In a groundbreaking clinical trial, researchers have unraveled the effects of cholesterol and saturated fat, finding that eggs may be far less harmful – and potentially more beneficial – than previously thought. It's the latest research, using robust scientific work, to recast a nutritional villain in a new light.
In a world-first study, University of South Australia (UniSA) researchers investigated the independent impact of dietary cholesterol and saturated fat on "bad" cholesterol – low-density lipoprotein, or LDL – levels. What they found was that even eating two eggs a day, in an overall high-cholesterol but low-saturated-fat diet, lowered LDL levels and cardiovascular disease risk.
“Eggs have long been unfairly cracked by outdated dietary advice,” said lead researcher Jon Buckley, a professor at UniSA. “They’re unique – high in cholesterol, yes, but low in saturated fat. Yet it’s their cholesterol level that has often caused people to question their place in a healthy diet.
In the randomized, controlled, cross-over trial, 61 healthy adults each tried three different diets for five weeks, with breaks in between to allow for a reset. While all diets contained the same amount of daily calories, the cholesterol and saturated fat content differed. An egg diet (two eggs a day) was high in cholesterol but low in saturated fat; an egg-free diet was low in cholesterol (no eggs) but high in saturated fat; and a control was high in both cholesterol and saturated fat, but included only one egg per week.
The egg diet featured 600 mg/day of cholesterol (6% saturated fat), the egg-free diet contained 300 mg/day (12% saturated fat), and the control plan included 600 mg/day (12% saturated fat).
They found that the egg diet significantly lowered LDL cholesterol, compared to the control (103.6 µg/dL compared to 109.3 µg/dL), while the egg-free plan saw LDL levels stay roughly the same as the control, even though it was lower much lower in dietary cholesterol. Across the board, saturated fat appeared to be the common denominator when it came to LDL shifts.
Investigating the mechanisms involved in this change, the scientists found that things got a little more complex. LDL cholesterol is made up of distinctly sized particles: large, fluffy LDL particles, which are generally considered less risky, and small, dense ones, which are more likely to sneak into artery walls and cause plaque buildup. The egg diet reduced overall LDL but changed the particle makeup – fewer large ones and a slight increase in the small ones. While this isn't necessarily negative, looking at the LDL drop overall compared to not eating any eggs, it's certainly something that isn't well understood and needs more research.
It's also worth noting that the no-eggs diet also saw a rise in small particles and a slight drop in large ones, but overall did nothing impactful in lowering LDL cholesterol levels.
However, the results revealed that the real culprit for raising LDL levels appears to be saturated fat, not the cholesterol in eggs as has long been believed. Cutting eggs out of a diet for health reasons, without also reining in saturated fat intake, is unlikely to shift the needle when it comes to LDL cholesterol.
Secondary results from the study also found that the egg diet raised levels of lutein and zeaxanthin – carotenoids in egg yolk known to support brain and eye health, and help protect the body from inflammation – in plasma. The scientists also found a link between a spike in these levels and an increase in incidental movement among the participants. While not causal, the researchers hypothesized that the carotenoids, known antioxidants, could play a role in regulating the brain’s motivation or energy systems.
“In this study, we separated the effects of cholesterol and saturated fat, finding that high dietary cholesterol from eggs, when eaten as part of a low saturated fat diet, does not raise bad cholesterol levels," said Buckley. “Instead, it was the saturated fat that was the real driver of cholesterol elevation."
This research follows on from the results of an observational study conducted by Monash University researchers in February, which found that eating up to six eggs a week was linked to a 29% lower likelihood of developing heart disease compared to no or infrequent consumption.
While some cynical readers might be quick to write off these studies as good PR work from "Big Yolk," they lift the lid on a broader discussion that needs to be had about how, in Western societies in particular, the villainization of certain foods was a byproduct of the "nutrient reductionism" era. Think "fat-free" trends and how cow's milk is a non-negotiable for human health.
From the 1950s, as the link between high blood cholesterol and cardiovascular disease risk became established, it was quickly accepted that eating high-cholesterol foods (like eggs) would also raise blood cholesterol levels and, in turn, jeopardize heart health. Dietary guidelines promoting low-cholesterol diets became entrenched in health messaging over the next few decades – despite limited scientific evidence that foods high in cholesterol were driving the rise in heart disease. And egg yolks – with around 185 mg of cholesterol in each – became "bad" for heart health.
Then, in the 1980s and 1990s, as low-fat, calorie-counting diets rose to prominence, eggs endured another identity crisis. Egg whites – low in calories and with almost no fat content – were embraced, while the yolks – with around 60 calories each and plenty of fat – were to be avoided. What that simplified good/bad approach ignored, however, was that the fat in yolks was largely healthy fats (unsaturated) and it housed most of the egg's nutrients (vitamins A, D, E, K, and choline).
The egg is a great example of nutrient reductionism, which focuses on a single nutrient – fat, protein, carbohydrates, cholesterol – in isolation, rather than assessing the entire package or considering the person consuming it. While nutritional guidelines are moving away from the good/bad dichotomy, we've lived through decades of poor scientific evidence and strong marketing campaigns that tell us where to get calcium (milk) and protein (meat), and that bread (carbs) will sabotage weight loss. After sugar was cast out, the rise of sugar-free artificial sweeteners became the healthy replacement – and there's growing scientific evidence linking various types to a host of health issues.
What this reductive approach missed is that our bodies don't metabolize isolated nutrients in a vacuum – they're absorbed and processed in a much more complex way, affecting health over time. Food exists in the context of meals, habits, microbiome and timing. While we're not advocating for an all-egg diet (as a vegan, I actually belong to the egg-free cohort), the UniSA research underpins the fact that, scientifically speaking, how food impacts our long-term health is far more nuanced.
"So, when it comes to a cooked breakfast, it’s not the eggs you need to worry about – it’s the extra serve of bacon or the side of sausage that’s more likely to impact your heart health," Buckley added.
That said, this research also demonstrates how more work is needed to better understand how eggs don't just impact LDL levels but the composition of that "bad" cholesterol itself.
Currently, the American Heart Association says that healthy people can eat one egg each day and that “older people with healthy cholesterol levels can have two” because of the nutritional value they provide.
The study was published in The American Journal of Clinical Nutrition.
Source: University of South Australia
