Australian diets have changed significantly over the last 60 years and when we consider the history of dietary fat recommendations, it has tended to imitate a swinging pendulum. One minute the consumption of high fat is the cause of disease and the next it’s the cure. So, what is the real story?
The Vilification of Dietary Fat
In the mid-1950s, rates of cardiovascular disease (CVD) were soaring in the USA, becoming the leading cause of death seemingly out of nowhere. Around this time, physiologist Ancel Keys came up with the “diet-heart hypothesis.” His theory was based on informal exploratory studies where he found elevated serum levels of low-density lipoprotein (LDL) in overweight, middle-aged businessmen who followed dietary patterns high in saturated fatty acids (SFA). From this, he hypothesized that it was the consumption of SFA that was raising the concentration of serum cholesterol, which in turn was causing fatty deposits in the arterial wall leading to CVD events.
While Keys’s theory was not supported by strong evidence, the logic was concrete and it caught the attention of Dr. Paul Dudley White, the chief physician for President Eisenhower. When President Eisenhower suffered his first heart attack in the mid-1950s, his chief physician gave a press conference blaming dietary fat, launching the ‘diet-heart hypothesis’ into stardom.
In the late 1950s, with the support of Dr. White, Keys recruited collaborating researchers to conduct an observational study that compared the level of SFA with heart-disease outcomes in seven countries. The aptly named Seven Countries Study gathered data on over 12,000 men and was published in 1970, citing that populations with the greatest SFA intake had the highest incidence of heart disease.
This seemingly solid scientific evidence created the foundation for the first set of USDA dietary guidelines in 1980, which declared “avoid too much fat, saturated fat, and cholesterol.” Not long after, in 1982, Australia followed suit, issuing advice that replicated the American example: “avoid eating too much fat.”
The Unintended Consequences
The intent was to displace foods high in fat with lean meats, vegetables, fruits, and whole grains; however, clinicians and the media promoted low-fat diets without specificity, cementing the societal belief that all fats are bad. Food manufacturers launched an onslaught of processed low-fat products, removing the fat content in everything from cookies to cheese, salad dressing to peanut butter, and replacing it with added sugars, which consumers embraced with careless abandon.
Ultimately, the message was a success, with a notable decrease in the intake of dietary fat as a percent of calories. Yet, it was accompanied by a significant increase in total energy intake from dietary carbohydrates. Populations were consuming less fat, including good quality fats such as those found in nuts, seeds, dairy, and olive oil, and were consuming more processed, low-fiber, high-glycemic index carbohydrates.
Further Research
While some were satisfied with the initial epidemiological evidence used to guide dietary recommendations, many scientists were dissatisfied and continued to conduct their own randomized controlled trials. Clear evidence was quickly established that SFA consumption leads to an increase in circulating lipids and lipoproteins and an overall increased disease risk. However, they also found that high consumption of processed, low-fiber, high-glycemic index carbohydrates had similar effects.
It was discovered that when consumed in excess, these carbohydrates could increase triglyceride levels in the liver, which then travel via lipoproteins to be stored in adipose tissue.
Ultimately, both SFA and highly refined carbohydrates can increase serum lipids and lipoproteins, and the advice to reduce SFA consumption without considering the replacement nutrient was premature.
The Glorification of Fat
As years went by and the CVD epidemic continued on unchanged, many began to doubt the efficacy of the low-fat diet. Slowly, snippets of research leaked into the media, linking high carbohydrate consumption with adverse outcomes and ultimately undermining the low-fat diet’s credibility.
In the early 2000s, high-fat, low-carbohydrate diets exploded in popularity. First came the Atkins Diet, and eventually it morphed into today’s widely popular ketogenic diet. Both diets promise weight loss and better health outcomes through severely restricting carbohydrate intake while promoting the consumption of high amounts of dietary fat and lean protein.
Where Are We Today?
Today, the pendulum is still swinging, with avid supporters of both low-fat and high-fat diets.
Scientifically, neither diet is superior. In a 2018 study, subjects were randomized to follow either a low-fat, high-carbohydrate diet or a high-fat, low-carbohydrate diet. After a year, there were positive health outcomes and weight loss identified in both groups, with no significant and clinically meaningful differences between the two dietary patterns.
What Should We Recommend?
If there is a single message to take away from the last 60 years of dietary recommendations, it is that dietary advice should not focus on single nutrients but rather on dietary patterns and overall diet quality.
Mediterranean-style diet as the world’s healthiest dietary pattern. Following a Mediterranean diet has been linked to a lower risk of heart disease, cancer, dementia, and diabetes, along with improved mental health and longevity.
A Mediterranean dietary pattern is abundant in vegetables, whole grains, legumes, and olive oil; moderate in fish, poultry, and red wine; and light in red meat and processed foods.
So, ironically, the world’s healthiest dietary pattern is high in carbohydrates and fats, but notably whole-grain carbohydrates and unsaturated fats.
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