You may have seen bad press surrounding dietary fats, but how much of it is true? Fats are an essential part of our diet, particularly when it comes to absorbing other vital nutrients and helping our bodies to function properly. The difficulty is that not all fats are the same, and when it comes to unsaturated vs saturated fat in particular, there are a few things to consider.
In general, unsaturated fats such as avocados, olive oil, nuts and seeds are the ‘good’ fats we want to include in our diet. These help to support heart and brain health, among other functions. Saturated fat, on the other hand, should be eaten in moderation, with excess levels associated with negative health outcomes.
Here, we’ll further explain the differences between unsaturated vs saturated fat and the functions they serve in the body. And while you're here, check our article on the safety and efficacy of low-fat diets. Plus, if you’re looking for a nutritionally dense diet with plenty of healthy fats, our guide to the Mediterranean diet is a great place to start.
What is dietary fat?
Dietary fat is characterized as the fat we consume from our food, making it different to body fat or blood triglycerides. It is one of three macronutrients (protein, carbohydrates and fats) that are needed for the essential running and function of our bodies.
All fats contain nine calories per gram, but not all fats are as nutritious as others. Polyunsaturated fats, particularly omega-3 and omega-6 fatty acids, are needed for the proper function of our brains and bodies, while monounsaturated fats help us to absorb fat-soluble vitamins such as vitamins A, D, E and K. Some fats, such as saturated fats and trans fats, have been linked to negative health outcomes, including metabolic syndrome (a combination of obesity, diabetes and high blood pressure) and cancer.
What is saturated fat?
Saturated fat is a single bonded carbon chain that is saturated with hydrogen atoms, which means that it is usually solid at room temperature. While the process of hydrogenation turns unsaturated fats into saturated fats (trans fats) by forcing hydrogen into empty spaces on the carbon chain, saturated fats are naturally this way. While eating saturated fat in excess can have negative health outcomes, consuming small amounts of saturated fat in moderation is fine, so there’s no need to completely cut out your favorite foods to avoid it.
Dr Kevin Barrett, a GP at New Road Surgery in Hertfordshire, UK, explains further: “We need to eat some fat because it is important for the absorption of the fat-soluble vitamins A, D, E and K, and is a source of essential fatty acids. Saturated fats in highly processed foods are associated with negative health outcomes, but those from less-processed foods do not have such strong links.”
Some sources of saturated fat include:
- Fatty cuts of meat
- Processed meats, such as sausages or bacon
- Butter, lard and shortening
- Hard cheeses, such as cheddar
- Cream and ice-cream
- Biscuits, cakes and pastries
- Savory snacks, such as crisps, crackers
- Fried foods
- Coconut oil
Overconsumption of saturated fats is one of the leading causes of obesity and related conditions in adults, according to a study in the International Journal of Molecular Sciences. With this in mind, it’s important to be aware of the amount of saturated fat you are consuming, as an estimated 70% of Americans over-consume on their recommended daily amount, according to the USDA. In a 2,000 calorie diet, this equals about 22g of saturated fat a day.
Dr Deborah Lee, from Dr Fox Online Pharmacy, says that the overconsumption of saturated fat can lead to heart problems. “In general, saturated fats are ‘bad fats’,” she says. “These are the fats we should all be eating less of. They tend to be linked to raised bad cholesterol and this increases the risk of atherosclerosis (the deposition of fatty plaques in the arteries), which cause heart disease, including heart attacks and strokes. In general, saturated fat should make up no more than 5-6% of your total daily calorie intake.”
What is unsaturated fat?
There are two types of unsaturated fat: monounsaturated and polyunsaturated. Unsaturated fats can promote ‘good’ HDL cholesterol levels in your body and reduce levels of ‘bad’ LDL cholesterol, which can accumulate in veins and arteries and cause high blood pressure.
These fats come from plant-based sources and include:
- Olive and canola oils
- Nuts, nut butters and nut oils
- Seeds, such as pumpkin or sesame seeds
A 2021 study in the Nutrients journal indicates that consumption of monounsaturated fatty acids can lead to positive cardiometabolic outcomes. Another study in the Annals of the New York Academy of Science also found that the promotion of HDL (good) cholesterol may also reduce inflammation in the body, giving it potentially cardioprotective qualities. As monounsaturated fats promote HDL (good) cholesterol, it is important to ensure you are consuming enough in order to support your heart health.
These fats come from plant-based sources and include omega-3 and omega-6 fatty acids
Sources of omega-3 include:
- Oily fish, such as mackerel and salmon
- Seeds such as flaxseed or chia seeds
- Nuts, such as walnuts
- Legumes, such as soybeans
“The omega-3 acids in oily fish are EPA (eicosapentaenoic acid) and DHA (docosahexaenoic acid),” explains Dr Lee. “Although the human body can synthesize EPA and DHA, it is not efficient at doing this, meaning levels tend to be low. So, making sure you take in enough omega-3, either through the diet or by having an omega-3 supplement, is important. Omega-3 fatty acids are thought to help prevent the onset of heart disease by helping to lower levels of triglycerides (fat in the blood), lowering blood pressure, and improving blood circulation.”
Sources of omega-6 include:
- Meat, fish and poultry
- Legumes, such as soybeans
- Sunflower oil
“Omega-6 fatty acids are essential fatty acids obtained from the diet, which are mainly used to give you energy,” explains Dr Lee. “The health benefits of omega- 6 are less clear. We are recommended to eat more omega-3 than omega-6. Omega-6 is found in meat, poultry, fish, eggs, soybean oil, corn oil, walnuts, almonds, and cashew nuts, for example.”
A review in the journal of Biomedicine & Pharmacotherapy tells us that omega-3 and omega-6 need to be consumed in balance with one another. Omega-3 is used to build our cellular structure, and they're also important to keep your immune system working properly. High levels of omega-6 can contribute to the development or worsening of cardiovascular diseases, cancer and inflammatory diseases, but when eaten in balance with omega-3, they serve to lower harmful LDL cholesterol levels, boost protective HDL and help improve insulin sensitivity.
Unsaturated vs saturated fat: Getting the balance right
The USDA guidance recommends 20-35% of your total calories should come from fat. This works out at about 44g-77g a day on a 2,000 calorie daily diet. Less than than 10% of your daily calories should come from saturated fat, 15-20% from monounsaturated fat and 5-10% from polyunsaturated fat.
Dr Lee is an advocate of the Mediterranean diet, as it is low in saturated fat and high in unsaturated fat. “It may be that eating less saturated fat and more unsaturated fats will help increase your longevity,” she says. “People who lived in Greece and other Mediterranean countries, who have always had a high intake of unsaturated fats have been noted to have a lower risk of heart disease than those in other western countries.”
For the best quality fats, opt for minimally processed liquid fats. For instance, you should be choosing olive oil, which has been shown to have cardioprotective properties, over cooking with butter. Additionally, looking for healthier alternatives to unhealthy foods that are high in saturated fat can help you to stay within the daily recommended limits.
Some healthy swaps you can make include:
This article is for informational purposes only and is not meant to offer medical advice.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.
Lou Mudge is a health writer based in Bath, United Kingdom for Future PLC. She holds an undergraduate degree in creative writing from Bath Spa University, and her work has appeared in Live Science, Tom's Guide, Fit & Well, Coach, T3, and Tech Radar, among others. She regularly writes about health and fitness-related topics such as air quality, gut health, diet and nutrition and the impacts these things have on our lives.
She has worked for the University of Bath on a chemistry research project and produced a short book in collaboration with the department of education at Bath Spa University.