Nutrition Diet: Which of the three types of fat is the unhealthiest?

October 15, 2025 •

5 min read

While fat is an essential nutrient for energy and supporting cell function, not all types are created equal. For long-term health, it is critical to understand and distinguish the effects of different fats. This is why knowing which of the three types of fat is the unhealthiest is crucial for making informed dietary choices.

Quick Summary

The unhealthiest type of dietary fat is trans fat, particularly industrially produced trans fat, which raises bad LDL cholesterol while lowering good HDL cholesterol and significantly increasing the risk of heart disease.

Key Points

Trans Fat is the Unhealthiest: Industrially produced trans fat is the worst type of fat for your health, offering no nutritional benefit and significantly increasing the risk of heart disease and stroke.
Saturated Fat is Moderately Unhealthy: Saturated fat, found primarily in animal products and some tropical oils, can raise LDL cholesterol and should be limited, but is less harmful than trans fat.
Unsaturated Fat is the Healthiest: Monounsaturated and polyunsaturated fats, found in plant-based oils, nuts, seeds, and fish, are 'good' fats that can improve cholesterol levels and heart health.
Check for 'Partially Hydrogenated Oil': The most reliable way to spot trans fat is to read the ingredients list and look for "partially hydrogenated oil," even if the nutrition panel says 0g trans fat.
Prioritize Whole Foods: Minimizing processed and fried foods is key to avoiding unhealthy fats. Opt for whole, unprocessed foods and cook at home using healthy oils whenever possible.

The Three Main Types of Dietary Fat

In the realm of nutrition, dietary fats are broadly categorized into three main types: unsaturated, saturated, and trans fats. While all fats provide nine calories per gram, their chemical structure and, consequently, their effect on health, differ significantly. Making mindful choices about the types of fat you consume is one of the most impactful decisions you can make for your overall well-being.

The Most Harmful: Trans Fat

Of all dietary fats, industrially produced trans fat is considered the most harmful with no known health benefits. Most trans fat is artificially created through a process called partial hydrogenation, which adds hydrogen to liquid vegetable oil to make it more solid and extend its shelf life. This process makes it cheaper and easier for food manufacturers to use. The World Health Organization attributes more than 278,000 deaths annually to the consumption of industrially produced trans fat.

Consuming trans fat is particularly dangerous for heart health. It has a double-whammy effect on cholesterol, both raising the level of 'bad' low-density lipoprotein (LDL) cholesterol and lowering the level of 'good' high-density lipoprotein (HDL) cholesterol. This harmful combination can cause cholesterol to build up in the arteries, making them hard and narrow, and greatly increasing the risk of heart attacks and stroke. Even small amounts can pose a risk, which is why the World Health Organization recommends limiting trans fat intake to less than 1% of total energy intake. Fortunately, many countries have banned or restricted the use of partially hydrogenated oils in foods.

Common sources of artificial trans fat include:

Commercial baked goods like cakes, cookies, and pies
Fried foods, such as french fries and doughnuts
Shortening and stick margarine
Frozen pizza and refrigerated doughs
Packaged snack foods, like microwave popcorn

Natural trans fats also occur in small amounts in meat and dairy products from ruminant animals, but it is the industrially produced version that poses the most significant health risk.

In the Middle: Saturated Fat

Saturated fats are another type of dietary fat that can be detrimental to health when consumed in excess. These fats are typically solid at room temperature and are primarily found in animal products. A high intake of saturated fat can raise LDL cholesterol levels, increasing the risk of heart disease.

However, saturated fat is not as dangerous as trans fat, and some nutrition experts suggest that the overall dietary pattern is more important than focusing solely on saturated fat intake. The American Heart Association recommends limiting saturated fat to less than 6% of your daily calories. It is important to remember that replacing saturated fat with healthy unsaturated fat is a better strategy than replacing it with refined carbohydrates or sugar.

Sources of saturated fat include:

Fatty cuts of meat and processed meats (e.g., sausages, bacon)
High-fat dairy products (e.g., cheese, butter, whole milk, cream)
Certain tropical oils (e.g., coconut oil, palm oil, palm kernel oil)
Lard and ghee

The Healthiest Choice: Unsaturated Fat

Unsaturated fats are considered the 'good' fats and should make up the majority of your fat intake. They are typically liquid at room temperature and can help lower 'bad' LDL cholesterol levels while providing other health benefits. Unsaturated fats are further divided into two types:

Monounsaturated fats: These fats have one double bond in their chemical structure and are found in olive oil, peanut oil, canola oil, avocados, and most nuts. They are known for their protective effects on heart health.
Polyunsaturated fats: These fats have two or more double bonds and include essential fatty acids like omega-3 and omega-6, which the body cannot produce on its own. Sources include fatty fish (salmon, mackerel, sardines), walnuts, and various plant-based oils (sunflower, soybean, flaxseed).

Comparing the Fats

To make the healthiest choices, a comparison of the three major types of fat is helpful:


Feature	Trans Fat	Saturated Fat	Unsaturated Fat
Chemical Structure	Unsaturated fat with hydrogen atoms added artificially (in most cases).	Fully saturated with hydrogen atoms, no double bonds.	One or more double bonds in the carbon chain.
State at Room Temp	Semi-solid, like shortening or stick margarine.	Solid, like butter or coconut oil.	Liquid, like olive or canola oil.
Primary Sources	Fried foods, commercial baked goods, some processed foods with 'partially hydrogenated oils'.	Fatty meats, high-fat dairy, some tropical oils.	Plant-based oils, nuts, seeds, avocados, fish.
Health Impact	Raises LDL (bad) and lowers HDL (good) cholesterol. Increases risk of heart disease and stroke.	Can raise LDL (bad) cholesterol when consumed in excess.	Lowers LDL (bad) cholesterol and provides essential fatty acids, benefiting heart health.
Dietary Recommendation	Avoid or consume as little as possible.	Limit intake (less than 10% of daily calories).	Replace saturated and trans fats with these, eat in moderation.

How to Spot and Avoid the Worst Fat

Since industrial trans fats are so dangerous, it's vital to know how to identify and avoid them, even though many countries have banned partially hydrogenated oils. You should still read the nutrition label and ingredient list carefully.

Check the ingredients list: Look for the words "partially hydrogenated oil" or "hydrogenated vegetable oil". If it's on the list, the product contains trans fat, even if the nutrition panel claims 0g trans fat per serving.
Look for 'Trans Fat Free' Claims: Be cautious. Foods labeled "0 trans fat" can contain up to 0.5 grams per serving, and consuming multiple servings can add up to a significant amount.
Choose Whole Foods: The best way to avoid unhealthy fats is to opt for whole, unprocessed foods like fruits, vegetables, lean proteins, nuts, and whole grains. Cooking meals at home with healthy oils like olive or canola oil gives you complete control over your ingredients.

Conclusion

While a healthy diet requires fat for proper bodily functions, the source and type of fat are what truly matter for your health. Which of the three types of fat is the unhealthiest? The clear answer is trans fat, which poses the most significant threat to your cardiovascular system by negatively impacting cholesterol levels. To build a healthier nutritional diet, you should strive to eliminate industrially produced trans fats, limit your intake of saturated fats, and prioritize healthier monounsaturated and polyunsaturated fats. By understanding the differences and reading food labels vigilantly, you can make smarter choices that protect your long-term heart health.

For more information on dietary fats and healthy eating, you can visit the American Heart Association's website.

Frequently Asked Questions

Saturated fats are typically solid at room temperature and primarily come from animal products, while unsaturated fats are usually liquid at room temperature and found in plant-based sources like oils, nuts, and seeds. Unsaturated fats are generally considered healthier for the heart.

Trans fats are worse because they have a uniquely damaging effect on cholesterol levels, raising bad LDL cholesterol while simultaneously lowering good HDL cholesterol. Saturated fats primarily only raise LDL cholesterol when consumed in excess.

Not always. In the US, food products can be labeled '0 trans fat' if they contain less than 0.5 grams per serving. The best way to know for sure is to check the ingredients list for 'partially hydrogenated oil'.

Healthy fats include monounsaturated and polyunsaturated fats. Good sources are olive oil, avocados, nuts, seeds, and fatty fish like salmon and mackerel, which are rich in omega-3 fatty acids.

While some natural trans fat occurs in meat and dairy from ruminant animals, studies indicate that industrially produced trans fat is more harmful and significantly increases the risk of heart disease.

To reduce your intake of unhealthy fats, limit your consumption of processed snacks, fried foods, and fatty meats. Instead, opt for cooking methods like steaming or baking, and use healthy oils such as olive or canola.

Excess calorie intake from any source, including fat, can lead to weight gain. However, focusing on healthy, unsaturated fats in moderation as part of a balanced diet is better than opting for processed, low-fat alternatives that are often high in sugar and refined carbs.