of Information Act request, the Vice-Chair of the 2015 DGA committee made a frank admission about the 10% limit on saturated fat:

“There is no magic/data for the 10% number or 7% number that has been used previously.”

5. The “Scientific Consensus” Isn’t as Solid as You Think

Over the past decade, the evidence challenging the diet-heart hypothesis has mounted significantly. More than 20 review papers by independent teams of scientists have now been published, largely concluding that saturated fats have no significant effect on cardiovascular disease, cardiovascular mortality, or total mortality.

The debate continues to play out in major scientific journals, with different meta-analyses reaching conflicting conclusions. For example, a 2020 Cochrane review found that reducing saturated fat led to a 21% reduction in cardiovascular events(like heart attacks and strokes) but had little effect on the risk of dying. In contrast, a 2025 systematic review in the JMA Journal found no significant benefit for either mortality or cardiovascular events. A key reason for these conflicting results is the inclusion of flawed trials; the JMA Journal review, for example, criticized other meta-analyses for including data from studies like the Finnish Mental Hospital Study, which was not properly randomized.

Despite this fierce and ongoing scientific debate, the new evidence has not yet been reflected in official dietary policies, which remain largely based on the older, contested science. As the authors of the 2025 JMA Journal meta-analysis bluntly concluded:

“The findings indicate that a reduction in saturated fats cannot be recommended at present to prevent cardiovascular diseases and mortality.”

Conclusion: A New Perspective on Fat

The history of the war on saturated fat serves as a powerful cautionary tale. It reveals how a scientific hypothesis, born from flawed studies and propelled by influential advocates, can become entrenched as government policy and public dogma, even as contradictory evidence is ignored, buried, or dismissed.

For decades, we’ve been told a simple story about fat, but the reality is that much of this advice was based on a shaky scientific foundation, compromised by unpublished trials and significant conflicts of interest. The conversation is finally changing, but it took the recovery of long-lost data to force a re-examination of decades-old beliefs.

It took decades and recovered data to question the war on fat. What official advice are you following today that might be based on a similarly fragile foundation?