In the first Canadian food guides of the 1940s, there was no shyness around fatty foods. Specific recommendations to enjoy cheese at least three times a week, along with frequent servings of eggs and butter, didn't raise any eyebrows.

And today, some 80 years later, we seem comfortable eating fats again. Certainly, no one worries about getting a heart attack from eating too many olives or avocados. Still, in many circles, even foods with high amounts of saturated fat, such as ghee and coconut oil, have attained a 'healthy fat' halo.

We have entered an era where all-natural, whole foods, including fatty ones, are off the hot seat, as ultra-processed foods have become 'public enemy number one.' In this nutritional climate, it's easy to forget that it wasn't so long ago that the 'healthy fats' category didn't even exist.

Beginning in the early 1980s, Canadian and American food guidelines advised strict limitations on total fat and cholesterol intake, urging North Americans not to get too much fat of any kind.

Low-fat versions of dairy products and lean cuts of meat like skinless chicken breast were the order of the day. Proud phrases like 'heart healthy' and 'cholesterol-free' were used interchangeably to market everything from breakfast cereals to potato chips. For three decades, an entire macronutrient group was given a bad reputation.

We can breathe a sigh of relief that the low-fat days are officially over. But while lipids are no longer the villains they once were, many myths from the age of fat-phobia persist right up until today. For example, the myth that calorie-rich fatty foods are the primary driver of unwanted weight gain or the myth that diets high in total fat are single-handedly responsible for heart disease epidemics still lurk stubbornly in popular imagination. Generations of people still, understandably, have lingering trust issues with fats.

Why did we fear fats in the first place?

Most of our fear of fat can be traced back to 1952, when Ancel Keys, a man who would become one of the most famous nutritionists of all time, presented his 'diet-heart hypothesis' to a group of lipid researchers in New York. The theory, based on data from 6 countries, was that fat in the diet raises blood cholesterol, and high cholesterol is what blocks the arteries, causing heart attacks.

By 1957, Keys had officially amended his theory demonizing all fats, favouring instead the notion that saturated fats from animal foods were the real bad guy. He contended that if we replaced them with vegetable fats, the heart disease epidemic would stop. By this point, many critics accused Keys of cherry-picking data to support his hypothesis. Even as early as 1955, national data were available for 22 countries, most of which did not support the diet-heart hypothesis. Germany, France, and Switzerland were all examples of populations eating plenty of saturated fat with comparatively low rates of heart disease.

Nevertheless, Keys' influence continued growing, and the diet-heart hypothesis seemed reasonable enough to readily take hold in American consciousness. Vegetable oils were promoted vigorously, and in 1958, margarine hit the market as a replacement for butter.

To counter his critics and settle the debate once and for all, Keys embarked on the infamous 7 Countries Study, for which Keys travelled to places he thought would prove his idea - Yugoslavia, the USA, Greece, Finland, the Netherlands, and Japan - avoiding places that would contradict it. The study covered a period from 1958 to 1964 and would be published in 1970, showing precisely what Keys had already believed - the more saturated fat people ate, the more likely they were to die of heart disease.

However, on closer inspection, it could be seen that within countries, extreme variations of diets and heart disease rates did not align at all. In Western Finland, for example, heart disease deaths were a third of those in Eastern Finland, where saturated fat consumption was the same. The Grecians of Corfu ate less saturated fat than their neighbours on the island of Crete but still had significantly higher rates of heart disease (Teicholz, 2014).

Nevertheless, Keys was already the darling of the American Heart Association and America's official nutrition and heart health guru. He was even on the cover of Time Magazine in 1961, the same year the American Heart Association - the authority of all authorities on all things cardiac - published its opinion that anyone at risk of coronary disease should strictly limit fat intake.

In 1977, six years after Keys' 7 Country Study was published, the first official American dietary recommendations were published, massively limiting cholesterol, saturated fat, and indeed all fat. By the 1980s, low-fat living, not just for those at risk of heart complications but the entire nation, had become dogma.

The dawn of good cholesterol

It's not hard to see why the image of arteries clogged with cholesterol gained traction- it's simple and relatable. We can think of the drain in our kitchen sink clogged with bacon grease and shrug, and it's basically the same in our bodies. Less goop means more flow and a healthier heart.

However, human metabolism is much more complicated than simple plumbing analogies can convey, an unavoidable fact that would become increasingly highlighted as we learned more about cholesterol in the final decades of the 20th century.

Cholesterol is essential for various critical biological functions. It is, in fact, such a necessary molecule for human life that if we don't eat any, our liver will produce its own. However, since (as we all know) oil and water don't mix, the body coordinates cholesterol transport through the blood by a sophisticated system of lipoproteins - little shuttles that ferry cholesterol to wherever it's needed.

By the end of the 1970s, our ability to measure different types of lipoproteins would change everything: where Ancel Keys' 7 Countries Study looked at total cholesterol, the conversation would quickly shift to specific cholesterol fractions, namely HDL (high-density lipoprotein) and LDL (low-density lipoprotein). While HDL and LDL are just different types of shuttles for the same cholesterol, they have radically different implications for health.

One major bombshell from the epic and epochal Framingham Heart Study arrived in 1977. To the astonishment of many, it was revealed that low HDL ('good cholesterol') was an even greater independent predictor of cardiac events than high LDL ('bad cholesterol') or high total cholesterol. High 'bad cholesterol' may be problematic, but having an average amount of 'bad cholesterol' and low 'good cholesterol' may be significantly more worrisome.

The rise of healthy fats

From the 1960s through the 1980s, polyunsaturated fats like vegetable, corn, and soybean oil were marketed as heart-healthy alternatives to butter, lard, suet and tallow. This was all based on the Ancel Keys-era logic that saturated fat raised total cholesterol and that avoiding it in favour of unsaturated fat was akin to preventing heart disease.

Little by little, the increasingly nuanced understanding of cholesterol fractions added more nuance to the perception of dietary fats, with various nutritional implications. By the mid-1990s, trans fats found in margarine were shown to raise the bad LDL while lowering the good HDL - the worst possible outcome! This was an ironic turn of events since margarine was meant to be an improvement over saturated fat sources, which can raise good HDL along with bad LDL. Cholesterol in foods like eggs, cheese, and meat can increase LDL and HDL.

However, natural foods rich in mono- and polyunsaturated fats that could lower bad LDL and raise HDL (the magic combination) received a new wave of acclaim in the 90s. This was perfectly in line with an emerging focus on what we now refer to as the Mediterranean diet, a decidedly fat-friendly paradigm that encourages liberal consumption of fatty fruits like olives and avocados, a variety of omega 3-rich seafood, nuts and seeds, and the healthy fat of all healthy fats: extra-virgin olive oil.

Saturated fat and LDL

Since a cultural fixation on lowering LDL seemed to trump any interest in raising HDL through diet, the evolving cholesterol research did little to exonerate saturated fats in the broader public view throughout the 1990s. They remained generally barred from the emerging 'healthy fats' club.

In 2007, Canadian guidelines shifted from the previous 1992 recommendations to limit fat intake, focusing instead on replacing trans and saturated fats with unsaturated. In 2013, the American Heart Association lifted its recommendation to limit total fat intake (also encouraging the same unsaturated swap as Canadians). In 2015, the same change was reflected in the Dietary Guidelines for Americans. This was the 30-year low-fat era coming to a decisive end. All nutritional guidelines in North America officially finished recommending low-fat diets.

So, really, we live in an age where it makes less sense to talk about healthy fats- which is most of them- than it does to talk about unhealthy fats, a tiny and exclusive club that seems to shrink daily. Within this increasingly rarefied territory, no one disagrees about avoiding trans-fats, but since they are mostly banned, avoiding them is pretty automatic.

Where saturated fats are concerned- the only naturally occurring fats left in the 'unhealthy fats' club - there is much more controversy. Part of this is because of their diversity- the medium-chain saturated fats in coconut oil, for example, are burned for cellular energy and don't raise LDL. Part of it is due to personal context, as LDL does not respond to saturated fat the same way in all persons. Part of it is due to more emerging science showing that while LDL may have a role to play in heart disease development, it (and, by extension, dietary saturated fat) appears to be a far smaller player than other drivers of the epidemic, such as diabetes, high blood pressure, and smoking.

The future looks rich

Now that all North American dietary guidelines have ultimately rescinded recommendations for reductions in total fat, we live in a different world than we were 30 years ago. On the contrary, new weekly studies show the remarkable benefits of high-fat diets, unfathomable to many cardiologists in the 1980s.

Perhaps our current moment in history is one where fats are mostly exonerated. We have no issues with salmon or olive oil and are opening up to eggs. However, we still need to find out whether bacon or butter has any place in a healthy diet. Nevertheless, while debates continue to swirl around contentious issues like seed oils and saturated fat, it's clear that the stigma which demonized fat in general, as an entire macronutrient category, has earned its place in the dustbin of history.