healthy fats

What are fats

Fats also known as lipids, is an essential nutrient (a primary storage form of energy, a kilojoule-dense nutrient) your body need for energy and to help your gut absorb vitamins A, D, E and K from foods. Fat has twice as many calories as proteins or carbohydrates. Dietary fat also plays a major role in your cholesterol levels. You need some fat in your diet but not too much. There are different types of fats, some are “good” and some are “bad”, however, you should try to avoid “bad” fats. When it comes to dietary fat, what matters most is the type of fat you eat. Contrary to past dietary advice promoting low-fat diets, newer research shows that healthy fats are necessary and beneficial for health.

Healthy fats are unsaturated. They keep cholesterol levels within a healthy range, reduce your risk of heart problems and may be good for the skin, eyes and brain. Unsaturated fats are the best choice for a healthy diet.

Unhealthy fats are saturated and trans fats, which can raise levels of ‘bad’ cholesterol and increase the risk of heart disease.

  • Saturated fats such as butter, solid shortening, and lard. Eating foods that contain saturated fats raises the level of cholesterol in your blood. High levels of LDL cholesterol (low-density lipoprotein or “bad” cholesterol) in your blood increase your risk of heart disease and stroke. The American Heart Association recommends aiming for a dietary pattern that achieves 5% to 6% of calories from saturated fat. For example, if you need about 2,000 calories a day, no more than 120 of them should come from saturated fat. That’s about 13 grams of saturated fat per day 1).
  • Trans fats also known as trans fatty acids or “partially hydrogenated oils”. These are found in vegetable shortenings, some margarines, crackers, cookies, snack foods, and other foods made with or fried in partially hydrogenated oils. By 2018, most U.S. companies will not be allowed to add partially hydrogenated oils to food.

“Bad” fats, such as artificial trans fats and saturated fats, are guilty of the unhealthy things all fats have been blamed for—weight gain, clogged arteries, an increased risk of certain diseases, and so forth. Large studies have found that replacing saturated fats in your diet with unsaturated fats and omega-3 fatty acids can reduce your risk of heart disease by about the same amount as cholesterol-lowering drugs. Since fat is an important part of a healthy diet, rather than adopting a low-fat diet, it’s more important to focus on eating more beneficial “good” fats and limiting harmful “bad” fats. For good health, the majority of the fats that you eat should be monounsaturated or polyunsaturated. Eat foods containing monounsaturated fats and/or polyunsaturated fats such as canola oil, olive oil, safflower oil, sesame oil or sunflower oil instead of foods that contain saturated fats and/or trans fats.

For years you’ve been told that eating fat will add inches to your waistline, raise cholesterol, and cause a myriad of health problems. When food manufacturers reduce fat, they often replace it with carbohydrates from sugar, refined grains, or other starches. Your body digests these refined carbohydrates and starches very quickly, affecting your blood sugar and insulin levels and possibly resulting in weight gain and disease 2). But now scientists know that not all fat is the same. Research has shown that unsaturated fats are good for you. Healthy fats play a huge role in helping you manage your moods, stay on top of your mental game, fight fatigue, and even control your weight. These fats come mostly from plant sources. Cooking oils that are liquid at room temperature, such as canola, peanut, safflower, soybean, and olive oil, contain mostly unsaturated fat. Nuts, seeds, and avocados are also good sources. Fatty fish—such as salmon, sardines, and herring—are rich in unsaturated fats, too. You should actively make unsaturated fats a part of your diet. Of course, eating too much fat will put on the pounds too. Note also that by swapping animal fats for refined carbohydrates—such as replacing your breakfast bacon with a bagel or pastry—won’t have the same benefits. In fact eating refined carbohydrates or sugary foods can have a similar negative effect on your cholesterol levels, your risk for heart disease, and your weight. Limiting your intake of saturated fat can still help improve your health—as long as you take care to replace it with good fat rather than refined carbs. In other words, don’t go no fat, go good fat.

Healthy-eating tips:

  • Use olive oil in cooking.
  • Replace saturated fats with unsaturated fats; for example, use avocado, tahini, nut or seed butter instead of dairy butter.
  • Eat fish, especially oily fish, twice a week.
  • Consume legume- or bean-based meals twice a week.
  • Snack on nuts or add them to your cooking.
  • Throw avocado in salads.
  • Choose lean meats and trim any fat you can see (including chicken skin).
  • Use table spreads that have less than 0.1g of trans fats per 100g.

Figure 1. Types of fats in food

Types of fats in food

Footnotes: The molecular composition of a fatty acid includes a hydrophilic carboxyl group (−COOH) in light blue and a hydrophobic methyl group (−CH3) at opposite terminals of a hydrocarbon backbone. Fats can differ from one another in three important ways—carbon chain length, degree of saturation, and shape. When the carbon chain length is shorter, the melting point of the fatty acid becomes lower—and the fatty acid becomes more liquid. The term saturation refers to whether or not a fatty acid chain is filled (or “saturated”) to capacity with hydrogen atoms. If each available carbon bond holds a hydrogen atom it’s a saturated fatty acid chain. All of the carbon atoms in a saturated fatty acid chain are bonded through single bonds. From a chemical standpoint, saturated fats are simply fat molecules that have no double bonds between carbon molecules because they are saturated with hydrogen molecules. Saturated fats are typically solid at room temperature. When one or more bonds between carbon atoms are a double bond (C=C), that fatty acid is called an unsaturated fatty acid, as it has one or more points of unsaturation. Any fatty acid that has only one double bond is a monounsaturated fatty acid, an example of which is olive oil (75 percent of its fat is monounsaturated). Monounsaturated fats help regulate blood cholesterol levels, thereby reducing the risk for heart disease and stroke. A polyunsaturated fatty acid is a fatty acid with two or more double bonds or two or more points of unsaturation. Soybean oil contains high amounts of polyunsaturated fatty acids . Both monounsaturated fats and polyunsaturated fats provide nutrition that is essential for normal cell development.

Does my body need fats?

Yes, it does. Dietary fats are essential to give your body energy and to support cell growth. Fats also help protect your organs and help keep your body warm. Fats help your body absorb some nutrients and produce important hormones, too. Your body definitely needs fat.

Do all fats have the same number of calories?

Yes. There are nine calories (37kJ) in every gram of fat, regardless of what type of fat it is. Fats are more energy-dense than carbohydrates and proteins, which provide four calories (17kJ) per gram.

Consuming high levels of calories – regardless of the source – can lead to weight gain or being overweight. Consuming high levels of saturated or trans fats can also lead to heart disease and stroke. Health experts generally recommend replacing saturated fats and trans fats with monounsaturated fats and polyunsaturated fats – while still maintaining a nutritionally-adequate diet.

Can fats be part of a healthy diet?

Eating foods with fat is definitely part of a healthy diet. Just remember to choose foods that provide good fats (monounsaturated and polyunsaturated fats) and balance the amount of calories you eat from all foods with the amount of calories you burn. Replacing foods that are high in saturated fat with healthier options can lower your blood cholesterol levels and improve lipid profiles. The American Heart Association recommends limiting saturated fats – which are found in butter, cheese, red meat and other animal-based foods. For people who need to lower their cholesterol, the American Heart Association recommends reducing saturated fat to less than 6% of total daily calories. For someone eating 2,000 calories a day, that’s about 11 to 13 grams of saturated fat 3). Aim to eat a dietary pattern that emphasizes intake of vegetables, fruits, and whole grains; includes low-fat dairy products, poultry, fish, legumes, non-tropical vegetable oils and nuts; and limits intake of sodium, sweets, sugar sweetened beverages and red meats. Doing so means that your diet will be low in both saturated fats and trans fats.

What are alternatives to replace saturated fats in the foods I eat?

To get the nutrients you need, eat a dietary pattern that emphasizes:

  • fruits, vegetables,
  • whole grains,
  • low-fat dairy products,
  • poultry, fish and nuts,
  • while limiting red meat and sugary foods and beverages.

Choose lean meats and poultry without skin and prepare them without added saturated and trans fat.

You should replace foods high in saturated fats with foods high in monounsaturated and/or polyunsaturate fats. This means eating foods made with liquid vegetable oil but not tropical oils. It also means eating fish and nuts. You also might try to replace some of the meat you eat with beans or legumes.

Are polyunsaturated fats better for me than saturated fats or trans fats?

Yes. While, all fats provide 9 calories (34kJ) per gram, monounsaturated fats and polyunsaturated fats can have a positive effect on your health, when eaten in moderation. The bad fats – saturated fats and trans fats – can negatively affect your health.

Are monounsaturated fats better for me than saturated fats or trans fats?

Yes. While, all fats provide 9 calories per gram, monounsaturated fats and polyunsaturated fats can have a positive effect on your health, when eaten in moderation. The bad fats –saturated fats and trans fats – can negatively affect your health.

Does eating more healthfully mean giving up my favorite foods?

A healthy diet can include the foods you love. You don’t have to avoid these treats entirely, but you do need to eat less of foods that are low in nutrition and high in calories.

Why do some companies use trans fats?

Trans fats are easy to use, inexpensive to produce and last a long time. Trans fats give foods a desirable taste and texture. Many restaurants and fast-food outlets use trans fats to deep-fry foods because oils with trans fats can be used many times in commercial fryers. Several countries (e.g., Denmark, Switzerland, and Canada) and jurisdictions (California, New York City, Baltimore, and Montgomery County, MD) have reduced or restricted the use of trans fats in food service establishments.

Are there naturally occurring trans fats?

Small amounts of trans fats occur naturally in some meat and dairy products, including beef, lamb and butterfat. There have not been sufficient studies to determine whether these naturally occurring trans fats have the same bad effects on cholesterol levels as trans fats that have been industrially manufactured.

Are all foods labeled “trans fat-free” healthy foods?

Not necessarily. Foods can be listed as “0 grams of trans fats” if they contain 0 grams to less than 0.5 grams of trans fat per serving. You can also spot trans fats by reading ingredient lists and looking for the ingredients referred to as “partially hydrogenated oils.” Foods labeled “0 trans fat” or cooked with “trans fat-free” oils may contain a lot of saturated fats, which raise your bad cholesterol levels. “Trans fat-free” foods may also be unhealthy in terms of their general nutrient content. For example, baked goods also tend to be high in added sugars and low in nutrients.

How much trans fat can I eat a day?

The American Heart Association recommends that adults who would benefit from lowering LDL cholesterol (low-density lipoprotein or “bad” cholesterol) reduce their intake of trans fat and limit their consumption of saturated fat to 5 to 6% of total calories. Replace the trans fats in your diet with monounsaturated or polyunsaturated fats.

Here are some ways to achieve that:

  • Eat a dietary pattern that emphasizes fruits, vegetables, whole grains, low-fat dairy products, poultry, fish and nuts. Also limit red meat and sugary foods and beverages.
  • Use naturally occurring, unhydrogenated vegetable oils such as canola, safflower, sunflower or olive oil most often.
  • Look for processed foods made with unhydrogenated oil rather than partially hydrogenated or hydrogenated vegetable oils or saturated fat.
  • Use soft margarine as a substitute for butter, and choose soft margarines (liquid or tub varieties) over harder stick forms. Look for “0 g trans fat” on the Nutrition Facts label and no hydrogenated oils in the ingredients list.
  • Doughnuts, cookies, crackers, muffins, pies and cakes are examples of foods that may contain trans fat. Limit how frequently you eat them.
  • Limit commercially fried foods and baked goods made with shortening or partially hydrogenated vegetable oils. Not only are these foods very high in fat, but that fat is also likely to be trans fat.

What are the best foods to eat?

Opt for foods that are high in unsaturated fats, which increase levels of ‘good’ cholesterol (HDL) and help lower levels of ‘bad’ cholesterol (LDL). These include:

  • avocado
  • almonds, cashews, peanuts, pine nuts, walnuts, Brazil nuts
  • cooking oils including canola, olive, peanut, soybean, rice bran, sesame and sunflower
  • spreads made from soybean, sunflower, safflower or canola
  • fish, especially tuna, salmon, sardines and blue mackerel
  • tahini
  • linseed (flaxseed)
  • chia seeds

Avoid foods that have higher levels of unhealthy fats. These include:

  • processed meats (such as bacon, ham, salami and frankfurts)
  • butter and cream
  • crisps and chips
  • pies and pastries
  • takeaway pizza
  • takeaway burgers
  • fried foods (e.g. spring rolls)
  • biscuits, doughnuts, muffins and cake
  • chocolate
  • ice cream

Types of fats in food

There are four major dietary fats in the foods you eat:

  1. Saturated fats
  2. Trans fats
  3. Monounsaturated fats (monounsaturated fatty acids or MUFAs)
  4. Polyunsaturated fats (polyunsaturated fatty acids or PUFAs)

The four types of fats in food have different chemical structures and physical properties. The bad fats, saturated and trans fats, tend to be more solid at room temperature (like a stick of butter), while monounsaturated and polyunsaturated fats tend to be more liquid (like liquid vegetable oil or olive oil).

Fats can also have different effects on the cholesterol levels in your body. The bad fats, saturated fats and trans fats raise bad cholesterol (LDL) levels in your blood. Monounsaturated fats and polyunsaturated fats can lower bad cholesterol levels and are beneficial when consumed as part of a healthy dietary pattern.

Saturated fats

Saturated fats are fat molecules that are “saturated” with hydrogen molecules (see Figure 1 above). Saturated fats are normally solid at room temperature. Saturated fats occur naturally in many foods — primarily meat and dairy foods (butter, cream, full-fat milk and cheese). Beef, lamb, pork on poultry (with the skin on) contain saturated fats, as do butter, cream and cheese made from whole or 2% milk. Plant-based foods that contain saturated fats include coconut, coconut oil, coconut milk and coconut cream, cooking margarine, and cocoa butter, as well as palm oil and palm kernel oil (often called tropical oils). Saturated fats are also found in snacks like chips, cakes, biscuits and pastries, and takeaway foods. Consuming more than the recommended amount of saturated fat is linked to heart disease and high cholesterol.

The American Dietary Guidelines recommend that:

  • men should not eat more than 30g of saturated fat a day
  • women should not eat more than 20g of saturated fat a day
  • children should have less

For people who need to lower their cholesterol, the American Heart Association recommends reducing saturated fat to less than 6% of total daily calories. For someone eating 2,000 calories a day, that’s about 11 to 13 grams of saturated fat 4).

Examples of foods with saturated fat are:

  • fatty beef,
  • lamb,
  • pork,
  • poultry with skin,
  • beef fat (tallow),
  • meat products including sausages and pies,
  • lard and cream,
  • butter and ghee,
  • cheese especially hard cheese like cheddar,
  • other dairy products made from whole or reduced-fat (2 percent) milk,
  • cream, soured cream and ice cream,
  • some savoury snacks, like cheese crackers and some popcorns,
  • chocolate confectionery,
  • biscuits, cakes, and pastries

In addition, many baked goods and fried foods can contain high levels of saturated fats. Some plant-based oils, such as palm oil, palm kernel oil, coconut oil and coconut cream, also contain primarily saturated fats, but do not contain cholesterol.

Trans fats

Trans fats also known as trans fatty acids or “partially hydrogenated oils”, are created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid, so they ‘behave’ like a saturated fat. There are two broad types of trans fats found in foods: naturally-occurring and artificial trans fats. Naturally-occurring trans fats are produced in the gut of some animals and foods made from these animals (e.g., milk and meat products) may contain small quantities of these fats. Artificial trans fats (or trans fatty acids) are created in an industrial process that adds hydrogen to liquid vegetable oils to make them more solid.

Trans fats increase the levels of ‘bad’ LDL cholesterol and decreases the levels of ‘good’ HDL cholesterol in your body, which increases your risk of developing heart disease and stroke. Trans fats is also associated with a higher risk of developing type 2 diabetes. Trans fats can be found in many foods such as in butter, margarine (in small amounts), deep-fried and processed foods like doughnuts, cakes and pastries. Baked goods, such as pastries, pizza dough, frozen pizza, pie crust, cookies, biscuits, and crackers also can contain trans fats.

Since 2006, the FDA has required trans fat content to be listed on the Nutrition Facts panel of packaged foods. In recent years, many major national fast-food chains and casual-dining restaurant chains have announced they will no longer use trans fats to fry or deep-fry foods.

The American Heart Association recommends that adults who would benefit from lowering LDL cholesterol eliminate trans fat from their diet.

To find the amount of trans fats in a particular packaged food, look at the Nutrition Facts panel. Companies must list any measurable amount of trans fat (0.5 grams or more per serving) in a separate line in the “Total Fat” section of the panel, directly beneath the line for “Saturated Fat.” This means if a food package states 0 grams of trans fats, it might still have some trans fats if the amount per serving is less than 0.5 g. You can also spot trans fats by reading ingredient lists and looking for the ingredients referred to as “partially hydrogenated oils.”

Figure 2. Trans fats

trans fatty acids structure

Footnotes: Cis and trans fatty acid configurations. The introduction of a carbon double bond in a carbon chain, as in an unsaturated fatty acid, can result in different structures for the same fatty acid composition. When the hydrogen atoms are bonded to the same side of the carbon chain, it is called a cis fatty acid. Because the hydrogen atoms are on the same side, the carbon chain has a bent structure. Naturally occurring fatty acids usually have a cis configuration. In a trans fatty acid, the hydrogen atoms are attached on opposite sides of the carbon chain. Unlike cis fatty acids, most trans fatty acids are not found naturally in foods, but are a result of a process called hydrogenation. Hydrogenation is the process of adding hydrogen atoms to an unsaturated fat (the hydrogen atoms are added where there are double bonds), thus making the fatty acid saturated (or less unsaturated, in the case of partial hydrogenation). This is how vegetable oils are converted into semisolid fats for use in the manufacturing process. The hydrogenation process makes the fat more similar to a saturated fat and makes the fat more stable which is advantageous for the shelf-life of products that include trans fats. However, trans fatty acids have been associated with increased risk for heart disease because of the way they negatively impact blood cholesterol levels. The Nutrition Facts panel includes trans fat as a separate line item under the “Total Fat” section. In addition, ingredients that include the word “hydrogenated” or “partially hydrogenated” indicate the presence of trans fat in the food.

Cholesterol

Dietary fat plays a major role in your cholesterol levels. Cholesterol is a type of fat, a wax-like substance that your body needs to function properly that comes from foods such as eggs and is also found in your blood mostly made by your body in your liver. In and of itself, cholesterol isn’t bad. But when you get too much of it, it can have a negative impact on your health. The 2 main types of cholesterol are:

  1. “Good” cholesterol or HDL (high-density lipoprotein) cholesterol. “Good” HDL cholesterol has a positive effect by taking cholesterol from parts of the body where there’s too much of it to the liver, where it’s disposed of.
  2. “Bad” cholesterol or LDL (low-density lipoprotein) cholesterol.

High levels of LDL cholesterol (low-density lipoprotein or “bad” cholesterol) can increase your risk of heart disease. The key is to keep your LDL levels low and HDL high, which may protect against heart disease and stroke. High levels of LDL cholesterol (low-density lipoprotein or “bad” cholesterol) can clog arteries and low HDL (high-density lipoprotein or “good” cholesterol) can be a marker for increased cardiovascular risk. However, eating foods that contain any type of cholesterol won’t actually raise your body’s cholesterol levels. Rather than the amount of cholesterol you eat, the biggest influence on your cholesterol levels is the type of fats you consume. Eating saturated or trans fats is far more likely to give you high cholesterol. So instead of counting cholesterol, it’s important to focus on replacing bad fats with good fats.

Figure 3. Cholesterol

Cholesterol structure

LDL (bad) cholesterol

LDL (low-density lipoprotein) cholesterol is considered the “bad” cholesterol, because it contributes to fatty buildups in arteries (atherosclerosis). This narrows the arteries and increases the risk for heart attack, stroke and peripheral artery disease. Your body naturally produces all the LDL cholesterol you need. Eating foods containing saturated fats and trans fats causes your body to produce even more LDL — raising the level of “bad” cholesterol in your blood.

HDL (good) cholesterol

HDL (high-density lipoprotein) cholesterol can be thought of as the “good” cholesterol because a healthy level may protect against heart attack and stroke. HDL carries LDL (bad) cholesterol away from the arteries and back to the liver, where the LDL is broken down and passed from the body. But HDL cholesterol doesn’t completely eliminate LDL cholesterol. Only one-third to one-fourth of blood cholesterol is carried by HDL.

Triglycerides

Triglycerides also known as triacylglycerols, are the most common type of fat in your body. They store excess energy from your diet. A high triglyceride level combined with high LDL (bad) cholesterol or low HDL (good) cholesterol is linked with fatty buildups within the artery walls, which increases the risk of heart attack and stroke.

Figure 4. Triglycerides

Triglycerides

Unsaturated fats

If you want to reduce your risk of heart disease, it’s best to reduce your overall fat intake and swap saturated fats for unsaturated fats. Unsaturated fats are in fish, such as salmon, trout and herring, and plant-based foods such as avocados, olives and walnuts. Liquid vegetable oils, such as soybean, corn, safflower, canola, olive and sunflower, also contain unsaturated fats.

There are 2 types of unsaturated fats: monounsaturated and polyunsaturated. Unsaturated fats help reduce your risk of heart disease and lower your cholesterol levels.

  • Polyunsaturated fats such as omega-3 and omega-6 fats are found in fish, nuts, and safflower and soybean oil.
  • Monounsaturated fats are found in olive and canola oil, avocado, cashews and almonds.

Monounsaturated fats have one (“mono”) unsaturated carbon bond in the molecule. Polyunsaturated fats have more than one (“poly,” for many) unsaturated carbon bonds. Both of these unsaturated fats are typically liquid at room temperature.

Eaten in moderation, both kinds of unsaturated fats may help improve your blood cholesterol when used in place of saturated and trans fats.

Polyunsaturated fats

Polyunsaturated fats are simply fat molecules that have more than one unsaturated carbon bond in the molecule, this is also called a double bond. Oils that contain polyunsaturated fats are typically liquid at room temperature but start to turn solid when chilled. Olive oil is an example of a type of oil that contains polyunsaturated fats.

There are 2 main types of polyunsaturated fats: omega-3 and omega-6. Oils rich in polyunsaturated fats also provide essential fats that your body needs but can’t produce itself – such as omega-6 and omega-3 fatty acids. You must get essential fats through food. Omega-6 and omega-3 fatty acids are important for many functions in the body. A deficiency of essential fatty acids—either omega-3s or omega-6s—can cause rough, scaly skin and dermatitis 5).

Polyunsaturated fats can help reduce bad cholesterol levels in your blood which can lower your risk of heart disease and stroke. Polyunsaturated fats also provide nutrients to help develop and maintain your body’s cells. Oils rich in polyunsaturated fats also contribute vitamin E to the diet, an antioxidant vitamin most Americans need more of.

Foods high in polyunsaturated fat include a number of plant-based oils, including:

  • soybean oil
  • corn oil
  • sunflower oil

Other sources include some nuts and seeds such as walnuts and sunflower seeds, tofu and soybeans.

Omega-6 fats are found in vegetable oils, such as:

  • rapeseed
  • corn
  • sunflower
  • some nuts

Omega-3 fats are found in oily fish, such as:

  • kippers
  • herring
  • trout
  • sardines
  • salmon
  • mackerel

The American Heart Association also recommends eating tofu and other forms of soybeans, canola, walnut and flaxseed, and their oils. These foods contain alpha-linolenic acid (ALA), another omega-3 fatty acid.

Polyunsaturated fats (PUFAs) are frequently designated by their number of carbon atoms and double bonds. Alpha-linolenic acid (ALA), for example, is known as C18:3n-3 because it has 18 carbons and 3 double bonds and is an omega-3 fatty acid. Similarly, eicosapentaenoic acid (EPA) is known as C20:5n-3 and docosahexaenoic acid (DHA) as C22:6n-3. Omega-6 fatty acids (omega-6s) have a carbon–carbon double bond that is six carbons away from the methyl end of the fatty acid chain. Linoleic acid (LA) known as C18:2n-6 and arachidonic acid (AA) known as C20:4n-6 are two of the major omega-6s.

The human body can only form carbon–carbon double bonds after the 9th carbon from the methyl end of a fatty acid 6). Therefore, alpha-linolenic acid (ALA) and linoleic acid (LA) are considered essential fatty acids, meaning that they must be obtained from the diet 7). Alpha-linolenic acid (ALA) can be converted into eicosapentaenoic acid (EPA) and then to docosahexaenoic acid (DHA), but the conversion (which occurs primarily in the liver) is very limited, with reported rates of less than 15% 8). Therefore, consuming EPA and DHA directly from foods and/or dietary supplements is the only practical way to increase levels of these fatty acids in the body.

Alpha-linolenic acid (ALA) is present in plant oils, such as flaxseed, soybean, and canola oils 9). Docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) are present in fish, fish oils, and krill oils, but they are originally synthesized by microalgae, not by the fish. When fish consume phytoplankton that consumed microalgae, they accumulate the omega-3s in their tissues 10).

Some researchers propose that the relative intakes of omega-6s and omega-3s—the omega-6/omega-3 ratio—may have important implications for the pathogenesis of many chronic diseases, such as cardiovascular disease and cancer 11), but the optimal ratio—if any—has not been defined 12). Others have concluded that such ratios are too non-specific and are insensitive to individual fatty acid levels 13). Most agree that raising eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) blood levels is far more important than lowering linoleic acid (LA) or arachidonic acid levels.

Currently, most clinicians do not assess omega-3 status, but it can be done by measuring individual omega-3s in plasma or serum phospholipids and expressing them as the percentage of total phospholipid fatty acids by weight 14). Experts have not established normal ranges, but mean values for serum or plasma phospholipid eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) among U.S. adults not taking omega-3 supplements are about 3%–4% 15). Plasma and serum fatty acid values, however, can vary substantially based on an individual’s most recent meal, so they do not reflect long-term dietary consumption 16).

It is also possible to assess omega-3 status via analysis of erythrocyte fatty acids, a measurement that reflects longer-term intakes over approximately the previous 120 days 17). The “omega-3 index” proposed by Harris and von Schacky reflects the content of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) in erythrocyte membranes expressed as a percentage of total erythrocyte fatty acids 18). This index can be used as a surrogate for assessing tissue levels of eicosapentaenoic acid (EPA) plus docosahexaenoic acid (DHA) 19). Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) typically comprise about 3%–5% of erythrocyte fatty acids in Western populations with low fish intakes. In Japan, where fish consumption is high, erythrocyte eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) levels are about twice those of Western populations 20).

Table 1. Alpha-linolenic acid (ALA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) content of selected foods

FoodGrams per serving
ALADHAEPA
Flaxseed oil, 1 tbsp7.26
Chia seeds, 1 ounce5.06
English walnuts, 1 ounce2.57
Flaxseed, whole, 1 tbsp2.35
Salmon, Atlantic, farmed cooked, 3 ounces1.240.59
Salmon, Atlantic, wild, cooked, 3 ounces1.220.35
Herring, Atlantic, cooked, 3 ounces*0.940.77
Canola oil, 1 tbsp1.28
Sardines, canned in tomato sauce, drained, 3 ounces*0.740.45
Mackerel, Atlantic, cooked, 3 ounces*0.590.43
Salmon, pink, canned, drained, 3 ounces*0.040.630.28
Soybean oil, 1 tbsp0.92
Trout, rainbow, wild, cooked, 3 ounces0.440.4
Black walnuts, 1 ounce0.76
Mayonnaise, 1 tbsp0.74
Oysters, eastern, wild, cooked, 3 ounces0.140.230.3
Sea bass, cooked, 3 ounces*0.470.18
Edamame, frozen, prepared, ½ cup0.28
Shrimp, cooked, 3 ounces*0.120.12
Refried beans, canned, vegetarian, ½ cup0.21
Lobster, cooked, 3 ounces*0.040.070.1
Tuna, light, canned in water, drained, 3 ounces*0.170.02
Tilapia, cooked, 3 ounces*0.040.11
Scallops, cooked, 3 ounces*0.090.06
Cod, Pacific, cooked, 3 ounces*0.10.04
Tuna, yellowfin, cooked 3 ounces*0.090.01
Kidney beans, canned ½ cup0.1
Baked beans, canned, vegetarian, ½ cup0.07
Ground beef, 85% lean, cooked, 3 ounces**0.04
Bread, whole wheat, 1 slice0.04
Egg, cooked, 1 egg0.03
Chicken, breast, roasted, 3 ounces0.020.01
Milk, low-fat (1%), 1 cup0.01

Footnotes: *Except as noted, the U.S. Department of Agriculture (USDA) database does not specify whether fish are farmed or wild caught. **The USDA database does not specify whether beef is grass fed or grain fed.

Figure 5. Polyunsaturated fats

Omega-3 fatty acids

Omega-3 fatty acids (omega-3s) are a type of polyunsaturated fat and have a carbon–carbon double bond located three carbons from the methyl end of the chain (see Figure 6). Omega-3 fatty acids, sometimes referred to as “n-3s,” are present in certain foods such as flaxseed and fish, as well as dietary supplements such as fish oil. Omega-3 fatty acids are especially beneficial to your health. Omega-3s play important roles in the body as components of the phospholipids that form the structures of cell membranes 21). There are different types of omega-3s: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are found in fish and algae and have the most health benefits, while alpha-linolenic acid (ALA) comes from plants and is a less potent form of omega-3, although the body does convert ALA to EPA and DHA at low rates. Alpha-linolenic acid (ALA) contains 18 carbon atoms, whereas eicosapentaenoic acid (EPA), and docosahexaenoic acid (DHA) are considered “long-chain” omega-3s because EPA contains 20 carbons and DHA contains 22 22).

Docosahexaenoic acid (DHA), in particular, is especially high in the retina, brain, and sperm 23). In addition to their structural role in cell membranes, omega-3s (along with omega-6s) provide energy for the body and are used to form eicosanoids. Eicosanoids are signaling molecules that have similar chemical structures to the fatty acids from which they are derived; they have wide-ranging functions in the body’s cardiovascular, pulmonary, immune, and endocrine systems 24). Higher concentrations of EPA and DHA than arachidonic acid tip the eicosanoid balance toward less inflammatory activity 25).

Research has shown that a diet rich in omega-3 fatty acids may help to:

  • Prevent and reduce symptoms of depression, ADHD, and bipolar disorder.
  • Protect against memory loss and dementia.
  • Reduce the risk of heart disease, stroke, and cancer.
  • Ease arthritis, joint pain, and inflammatory skin conditions.
  • Support a healthy pregnancy.
  • Battle fatigue, sharpen your memory, and balance your mood.

Fish the best source of omega-3 (high in EPA and DHA):

  • Anchovies
  • Herring
  • Salmon
  • Mackerel
  • Sardines
  • Trout
  • Tuna
  • Mussels
  • Oysters
  • Halibut

Vegetarian sources of omega-3s (high in ALA):

  • Algae such as seaweed (high in EPA and DHA)
  • Eggs (small amounts of DHA)
  • Flaxseeds and flaxseed oil
  • Chia seeds
  • Canola and soybean oil
  • Walnuts
  • Mayonnaise
  • Edamame
  • Beans (refried, kidney, etc.)
  • Brussels sprouts
  • Kale
  • Spinach

Fish is a good source of protein and omega-3 fatty acids, which are good for your heart. Research has shown that omega-3 fatty acids can reduce your risk of heart disease and stroke. A 2020 Cochrane review 26) of 86 randomized controlled trials published between 1968 and 2019 found that 0.5 g/day to more than 5 g/day omega-3 fatty acids for 12 to 88 months in a total of 162,796 participants reduced serum triglyceride levels by about 15% and slightly decreased rates of cardiovascular mortality and coronary heart disease events. However, the omega-3 fatty acids supplements did not affect all-cause mortality, cardiovascular events, stroke, or arrhythmia. The authors of several earlier meta-analyses and systematic reviews, as well as a 2016 report from the Agency for Healthcare Research and Quality, concluded that omega-3 fatty acids supplements do not appear to significantly reduce the risk of most cardiovascular events 27). Many of these analyses 28), however, but not all 29), did find that omega-3s reduce the risk of cardiac death.

The American Heart Association recommends eating 2 servings of fish (particularly fatty fish) per week. A serving is 3.5 ounce (100 g) cooked, or about ¾ cup of flaked fish. Fatty fish like salmon, mackerel, herring, lake trout, sardines and albacore tuna are high in omega-3 fatty acids. For people with existing coronary heart disease, such as a recent heart attack (myocardial infarction), the American Heart Association recommends approximately 1 gram/day EPA plus DHA, preferably from oily fish; however, supplements could also be considered under the direction of a physician 30). The American Heart Association does not recommend omega-3 supplements for people who do not have a high cardiovascular disease risk.

While omega-3s are best obtained through food, there are many omega-3 and fish oil supplements available. A typical fish oil supplement provides about 1,000 mg fish oil, containing 180 mg EPA and 120 mg DHA, but doses vary widely 31). If you need to substantially lower your triglycerides, your doctor may recommend prescription fish oil, which has been concentrated to contain about 900 mg of EPA plus DHA per capsule. Cod liver oil supplements provide vitamin A and vitamin D in addition to omega-3s. For strict vegetarians or vegans, as well as obtaining ALA from food sources, look for capsules containing DHA and EPA extracted from algae, the original source of omega-3s for fish. Although seafood contains varying levels of methyl mercury (a toxic heavy metal) 32), omega-3 supplements have not been found to contain this contaminant because it is removed during processing and purification 33).

Some types of fish may contain high levels of mercury, PCBs (polychlorinated biphenyls), dioxins and other environmental contaminants. Levels of these substances are generally highest in older, larger, predatory fish and marine mammals.

The benefits and risks of eating fish vary depending on a person’s stage of life.

Children and pregnant women are advised by the U.S. Food and Drug Administration (FDA) to:

  • Avoid eating those fish with the potential for the highest level of mercury contamination (such as shark, swordfish, king mackerel or tilefish).
  • Eat a variety of fish and shellfish that are lower in mercury (such as canned light tuna, salmon, pollock, catfish).
  • Check local advisories about the safety of fish caught by family and friends in local lakes, rivers and coastal areas.

For middle-aged and older men and postmenopausal women, the benefits far outweigh the potential risks when the amount of fish eaten is within the recommendations established by the FDA and Environmental Protection Agency.

Eating a variety of fish will help minimize any potentially adverse effects due to environmental pollutants. Five of the most commonly eaten fish or shellfish that are low in mercury are shrimp, canned light tuna, salmon, pollock, and catfish. Avoid eating shark, swordfish, king Mackerel, or tilefish because they contain high levels of mercury.

Figure 6. Omega-6 and omega-3 fatty acids

Omega-6 and omega-3 fatty acids

Footnotes: Polyunsaturated fats (PUFAs) are frequently designated by their number of carbon atoms and double bonds. Alpha-linolenic acid (ALA), for example, is known as C18:3n-3 because it has 18 carbons and 3 double bonds and is an omega-3 fatty acid. Similarly, eicosapentaenoic acid (EPA) is known as C20:5n-3 and docosahexaenoic acid (DHA) as C22:6n-3. Omega-6 fatty acids (omega-6s) have a carbon–carbon double bond that is six carbons away from the methyl end of the fatty acid chain. Linoleic acid (LA) known as C18:2n-6 and arachidonic acid (AA) known as C20:4n-6 are two of the major omega-6s.

Monounsaturated fats

Monounsaturated fats are simply fat molecules that have one unsaturated carbon bond in the molecule, this is also called a double bond. Oils that contain monounsaturated fats are typically liquid at room temperature but start to turn solid when chilled. Olive oil is an example of a type of oil that contains monounsaturated fats.

Monounsaturated fats can have a beneficial effect on your heart when eaten in moderation and when used to replace saturated fat and trans fat in your diet. Monounsaturated fats can help reduce bad cholesterol levels in your blood which can lower your risk of heart disease and stroke. Monounsaturated fats also provide nutrients to help develop and maintain your body’s cells. Oils rich in monounsaturated fats also contribute vitamin E to the diet, an antioxidant vitamin most Americans need more of.

Examples of foods high in monounsaturated fats include plant-based liquid oils such as:

  • olive oil,
  • canola oil,
  • peanut oil,
  • safflower oil and
  • sesame oil.

Other sources include avocados, peanut butter, and many nuts and seeds.

Figure 7. Monounsaturated fats

Monounsaturated fats

Healthy fats

Monounsaturated fats and polyunsaturated fats are known as the “good fats” because they are good for your heart, your cholesterol, and your overall health. These fats can help to:

  • Lower the risk of heart disease and stroke.
  • Lower bad LDL cholesterol levels, while increasing good HDL cholesterol levels.
  • Prevent abnormal heart rhythms.
  • Lower triglycerides associated with heart disease and fight inflammation.
  • Lower blood pressure.
  • Prevent atherosclerosis (hardening and narrowing of the arteries).

Adding more of these healthy fats to your diet may also help to make you feel more satisfied after a meal, reducing hunger and thus promoting weight loss.

Monounsaturated fat good sources include:

  • Olive, canola, peanut, and sesame oils
  • Avocados
  • Olives
  • Nuts (almonds, peanuts, macadamia, hazelnuts, pecans, cashews)
  • Peanut butter

Polyunsaturated fat good sources include:

  • Sunflower, sesame, and pumpkin seeds
  • Flaxseed
  • Walnuts
  • Fatty fish (salmon, tuna, mackerel, herring, trout, sardines) and fish oil
  • Soybean and safflower oil
  • Soymilk
  • Tofu

Unhealthy fats

Trans fat

Small amounts of naturally occurring trans fats can be found in meat and dairy products but it’s artificial trans fats that are considered dangerous. This is the worst type of fat since it not only raises bad LDL cholesterol but also lowers good HDL levels. Artificial trans fats can also create inflammation, which is linked to heart disease, stroke, and other chronic conditions and contributes to insulin resistance, which increases your risk of developing type 2 diabetes.

In the U.S., the Food and Drug Administration (FDA) has effectively outlawed the use of artificial trans-fats in commercially prepared food and the World Health Organization (WHO) has called on other governments around the world to eliminate the use of trans fats by 2023. However, products made before the FDA ban may still be available for sale. Since products can be listed as having “zero trans fats” even if they contain up to 0.5 grams of trans fat per serving, it’s still important to carefully read food labels. Look for ingredients referred to as “partially hydrogenated oils.” These hidden sources of artificial trans fats can add up quickly.

If your country still allows the use of artificial trans fats, remember that no amount is considered safe, so aim to eliminate trans fats from your diet.

Trans fat primary sources include:

  • Commercially-baked pastries, cookies, doughnuts, muffins, cakes, pizza dough
  • Packaged snack foods (crackers, microwave popcorn, chips)
  • Stick margarine, vegetable shortening
  • Fried foods (French fries, fried chicken, chicken nuggets, breaded fish)
  • Anything containing hydrogenated or partially hydrogenated vegetable oil, even if it claims to be “trans fat-free”

Saturated fat

While not as harmful as trans fat, saturated fat can raise bad LDL cholesterol and too much can negatively impact heart health, so it’s best consumed in moderation. While there’s no need to cut out all saturated fat from your diet, most nutrition experts recommend limiting it to 10% of your daily calories.

Saturated fat primary sources include:

  • Red meat (beef, lamb, pork)
  • Chicken skin
  • Whole-fat dairy products (milk, cream, cheese)
  • Butter
  • Ice cream
  • Lard
  • Tropical oils such as coconut and palm oil

Limiting saturated and trans fats

Here are some ways to lower your intake of saturated and trans fats:

  • Maintain a diet that emphasizes fruits, vegetables, whole grains, low-fat dairy products, poultry, fish and nuts. Also limit red meat and sugar-sweetened foods and beverages.
  • Opt for naturally occurring unhydrogenated vegetable oils such as canola, safflower, sunflower or olive oil.
  • Look for processed foods made with unhydrogenated oil rather than saturated fat or hydrogenated (or partially hydrogenated) vegetable oils.
  • Use soft margarine as a substitute for butter and choose soft margarines (liquid or tub varieties) over harder stick forms. Look for “0 g trans fat” on the Nutrition Facts label.
  • Doughnuts, cookies, crackers, muffins, pies and cakes are examples of foods high in trans fat. Don’t eat them often.
  • Limit commercially fried foods and baked goods made with shortening or partially hydrogenated vegetable oils. These foods are very high in fat, and it’s likely to be trans fat.
  • Limit fried fast food. Commercial shortening and deep-frying fats are still made by hydrogenation and contain saturated and trans fats.

Consider using a food diary to keep track of what you eat. It’s a handy way to evaluate the healthy, not-so-healthy and unhealthy foods you’re making a part of your everyday diet.

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