Fat research is confusing, and the internet is rife with conflicting recommendations.
Much of the confusion occurs when people make generalizations about dietary fat. Many diet books, media and blogs talk about fat as if it were all the same.
In fact, dozens of fats are common in the diet, and each has a different role in your body and affects your health. Even within fat groups such as saturated, unsaturated and polyunsaturated, specific fats have different roles.
This article will explain the differences between some of the main dietary fats and their health effects, both good and bad.
It is important to understand that each type of fat has its own effect on the body. When you start thinking about fats more specifically, you'll be better equipped to make healthy dietary choices.
How fat became a dirty word
Decades ago, common sense was to eat fatty foods because it was the most efficient way to get energy. Fat contains more calories by weight than any other nutrient.
Over time, scientists began to understand that some fats are healthier than others. In the 1930s, Russian scientists discovered that feeding animals a diet high in cholesterol caused atherosclerosis.
This is a condition in which plaque builds up in the arteries, narrowing them and increasing the risk of heart disease. Atherosclerosis is the most prominent cause of heart disease and stroke
During the 1940s and 50s, heart disease in many countries declined. Many attribute this phenomenon to wartime rations during World War II. This promotes the belief that fat and cholesterol, which are highly restricted foods, contribute to heart disease.
The Seven Countries Study, a large international study conducted by American physiologist Ancel Keys and other international scientists, has revealed several important risk factors for heart disease.
These include smoking, high blood pressure, weight gain, yo-yo dieting, and blood cholesterol.
The Seven Countries Study contributed to the hypothesis that saturated fat raises blood cholesterol, predicting atherosclerosis and heart disease.
However, even decades ago Ancel Keys realized that not all fats are bad. He was skeptical about the importance of dietary cholesterol and showed that unsaturated fats reduce the risk of heart disease.
Unfortunately, his and other researchers' science has been misjudged by policymakers, nutritionists, and journalists.
Black and white, extreme conclusions, such as that all saturated fat is bad and everyone should eat a low-fat diet, are neither helpful nor true. This article will clear up the confusing fat literature by looking at a mix of old and new research.
SUMMARY Since the 1930s, scientists have suspected that fat and cholesterol can cause atherosclerosis, heart disease, and stroke. However, later research has shown that valuing all fats together - even all saturated fats - is an incorrect oversimplification.
Dietary cholesterol has little effect on heart health
Cholesterol is made by the liver in humans and animals. For this reason, you only get it in your diet from animal products.
Main sources include egg yolks, animal liver, fish or fish oil, animal fats or oils such as butter, shellfish, meat, cheese, and fatty baked goods.
The liver regulates the amount of cholesterol it makes depending on levels from the diet. When you eat large amounts of cholesterol, the liver makes less.
The cholesterol you eat has a small effect on your blood cholesterol levels. Even 50 years ago, Ancel Keys realized this effect was trivial for most people.
“Paying attention to [cholesterol] alone accomplishes little,” says Keys.
According to a large study that combined evidence from more than 350,000 adults, dietary cholesterol was not linked to heart attack or stroke.
However, a combination of several large studies shows that up to 25% of people are more sensitive than average to dietary cholesterol. For these people, high dietary cholesterol increased both bad LDL cholesterol and good HDL cholesterol.
SUMMARY Dietary cholesterol does not change heart disease risk for most people, according to the largest studies available. However, in a quarter of the population, high dietary cholesterol increases bad LDL cholesterol and good HDL cholesterol.
Calling all saturated fats an oversimplification
Saturated fat differs from unsaturated fat in that it has no chemical double bonds. This makes it more stable, so it is solid at room temperature.
Saturated fat is the subject of a lot of controversy, and nutritionists don't always agree on how it affects health. There are several reasons why research on saturated fat can be confusing.
Not all saturated fats are created equal
While people who give dietary advice often lump saturated fats together, there are different types of saturated fat that have different health effects. Labeling all saturated fats as healthy and unhealthy is an oversimplification.
A distinguishing feature of fats is their length, that is, the number of carbon atoms they contain. Fats can be short (containing less than six carbons), medium (6–10 carbons), long (12–22 carbons), or very long (22 or more).
Your cells process fat very differently depending on their chain length, which means that fats of different lengths can have different effects on health.
A study of 16,000 European adults found that consumption of very long-chain fatty acids (VLCFA) was associated with a reduced risk of type 2 diabetes.
VLCFAs are found in nuts, including peanut and canola oils. Research also shows that the long-chain fatty acid arachidic acid, found in vegetable oils, has a protective effect.
Whether saturated fat has an even or odd number of carbons in its chain is also important.
The same study of 16,000 European adults found saturated fatty acids with an even number of carbons were associated with type 2 diabetes, while odd-length fats were associated with a lower risk.
Uniform-length saturated fats include stearate, which is found mainly in meats, cheese, and baked goods.
They also include palmitate, named for palm oil, but also found in milk, meat, cocoa butter, and fully hydrogenated vegetable oils. A different long saturated fat, myristate, can be found in butter, coconut, and palm oil.
The odd length saturated fats, including heptadecanoate and pentadecanoate, mostly come from beef and dairy.
Because the health effects of saturated fats and the way they are metabolized are so nuanced, it doesn't help to think of them as a collective good.
People who eat food, not individual nutrients
While most nutrition research looks at the effects of individual nutrients, even the same specific type of fat can have different effects depending on its source.
For example, saturated fat from lard causes atherosclerosis in animals, but the same palmitate derived from animal fat does not.
Furthermore, reorganizing how fats in lard are interconnected to resemble tallow reverses the harmful effects of palmitate.
While these differences are nuanced, it's worth mentioning that the specific food is more important than the type of fat it contains.
For example, one avocado contains the same amount of saturated fat as three slices of bacon.
Bacon increases the level of bad cholesterol (LDL).
However, according to a study of 229 adults, eating about half to 1.5 avocados per day actually lowers “bad” LDL cholesterol levels.
This is probably due in part to differences in the types of saturated fats in butter and the way they are structured. However, avocados also contain healthy plant compounds that may offer other benefits.
When you're deciding which fats to include in your diet, it's more important to choose a variety of healthy foods including vegetables, nuts, seeds, and fish than to focus on each fatty acid.
Other factors in your diet change the effects of saturated fat
When researchers look at the link between saturated fat and health, they often think that saturated fat comes from meat, cheese, and other dairy.
In fact, 15% of the saturated fat in the American diet comes from high-carb desserts including cakes, cookies, cakes, and candy. Another 15% came from Japanese snacks such as burgers, fries, pizza and chips, and another 6% from dairy desserts.
When these snacks and desserts are shown in research only by their saturated fat content, it can be difficult to talk about their health effects beyond other foods that also contain saturated fat.
For example, cheese contributes more saturated fat to the Western diet than any other food. However, the largest study of cheese looked at its effects in 177,000 adults over the course of 5–15 years and found no link between cheese and early death.
Another large study that followed hundreds of thousands of adults for 25 years found that consuming milk, cheese and yogurt did not increase heart disease and even slightly reduce the risk of stroke.
Regarding meat, a study of more than 1.6 million adults found that those who ate the most processed meat had an approximately 20% higher risk of heart disease and all-cause mortality than those who ate the most processed meat. lowest amount.
The study also found that people who ate the most red meat had a 16% higher risk of dying from heart disease than those who ate the lowest amount.
However, it's important to note that sometimes people mistakenly attribute the impact of an unhealthy diet to saturated fat.
Diets high in saturated fat tend to be high in calories and can lead to weight gain, so it can be easy to blame saturated fat for the effects that may actually be on excess calories and weight gain.
For example, some studies have shown that heart disease is actually more closely related to extra calories and weight gain than it is to saturated fat.
This is important because it means that many foods high in saturated fat are safe as long as they are eaten in moderation on a diet that does not cause weight gain.
SUMMARY Some saturated fats contribute to heart disease. However, calling all saturated fats is an oversimplification. In fact, when they come from dairy and vegetable sources, as well as some meats, some saturated fats are healthy.
Industrial - Unnatural - Trans fats cause heart disease
Trans fats are produced industrially with hydrogenated vegetable oils in a process that involves bombarding it with hydrogen gas. This transforms liquid unsaturated fats into saturated fats and solid or nearly solid saturated fats.
The most common sources of trans fats include cakes, pies, frostings, cream fillings, fried foods, and cookies and crackers made with shortening or margarine.
The oil is fully hydrogenated, becomes indistinguishable from saturated fat and is considered by the body as saturated fat.
However, trans fats - at least fats made from vegetable oils - are foreign to the body and contribute to atherosclerosis and heart disease.
A 39-month study of atherosclerosis in the heart arteries of 50 men found that the disease was worse in men who consumed more trans fats.
This increase in atherosclerosis increases the risk of heart attack. One study examined 209 people who had recently had a heart attack and found they had higher levels of trans fat in their fat cells compared with 179 adults who had not had a heart attack.
In the US, food labels are now required to list the amount of trans fat per serving. Unfortunately, companies are allowed to round down to zero if the amount per serving is less than 0.5 grams.
This is especially troublesome because serving sizes are not regulated and companies can manipulate serving sizes lower than you would normally eat at one time to claim 0 grams of trans fat per serving.
To avoid this trap, take a look at the ingredients. If they list partially hydrogenated, then the food contains trans fats and should be used sparingly.
While industrial or artificial trans fats are clearly harmful, dairy products and meat contain small amounts of naturally occurring trans fats. These natural trans fats have not been linked to heart disease and may actually be beneficial.
SUMMARY Industrial or man-made trans fats cause heart disease. Avoid them. Even if a food label claims it contains 0 grams of trans fat, if its ingredient list says the oil is partially hydrogenated, it means it contains unhealthy industrial trans fats.
Unsaturated fats are heart healthy
Unlike saturated fats, unsaturated fats have double chemical bonds that change the way your body stores and uses them for energy.
Unsaturated fats are heart healthy, although some are more so than others. As with saturated fats, there are different types of unsaturated fats. Their length and the number and location of double bonds affect their effects in the body.
Monounsaturated fats have one double bond, while polyunsaturated fats have two to six double bonds.
Monounsaturated fats are good
Monounsaturated fats are abundant in olive and canola oils and avocados. They can also be found in tree nuts including almonds, walnuts, pecans, hazelnuts and cashews.
A study that followed 840,000 adults over a period of 4–30 years found that those who consumed the most monounsaturated fats had a 12% lower risk of dying from heart disease than those who ate the least.
This benefit was strongest for oleic acid and olive oil, compared with other monounsaturated fat sources.
Polyunsaturated fats are even better
Polyunsaturated fats are potentially even better than monounsaturated fats. In one study, replacing foods high in saturated fat with sources of polyunsaturated fat reduced the risk of heart disease by 19%.
This reduces the risk of heart disease by 10% for every 5% of daily calories people consume from polyunsaturated instead of saturated fat.
Polyunsaturated fats are found mainly in vegetable and seed oils.
Omega-3 fatty acids have many health benefits
Omega-3 fatty acids, a special type of polyunsaturated fat, are found in seafood, especially fatty fish like salmon, herring, bluefin and albacore tuna.
A study of 45,000 adults used omega-3 fatty acids in blood and adipose tissue to estimate dietary omega-3 intake. It found that a high omega-3 intake was associated with a 10% lower risk of heart disease.
Not all studies have found the same benefits, and some people are concerned about eating fish because it can be a source of mercury, which is toxic if consumed in large enough quantities.
The US Food and Drug Administration and the Environmental Protection Agency have stated that two to three weekly servings of fish are the safe upper limit, although this depends on the type of fish.
They advise against regularly eating fish with the highest levels of mercury, including large fish such as king mackerel, marlin, swordfish and bigeye tuna.
Albacore and yellowfin tuna have smaller amounts of mercury and are considered safe to eat up to once per week, while salmon, trout, and whitefish are safe to eat 2–3 times a week.
SUMMARY Olive, canola, and seed oils are great for cooking and a good source of heart-healthy monounsaturated and polyunsaturated fats. Nuts and fish are also good sources of healthy polyunsaturated fats, including omega-3s.
Key point
The more you know about fats, the more equipped you will be to make healthy choices.
It is important to understand that each specific type of fat has unique effects on the body and these effects can be good or bad.
For example, many studies lump all saturated fats together, when in fact there are many different types of saturated fat, each with a different role in the body.
Also, people don't eat saturated fats in isolation - they choose foods with a wide variety of fats and other nutrients.
Even the same type of saturated fat can have different effects depending on how it is connected to other fats and what else is in the diet. For example, the saturated fats in milk, poultry, and some vegetable oils are neutral or even heart healthy.
Unsaturated fats are always heart healthy, while industrial trans fats are always bad. In contrast, the small amounts of naturally occurring trans fats in milk are harmless, as are the cholesterol in eggs and other animal products.
In general, choose good fats, including unsaturated and saturated fats from a variety of vegetables, nuts, seeds, fish, and unprocessed meat. Avoid bad fats like partially hydrogenated oils and saturated fats in processed meats.
Following these guidelines will help control your risk of heart disease and prolong your life.
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