Saturated Fat and Dairy: Then and Now – How Science Has Moved Beyond Ancel Keys

In the 1960s and 70s, Ancel Keys’ diet-heart hypothesis cast saturated fat as the chief villain in our diets. Butter, cheese, full-fat milk, cream, and fatty meats were all branded as threats to heart health.

Fast forward to today, and the story is far more nuanced. Modern research still acknowledges that diet impacts cardiovascular health—but saturated fat’s role isn’t quite what Keys claimed. Let’s explore how the science has evolved.

The Old View: Saturated Fat as the Enemy

Keys’ work linked high saturated fat intake to high cholesterol, and high cholesterol to heart disease.

For decades, health authorities advised the public to replace saturated fats with polyunsaturated vegetable oils and to choose low-fat dairy over full-fat.

Supermarkets filled with “low-fat” yoghurts, margarines, and dairy alternatives. The underlying message:

Less fat = healthier heart.

The New Evidence

Over the past two decades, large-scale studies and meta-analyses have painted a more complex picture:

Not all saturated fats are equal

Saturated fats in processed meats don’t behave the same way in the body as those in dairy or dark chocolate.

Dairy has unique benefits

Fermented dairy products like yoghurt and cheese are linked with lower heart disease risk in several studies. They contain beneficial bacteria, calcium, and bioactive compounds that may counteract any negative cholesterol effects.

It’s what you replace saturated fat with that matters

Replacing saturated fat with refined carbohydrates (like white bread and sugary snacks) doesn’t reduce—and can even increase—heart disease risk. Replacing it with unsaturated fats from nuts, seeds, olive oil, and fish is where benefits show up.

The sugar factor

John Yudkin’s once-dismissed warnings about sugar have been vindicated. Diets high in added sugars, especially from ultra-processed foods, are now strongly linked with obesity, type 2 diabetes, and cardiovascular disease.

Modern Consensus

The latest UK and international dietary guidance no longer calls for an aggressive “low-fat at all costs” approach.

Instead, it recommends:

Balancing fat types – prioritising unsaturated fats, but not automatically fearing all saturated fats.

Eating whole foods – choosing minimally processed dairy, meats, and plant foods over ultra-processed options.

Looking at diet patterns – the Mediterranean and Nordic diets, which include dairy and moderate saturated fat, remain among the healthiest.

From Demonisation to Context

Where Keys’ era saw dairy fat as a universal danger, modern science takes a context-based view:

Cheese and yoghurt? Often beneficial.

Butter? Fine in moderation.

Ultra-processed cakes and biscuits made with palm oil and sugar? Best avoided, regardless of fat type.

Final Thoughts

We owe a lot to Ancel Keys for focusing the world’s attention on diet and heart health. But today’s evidence shows we can put full-fat dairy back on the table—provided it’s part of a balanced, whole-food diet.

The big takeaway? Nutrition science evolves. What was “bad” in the 1960s may, in the light of new evidence, turn out to be far more complicated—and sometimes even good for you.

Ancel Keys: The Man Who Shaped Modern Nutrition – And Why His Work Still Divides Opinion

Few scientists have influenced how we eat as much as Ancel Keys.

In the mid-20th century, his research linking saturated fat to heart disease helped shape decades of public health policy. 

Whole milk, butter, cheese, and fatty meats were pushed aside in favour of low-fat alternatives. 

His famous, some would say infamous, Seven Countries Study became the foundation for the “diet-heart hypothesis” – the idea that reducing saturated fat reduces heart disease risk.

But there’s a twist: later scientists have struggled to reproduce some of his key findings, raising questions about his methodology and the robustness of the evidence that drove this global dietary shift.

The Rise of the Diet-Heart Hypothesis

In the 1950s and 60s, heart disease rates were soaring in the West. Keys proposed that saturated fat raised blood cholesterol, which in turn raised the risk of heart attacks.

The Seven Countries Study seemed to show a strong correlation between nations that ate more saturated fat and those that had higher heart disease rates.

Keys’ message was clear: cut the fat, especially from animal products like dairy, and you could protect your heart. Governments listened. The “low-fat” era had begun.

The Reproducibility Problem

Over time, other scientists tried to repeat Keys’ work. The results? Not as clear-cut.

Different results in different countries – Later studies found populations that ate a lot of saturated fat but had low heart disease rates (for example, the French, often dubbed the “French Paradox”).

The “cherry-picking” criticism – Keys chose seven countries out of a possible 22 for his study. Critics argued that if more countries had been included, the link between fat and heart disease would have been weaker.

Changing dietary science – Large modern meta-analyses, looking at decades of research, have found that the relationship between saturated fat and heart disease is more complicated than Keys suggested. Total diet quality, food processing, and sugar intake all play bigger roles than once thought.

Why His Findings Couldn’t Always Be Replicated

There are several reasons why Keys’ results didn’t hold up consistently:

Observational study limitations – His study could only show associations, not cause-and-effect.

Measurement challenges – Diets were assessed with limited tools, often based on small samples that may not have been representative.

Lifestyle and cultural differences – Exercise, smoking rates, and other factors varied widely and could have influenced heart health as much as diet.

Nutrient focus vs. food focus – Keys looked at nutrients in isolation, but today’s research suggests whole dietary patterns are more important than one nutrient alone.

The Legacy Debate

Some defend Keys, saying he was working with the best data and tools available at the time, and that his work did help reduce certain diet-related risks.

Others argue that his conclusions were overstated, and that public health policy moved too quickly to demonise saturated fat while ignoring sugar and ultra-processed foods.

What’s certain is that his research shaped everything from supermarket shelves to school canteens – and that its reproducibility problems remind us how science evolves.

What We Can Learn Today

Be wary of simple answers – Nutrition is complex; no single nutrient is the whole story.

Wait for weight of evidence – Policy should be based on multiple studies, not one big finding.

Consider the whole diet – Balance, variety, and food quality matter as much as any one nutrient.

Ancel Keys changed the way the world eats – but his work also shows how early science, even from brilliant minds, can be flawed.

The inability to reproduce some of his findings doesn’t erase his impact, but it should make us think twice before we let one study – or one scientist – define our diets for decades to come.

"Debunking Ancel Keys: Why His Dietary Dogma Was Flawed"

https://thatsfoodanddrink.blogspot.com/2024/03/debunking-ansel-keys-why-his-dietary.html

Debunking Ancel Keys: Why His Dietary Dogma Was Flawed

Following on from our recent post of the potential problems of replacing dairy products with vegetable products, we examine Ancel Keys and his controversial research that has been debunked in recent years.

In the realm of nutritional science, few figures have been as influential and controversial as Ancel Keys. Widely celebrated for his research on the Mediterranean diet and the formulation of the lipid hypothesis, Keys played a pivotal role in shaping dietary guidelines around the world. 

However, as time progresses and research evolves, it becomes increasingly apparent that some of Keys' assertions were flawed and may have led us down the wrong path in understanding nutrition and health.

Ancel Keys rose to prominence in the mid-20th century with his research on the relationship between dietary fat, cholesterol, and heart disease. His landmark "Seven Countries Study" seemed to demonstrate a clear link between saturated fat intake and heart disease mortality. 

This laid the groundwork for the vilification of dietary fat, particularly saturated fat, and the promotion of low-fat diets as a means of preventing cardiovascular disease.

But upon closer examination, several flaws in Keys' research methodology and conclusions have emerged. 

One of the most glaring issues with the Seven Countries Study is its selective sampling. Keys cherry-picked data from countries that supported his hypothesis while ignoring data from countries that did not fit his narrative.

This cherry-picking bias has been heavily criticised by subsequent researchers, who argue that it skewed the results and led to an oversimplified understanding of the relationship between diet and heart disease.

Moreover, Keys' focus on total fat consumption as a risk factor for heart disease overlooked the importance of other dietary and lifestyle factors. Subsequent studies have demonstrated that the quality of fats consumed, rather than the quantity, may be more important for heart health. 

For instance, replacing saturated fats with refined carbohydrates, as recommended by low-fat dietary guidelines, may actually increase the risk of heart disease by raising levels of triglycerides and lowering levels of beneficial HDL cholesterol.

Furthermore, the demonisation of dietary fat led to the proliferation of low-fat and fat-free products, many of which replaced fat with added sugars and refined carbohydrates. 

This shift in dietary patterns may have contributed to the obesity and metabolic health epidemics observed in recent decades. Ironically, while fat intake decreased, rates of obesity, type 2 diabetes, and other metabolic disorders skyrocketed, challenging the notion that fat is solely to blame for poor health outcomes.

In addition to his views on dietary fat, Ancel Keys also promoted the Mediterranean diet as a model of healthy eating. While the Mediterranean diet is indeed associated with numerous health benefits, it is important to recognise that it is not a one-size-fits-all solution. Cultural, socioeconomic, and individual differences must be taken into account when prescribing dietary recommendations. What works for one population may not necessarily work for another.

In conclusion, while Ancel Keys made significant contributions to the field of nutrition science, his dietary dogma was not without its flaws. His oversimplified conclusions about the role of dietary fat in heart disease and the promotion of low-fat diets have been called into question by subsequent research.

Moving forward, it is imperative that we adopt a more nuanced understanding of nutrition, one that considers the complex interactions between diet, lifestyle, genetics, and environment. By learning from the mistakes of the past, we can pave the way for a healthier future.