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.