1 - DISTINGUISHING BETWEEN HEALTHY & UNHEALTHY FATS
Decades ago, Americans were eating about 40% of their daily calories from fat (with most of this coming from saturated fat). Currently, the average American diet gets just under half of all its fat as saturated fat and very little from polyunsaturated fat. Unfortunately, this type of diet is considered to contribute to obesity and heart disease. In the early 1990's it would have been uncommon to hear the terms "health" and "fat" used together. However, things have changed. Research has found that replacing saturated fat (such as that in red meat, cheese, and butter) with unsaturated fat and essential fatty acids (such as those from fish and flaxseed oil) can favorably impact health.
Unfortunately, healthy fat is still a complicated issue. Current research and opinion is controversial when it comes to prescribing optimal levels of essential fatty acid (EFA) supplementation. The message is getting out that people need certain fats, but the question is still coming back, "How much?" Regrettably, dietary fat can be an overwhelming topic (just like dietary carbohydrate intake) because there are many categories of fats.
Healthy fats include EFAs, polyunsaturated fats, and monounsaturated fats. Saturated fat should be limited and hydrogenated fats should be eliminated from the diet. One important rule to remember when discussing fats is, "Structure dictates function". That means the microscopic structure of the fat determines whether the fat is healthy or harmful. Very minor changes in the structure of a fat may dictate whether it inflicts damage or promotes healing.
Without getting too detailed, it is sufficient to know that the structure of a fat contains a long chain of carbon atoms. Each of the carbon atoms is attached to one another, and 2 hydrogen atoms can be attached to each carbon, as is the case in a saturated fat. Imagine if you will, a row of chairs. In each chair sits one person. That line of chairs is saturated, just like a saturated fat.
In a monounsaturated fat, one hydrogen atom is removed, thus leaving an "empty seat" in the row of chairs. At this empty seat, something called a double bond occurs between the 2 carbons. This is analogous to one person taking up two chairs in the row. In a polyunsaturated fat, there are two and sometimes three double bonds. The result of the change in structure is a change in function.
Fats not only add taste and calories to food but also are vital to your health because they are a component of cell membranes. Our bodies are composed of millions upon millions of cells, and thus without healthy fats to make healthy cell membranes, disease could occur in any of your body's systems. This review covers what is generally known about "healthy fats" up to August 2001, so let's start with the worst (the unhealthy fats) and finish with the healthy fats that should be emphasized in your diet.
HYDROGENATED FATS
"Hydrogenation" refers to a change in the structure of the fat. In this case, food processing actually adds hydrogen atoms back to unsaturated fat molecules (i.e. a person sits in one of the empty chairs). Unfortunately, hydrogenation is done to many otherwise healthy vegetable oils. These are the worst cases of fats, and are called "trans-fatty acids". Trans-fatty acids are made mainly in the process of turning liquid oils into a solid fat (such as margarine).
Some experts consider margarine and trans-fatty acids as the greatest evils of dietary fat. The Danish Nutrition Council has recommended that the addition of all trans-fatty acids to food should end by 2005 because a high intake of trans fatty acids increases to the risk of coronary heart disease (Stender and Dyerberg, 2001). Trans-fatty acids may damage some of the body's system and may lead to increased risks of heart disease and diabetes. Other experts suggest that intake of hydrogenated fats may even increase the need for EFAs! You can live without hydrogenated fats, but not without EFAs.
Individuals that frequently consume French fries, microwave popcorn, chocolate bars, and fast food likely consume trans-fatty acids in amounts far exceeding the recommended maximum levels. Margarine, shortening, and partially hydrogenated vegetable oil also contain trans-fatty acids. FDA researchers believe that removing all trans-fatty acids from margarine and other foods could prevent 17000 heart attacks and 5000 deaths per year! Unfortunately, with the abundance of these foods in North America, many uneducated people are subject to ill health until they learn to avoid fast food and processed bakery goods.
A recent study suggested that trans-fatty acid intake increases the risk of diabetes while polyunsaturated fatty acid intake reduces the risk. The researchers estimated that replacing all dietary trans-fatty acids with an equal amount of polyunsaturated fat would lead to a 40% lower risk in diabetes for women (Salmeron et al., 2001). Surprisingly, the study also showed that total fat, saturated fat, and monounsaturated fatty acid intakes are not associated with risk of type 2 diabetes.
Salmeron, J., et al. Dietary fat intake and risk of type 2 diabetes in women. Am. J. Clin. Nutr.73: 1019-1026, 2001.
Stender, S., and J. Dyerberg. The importance of trans-fatty acids for health. Update 2001. Ugesker Laeger 163: 2349-2359, 2001 (abstract only).
SATURATED FATS
Structurally speaking, a saturated fat has as many hydrogen molecules attached to them as is chemically possible. Saturated fats are solid at room temperature (i.e. butter), and high-saturated fat sources include cheese and animal meats. Saturated fats are linked to cardiovascular disease, insulin resistance, and obesity (although not all studies show that saturated fat increases the risk of diabetes - see Salmeron et al. above). It is recommended that saturated fat intake be kept to less than 10% of total calories.
UNSATURATED FATS
Unsaturated fats may have one, two, or three double bonds (meaning one, two, or three fewer hydrogen atoms). With respect to the essential fatty acids, linoleic acid (Omega-6) has two double bonds and linolenic acid (Omega-3) has three double bonds. These are examples of polyunsaturated fatty acids, both of which are found in the most recommended healthy fat, flaxseed oil.
UNSATURATED - Monounsaturated
Monounsaturated fats are found in olive and canola oils. Olive oil provides the monounsaturated fat oleic acid, but despite olive oil's reputation (also, you must insist on non-processed extra virgin olive oil!), flaxseed oil is likely still a far superior source of fat. Monounsaturated fats that are incorporated into cell membranes may protect against free radical "lipid peroxidation". This is unhealthy cellular damage (oxidative damage) that antioxidants (such as vitamin E) also help to protect against. Substituting monounsaturated fats for saturated fat may help protect against damage induced by aging and toxins, as well as insulin resistance from poor dietary choices (Vessby et al., 2001).
Vessby, B., et al. Substituting dietary saturated for onounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU Study. Diabetologia 44: 312-319, 2001.
UNSATURATED - Polyunsaturated
Polyunsaturated fats are most commonly associated with vegetable (plant) or fish oils. They are also referred to as OMEGA-fatty acids. The most important polyunsaturated fatty acids are the essential fatty acids, linoleic acid (OMEGA-6) and linolenic acid (OMEGA-3).
Interestingly, fat from animal products (meat, dairy, and eggs) can provide more than just saturated fat. Depending on the diet of the animal, these products can also provide small amounts of polyunsaturated fats (i.e. feeding hens a diet of flaxmeal can increase the Omega-3 fatty acid content of eggs). In contrast, animals fed corn will have a high Omega-6 fatty acid content.
Modifying the fat content of animals through feeding strategies may be one way to help increase the healthy fat intake of the North American population. In a recent study, modified pork meat with a high content of polyunsaturated fatty acids (PUFAs) and a low content of saturated fat lowered plasma LDL-cholesterol (bad cholesterol) concentrations in women despite a diet of 42% fat (Stewart et al., 2001)!
Stewart, J., et al. Pork with a high content of polyunsaturated fatty acids lowers LDL cholesterol in women. Am. J. Clin. Nutr. 74: 179-187, 2001.
Decades ago, Americans were eating about 40% of their daily calories from fat (with most of this coming from saturated fat). Currently, the average American diet gets just under half of all its fat as saturated fat and very little from polyunsaturated fat. Unfortunately, this type of diet is considered to contribute to obesity and heart disease. In the early 1990's it would have been uncommon to hear the terms "health" and "fat" used together. However, things have changed. Research has found that replacing saturated fat (such as that in red meat, cheese, and butter) with unsaturated fat and essential fatty acids (such as those from fish and flaxseed oil) can favorably impact health.
Unfortunately, healthy fat is still a complicated issue. Current research and opinion is controversial when it comes to prescribing optimal levels of essential fatty acid (EFA) supplementation. The message is getting out that people need certain fats, but the question is still coming back, "How much?" Regrettably, dietary fat can be an overwhelming topic (just like dietary carbohydrate intake) because there are many categories of fats.
Healthy fats include EFAs, polyunsaturated fats, and monounsaturated fats. Saturated fat should be limited and hydrogenated fats should be eliminated from the diet. One important rule to remember when discussing fats is, "Structure dictates function". That means the microscopic structure of the fat determines whether the fat is healthy or harmful. Very minor changes in the structure of a fat may dictate whether it inflicts damage or promotes healing.
Without getting too detailed, it is sufficient to know that the structure of a fat contains a long chain of carbon atoms. Each of the carbon atoms is attached to one another, and 2 hydrogen atoms can be attached to each carbon, as is the case in a saturated fat. Imagine if you will, a row of chairs. In each chair sits one person. That line of chairs is saturated, just like a saturated fat.
In a monounsaturated fat, one hydrogen atom is removed, thus leaving an "empty seat" in the row of chairs. At this empty seat, something called a double bond occurs between the 2 carbons. This is analogous to one person taking up two chairs in the row. In a polyunsaturated fat, there are two and sometimes three double bonds. The result of the change in structure is a change in function.
Fats not only add taste and calories to food but also are vital to your health because they are a component of cell membranes. Our bodies are composed of millions upon millions of cells, and thus without healthy fats to make healthy cell membranes, disease could occur in any of your body's systems. This review covers what is generally known about "healthy fats" up to August 2001, so let's start with the worst (the unhealthy fats) and finish with the healthy fats that should be emphasized in your diet.
HYDROGENATED FATS
"Hydrogenation" refers to a change in the structure of the fat. In this case, food processing actually adds hydrogen atoms back to unsaturated fat molecules (i.e. a person sits in one of the empty chairs). Unfortunately, hydrogenation is done to many otherwise healthy vegetable oils. These are the worst cases of fats, and are called "trans-fatty acids". Trans-fatty acids are made mainly in the process of turning liquid oils into a solid fat (such as margarine).
Some experts consider margarine and trans-fatty acids as the greatest evils of dietary fat. The Danish Nutrition Council has recommended that the addition of all trans-fatty acids to food should end by 2005 because a high intake of trans fatty acids increases to the risk of coronary heart disease (Stender and Dyerberg, 2001). Trans-fatty acids may damage some of the body's system and may lead to increased risks of heart disease and diabetes. Other experts suggest that intake of hydrogenated fats may even increase the need for EFAs! You can live without hydrogenated fats, but not without EFAs.
Individuals that frequently consume French fries, microwave popcorn, chocolate bars, and fast food likely consume trans-fatty acids in amounts far exceeding the recommended maximum levels. Margarine, shortening, and partially hydrogenated vegetable oil also contain trans-fatty acids. FDA researchers believe that removing all trans-fatty acids from margarine and other foods could prevent 17000 heart attacks and 5000 deaths per year! Unfortunately, with the abundance of these foods in North America, many uneducated people are subject to ill health until they learn to avoid fast food and processed bakery goods.
A recent study suggested that trans-fatty acid intake increases the risk of diabetes while polyunsaturated fatty acid intake reduces the risk. The researchers estimated that replacing all dietary trans-fatty acids with an equal amount of polyunsaturated fat would lead to a 40% lower risk in diabetes for women (Salmeron et al., 2001). Surprisingly, the study also showed that total fat, saturated fat, and monounsaturated fatty acid intakes are not associated with risk of type 2 diabetes.
Salmeron, J., et al. Dietary fat intake and risk of type 2 diabetes in women. Am. J. Clin. Nutr.73: 1019-1026, 2001.
Stender, S., and J. Dyerberg. The importance of trans-fatty acids for health. Update 2001. Ugesker Laeger 163: 2349-2359, 2001 (abstract only).
SATURATED FATS
Structurally speaking, a saturated fat has as many hydrogen molecules attached to them as is chemically possible. Saturated fats are solid at room temperature (i.e. butter), and high-saturated fat sources include cheese and animal meats. Saturated fats are linked to cardiovascular disease, insulin resistance, and obesity (although not all studies show that saturated fat increases the risk of diabetes - see Salmeron et al. above). It is recommended that saturated fat intake be kept to less than 10% of total calories.
UNSATURATED FATS
Unsaturated fats may have one, two, or three double bonds (meaning one, two, or three fewer hydrogen atoms). With respect to the essential fatty acids, linoleic acid (Omega-6) has two double bonds and linolenic acid (Omega-3) has three double bonds. These are examples of polyunsaturated fatty acids, both of which are found in the most recommended healthy fat, flaxseed oil.
UNSATURATED - Monounsaturated
Monounsaturated fats are found in olive and canola oils. Olive oil provides the monounsaturated fat oleic acid, but despite olive oil's reputation (also, you must insist on non-processed extra virgin olive oil!), flaxseed oil is likely still a far superior source of fat. Monounsaturated fats that are incorporated into cell membranes may protect against free radical "lipid peroxidation". This is unhealthy cellular damage (oxidative damage) that antioxidants (such as vitamin E) also help to protect against. Substituting monounsaturated fats for saturated fat may help protect against damage induced by aging and toxins, as well as insulin resistance from poor dietary choices (Vessby et al., 2001).
Vessby, B., et al. Substituting dietary saturated for onounsaturated fat impairs insulin sensitivity in healthy men and women: The KANWU Study. Diabetologia 44: 312-319, 2001.
UNSATURATED - Polyunsaturated
Polyunsaturated fats are most commonly associated with vegetable (plant) or fish oils. They are also referred to as OMEGA-fatty acids. The most important polyunsaturated fatty acids are the essential fatty acids, linoleic acid (OMEGA-6) and linolenic acid (OMEGA-3).
Interestingly, fat from animal products (meat, dairy, and eggs) can provide more than just saturated fat. Depending on the diet of the animal, these products can also provide small amounts of polyunsaturated fats (i.e. feeding hens a diet of flaxmeal can increase the Omega-3 fatty acid content of eggs). In contrast, animals fed corn will have a high Omega-6 fatty acid content.
Modifying the fat content of animals through feeding strategies may be one way to help increase the healthy fat intake of the North American population. In a recent study, modified pork meat with a high content of polyunsaturated fatty acids (PUFAs) and a low content of saturated fat lowered plasma LDL-cholesterol (bad cholesterol) concentrations in women despite a diet of 42% fat (Stewart et al., 2001)!
Stewart, J., et al. Pork with a high content of polyunsaturated fatty acids lowers LDL cholesterol in women. Am. J. Clin. Nutr. 74: 179-187, 2001.