Healthy fats: which to eat and which to avoid

Fat is not the enemy

The idea that "fat makes you fat and clogs your arteries" dominated nutrition for decades and turned out to be a misdirected approach. When people cut fat, the industry replaced it with sugar and refined starches in "light" products, and health did not improve. Today the evidence is clear: fat is an essential macronutrient — needed to absorb vitamins, make hormones and protect organs — and many fats are beneficial. The right question is not "how much fat" but "what TYPE of fat".

The three types of fat

Simplifying, there are three big families that behave very differently in your body:

• Unsaturated (mono and poly): the good ones. Olive oil, avocado, nuts, seeds, oily fish. They improve cardiovascular health.
• Saturated: to moderate. Fatty meats, butter, aged cheeses, cured meats, coconut and palm oil, pastries. Neither demon nor free pass.
• Trans (industrial): to avoid. Partially hydrogenated oils in some ultra-processed foods and commercial fried food. The only clearly harmful ones.

Unsaturated fats: the ones to prioritize

They are the foundation of a healthy diet. Monounsaturated fats (extra virgin olive oil, avocado, most nuts) and polyunsaturated fats (omega-3 from oily fish, walnuts and flax; omega-6 from seeds and vegetable oils) improve your cholesterol profile and reduce cardiovascular risk, especially when they replace saturated fats or sugars. The PREDIMED trial (Estruch et al., 2018), one of the most solid nutrition studies, showed that a Mediterranean diet rich in extra virgin olive oil and nuts prevents heart attacks and strokes. It is no coincidence that the Mediterranean diet revolves around these fats.

Saturated fat: neither demon nor free pass

It is the most misunderstood type. For years it was blamed for everything; later, some headlines "rehabilitated" it completely. The truth is in the middle. The Cochrane review by Hooper et al. (2020) found that reducing saturated fat and replacing it with unsaturated fat lowers cardiovascular events, and the American Heart Association (Sacks et al., 2017) recommends limiting it. The key nuance is the replacement: swapping saturated fat for unsaturated improves health; swapping it for sugar or refined flours does not. In practice: enjoy good cheese or a little butter without guilt, but let most of your fat come from unsaturated sources.

Trans fats: the only truly bad ones

If there is one fat to avoid without nuance, it is industrial trans fat. It is created by partially hydrogenating vegetable oils to make them solid and long-lasting, and it is (or was) in industrial pastries, low-quality margarines, commercial fried food and ultra-processed products. Its effect on health is doubly bad: it raises LDL cholesterol and lowers HDL, and it clearly increases cardiovascular risk (Mozaffarian et al., 2006). The good news is that many countries have restricted or banned them, but it pays to keep checking labels: run from any product listing "partially hydrogenated oils". Learn to spot them in how to read labels.

Does fat make you fat? How much to eat?

Fat does not fatten more than other calories; it simply packs more energy into less volume (9 kcal per gram, versus 4 for protein and carbohydrate). That makes it easy to overconsume — a generous glug of oil adds calories fast — but it does not make it "fattening". Very low-fat diets are neither necessary nor superior for losing weight. As a guideline, 25-35% of your calories from fat, prioritizing unsaturated sources, is a practical, healthy range. The essentials are quality and fitting it into your total calories; adjust the split with the macro calculator.

Choosing good fats is simple when you can actually see what you eat. With Renzy you photograph your meals and instantly see how much fat you are having and how it fits your day's calories, without weighing anything. That way you can prioritize olive oil, avocado or fish, moderate the saturated stuff and spot the ultra-processed, making decisions with data instead of guesswork.