Good Fats vs Bad Fats: What Every UK Shopper Actually Needs to Know

Fat was wrongly blamed for heart disease for four decades, and that mistake may still be shaping what goes in your trolley. The distinction between good fats and bad fats is the detail that matters: unsaturated fats from oily fish, olive oil, nuts, and avocados actively support cardiovascular health, while trans fats and excess saturated fat are the ones UK health authorities recommend limiting.

Why All Fat Got a Bad Name (and Why the Science Has Moved On)

From the 1970s onward, low-fat dietary guidelines dominated UK and US public health advice. Food manufacturers responded by stripping fat from products and replacing it with sugar, a substitution that arguably made the nation's diet worse, not better. The NHS and independent researchers now recognise that fat type matters far more than fat quantity alone.

The British Heart Foundation reflects the current scientific consensus: replacing saturated fat with unsaturated fat, rather than simply cutting all fat, is the more meaningful strategy for heart health. It's a subtle but important shift that changes how you should interpret food labels on your next Sainsbury's or Tesco shop.

Unsaturated Fats: The Ones Worth Prioritising

Unsaturated fats divide into two groups, monounsaturated and polyunsaturated, and both earn their place in a healthy diet.

Monounsaturated fats are found in olive oil, rapeseed oil, avocados, and most nuts. They help maintain healthy LDL cholesterol levels. Extra virgin olive oil, stocked in every major UK supermarket from Waitrose to Aldi, is one of the most practical ways to increase your intake. Rapeseed oil, widely sold in the UK as plain 'vegetable oil', offers a similarly favourable fat profile at a lower price point and is well suited to higher-heat cooking.

Polyunsaturated fats include omega-3 and omega-6 fatty acids, which your body cannot produce on its own. Omega-3s carry the strongest evidence: NHS guidance recommends at least two portions of fish per week, one of which should be oily. Mackerel, salmon, sardines, and fresh tuna all qualify. Budget-friendly tinned mackerel from John West or Princes delivers meaningful omega-3 even on a tight weekly shop. For those who don't eat fish, walnuts, ground flaxseed, and chia seeds offer a plant-based alternative, though the conversion to active omega-3 in the body is less efficient than from marine sources.

Most people in the UK already consume sufficient omega-6 (found in sunflower oil and many processed foods), so the practical focus should be on increasing omega-3 rather than adding more omega-6.

Saturated Fat: A More Nuanced Picture Than You Might Expect

NHS guidance sets the daily saturated fat limit at 30g for men and 20g for women. Saturated fat is found predominantly in animal products: butter, hard cheese, full-fat dairy, fatty cuts of meat, and processed meats such as sausages, bacon, and salami.

The evidence here is less clear-cut than older guidelines suggested. Research published in the British Medical Journal and elsewhere indicates that the health impact of saturated fat depends partly on what replaces it in the diet. Swapping saturated fat for refined carbohydrates, as many low-fat diets inadvertently encouraged, does not reduce cardiovascular risk. Swapping it for unsaturated fat does.

Some saturated fat sources also appear less harmful than others. Full-fat dairy, yoghurt, milk, and cheese, shows a more neutral or even modestly protective association in several large observational studies, which is part of why blanket 'avoid all saturated fat' advice has softened in recent years. That said, current NHS guidance still supports choosing lower-saturated-fat options where practical, particularly for processed and cured meats.

In everyday terms: a slice of mature cheddar in a sandwich is unlikely to harm an otherwise balanced diet. A daily fry-up featuring back bacon, sausages, and a buttered white roll is a different matter. Overall dietary pattern counts for more than any single food.

Trans Fats: The One Type to Genuinely Avoid

If there is a clear villain in the fat story, it is industrially produced trans fats, partially hydrogenated vegetable oils once used widely in UK biscuits, pastries, and margarines to extend shelf life. Trans fats raise LDL ('bad') cholesterol and simultaneously lower HDL ('good') cholesterol, a uniquely damaging combination with strong links to cardiovascular disease.

The better news for UK shoppers: voluntary industry action and Food Standards Agency pressure have dramatically reduced trans fats in UK foods over the past two decades. Most major supermarkets and manufacturers, including Marks & Spencer, Tesco own-brand, and Greggs, have committed to eliminating or minimising them. It is still worth checking the ingredients list for 'partially hydrogenated oil' or 'hydrogenated vegetable fat' when buying imported biscuits, certain cheaper baked goods, or takeaway pastry products.

Small amounts of naturally occurring trans fats exist in beef and dairy. These appear to behave differently to industrial trans fats and are not a health concern at typical dietary levels.

How to Read UK Fat Labels Quickly

UK nutrition labels use the traffic light system, making fat comparisons relatively straightforward in the supermarket aisle. Per 100g, the thresholds are:

• Green (low): 3g or less total fat; 1.5g or less saturated fat
• Amber (medium): 3–17.5g total fat; 1.5–5g saturated fat
• Red (high): more than 17.5g total fat; more than 5g saturated fat

A red light for total fat does not automatically signal a poor food choice, extra virgin olive oil and tinned salmon would both score red for total fat, yet both are nutritionally valuable. Use the traffic light system as a guide for comparing processed foods rather than as a reason to avoid whole foods with a naturally high fat content. When choosing between two similar ready meals or snacks, the option with fewer red lights and lower saturated fat per serving is a reasonable rule of thumb.

Practical Swaps That Make a Real Difference

A few consistent changes at the supermarket and in the kitchen shift your fat balance meaningfully without requiring a dietary overhaul:

• Switch from butter to extra virgin olive oil or a rapeseed-based spread for everyday cooking and spreading.
• Add a tin of mackerel, sardines, or salmon to your weekly shop, Aldi, Lidl, and most UK supermarkets stock these for under $1.50 a tin.
• Replace crisps and biscuits as a snack with a small handful of unsalted mixed nuts (walnuts and almonds are particularly good choices for fat quality).
• Choose leaner cuts of meat for midweek meals and trim visible fat before cooking; save higher-fat cuts like lamb shoulder for occasional use.
• Use full-fat plain Greek yoghurt instead of cream in sauces and dressings, you get some saturated fat alongside protein, probiotics, and fewer calories overall.
• When buying spreads, choose products labelled as olive oil– or rapeseed-based rather than those listing 'hydrogenated' ingredients.