Deep frying is a common cooking method used across the globe. It’s often used by restaurants and fast food chains as a quick and inexpensive way to prepare foods.
Popular fried foods include fish, french fries, chicken strips and cheese sticks, although you can deep fry just about anything.
Many people like the taste of fried foods. Yet these foods tend to be high in calories and trans fat, so eating a lot of them can have negative effects on your health.
This article explains why commercially fried foods are bad for you and provides some healthier alternatives to consider.
Compared to other cooking methods, deep frying adds a lot of calories.
For starters, fried foods are typically coated in batter or flour prior to frying. Furthermore, when foods are fried in oil, they lose water and absorb fat, which further increases their calorie content ().
Generally speaking, fried foods are significantly higher in fat and calories than their non-fried counterparts.
As you can see, calories add up quickly when eating fried foods.
Summary Fried foods contain more calories than their non-fried counterparts. Eating a lot of them can significantly increase your calorie intake.
Trans fats are formed when unsaturated fats undergo a process called hydrogenation.
Food manufacturers often hydrogenate fats using high pressure and hydrogen gas to increase their shelf life and stability, but hydrogenation also occurs when oils are heated to very high temperatures during cooking.
The process changes the chemical structure of fats, making them difficult for your body to break down, which can ultimately lead to negative health effects.
Since fried foods are cooked in oil at extremely high temperatures, they are likely to contain trans fats.
What’s more, fried foods are often cooked in processed vegetable or seed oils, which may contain trans fats prior to heating.
One US study on soybean and canola oils found that 0.6–4.2% of their fatty acid contents were trans fats (9).
When these oils are heated to high temperatures, such as during frying, their trans fat content can increase ().
In fact, one study found each time an oil is re-used for frying, its trans fat content increases ().
However, it’s important to distinguish between these artificial trans fats and trans fats that occur naturally in foods like meat and dairy products.
These have not been shown to have the same negative effects on health as those found in fried and processed foods.
Summary Fried foods are often cooked in processed vegetable or seed oils. When heated, these oils can form trans fats, which are associated with a number of health problems, including an increased risk of several diseases.
Several studies in adults have found an association between eating fried foods and the risk of chronic disease.
Generally speaking, eating more fried foods is associated with a greater risk of developing type 2 diabetes, heart disease and obesity ().
Eating fried foods may contribute to high blood pressure, low “good” HDL cholesterol and obesity, which are all risk factors for heart disease (, , , ).
In fact, two large observational studies found that the more often people ate fried foods, the greater their risk of developing heart disease ().
One study found that women eating one or more servings of fried fish per week had a 48% higher risk of heart failure, compared to those who consumed 1–3 servings per month ().
On the other hand, increased baked or broiled fish intake was associated with a lower risk.
Another observational study found that a diet high in fried foods was associated with a significantly higher risk of heart attack ().
Meanwhile, those who ate a diet high in fruits and vegetables were at a significantly lower risk.
Several studies have found that eating fried foods puts you at a higher risk of developing type 2 diabetes (, ).
One study found that people who ate fast food more than two times per week were twice as likely to develop insulin resistance, compared to those who ate it less than once a week ().
Furthermore, two large observational studies found a strong association between how often participants ate fried food and the risk of type 2 diabetes.
Those consuming 4–6 servings of fried food per week were 39% more likely to develop type 2 diabetes, compared to those consuming less than one serving per week.
Similarly, those who ate fried food seven or more times per week were 55% more likely to develop type 2 diabetes, compared to those consuming less than one serving per week. ().
Fried foods contain more calories than their non-fried counterparts, so eating a lot of them can significantly increase your calorie intake.
Furthermore, studies indicate that the trans fats in fried foods may play a significant role in weight gain, as they can affect the hormones that regulate appetite and fat storage ().
A study in monkeys found that even in the absence of additional calories, trans fat consumption significantly increased belly fat ().
Thus, the problem may be the type of fat, rather than the amount of fat.
In fact, an observational study that reviewed the diets of 41,518 women over eight years found that increasing trans fat intake by 1% resulted in a weight gain of 1.2 pounds (0.54 kg) in normal-weight women.
Among women who were overweight, a 1% increase in trans fat intake resulted in a weight gain of 2.3 pounds (1.04 kg) over the course of the study ().
Meanwhile, increases in monounsaturated and polyunsaturated fat intakes were not associated with weight gain.
Regardless of whether it’s because fried food is high in calories or trans fat, multiple observational studies have shown a positive association between its intake and obesity (, ).
Summary Individuals who regularly consume fried foods may be at a higher risk of developing type 2 diabetes, heart disease and obesity. It seems that the higher your intake, the greater your risk.
Acrylamide is a toxic substance that can form in foods during high-temperature cooking, such as frying, roasting or baking.
It is formed by a chemical reaction between sugars and an amino acid called asparagine.
Starchy foods like fried potato products and baked goods typically have higher concentrations of acrylamide (28).
Animal studies have found that it poses a risk for several types of cancer (28, ).
However, most of these studies used very high doses of acrylamide, ranging from 1,000–100,000 times the average amount that humans would be exposed to through diet ().
While a handful of human studies have investigated acrylamide intake, the evidence is mixed.
One review found a modest association between dietary acrylamide in humans and kidney, endometrial and ovarian cancers ().
Other studies indicate that dietary acrylamide in humans is not related to the risk of any type of common cancer (, ).
Summary Animal studies suggest that dietary intakes of acrylamide may increase the risk of several types of cancer, but more studies in humans are needed to say for sure.
If you enjoy the taste of fried foods, consider cooking them at home using healthier oils or alternative “frying” methods.
The type of oil used for frying heavily influences the health risks associated with fried foods. Some oils can withstand much higher temperatures than others, making them safer to use.
Generally speaking, oils that consist mostly of saturated and monounsaturated fats are the most stable when heated.
Coconut oil, olive oil and avocado oil are among the healthiest.
- Coconut oil: Over 90% of the fatty acids in coconut oil is saturated, which makes it very resistant to heat. In fact, studies have shown that even after eight hours of continuous deep frying, its quality does not deteriorate ().
- Olive oil: Olive oil contains mostly monounsaturated fats, making it relatively stable for high-temperature cooking. One analysis found that olive oil can be used in a deep fryer for up to 24 hours before a significant amount of oxidation begins to occur ().
- Avocado oil: The composition of avocado oil is similar to that of olive oil. It also has an extremely high heat tolerance, making it a great choice for deep frying.
Using these healthier oils may decrease some of the risks associated with eating fried foods.
Cooking oils that contain a high amount of polyunsaturated fats are far less stable and known to form acrylamide when exposed to high heat (36).
These include, but are not limited to:
- Canola oil
- Soybean oil
- Cottonseed oil
- Corn oil
- Sesame oil
- Sunflower oil
- Safflower oil
- Grape seed oil
- Rice bran oil
These oils are processed, and up to 4% of their fatty acid content is trans fats prior to frying (37).
Unfortunately, they are commonly used by restaurants, as they tend to be cheaper. Not only should you avoid these oils for deep frying, you should try to avoid them altogether.
Alternatives to Traditional Frying
You may also want to consider some alternative cooking methods, including:
- Oven-frying: This method involves baking foods at a very high temperature (450°F or 232°C), which allows foods to get crispy using little or no oil.
- Air-frying: You can also “fry” foods in a hot air fryer. These machines work by circulating extremely hot air around food. The foods end up crispy on the outside and very moist on the inside, similar to traditionally fried foods, but using 70–80% less oil.
Summary Coconut oil, olive oil and avocado oil are among the healthiest oils to fry foods in. You can also try oven-frying or air-frying foods, which yield similar results using very little oil.
Consuming foods fried in unstable or unhealthy oils can have several negative health effects.
In fact, eating them regularly can put you at a higher risk of developing diseases like diabetes, heart disease and obesity.
Therefore, it’s probably best to avoid or severely limit your intake of commercially fried foods.
Fortunately, there are several other cooking methods and healthier fats you can use instead.