When you think of cholesterol, what’s the first food that comes to mind? For many, the answer is eggs.
And for good reason: their yolks contain relatively high amounts of the waxy fat found in our blood and decades-old studies warned that eating too many could send your cholesterol levels soaring.
As any doctor will tell you, that would be a very bad thing. High cholesterol raises your risk of cardiovascular disease – the world’s leading cause of death – as well as stroke and dementia.
According to several recent papers, however, eggs may not deserve their bad reputation.
In fact, one Australian study suggests that eating two a day could lower your levels of ‘bad’ low-density lipoprotein (LDL) cholesterol – the kind that clogs your arteries.
“For your average person, eating a few eggs a day won’t increase their cholesterol,” says Dr Nick Norwitz, a researcher at Harvard Medical School in Boston.
How could this be? Well, as emerging studies have demonstrated, dietary cholesterol – the cholesterol that’s in our food – has little bearing on the LDL cholesterol in our bodies.
Instead, researchers have uncovered what really matters in your diet, and which foods actually make the biggest difference.
Fat truths about high cholesterol
Somewhat confusingly, LDL cholesterol isn’t actually all bad – your body needs some in order to function properly.
It’s a key component of the outer membrane of every cell, for example, and is needed to make vitamin D and certain hormones such as oestrogen and testosterone.
You don’t need to get this helpful cholesterol from your diet, however. The liver makes all the cholesterol your body requires. And if you eat cholesterol-rich foods, it automatically scales back its production.
“If you increase your dietary cholesterol intake, that suppresses your liver’s cholesterol production,” says Prof Jon Buckley, a researcher at the University of South Australia in Adelaide, Australia. “So it balances out.”
In other words, your liver can regulate dietary cholesterol without much trouble. Through a finely tuned feedback system, it senses changes in intake and compensates to maintain stable levels in the bloodstream.
The real problem, as Buckley’s research shows, isn’t dietary cholesterol, but saturated fat.
The distinction between the two substances isn’t always obvious, since many foods that are high in cholesterol are also rich in saturated fat – red meat, butter, cheese and fried foods, for example.
Eggs and shellfish, however, are the exception, being high in cholesterol and low in saturated fat.
To untangle the effects of each, Buckley’s team ran a five-week study with 61 healthy volunteers, comparing diets with different levels of cholesterol and saturated fat.
The results: the more saturated fat participants ate, the higher their blood cholesterol climbed. But the amount of cholesterol in their food didn’t seem to matter.
“This was the first study that had really been designed in a way that we could tease out those effects so convincingly,” says Buckley.
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How to cook a heart-smart menu
As Buckley’s results suggest, reducing the amount of saturated fat in your diet can help limit bad cholesterol.
If you’re tempted by a cooked breakfast, for example, he suggests swapping out some of the bacon and sausages, which are high in saturated fat, for extra eggs to help keep blood cholesterol levels low.
Cutting them out completely would be a positive step too, but may be more difficult.
“The best thing is to try and make very small changes that are achievable and sustainable, rather than trying to change a whole diet,” says Buckley.
Switching up the type of fat in your diet can also help manage bad cholesterol. While the body requires some fat to function– including for the absorption of vitamins A and D – most people consume excessive saturated fat and too little polyunsaturated fat, which is abundant in walnuts, oily fish such as salmon and plant-based oils.
“Polyunsaturated fat actually reduces LDL cholesterol,” says Javier Gonzalez, a professor at the Centre for Nutrition, Exercise and Metabolism at the University of Bath, in the UK.
It does this by encouraging the liver to remove LDL particles from the bloodstream more effectively, lowering your overall levels.
Conversely, Gonzalez adds, saturated fat is twice as potent as polyunsaturated fat, meaning that it can raise your cholesterol levels to a greater extent than polyunsaturated fat can reduce them.
Yet it’s not just about the fats you eat – fibre plays a key role too. As recently confirmed in a study from India, eating a diet rich in fruits, oats, nuts and seeds can keep blood cholesterol levels in check.
These foods are particularly high in soluble fibre, which binds to bile acids (compounds made from cholesterol) in the gut and carries them out of the body. To replace those lost bile acids, the liver draws more cholesterol from the blood, helping to keep levels healthy.
Insoluble fibre, which is found in foods such as whole wheat, brown rice and many vegetables, has other digestive benefits, but a smaller effect on cholesterol.
Typically high in both polyunsaturated fat and fibre, a plant-based diet is an effective way to keep blood cholesterol within a healthy range.
In fact, a recent large-scale trial where participants were randomly assigned different eating patterns found that those on vegetarian or vegan diets recorded lower cholesterol levels than people who had meat in their diets.
The ketogenic diet: a metabolic mystery
Cut back on the bacon and eat more oats – simple enough, right? Yet cholesterol is still only partly understood, and emerging research could point to even more effective dietary approaches in the years ahead.
One area stirring debate is the ketogenic diet. Still in its early days of research, this low-carb, high-fat, moderate-protein diet is raising unexpected questions about how the body handles fat and cholesterol.
Let’s be clear: doctors aren’t recommending the keto diet as a shortcut to better cholesterol – quite the opposite. At present, it’s mainly prescribed under medical supervision for conditions such as epilepsy and diabetes.
Even so, many people turn to keto for weight loss. The idea is that when the body runs low on carbohydrates, it switches to burning fat for fuel (a state known as ketosis), which may also reduce hunger.
Evidence for its long-term benefits is mixed and side effects (including constipation, nutrient deficiencies and fatigue) are common. Still, for researchers, the diet offers a unique window into how cholesterol levels respond to a dramatic dietary change.
One such researcher is Nick Norwitz, the Harvard Medical School researcher quoted earlier. When he was following a keto diet to help manage a chronic bowel condition, he noticed that something strange happened to his blood cholesterol levels.
Although he was eating healthily, consuming very little saturated fat and lots of leafy greens, fatty fish and fibre, his cholesterol levels skyrocketed to five times over what’s considered healthy (see ‘Measure your cholesterol’ for more on healthy levels of cholesterol).
“This was scary and very bizarre because there was nothing like this in the literature,” says Norwitz, who is lean and metabolically healthy.
Norwitz’s personal experience drove him to start researching why he and other people were having this response.
In recent work, he and his team examined how a low-carb diet affected cholesterol levels in people with different body mass indexes (BMIs) – a measure of whether someone’s weight is healthy for their height – to see if this could explain the pattern.
Their analysis combined data from 41 studies reporting both BMI and cholesterol outcomes in people following low-carb diets.
The results were striking: cholesterol levels tended to rise in leaner participants, but stayed largely stable in those who were overweight. It’s a counterintuitive finding, given that slimmer people are generally considered fitter and healthier.
So, could another hidden factor be driving cholesterol levels? Could, perhaps, the answer be found not in what we eat, but in how our bodies process it?
“This is one of the areas we don’t fully understand,” says Norwitz. “It might be linked to switching from a carb and sugar-based metabolism to a fat-based metabolism, and your body using cholesterol-enriched particles to help traffic that fat.”
Norwitz was also curious to see if simply adding carbs back into his diet could lower his blood cholesterol. He decided to supplement his keto diet with cookies for 16 days.
Later, after returning to the keto diet for three months, he tried a six-week course of statins to compare the effects. Surprisingly, his cholesterol dropped more during the cookie phase than it did while taking the medication.
Of course, as Norwitz acknowledges, he is a sample size of one – and the scientific consensus will remain sceptical until far more rigorous, large-scale studies are carried out. Still, his case hints that there’s a lot about cholesterol that we still don’t understand.
“This will not generalise to your average person, but the point is context,” says Norwitz. “The fact that you could accurately predict that cookies will effectively lower cholesterol in one patient highlights just how much is unknown about cholesterol metabolism in humans.”
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Profound results with weight loss
Norwitz’s case is certainly unusual – and hasn’t yet been replicated in a large, rigorous study of other lean people.
That’s partly because most keto research focuses on the diet’s effects on weight loss and cholesterol, rather than the underlying metabolic mechanisms. And weight loss itself can strongly influence your cholesterol levels.
Studies show that overweight adults who lose 5–10 per cent of their body weight through a balanced, calorie-controlled diet and exercise see clear improvements in their cholesterol levels.
Gonzalez and his colleagues found, however, that the story changes on keto. In their study, one group of participants cut back only on sugar, while another restricted almost all carbohydrates – the defining feature of a keto diet. A third control group ate a balanced mix of fats, proteins and carbohydrates.
Both the low-sugar and keto groups lost a similar amount of weight, but their blood cholesterol told two completely different stories. In the low-sugar group, cholesterol levels fell; among those on keto, they surged dramatically.
It’s tempting to simply focus on which diet works best here, but the results point to something more profound.
As Gonzalez says, “It seems like the way in which you achieve weight loss can influence your cholesterol response.”
In other words, working out why some routes to weight loss send cholesterol soaring could help uncover how the whole system really works – and how to manage it more effectively.
A personalised response
As Gonzalez says, part of the reason keto can send cholesterol soaring may be straightforward: the diet involves eating more saturated fat and less fibre – both known risk factors for high cholesterol. But his team also suspects there’s more to the story.
For instance, changes in the gut microbiome. Trillions of microbes live in your digestive tract and are known to play a big role in metabolism, body weight and appetite.
Gonzalez found that a particular type of bacteria, called Bifidobacteria, was reduced in people eating a keto diet compared to the control diet.
“We know from other studies that Bifidobacteria play a role in cholesterol metabolism,” he says. “We have a project starting very soon to understand whether fibre intake can help mitigate the increase in LDL cholesterol on a ketogenic diet.”
Gonzalez’s study uncovered another layer of complexity. Participants following the same diet often experienced markedly different changes in their cholesterol levels.
This suggests that there isn’t a single diet that will help everyone maintain healthy cholesterol levels and that nutritional advice may need to be personalised.
In some cases, genetics could play a role, which has been examined in people eating a standard mixed diet. A few different genes can influence the liver’s ability to clear cholesterol from the blood, for example, or how well it’s absorbed from the food you’re eating.
Gonzalez and his team are now planning to study this in more detail. “We will look at those genes and markers of absorption and synthesis to understand that better,” he says.
Norwitz also believes there’s an open question over how personal factors might influence the risk that high cholesterol actually plays in cardiovascular health.
Because most cholesterol studies focus on people with obesity or diabetes, it can be difficult to tease out how cholesterol behaves in other people.
“It’s not that cholesterol isn’t important,” he says. “But it does absolutely need to be taken into the broader context of a person’s health profile and not be looked at through the keyhole.”
Cholesterol clearly has more secrets to give up and it may be some time before researchers can explain every twist in its story.
In the meantime, the best approach is the boring but reliable one: limit saturated fat, load up on fibre and healthy oils – and, yes, you can still enjoy your morning eggs.
Measure your cholesterol
The most accurate way to check your cholesterol is with a blood test. Some clinics and pharmacies offer quick finger-stick tests that give results in minutes, but most require a blood sample from your arm after fasting for 9–12 hours.
Your results will show levels of ‘bad’ low-density lipoprotein (LDL) cholesterol, which can build up in arteries, and ‘good’ high-density lipoprotein (HDL) cholesterol, which helps remove it.
A total cholesterol reading combines both, plus some of your triglycerides – another type of blood fat linked to heart disease.
According to Johns Hopkins University, in the US, healthy LDL levels in adults are below 100 milligrams per deciliter (mg/dL). Levels between 160–189mg/dL are high, and over 190mg/dL may require treatment.
Levels below 40mg/dL are classed as very low. It’s unclear if this is harmful, although some studies suggest possible links to depression and diabetes.
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