Do you feel virtuous when you order a “slimming” skinny latte? Have you swapped oozy brie for reduced-fat cheddar to protect your heart? Have you ditched delicious olive oil in favour of a low-fat frying spray? Would it surprise you to learn that all these decisions are probably a mistake?
Everything that we know about fat is being challenged by the latest science. And it could change the way you eat. Like short skirts and kitten heels, fats have gone in and out of fashion over the decades. A 1918 nutrition guide for children insisted that fat was the most important nutrient of all. Bacon, it declared, should always be fried with bread or potatoes lest any precious fat be left in the pan.
Delicious, yes. Dangerous? Perhaps. During the 1950s and ‘60s US researcher Ancel Keys became one of the first scientists to look at dietary patterns around the world. He noted that the Japanese diet was generally lower in fat, particularly saturated fat, and Japanese people were long-lived and had low rates of heart trouble. He also realised that in Finland, farmers buttered their cheese and many had heart disease. Keys declared cholesterol as the main cause of heart disease – and saturated fats in food were the key reason for elevated cholesterol.
To cut heart disease rates, it was suggested, we should eat a lot less fat overall – obtaining around 30 per cent of our calories from fat – and switch to what he called a Mediterranean diet, exchanging foods rich in saturated animal fats, such as those in butter and lard, for plant-derived unsaturated fats, such as those found in olive oil.
But by the 1980s, a “fat is bad” mantra had taken over. Traditional fats were replaced not by olive oil, but by lab-made fats, sugar and refined carbohydrates. Full-fat milk was out; skimmed was in. Ultra-processed alternatives to butter and cream, such as margarine and low-fat fruit yoghurts – even fat-free cakes and ice-creams – hit the supermarket shelves. But instead of getting thinner, we got fatter and fatter. Had we made a terrible mistake?
Fat is vital
If you grew up in the leotard-loving 1980s, you might still plump for low-fat yoghurt. But fat doesn’t deserve its shady reputation. In fact, it is essential in any healthy, balanced diet.
“Eating low fat used to be the recommendation, but now we know that this can lead to eating a less varied and nutritious diet,” says dietician Priya Tew. “We need some fat in our diets to help us absorb the fat-soluble vitamins A, D, E and K. Fats are also a source of essential fatty acids, which the body cannot make itself.”
And when we ditch fat, we tend to eat more starch, sugar and even less healthy fake fats instead. So if you fancy a little bit of butter on your toast, that’s fine, but don’t overdo it – and read on.
The truth about trans fats
To replicate the creaminess of fat in yoghurt, the food industry introduced processed, laboratory-made “modified starches”. The natural sweetness of milk fat was replaced with sugar. Instead of butter, croissants were filled with synthetic emulsifiers. These additives have been shown to mess with our gut bacteria, which plays a role in weight control.
In 1911, Procter & Gamble developed man-made fats (often described as trans fats) in one of the most monumental changes to the Western diet. Lab-made “Frankenfats”, created from vegetable oils processed with hydrogen, emerged. They became solid at room temperature and lasted a long time without becoming rancid, so the food industry loved them.
But, as Tew points out: “Trans fats are associated in studies with a 16 per cent increased risk of coronary events, a 34 per cent increase in all-cause mortality, a 28 per cent increase in coronary heart mortality, and a 21 per cent increase in risk of heart disease.”
They have also been associated with a greater risk of weight gain. Due to the health risks, they have been largely phased out of ready meals and other products, but can still be found in some processed bakery goods, such as doughnuts and fried foods.
The key message is to eat fats in their natural forms. “Fats found in their natural form in food all individually contribute to health in different ways,” says Tew. “For example, dairy foods contain saturated fats but also vitamins A and D and minerals such as calcium and phosphorus.”
Why low-fat options aren’t always healthiest
Low-fat foods can contain more sugar and additives than higher-fat foods. What’s more, low-fat eating can make us hungrier. “Combining fat with carbohydrates slows down the release of sugars into the bloodstream, helping stabilise blood-sugar levels,” says nutritionist Kim Pearson, whose clinic specialises in weight loss. “Fluctuations promote hunger, cravings and fat storage. Focusing more on dietary fat and less on starchy carbs can help stabilise blood glucose levels.”
When we eat too many carbs, our bodies don’t draw on their fat stores. “The primary role of carbs is to provide energy, so while your diet is focused on them, your body isn’t going to be interested in turning to stored fat for energy.”
So full-fat milk and even butter are back in favour. In fact, many studies show that eating full-fat dairy rather than skimmed milk and reduced-fat cheese is linked to a lower risk of obesity. A 2019 paper in Advances in Nutrition concluded that “whole-fat dairy foods do not cause weight gain, that overall dairy consumption increases lean body mass and reduces body fat, that yogurt consumption and probiotics reduce weight gain, that fermented dairy consumption, including cheese, is linked to lower cardiovascular disease risk, and that yogurt, cheese and even dairy fat may protect against type-2 diabetes”.
Go nuts for nuts and fish
Walnuts and pine nuts are rich in heart-healthy polyunsaturated fat; monounsaturate-rich almonds, pistachios, pecans and hazelnuts are even healthier. Eating nuts has also been shown to lower body fat. A 2019 review published in the journal BMJ Nutrition Prevention and Health reported: “Increasing daily consumption of nuts is associated with less long-term weight gain and a lower risk of obesity in adults.”
The key, says nutritionist Dr Federica Amati, is that we should get our fats from whole, natural foods. Omega 3 fats, as found in oily fish, are known to improve brain and heart health. “Studies indicate that nuts improve cognitive function and lower inflammation markers,” she says.
Unsaturated fat, which includes polyunsaturated fats such as plant-based oils (rapeseed, sunflower oil and peanut oil) and oily fish (think salmon, sardines and mackerel), can decrease bad cholesterol, while also increasing good cholesterol and reducing the risk of heart disease.
But it is the monounsaturated fats such as olive oil that are the undoubted kings of fats. Research shows they could reduce our risk of heart disease, and that adding moderate amounts of extra virgin olive oil to the diet can reduce weight and trim waistlines. According to Dr Amati, extra virgin olive oil, which is rich in inflammation-fighting polyphenols, “outperforms anything else”.
Don’t be scared of a (little) bit of saturated fat
Not all saturated fats are created equal. A 2021 study found no link between the total amount of saturated fat people consumed and their risk of developing heart disease. Writing on news website The Conversation, study co-author Nita Forouhi, a professor of population health and nutrition at the University of Cambridge School of Clinical Medicine, said, “We found that people who ate more saturated fats from red meat were more likely to develop heart disease. But the opposite was true for those who ate more saturated fats from cheese, yoghurt and fish.”
Why should saturated fat from cheese and yoghurt have a different impact on our bodies than the saturated fat in red meat? “Yoghurt and cheese contain vitamin K2 and fermentation products that previous studies have linked to lower heart disease risk,” says Professor Forouhi. “Pentadecanoic acid that is found in proportionally higher amounts in dairy fat is related with lower heart disease risk. On the other hand, a saturated fatty acid called palmitic acid is present in greater amounts in red meat and it is related to greater heart disease risk.”
Steady on, though. “The existing guidelines are that saturated fats should account for less than 10 per cent of our calorie intake,” says Tew. “Men should eat no more than 30g of saturated fat a day, and no more than 75g of total fat, and women no more than 20g of saturated fat and 50g of total fat.”
How metabolism and fat are linked
Even more surprising than the link between high-fat foods and weight control is new research suggesting that our aversion to saturated fats could explain the obesity epidemic. Scientists know that our metabolism – the rates at which we burn calories – has mysteriously dipped over the decades. It was widely assumed this was down to our lazy modern lifestyles, but a study published last month in the journal Nature Metabolism suggests we are not, in fact, moving less. Even so, it found that our metabolisms have fallen by an average of 7.7 per cent in men and 5.6 per cent in women between 1981 and late 2017.
“The proportion of saturated fat in our diets has declined from 90 per cent in the 1920s to less than 20 per cent now,” says the study’s lead author, Professor John Speakman of the University of Aberdeen. He adds that this may be because the densely linked structure of saturated fats means that the body must use more energy to break them up.
So, if saturated fats aren’t all bad, and fats can even help us get and stay slim, what should we eat? Forouhi’s research suggests it’s a good idea to get most of our fats from natural foods like milk, cheese, fish and olive oil. And don’t be afraid of a little bit of butter or red meat – just don’t go crazy.
Your guide to healthy fats
Go ahead
Olive oil
Improves brain and heart health
Oily fish
Good for your brain and good for your heart. Salmon, mackerel, tuna and sardines are rich in heart-healthy omega-3s
Plant oils
Corn oil, safflower oil, sesame oil and sunflower oil all contain polyunsaturated fats
Avocados
Millennials’ favourite breakfast food comprises mainly unsaturated fats (specifically, monounsaturated)
Nuts
All are healthy – but high in calories
Eat in moderation
Butter
A little bit of butter is fine. Use sparingly
Tropical oils (coconut oil, palm oil, cocoa butter)
These are high in saturated fat, so use only sparingly, as they are not as healthy as monounsaturated and polyunsaturated fats can be
Red meat
Eat in moderation
Full-fat milk, cheese and yoghurt
Contains some saturated fat, but the heart-healthy kind
Avoid
Trans fats
Watch out for ‘hydrogenated’ or ‘partially hydrogenated’ on the label. Trans fats can increase the risk of inflammation and drive heart disease and type 2 diabetes. They are present in fried foods, hard margarines and many shop-bought snacks, which should be avoided as far as possible
Low-fat dairy
These products are often full of sugar and low-fat eating can make us hungrier