Healthy Fats Explained: Good Fats, Bad Fats and Everything In Between

Why your body needs fat

Fat is not the dietary villain it was made out to be in the low-fat era of the 1980s and 90s. It is an essential macronutrient — every cell membrane in your body contains fat, your brain is roughly 60% fat by dry weight, and you cannot absorb vitamins A, D, E or K without it. Fat also provides 9 kcal per gram, making it the most energy-dense macronutrient, which is exactly why quality and quantity both matter.

The NHS Eatwell Guide recommends that fat contributes around 35% of total dietary energy. On a 2,000 kcal per day intake, that is approximately 78 g of fat. The goal is not to eat less fat at any cost — it is to eat the right types of fat in reasonable amounts, and to understand what 'right' actually means.

General information only — this guide does not replace personalised advice from a dietitian or GP.

Saturated vs unsaturated fat: the critical difference

All dietary fats are combinations of fatty acid chains, classified by their chemical structure.

Saturated fats have no double bonds in their carbon chains — they are 'saturated' with hydrogen. They are solid at room temperature (think butter, lard, coconut oil, the fat on meat). The Scientific Advisory Committee on Nutrition (SACN) recommends saturated fat contributes no more than 10% of total energy — roughly 30 g per day for men and 20 g per day for women. Exceeding this consistently raises LDL ('bad') cholesterol, a well-established cardiovascular risk factor (strong evidence).

The main sources in the UK diet are:

• Full-fat dairy (cheese, butter, cream)
• Fatty and processed meat (bacon, sausages, pies)
• Coconut oil and palm oil
• Ultra-processed baked goods (pastries, biscuits, cakes)

Unsaturated fats carry one or more double bonds and are liquid or soft at room temperature. They divide into two families:

• Monounsaturated (MUFAs): oleic acid is the dominant example. Found in olive oil, avocado, almonds, and cashews. These fats maintain or gently lower LDL without reducing HDL, and form the fat foundation of the Mediterranean diet — the highest-evidence dietary pattern for cardiovascular health.
• Polyunsaturated (PUFAs): multiple double bonds; include the essential omega-3 and omega-6 families your body cannot synthesise. Sunflower oil, walnuts, and oily fish are rich sources.

The decisive intervention is replacement — swapping saturated fat for unsaturated fat — not simply removing fat from the diet. When saturated fat is replaced with refined carbohydrate (as happened during the low-fat boom), cardiovascular outcomes do not improve.

Omega-3 and omega-6: the essential fatty acids

Omega-3 and omega-6 fatty acids are 'essential' because the body cannot make them; they must come from food.

Omega-3:

• ALA (alpha-linolenic acid): the plant form, found in flaxseed, chia seeds, walnuts, and rapeseed oil. The body converts ALA to the longer-chain EPA and DHA, but conversion is inefficient (roughly 5–10% for EPA; much lower — under 4% — for DHA).
• EPA and DHA: the long-chain forms found directly in oily fish. These are the forms with the strongest evidence for reducing triglycerides, supporting brain function, and reducing cardiovascular event risk (moderate-strong evidence). The NHS recommends 2 portions of oily fish per week (salmon, mackerel, sardines, herring, fresh tuna), with at least one being oily — this delivers around 450–900 mg EPA+DHA per day.

Omega-6:

• LA (linoleic acid): abundant in sunflower oil, corn oil, seeds, and nuts. Converted to arachidonic acid in the body. Omega-6 supports healthy cell function and has a mild LDL-lowering effect when used in place of saturated fat.
• UK diets tend to be adequate in omega-6 but lower in omega-3 — oily fish consumption falls well short of the 2-portions-per-week recommendation for most adults.

For those who do not eat oily fish, algae-based DHA+EPA supplements provide the direct long-chain form without the mercury considerations associated with high-dose fish oil. See relevant supplements pages for evidence-graded options.

Best sources of healthy fats

Here are the top unsaturated fat sources to prioritise, with approximate fat content per typical serving:

Food	Serving	Total fat	Key type
Extra-virgin olive oil	1 tbsp (14 g)	14 g	MUFA (oleic acid)
Avocado	½ medium (75 g)	11 g	MUFA
Salmon (grilled)	120 g fillet	13 g	Omega-3 EPA+DHA
Mackerel (grilled)	120 g fillet	19 g	Omega-3 EPA+DHA
Mixed nuts	Small handful (30 g)	17 g	MUFA + PUFA mix
Walnuts	6 halves (30 g)	19 g	PUFA (ALA + LA)
Chia seeds	2 tbsp (28 g)	9 g	PUFA (ALA)
Flaxseed (ground)	1 tbsp (10 g)	4 g	PUFA (ALA)
Almonds	Small handful (30 g)	15 g	MUFA
Rapeseed oil	1 tbsp (14 g)	14 g	MUFA + ALA

Rapeseed oil (the basis of most UK 'vegetable oil') is an excellent, affordable everyday cooking oil — high in MUFAs and a useful ALA source. Extra-virgin olive oil is ideal for dressings and lower-heat cooking; for high-heat cooking, refined olive oil or rapeseed oil are better choices due to their higher smoke points.

Trans fats — the one fat to actively avoid

Artificial trans fats — created by partially hydrogenating vegetable oils — are the single dietary fat type with near-universal scientific condemnation. They raise LDL cholesterol and lower HDL ('good') cholesterol simultaneously, creating the worst possible cardiovascular profile (strong evidence). The UK food industry has largely removed artificial trans fats under Food Standards Agency guidance, but they can still appear in some imported foods and older ultra-processed products. Check ingredient labels for 'partially hydrogenated' oils — if listed, avoid the product.

Naturally occurring trans fats (found in small amounts in dairy and ruminant meat) appear to behave differently and are not subject to the same concerns at typical dietary levels.

Fat and weight loss: separating myth from mechanism

The fear that 'eating fat makes you fat' was a costly public health mistake. Fat does not trigger weight gain independently — a sustained calorie surplus does. That said, at 9 kcal per gram, fat is calorie-dense, so high-fat foods add calories quickly if portions are not considered.

The evidence on dietary fat composition and fat loss:

• Low-fat vs low-carb vs Mediterranean: multiple meta-analyses find no clinically meaningful difference in long-term weight loss between dietary patterns when calories and protein are matched (moderate evidence). Adherence is the decisive variable.
• Satiety: fat slows gastric emptying and triggers satiety hormones, which helps manage hunger. Cutting fat too aggressively can increase hunger and undermine adherence.
• Nuts — the paradox: observational studies consistently show nut consumers have lower body weight despite nuts being calorie-dense. Likely mechanisms include satiety, partial calorie excretion, and displacement of other foods. A small handful (30 g) per day is supported by cardiovascular and weight data.

For a personalised calorie and fat target, use the macro calculator or calorie target tool.

How much fat per day: practical targets

Based on NHS Eatwell Guide and SACN guidance, a practical framework for most adults:

• Total fat: ~35% of energy (approximately 70–90 g/day on 1,800–2,300 kcal)
• Saturated fat: ≤10% of energy (≤20 g/day women; ≤30 g/day men)
• Oily fish: 2 portions per week for omega-3 EPA+DHA
• Trans fats: as close to zero as possible

There is no specific government target for unsaturated fat, but the implicit guidance is for it to dominate your fat intake — prioritise olive oil, avocado, nuts, seeds, and oily fish over butter, cream, and processed meat.

If you are following a programme focused on fat loss, muscle growth, or body recomposition, fat targets shift in context of your total macros. A coach builds the exact split around your goal, food preferences, and training — if you want that done for you, book a free consultation.

Smart swaps to improve your fat quality

You do not need to overhaul your diet overnight. These targeted swaps shift your fat profile without sacrifice:

• Butter → extra-virgin olive oil or rapeseed oil for cooking and spreading (saves ~3 g saturated fat per tablespoon)
• Crisps and pastries → mixed nuts for snacking (swaps saturated/trans for MUFA+PUFA)
• Chicken breast only → oily fish twice per week to hit your omega-3 target
• Full-fat processed cheese → avocado or nut butter on toast
• Cream-based sauces → olive oil + garlic + lemon — fewer calories, far better fat profile
• Coconut oil → rapeseed or olive oil — coconut oil is ~90% saturated fat, not the health food marketing suggests
• Deep-fried sides → air-fried or oven-roasted — see cooking methods guide for the calorie maths

These swaps align with Mediterranean diet principles — the dietary pattern with the strongest evidence base for both heart health and longevity.

Putting it all together: your healthy-fat verdict

Fat is essential, not optional. The goal is smart fat: prioritise unsaturated sources (olive oil, oily fish, nuts, avocado, seeds), keep saturated fat within SACN limits, eliminate artificial trans fats, and get 2 portions of oily fish per week for EPA+DHA. Cutting all fat in pursuit of weight loss is a 1990s mistake — cutting the wrong fats while keeping calories in check is where the evidence points.

Understand how fat fits into your total macronutrients, cross-reference with complex carbs, and if you are serious about body composition, pair this knowledge with a structured programme. The best nutrition plan is the one a coach builds around your real life, food preferences, and goals — book a free consultation with Bez and we will build yours.

General information only — not a substitute for personalised dietetic or medical advice.