Nutrition Science: Dietary Fats
The Fat That Was Innocent All Along
For four decades, the nutrient that makes food delicious, keeps your brain sharp, and regulates your hormones was officially the enemy — and the science behind that verdict was shakier than anyone admitted.
The Idea
The demonisation of dietary fat is one of the great misdirections in modern public health. It began in earnest in the 1960s, when physiologist Ancel Keys published research linking saturated fat consumption to heart disease. What most people were never told is that Keys selected data from 7 countries out of 22 he had available — the others inconveniently failed to support his hypothesis. That selective analysis shaped government dietary guidelines, the food industry, and the contents of breakfast tables worldwide for generations. The picture we now have is considerably more nuanced. Dietary fat is not a single substance. Saturated fats (think butter, coconut oil, red meat) are still contested — some research suggests certain types raise LDL cholesterol, though the relationship with actual cardiovascular events is murkier than the headlines suggest. Monounsaturated fats — found in olive oil, avocados, and most nuts — are broadly associated with reduced inflammation and better metabolic markers. Polyunsaturated fats split into two families: omega-6s, which are abundant in most processed seed oils and can be pro-inflammatory in excess, and omega-3s, found in oily fish, walnuts, and flaxseed, which are robustly anti-inflammatory and critical to brain structure. The real villain hiding in plain sight throughout the low-fat era was refined carbohydrate. When fat was stripped from processed foods, sugar and starch replaced it — and those substitutions carried their own metabolic consequences. The fat was never the whole story.
In the World
In 2015, the United States quietly dropped its long-standing recommendation to limit dietary cholesterol — the one that had condemned eggs for thirty years. The scientific advisory committee admitted the evidence simply didn't support it. One nutritional orthodoxy, undone. But the practical consequences of the original error had already played out across millions of lives. Consider what happened in Finland in the 1970s. The country had the highest rate of heart disease in the world, and a landmark public health campaign in North Karelia set out to fix that — reducing saturated fat, replacing butter with margarine, cutting fatty meats. Heart disease rates did fall substantially over the following decades, and the project became a global model. Here's the complication: North Karelia also made parallel changes — people smoked less, ate more vegetables, and access to medical care improved. Attributing the outcome to fat reduction alone was always an overreach. Meanwhile, the margarine that replaced butter was typically made with partially hydrogenated vegetable oils — trans fats — which we now know are genuinely harmful, raising LDL and lowering HDL simultaneously. A public health intervention intended to protect hearts introduced, at scale, a fat demonstrably worse than the one it replaced. Trans fats have since been banned or phased out in most countries. The lesson wasn't just about fat — it was about what happens when a complex biological system gets reduced to a single variable, and policy moves faster than evidence.
Why It Matters
Knowing this history changes how you read nutritional news. The pattern — confident consensus, inconvenient data quietly sidelined, policy outpacing evidence, eventual revision — repeats. It's not a reason to become a cynic who ignores all dietary research, but it is a reason to hold nutritional headlines more lightly than feels natural when they're packaged with authority. More practically: if you've been avoiding fat out of habit rather than conviction, it's worth revisiting. Olive oil on vegetables isn't an indulgence to be rationed — it actually improves the absorption of fat-soluble vitamins in those same vegetables. Oily fish twice a week is one of the most consistently supported dietary recommendations in the literature. A handful of walnuts is not a guilty pleasure. The question worth carrying into your next meal isn't 'is this food high in fat?' — that framing is a relic. The better question is what kind of fat, in what context, alongside what else. Your brain is roughly sixty percent fat by dry weight. It is, quite literally, built from what you eat.
A Question to Ponder
How many of your current eating habits are based on evidence you've actually examined — and how many are inherited from an era when the evidence was wrong?
Get a new one of these every morning.
Start learning with Thinkable