Matières grasses nuisibles exposées : les aliments à éviter pour un cœur en meilleure santé

Not all dietary fats are the same. Some are widely regarded as part of a balanced diet, while others — the fats health organizations most often advise keeping low — are what people usually mean by 'unhealthy fats'. This tag page brings together the essentials in one place: what unhealthy fats are, which types raise the most concern, how they may affect health, where they commonly appear in everyday foods, and which simple swaps can help shift the balance. Related articles exploring parts of this topic in more depth are collected below.

What Are Unhealthy Fats?

In nutrition conversations, 'unhealthy fats' is a broad shorthand for the types of fat most often linked with negative health outcomes when consumed in excess. There is no single official definition, but in practice the term almost always refers to two categories: trans fats and — when eaten in large amounts — saturated fats. Because it is shorthand rather than a precise classification, the way the term is used can vary from one source to another.

The label matters because it highlights a key principle in mainstream nutrition guidance: the type of fat in the diet may influence health differently than the total amount of fat. Public health bodies such as the NHS and Harvard Health focus less on total fat intake and more on the balance between fat types — encouraging people to keep certain fats low and to favour unsaturated fats where possible. The information on this page is general education, not personal medical advice.

The Main Types of Unhealthy Fats

Two fat types account for nearly all of the concern around unhealthy fats. Understanding where each comes from — and how they behave in food — makes them much easier to spot on a label or a menu.

Trans Fats

Trans fats occur in two forms: small amounts found naturally in some animal products, and industrially produced trans fats created when liquid vegetable oils are turned into solid fats through a process called partial hydrogenation. The industrial form is the one that raises the most concern. It was widely used to give processed foods a longer shelf life and a firmer texture, and it is the fat type most consistently associated in research with unfavourable cholesterol changes. Many countries have since restricted or banned artificial trans fats, but small amounts may still appear in some fried and packaged foods, which is why labels are still worth checking.

Saturated Fats

Saturated fats occur naturally in foods such as butter, cheese, cream, fatty cuts of meat, lard and some tropical oils, including coconut oil. Unlike trans fats, they are not treated as something to eliminate — they are simply present in many everyday foods. Most guidance from health authorities recommends limiting them rather than cutting them out completely, and replacing part of the saturated fat in the diet with unsaturated fats where possible. A useful visual cue: fats that are solid at room temperature, such as butter and lard, tend to be higher in saturated fat, while most liquid oils are higher in unsaturated fat.

How Unhealthy Fats May Affect Your Health

Research examining dietary patterns consistently connects high intakes of trans fats — and, to a lesser degree, excess saturated fat — with raised LDL ('bad') cholesterol in the blood. Because raised LDL cholesterol is a well-established risk factor for cardiovascular disease, keeping these fats low sits at the centre of most mainstream dietary guidance for heart health.

Beyond cholesterol, diets high in unhealthy fats have also been associated in research with an increased risk of heart disease and stroke, and with insulin resistance and type 2 diabetes. These are population-level associations rather than predictions for any individual: overall diet quality, body weight, activity levels and genetics all play a part. If you have specific health concerns or a family history of heart disease, a healthcare professional can help you interpret this guidance for your own situation.

Common Food Sources of Unhealthy Fats

Unhealthy fats rarely announce themselves on a plate. They appear most often in processed and prepared foods, where fats are used for texture, flavour and shelf life. Familiar examples include:

• Deep-fried foods, such as fried chicken, chips and battered takeaway items
• Commercially baked goods, including cakes, pastries, biscuits and doughnuts
• Processed snack foods, such as crisps, some crackers and coated savoury snacks
• Fatty and processed meats, including sausages, bacon and salami
• Hard margarines, shortening and some vegetable-based spreads
• Some ready meals, frozen coated foods and takeaway dishes

Because these fats are often baked into a biscuit or blended into a sauce rather than sitting visibly on the plate, a single dish can contain far more of them than it appears to. That is one reason food labels, covered below, are such a practical everyday tool.

Good Fats vs. Unhealthy Fats: What's the Difference?

The simplest way to compare the two sides is to look at the fat types themselves rather than at individual foods. Unsaturated fats — found in plant oils, nuts, seeds and oily fish — are the fats nutrition guidance generally encourages, while trans fats and excess saturated fat are the ones most advice suggests keeping low.

Characteristics of Unhealthy Fats

• Typically solid at room temperature, like butter, lard and hard margarine
• Trans fats usually come from partially hydrogenated oils used in food processing
• Strongly associated in research with raised LDL ('bad') cholesterol
• Recommended to be kept as low as possible by mainstream health guidance

Characteristics of Healthier Fats

• Mostly unsaturated, and usually liquid at room temperature
• Found in foods such as olive oil, nuts, seeds, avocado and oily fish
• Commonly recommended by health organizations as part of a balanced diet
• Plant sources such as nuts and seeds also contribute other useful nutrients

Healthier Fat Choices and Simple Swaps

Shifting the balance of fats in your diet does not require a complete overhaul. Small, repeatable changes tend to be the most sustainable, and many commonly suggested swaps are surprisingly modest. It helps to start from a short list of fat sources that health organizations most often recommend:

• Olive oil — an unsaturated staple for cooking, dressings and drizzling
• Oily fish, such as salmon, mackerel and sardines — the main dietary source of omega-3 fats
• Nuts, such as walnuts and almonds — unsaturated fats alongside protein and fibre
• Seeds, such as flaxseed, chia and sunflower seeds
• Avocado — a whole-food source of predominantly unsaturated fat

If you don't regularly eat oily fish, our DHA and EPA omega-3 supplements offer another way to include these particular fats in your routine.

Plant-based fat sources earn their place for reasons beyond their fat profile: nuts, seeds and their oils also contribute other nutrients, including vitamin E.

Typical swaps worth considering include using olive or rapeseed oil for most cooking instead of butter, grilling or baking instead of deep-frying, reaching for unsalted nuts rather than crisps, and comparing labels on packaged baked goods. Each change is small on its own, but together they can noticeably reshape the overall pattern of fats in your diet.

Reading Food Labels and Practical Limits

Food labels are the most practical tool for spotting unhealthy fats. On the nutrition panel, compare the saturated fat figure between similar products — differences can be significant. Trans fat is listed separately in some countries; where it is not, the ingredient list does the work. A few practical checks include:

• Comparing the saturated fat values of similar products per serving
• Scanning ingredient lists for 'partially hydrogenated' or 'hydrogenated' oils
• Favouring products where unsaturated oils, such as olive or rapeseed oil, appear early in the ingredients
• Checking your national health service's published guidance for daily saturated fat limits

Health organizations such as the NHS and Harvard Health publish clear guidance on saturated fat intake and on keeping trans fats as low as possible. Exact figures vary between countries and individual circumstances, so rather than memorizing a single number, the label checks above combined with official national guidance will give the most accurate picture. If you have been given specific dietary targets — for example, to help manage cholesterol — a registered dietitian can help you turn label reading into a realistic daily plan.

Common Questions About Unhealthy Fats

Which Fats Are Considered the Most Unhealthy?

Industrially produced trans fats top nearly every list, which is why many countries have restricted them and why guidance is to keep intake as low as possible. Large amounts of saturated fat come a close second: they are a natural part of many foods, but most health authorities recommend limiting them and swapping part of them for unsaturated fats.

Are Eggs High in Unhealthy Fats?

Most of the fat in a typical egg is unsaturated, although the yolk also contains some saturated fat and dietary cholesterol. Whether eggs fit into a lower-saturated-fat eating pattern depends on the diet as a whole, portion sizes and personal health circumstances. If you have been advised to watch your cholesterol, it is a question worth raising with your doctor or a dietitian rather than deciding in isolation.

Which Foods Most Often Contain Unhealthy Fats?

Fried foods, packaged baked goods, processed snacks, fatty processed meats and products made with hydrogenated or partially hydrogenated oils are the usual suspects. To check a specific product quickly, look at the saturated fat figure on the nutrition panel and scan the ingredient list for hydrogenated oils.

Understanding unhealthy fats comes down to three practical ideas: know the two fat types that raise concern, recognize the foods where they most often hide, and use labels to compare products before you buy. The articles collected under this tag explore individual parts of the topic in more depth, from specific food groups to label reading and everyday swaps. This page offers general education rather than personal advice — for guidance tailored to your health, speak with a qualified healthcare professional.