Saturated vs. unsaturated fat: How do fats affect your health

For decades advice about dietary fats change constantly. One minute fat was the enemy, the next it was back on the menu. So, what's the truth?

Not all dietary fat is equal. The type and quality of the fat we consume can have significant impact on long-term health, affecting risk for both metabolic and cardiovascular. Saturated fats are typically solid at room temperature and tend to raise LDL or “bad” cholesterol, while unsaturated fats are typically liquid and can help lower it.

Here’s what the evidence says about the different types of fats, which foods are high in saturated fat, and how much of it you should be eating (and avoiding).

What are dietary fats, and why does your body need them?

Fat is not the enemy. You need to eat fat, it’s one of the three essential macronutrients your body needs to foundation alongside carbohydrates and protein. Dietary fat is important for:

• Building healthy cells
• Producing important hormones
• Protecting your organs
• Providing energy
• Absorbing fat soluble vitamins A, D, E and K

Instead of cutting fat from your diet completely, it’s important to choose healthier sources more often.

These are the types of dietary fats to know about:

1. Saturated
2. Unsaturated (monounsaturated and polyunsaturated)
3. Trans fat

The different types of fats

Saturated and unsaturated fats have different chemical structures.

Saturated fats have no double bonds between their carbon atoms. This allows them to pack closely together, making them solid at room temperature.

Unsaturated fats contain one (monounsaturated) or more (polyunsaturated) double bonds. These create bends in the structure, preventing the molecules from packing tightly together, which is why they're usually liquid at room temperature.

A third type of fat is trans fats. These are artificially altered unsaturated fats with hydrogen atoms on opposite sides, making them straight like saturated fats and solid or semi-solid at room temperature.

What is saturated fat?

Saturated fat is found mainly in animal products (such as meat, butter and cheese) and some tropical plant oils. Eating too much saturated fat over time has been linked to a higher risk of heart disease and stroke because it can increase LDL, or “bad”, cholesterol.

When LDL cholesterol builds up in the bloodstream, it can contribute to fatty plaque forming inside the arteries. This narrows the blood vessels and makes it harder for blood to flow efficiently, increasing the risk of cardiovascular disease.

For this reason, the World Health Organization recommends limiting saturated fat to less than 10% of your total daily energy intake.

That doesn't mean you need to avoid foods containing saturated fat altogether. Instead, aim for balance by treating saturated fats as sometimes foods while including plenty of healthier fat sources in your diet.

What are unsaturated fats?

Unsaturated fats are the healthier type of dietary fat because they support heart health and healthy cholesterol levels. These fats are found naturally in foods like oily fish, nuts, seeds, avocados and olive oil.

Eating moderate amounts of unsaturated fats can help lower LDL cholesterol while maintaining or increasing HDL, or “good”, cholesterol. HDL helps remove excess cholesterol from the bloodstream, reducing plaque build-up in the arteries.

There are 2 main types of unsaturated fats:

1. Monounsaturated fats can be found in olive oil, avocado and many nuts
2. Polyunsaturated fats (including omega-3 and omega-6 fatty acides) can be found in oily fish, walnuts, flaxseed and sunflower seeds

High-saturated fat foods and what to eat instead?

Many everyday foods contain higher amounts of saturated fat, including:

• Fatty cuts of red meat, sausages and processed meats
• Butter, cream, full-fat milk and hard cheeses
• Coconut oil, palm oil and copha
• Pastries, pies, sausage rolls and commercial baked goods
• Chocolate, biscuits and many packaged snacks

Unsaturated alternatives are just as easy to find:

• Oily fish such as salmon, sardines and mackerel
• Nuts and seeds (e.g. walnuts, almonds, flaxseed, chia)
• Avocado
• Extra-virgin olive oil

When comparing products at the supermarket, check the nutrition information panel and compare the saturated fat per 100 g. It's a quick way to spot the difference when choosing between similar products.

Are animal fats bad for you?

Current health guidelines recommend replacing some saturated fat with healthier unsaturated fats where possible. Research suggests this can help reduce the risk of cardiovascular disease, particularly for people already at higher risk.

That doesn't mean you should never eat animal-based foods. Many provide valuable nutrients including protein, iron, and vitamin B12. Instead, consider choosing leaner cuts of meat more often, including fish regularly and balancing your meals with plant-based sources of healthy fats.

Small, sustainable changes are often easier to maintain than completely removing foods you enjoy.

Limiting trans fats

Trans fats are another type of dietary fat that can occur naturally in small amounts but are more commonly created during food processing through partial hydrogenation.

They are widely used because they improve texture, shelf life and stability in processed foods. However, research consistently shows that trans fats increase LDL cholesterol while also lowering HDL cholesterol, making them extra harmful for heart health.

Are seed oils bad for you?

Seed oils have attracted plenty of attention online, but current evidence shows that they're not inherently harmful as part of a balanced diet. For reducing the risk of cardiovascular disease, experts just recommend lowering saturated and trans fat intake rather than avoiding seed oils altogether.

Many seed oils are affordable, versatile and commonly used for cooking because they remain stable at higher temperatures. They also appear in many packaged foods.

The main concern isn't the oils themselves, but some undergo partial hydrogenation during food processing, which can create trans fats. These behave similarly to saturated fats and may negatively affect cardiovascular health.

What is olegel and how can it reduce saturated fat?

Oleogels represent an emerging food technology that enables the transformation of liquid oils into structured systems with functional and textural properties resembling those of solid fats. This lets manufacturers make foods like pastries and sausage rolls using significantly less saturated fat while maintaining texture and quality. 

There is also some early evidence that oleogels may improve the absorption of certain fat soluble vitamins.

Healthy eating isn't about eliminating individual foods. It's about building balanced dietary patterns that include a variety of nutritious foods while limiting energy dense, nutrient poor options.

The ongoing discussion around saturated fat highlights how nutrition science continues to evolve. As researchers learn more, dietary advice and food innovation continue to develop alongside the latest evidence.

The debate over saturated fat is a good illustration of what nutrition science does. If you're interested in understanding the science behind nutrition and helping others make informed food choices, studying Nutrition could be the next step in your career.