Two types of dietary fat are consistently linked to harm: artificial trans fats and, in excess, saturated fats. But the story is more nuanced than “fat is bad.” The type of fat you eat matters enormously, and so does what you eat instead when you cut a fat out of your diet. Swapping saturated fat for the wrong replacement can be just as unhelpful as eating too much of it in the first place.
Artificial Trans Fats: The Worst Offender
Industrial trans fats are created when manufacturers pump hydrogen into liquid vegetable oils to make them solid and shelf-stable, a process called partial hydrogenation. These fats raise LDL (“bad”) cholesterol while simultaneously lowering HDL (“good”) cholesterol, a double hit that no other common dietary fat delivers. They also promote inflammation and interfere with your body’s ability to use insulin effectively. Animal research shows trans fats suppress key proteins in the insulin signaling pathway, contributing to insulin resistance, a precursor to type 2 diabetes.
Because the evidence against them is so strong, governments around the world have moved to ban or restrict them. As of May 2025, nearly 60 countries have best-practice elimination policies in effect, covering 46% of the global population. The United States effectively banned partially hydrogenated oils from the food supply in 2018, and the World Health Organization has called for their global elimination.
Where Trans Fats Still Show Up
Despite regulations, artificial trans fats haven’t vanished entirely. The WHO identifies several food categories that still commonly contain them: margarine, vegetable shortening, Vanaspati ghee (widely used in South Asia), fried foods, and commercially baked goods like crackers, biscuits, and pies. Street food and restaurant-fried items are particularly common sources in countries without strict regulations. If you travel internationally or buy imported packaged foods, check labels for “partially hydrogenated” oils in the ingredient list.
A small amount of trans fat also occurs naturally in meat and dairy from cows, sheep, and goats. These ruminant trans fats have a slightly different chemical structure, and some researchers have wondered whether they’re less harmful than the industrial version. A USDA evidence review found only limited evidence to support a meaningful biological difference between the two, and even that limited data only emerged when ruminant trans fats were consumed at seven to ten times normal dietary levels. At the small amounts you’d get from a normal diet that includes meat and dairy, naturally occurring trans fats are not a major concern.
Saturated Fat: Harmful in Excess, Not in Isolation
Saturated fat is more complicated. Found in butter, cheese, red meat, coconut oil, and palm oil, it raises LDL cholesterol and promotes inflammation. Studies in people with high cholesterol have shown that diets low in saturated fat reduce C-reactive protein, a key marker of inflammation in the blood. The American Heart Association recommends keeping saturated fat below 6% of your total daily calories, which works out to about 13 grams on a 2,000-calorie diet.
But here’s the critical detail that gets lost in headlines: the health impact of cutting saturated fat depends almost entirely on what replaces it. A 2017 American Heart Association presidential advisory laid this out clearly. Replacing just 5% of your daily calories from saturated fat with polyunsaturated fats (found in fish, walnuts, flaxseed, and vegetable oils like soybean and sunflower) was associated with a 25% lower risk of coronary heart disease. Replacing it with monounsaturated fats (olive oil, avocados, most nuts) lowered risk by 15%. Whole grains as a replacement lowered risk by 9%.
Replacing saturated fat with refined carbohydrates and added sugars, on the other hand, showed essentially no benefit at all. The risk of heart disease stayed flat, with a statistically insignificant 1% increase. Randomized controlled trials confirmed the same pattern: swapping saturated fat for polyunsaturated vegetable oils reduced cardiovascular disease by roughly 30%, a reduction comparable to what statin medications achieve. But trials where people replaced saturated fat mainly with carbohydrates showed no significant reduction in cardiovascular events.
This is why the low-fat diet craze of the 1990s, which led food manufacturers to replace fat with sugar and refined starch, failed to improve heart disease rates. The fat you remove matters, but so does what takes its place.
Not All Saturated Fats Are Identical
Saturated fat is actually a family of molecules with different chain lengths, and they don’t all behave the same way in your body. Shorter-chain saturated fats like myristic acid (found in dairy fat and coconut oil) are the ones most clearly linked to raising total and LDL cholesterol. Palmitic acid, the most common saturated fat in the Western diet (abundant in palm oil and meat), has a less clearly defined relationship with heart disease risk. Stearic acid, a long-chain saturated fat found in cocoa butter and beef tallow, does not appear to raise cholesterol or increase cardiovascular disease risk based on clinical evidence.
This doesn’t mean you should ignore saturated fat from any particular source. The foods you eat contain a mix of these fatty acids, and teasing apart their individual effects in a real diet is difficult. But it does help explain why some saturated-fat-rich foods (like dark chocolate, which is high in stearic acid) seem to have a neutral or even favorable effect on blood lipids, while others (like butter, high in myristic and palmitic acid) tend to push cholesterol upward.
What to Eat Instead
The strongest evidence points to polyunsaturated fats as the most beneficial replacement for harmful fats. These include omega-3 fatty acids from fatty fish (salmon, mackerel, sardines), walnuts, and flaxseed, as well as omega-6 fatty acids from soybean oil, sunflower oil, and corn oil. Monounsaturated fats from olive oil, avocados, and almonds are the next best option.
Whole grains offer a modest benefit as a replacement for saturated fat, but refined carbohydrates do not. This is a practical point worth remembering: if you order a salad instead of a burger but load it with croutons and fat-free dressing sweetened with sugar, you haven’t necessarily improved your cardiovascular outlook. The goal isn’t to eat less fat overall. It’s to shift the type of fat you eat toward unsaturated sources while keeping refined carbohydrates from filling the gap.
A useful rule of thumb: fats that are liquid at room temperature (olive oil, canola oil, fish oil) are generally unsaturated and protective. Fats that are solid at room temperature (butter, lard, shortening, the white fat on a steak) are generally saturated or trans fats. Coconut oil is an exception that stays solid despite being plant-based, and it is high in saturated fat, though its specific fatty acid profile makes its health effects a matter of ongoing debate.