Fats, or lipids, are the third main class of the macronutrients needed in human nutrition. The lipids are found primarily in meats and dairy foods, at least, these are the most visible sources, but most foods contain some fat. Some of the richer vegetable sources of dietary fat are nuts and seeds, soybeans, olives, peanuts, and avocados, and these contain the needed or essential fatty acids (EFAs). Fats are an important component of our diet, and at least a minimum intake is essential. However, many problems are associated with excessive intake of dietary fat, including obesity, cardiovascular disease, and some forms of cancer.
Primarily a form of energy reserves and insulation in the body, fats can be burned to make energy when we need energy and are not getting enough from our diet. Fats are important in transporting other nutrients, such as vitamins A, D, E, and K—the “fat-soluble vitamins.” Fats are also an essential component of the cell membrane, and internal fatty tissues protect the vital organs from trauma and temperature change by providing padding and insulation. Fatty tissue, in fact, even helps regulate body temperature.
An important component of lipids is the fatty acids. Three essential fatty acids are needed biochemically by our bodies and are available to us only from our diet: linoleic acid (LA), arachidonic acid, and linolenic acid (LNA). All are commonly contained in plant oils. Some sources describe linoleic acid as the only true essential fatty acid, as the others may be made from it. With more recent research it appears that this is true in plants but not in humans. We can make arachidonic acid from linoleic acid but not the important linolenic acid. Actually humans need higher amounts of alpha-linolenic acid than the other fatty acids, and luckily, these three fatty acids are commonly found together in food sources anyway. Most of our dietary intake of fat is in the form of triglycerides, which are composed of three fatty acids and a glycerol molecule. A less prevalent form of dietary fat is the phospholipids, such as lecithin, which is important to cell membranes and the brain and nerves. Cholesterol, a member of the sterol family, is both found in foods and manufactured by the body. It is essential to many body functions but has been implicated as a primary factor in heart and blood vessel disease.
Levels of fat intake are highly correlated with weight. High consumption of dietary fat is associated with both increased body fat and obesity. Fats are the most concentrated source of food energy, supplying nine calories per gram, more than double the calorie content of the proteins and carbohydrates. They provide about 42 percent of the calories in the average American diet. A diet that derives closer to 20–25 percent of total calories from fat is probably healthier. A range of 10–20 percent is also acceptable and may be helpful in reducing the incidence and progression of cardiovascular disease by lowering blood levels of triglycerides and cholesterol. Reducing fat intake to this level means cutting down greatly on consumption of red meats and dairy products such as milk, cheese, and butter. Restricting dietary fat (which usually reduces calorie intake as well) while maintaining adequate protein and complex carbohydrate intake is probably the best long-range approach to weight loss, maintenance of optimal body weight, and general good health.
Classification and Biochemistry
Fats, like carbohydrates, are composed of carbon, hydrogen, and oxygen; however, some phospholipids also contain nitrogen and phosphorus. The common property of all fats is that they are insoluble in water and dissolve only in the fat solvents. Tissue lipids (found in normal tissues such as liver or muscle and surrounding or covering the abdominal organs) make up about 10–15 percent of the average adult’s weight; total body fat consists of all the tissue lipids plus the stored fat (this subcutaneous fat and brown fat can vary with weight and diet). Though we should keep our fat levels down, dietary fat is a high-energy food source and gives food a special flavor to which many people are attracted. The lipids include the triglycerides, the phospholipids, and the sterols.
Triglycerides and Fatty Acids
Triglycerides comprise about 95 percent of the lipids in food and in our bodies. They are the storage form of fat when we eat calories in excess of our energy needs. Burning up the stored fat allows us to live without food for periods of time, as I have done during my many fasts.
All triglycerides have a similar structure, being composed of three fatty acids attached to a glycerol molecule. Glycerol is a short-chained carbohydrate molecule that is soluble in water, and when triglycerides are metabolized, the glycerol can be converted to glucose. Fatty acids may differ in their length and their degree of saturation. They are commonly composed of a series of 16–18 carbon molecules attached to hydrogen molecules. The number of hydrogen molecules is what determines the saturation of the fat. When each carbon has its maximum number of hydrogens attached, the fat is said to be saturated—that is, filled to capacity with hydrogen.
Saturated fats, which are commonly found in animals, are hard at room temperature. Lard, suet, and butter are common saturated animal fats; coconut and palm oil are two saturated vegetable oils. Saturated fats are generally more stable than the unsaturated fats and go rancid (undergo an oxidative change in molecular structure) less easily.
Unsaturated fats are of two varieties—monounsaturated and polyunsaturated. If two adjoining carbon atoms are attached by a double bond, there is room for one more pair of hydrogen atoms, and the fatty acid is said to be monounsaturated. Oleic acid, present in olive oil, is a monounsaturated fat. When more than one area of the carbon chain can accept additional hydrogen atoms, the fat is said to be polyunsaturated. Linoleic acid, an essential fatty acid found in safflower oil, soybean oil, and other vegetable oils, is an example of a polyunsaturated fat. Other oils of this category include peanut, corn, and cottonseed oils.
Unsaturated fats are unstable at room temperature and sensitive to interaction with oxygen, light, and heat. This is why storage in dark glass or cans and/or under refrigeration is ideal. There are two other ways besides refrigeration to prevent rancidification (spoiling) of an oil. The first is to use antioxidants. (Points of unsaturation, the weak spots in the fatty acid, can be “attacked” by oxygen; antioxidants protect the molecules from oxidation.) Vitamin E is a common antioxidant; beta-carotene and the chemicals BHA and BHT are others.
Hydrogenation is another way of dealing with the spoilage problem of unsaturated oils. With chemically induced hydrogen saturation of the carbon bonds, the structure of the unsaturated oils is changed. This alters the way the body metabolizes these fats and often changes the physical form, as with margarines. Many manufacturers hydrogenate oils to make margarine and other spreads. These hydrogenated products are consumed in large amounts in the American culture and there is some question as to their carcinogenicity. Also, they no longer provide their once-available polyunsaturated fats and, since they are now saturated, tend to raise the level of blood cholesterol rather than lower it, increasing risk of cardiovascular disease.
The essential fatty acids (EFA) include linoleic, linolenic, and arachidonic acids, collectively termed vitamin F. They are all polyunsaturated fatty acids that cannot ordinarily be synthesized in the body; although, if sufficient quantities of linoleic acid (omega-6) are present, arachidonic acid can be made. Alpha-linolenic, an omega-3 fatty acid that is found in special oils such as linseed (flax), rapeseed (canola), and soybean, is also essential and is the precursor of other important omega-3 oils EPA and DHA commonly found in fish. Ideally we need more linolenic, about a 2:1 ratio, than linoleic. The essential fatty acids are important for normal growth, especially of the blood vessels and nerves, and to keep the skin and other tissues youthful and supple through their lubricating quality.
Linoleic acid is necessary for synthesis of prostaglandins in the E1 and E2 series; linolenic acid is the precursor of the E3 series and other omega-3 fatty acids. Prostaglandins, hormonelike substances, have various effects on smooth muscle and inflammatory processes. The E3 (PGE3) series seems to reduce cholesterol levels as well as platelet aggregation and thrombosis and are generally anti-inflammatory. Prostaglandin E2, related to arachidonic acid, tends to promote platelet aggregation, is more inflammatory, and may even be related to high blood pressure and cancer. PGE1 is mildly inflammatory as it prevents release of arachidonic acid from the cells. Safflower oil is particularly high in linoleic acid, as are sunflower and corn oils; other vegetable oils, nuts, and seeds are also good sources. As stated, soybean, flaxseed, canola, as well as pumpkin and walnut are the best sources of alpha-linolenic acid. (See Vitamin F, Chapter 5, Vitamins.)
Another fatty acid recently shown to be beneficial is eicosapentaenoic acid (EPA). It is a polyunsaturated, omega-3 fatty acid found in high concentrations in cold-water fish. Where it is consumed in large amounts, as among Greenland Eskimos or in fishing villages in Japan, there is reduced cardiovascular disease. EPA seems to reduce serum triglycerides, raise HDL (good) cholesterol, and prolong bleeding time by reducing platelet aggregation, thus preventing thrombosis. Fish such as mackerel, sardines, and salmon are high in eicosapentaenoic acid. Consumption of cold-water fish once or twice a week seems to have a positive effect on cholesterol levels. When taken as a supplement such as MaxEPA (there are many products now available), which contains EPA and another omega-3 fatty acid, decosahexaenoic acid (DHA), may decrease the risk of vascular thrombosis and cardiovascular disease. (See more on EPA in Chapter 7, Accessory Nutrients.)
Phospholipids, of which the most common is lecithin, are important in the structure of all membranes. Their structure is similar to that of triglycerides, but they contain only two fatty acids (both polyunsaturated). The third molecule attached to the glycerol is a phosphatidylcholine molecule (choline is one of the B vitamins). Certain phospholipids also contain inositol (another B vitamin) as phosphatidylinositol, as well as phosphatidylethanolamine, another phospholipid that has several functions, such as being a precursor to choline and acetylcholine. Lecithin is found in highest concentration in soybeans and egg yolks. Recently, egg lecithin has been used in the treatment of acquired immune deficiency syndrome (AIDS). There is some question as to whether supplemental lecithin helps to lower cholesterol levels. It seems to have a mild influence, perhaps due to its polyunsaturated nature. Because of their carbohydrate-fat construction, phospholipids move well in fats as well as in water and thus move easily
|Lamb||Cheese||Almond oil||Sunflower||Peanut||Poultry||Yogurt||Cottonseed||Others||Coconut oil|
|Linoleic Acid (Omega-6)||Linolenic Acid (Omega-3)|
*These foods are listed under their primary lipid components
|Most Vegetable Oils||Flaxseed or Canola Oils|
||can be converted to||
|Linoleic acid (LA)||———––in plants, but–––———||Alpha-linolenic acid (LNA)|
||not in humans||
|Gamma-linolenic acid (GLA)||COLD WATER FISH———||Eicosapentaenoic acid (EPA)|
||such as salmon or mackerel||
||in the diet will introduce||
|Dihomogamma-linolenic||EPA and DHA directly——||Decosahexaenoic acid (DHA)|
|acid (DGLA)||into the body||
|Arachidonic acid (AA)||Prostaglandin E3 series (PGE3)|
|Prostaglandin E1 series (PGE1)|
|Prostaglandin E2 series (PGE2),|
in and out of cells. Another phospholipid, sphingomyelin, consists of glycerol, fatty acid, phosphate, choline, and an amino alcohol called sphingosine and is part of the tissues covering brain and nerve cells, as are the cerebrosides, phospholipids that contain galactose, fatty acid, and sphingosine.
Sterols, the third primary lipid, include cholesterol, phytosterols (plant sterols), and some of the steroid hormones. Cholesterol, the best known of the sterols, is the precursor of the bile acids and the sex hormones. Manufactured in the body, primarily in the liver, although all tissues of the body except the brain can make it, cholesterol is present in almost all cells and is particularly high in the liver, brain and nervous tissue, and the blood. Cholesterol, like lecithin, is also available in foods, such as egg yolk, meats, and other animal fats, including milk products. It is not readily available in most vegetable foods.
Cholesterol has been implicated in occlusive cardiovascular disease, causing plaque and obstruction of the arteries. The cholesterol in foods, however, is not really the villain. It is the oxidized cholesterol in the blood that causes the trouble, and the level of this is more a function of total dietary fat intake and genetically determined aspects of cholesterol metabolism, than of the amount of cholesterol in our food. In particular, a transport mechanism of cholesterol called the low-density lipoprotein (LDL) is likely the villain in our society’s rampant disease—atherosclerosis. This LDL is contrasted to the so-called “good” cholesterol-carrying high-density lipoprotein (HDL). The ratio of these two (LDL:HDL) is the blood test currently favored to evaluate our risk of cardiovascular disease.
Lipoproteins, the fat-protein combination molecules circulating in our blood and tissues, can move around the body only if they are surrounded by protein, because fats are not soluble in water (the basic makeup of blood and lymph). The fatty acids in these large lipoprotein molecules are positioned at the inside, as far away from the water as possible. The higher the protein portion in these molecules, the higher their density.
There are several important lipoproteins.
Chylomicrons are made in the intestines to transport digested fats (mainly triglycerides) into the circulation to be carried to the liver and other organs.
VLDLs (very-low-density lipoproteins) are made in the intestines and the liver to carry fats throughout the body. Though VLDLs carry mostly triglycerides, they carry a small component, maybe 5–15 percent, of the cholesterol to the tissues of the body.
LDLs (low-density lipoproteins) are made by the liver (and possibly by transformation of VLDLs in the blood) and are the primary molecular complexes that carry cholesterol in the blood to the organs and cells. LDL contains the highest percentage of cholesterol in most people.
HDLs (high-density lipoproteins) are large, dense protein-fat molecules that circulate in the blood, picking up already used or unused cholesterol and cholesterol esters and taking them back to the liver as part of a recycling process. Where in the body HDL is made is not certain (probably in the liver), but it may be the most protective form of lipoprotein in preventing buildup of cholesterol. People with higher HDL levels have less risk of cardiovascular disease because their cholesterol is cleared more readily from the blood. It also appears that HDL may be able to collect cholesterol from artery plaque, thus reversing the atherosclerotic process that leads to heart attacks. HDL will deliver cholesterol to the VLDL, converting them to LDL, which have more density; the liver then removes the LDLs from the blood and converts their cholesterol into bile acids, which are then eliminated.
Estrogen helps raise HDL levels, and women have less cardiovascular risk than men, possibly because of this hormone. Smoking, obesity, and a sedentary lifestyle cause a low level of HDLs, whereas low dietary fat and cholesterol intake, aerobic exercise, and keeping weight near the ideal level are factors that help raise the HDL level and diminish cardiovascular risk.
Digestion and Metabolism
Because of their viscosity and insolubility in water, fats and oil require our bodies to take special care to digest and transport them to the cells and organs. The chewing process is the first act of digestion to help separate the fats. In the stomach, gastric lipase has a very minimal effect in beginning the breakdown of fats; other enzymes and hydrochloric acid do more to digest protein and carbohydrates and free the lipids from the food. Fats and oils are less dense than water; unless they are emulsified they rise and pool at the top of the gastric contents and so are acted upon last, thus taking the longest to digest and in some ways slowing the digestion. Fatty meals seem to satisfy us longer as they cause the stomach to empty more slowly.
When the fats move into the small intestine, their main place of digestion, bile is secreted from the gallbladder (bile is made by the liver and concentrated in the gallbladder). Bile first emulsifies the fats, that is, breaks down the fat globules into smaller groups of molecules so the other enzymes can actually work on the individual triglycerides to release the fatty acids. Pancreatic lipase is the main enzyme that splits the triglycerides into diglycerides and monoglycerides, which are ultimately hydrolyzed into their components, fatty acids and glycerol.
When the digestive system is working well, most (up to 95 percent) dietary fats are absorbed into the body. (Some are excreted through the colon.) Many of the fatty acids need now be altered in order to be absorbed and transported to the liver, the principal site of fat metabolism. The short-chained fatty acids, up to 12 carbons in length, are more hydrophilic, or attracted to water, and can be absorbed directly through the cell membranes of the small intestine villi (small protrusions into the intestinal lumen lined by epithelial cells and filled with capillaries; they increase the absorption surface of the small intestine). Within the villi, these short-chained fatty acids are picked up in the capillaries and transported through the bloodstream to the liver.
The longer-chained fatty acids with 14 carbons or more, and the mono- and diglycerides must be reconverted to triglycerides in the intestinal wall. These triglycerides are then surrounded with a protective protein coat (like rain gear) in order to be transported to the liver. These become large transporter molecules, the chylomicrons, which first go into the lymph circulation before entering the blood to go to the liver. VLDLs also carry some of the triglyceride molecules. Phospholipids and cholesterol are also incorporated into chylomicrons in order to get to the liver. After a fatty meal, the blood may be filled with chylomicrons, and the blood serum may have a milky appearance.
In the multifunctional liver, the chylomicrons are separated and the fats may be dismantled and reassembled into other needed fats. Lipids can also combine with proteins to make lipoproteins, with phosphate to make phospholipids, or with carbohydrates to form glycolipids. In the blood, free fatty acids, the active lipids for cell use, are bound to albumin, a protein. The other fats, such as cholesterol, are bound mainly to the high- and low-density lipoproteins. Each cell can take the triglycerides out of the lipoproteins and use the fatty acids for energy. Excess fat in the body is often stored in the fat cells. The adult human has a set number of fat cells, which enlarge to accommodate the increased triglyceride stores; an obese person’s fat cells may be many times larger than a thin person’s. These fat cells are formed at specific times of growth, such as infancy and adolescence. So later in life when we work to lose or gain weight, we are just shrinking or expanding our existing cells. And these fat cells are in a constant state of metabolism; they do not just sit there as many people think.
Lipids perform many life-supporting functions in each cell of our body. They are part of every cell membrane and every organ and tissue. The fatty acids keep our cells strong to protect against invasion by microorganisms or damage by chemicals. Fats are very important to our nervous system and in the manufacture of the steroid and sex hormones and the important hormonelike prostaglandins. Cholesterol is responsible for some of these functions that support the health of the brain, nervous system, liver, blood, and skin.
Beside the fact that fats add a lot of the flavor to the foods that many of us are used to and savor, such as buttery treats, gravies, and juicy meats, fats serve three primary functions in the body. They are first and foremost a ready energy source, contributing nine calories for every gram of fat used, more than 4,000 calories per pound of fat.
From Ingestion to the Liver
|Chewing begins to separate fats.|
|Hydrochloric acid begins to break down fats and|
separate lipids from
foods so that Pancreatic Lipase
can begin splitting the fats.
|Bile emulsifies fats, breaking them down further|
so that enzymes can act on individual Triglycerides
to release Fatty Acids. Pancreatic Lipase splits
Triglycerides into Diglycerides, Monoglycerides
and Fatty Acids.
|Diglycerides and Monoglycerides are then|
hydrolyzed into their components:
|FATTY ACIDS & GLYCEROL|
|Shorter chain Fatty Acids (up to 12 carbons)|
are attracted to water and are absorbed directly
through the intestinal wall. Longer chain Fatty
Acids, Diglycerides and Monoglycerides are
reconverted into Triglycerides to be transported
through the intestinal the help of GLYCEROL.
The bloodstream then carries them to the LIVER.
|THE PRINCIPAL SITE OF FAT METABOLISM|
That’s a lot of potential energy we are carrying, both from dietary intake of those fatty foods and in the stored fat of our body. This stored fat helps give the body its curves and can be used for fuel during times of reduced food intake.
Fats in the body also act as a protective blanket shielding the organs from trauma and cold. The fat deposits surround and hold in place important organs such as the heart and kidneys. Fat below the skin helps prevent heat loss and protects against external temperature changes.
Third, as I have already said, the lipids are an integral part of the cell membranes. Every body cell and thus every tissue and organ is dependent on lipids in the body for its health. Also, fats are needed for absorption of vitamins A, D, E, and K, and by assisting in vitamin D absorption, they help calcium get into the body, especially to the bones and teeth.
Requirements, Deficiency, and Excess
There is no specific Recommended Daily Allowance (RDA) for dietary fats, though the National Academy of Science suggests at least 15–25 grams (that’s less than 10 percent of the fat in the average diet) of fats from foods, including some vegetable sources, to obtain sufficient amounts of our essential fatty acids. Though we could actually live on very little fat, meeting our minimum requirements is seldom difficult, since it is found in many protein and carbohydrate foods. Basically, our only dietary fat requirement is for the key essential fatty acids, linolenic (omega-3) and linoleic (omega-6), ranging from 2–5 percent of calorie intake. Our needs are based on many factors, and most people need a 2:1 ratio of omega-3 to omega-6 fatty acids. Whenever supplementing essential fatty acids, such as safflower, flaxseed, or canola oils, it is wise to take additional vitamin E (100–400 IU) to reduce potential oxidation of these polyunsaturated oils.
A general health recommendation is that our diet provide no more than 25–30 percent* of our total calories from fat nutrients, and that is for food intake in an amount just sufficient to maintain optimum weight, not to supply any excess body weight. Climate and body temperature are important factors in determining fat requirements. If we get cold easily, we may need more fat in our diet, provided our weight and thyroid are normal.
Since linoleic and linolenic acids are polyunsaturated fats available mainly in vegetable sources, such as corn, safflower, and soybean oils, as well as many nuts and seeds, it is conceivable that we could eat solely animal fats and still not get our needed amounts of essential fatty acids. Deficiency of vitamin F (essential fatty acids) can lead to dryness, scaliness, or eczema of the skin, as well as to reductions in the oil-soluble vitamins A, D, E, and K. Also, if there is deficient fat intake during growth periods, a retardation in the growing process may occur. Fortunately, however, fat deficiencies are not very common, though obtaining the right balance of fats, particularly of alpha-linolenic acid, given the standard diet is not easy, but very important.
*This can be analyzed through a diet record (see Appendix). Since a gram of fat es 9 calories, a 2000-calorie daily diet could include 500–600 calories of fat, or 55–66 grams, daily.
In most Western cultures, as in American society, the real concern is over an excess intake of fat. The average daily diet (higher than needed for ideal weight and health) includes about 150 grams of fat, providing 1,350 calories, well over 40–50 percent of needed daily dietary calories. This is an increase over fat consumption earlier in the century, which averaged about 120 grams per day. And much of this is from the so-called “unhealthy” fats—meat and its saturated fats, hydrogenated oils, such as vegetable shortening, and foods fried in cooking oils. In the last 10–15 years, however, there has been a great deal of public education about the high-fat diet and, as a result, a small reduction in average fat intake has occurred. In the early 1970s, fat intake was about 160 grams per day; now it has dropped to under 150 grams.
An analysis of fat consumption of the typical North American’s diet was done by the Select Committee on Nutrition and Human Needs of the U.S. Senate. The reason for this study is the obvious role that dietary fat plays in disease. In 1977, they published their Dietary Goal for the United States, revealing that the average American consumed 42 percent of his or her calories from lipids, approximately 16 percent saturated fats, 19 percent monosaturated, and 7 percent polyunsaturated. To obtain a higher percentage of polyunsaturated fat and a lower percentage of fats in total, the Senate Select Committee has suggested the following:
- Reduce the consumption of red meats, organ meats, eggs, and dairy products in the diet.
- Choose low-fat protein sources, such as fish, turkey, chicken, and legumes (dried peas and beans).
- When consuming meats, use lean cuts and trim excess fats.
- Substitute skim and low-fat milk products for whole-fat dairy foods.
- Broil, bake, or boil foods instead of frying.
- Increase the consumption of fruits, vegetables, and whole grains in the diet. More long-range and specific goals* for our fat consumption include:
- Reduce dietary fat consumption from about 40 percent to 30 percent of calorie intake.
- Reduce saturated fats to about 10 percent of intake, with approximately equal amounts of monounsaturated and polyunsaturated fats—that is, more vegetable-source lipids.
- Reduce cholesterol intake to about 300 mg. per day.
Dietary Fat and Disease
A topic of great concern in modern nutritional medicine, which will be discussed throughout this book, is the correlation between increased dietary fat intake and disease. Research continues regarding the relationship between disease and cholesterol and the types of fats consumed. We now know that two aspects of diet must be considered: first, the total amount of fat intake—that is, the percentage of the total diet consisting of fats and oils, both saturated and unsaturated fats (mono- or polyunsaturated), and second, the types of fats consumed. Saturated and hydrogenated fats seem to be worse in regard to increasing cholesterol and causing vascular congestive problems than the vegetable-source unsaturated ones, which may actually improve cholesterol by reducing the LDL:HDL ratio and decreasing total cholesterol. Fried foods seem to be more difficult for the body to process, as well.
Of the diseases related to increased fat intake, number one is atherosclerosis. Clogging, or atherosclerosis, of the coronary arteries (the blood vessels that nourish the heart muscle itself with blood) is the disease process causing the most deaths in the Western “affluent diet” cultures. Clogging vital arteries with plaque (consisting of fat, mucopolysaccharides, calcium, platelets, and smooth muscle cells) decreases the delivery of life-supporting blood to the tissues and is related to a variety of other diseases. Narrowing and stiffness of the blood vessel resulting from arterial plaque leads to high blood pressure, or hypertension, which forces the heart to work harder to get the blood to the body. This constant extra effort can lead to enlargement of the heart, general heart disease, and congestive heart failure. Coronary artery disease leads to the physical limitations associated with angina pectoris and is the primary cause for the big business of coronary artery bypass surgery.
Two major types of cancer are associated with excessive dietary fat intake. The first one is the most common cancer in men and women combined, cancer of the colon and rectum. The other is the most common major female cancer, cancer of the breast. Both of these can be deadly, especially if they are not diagnosed early, and both are associated with a high-fat, low-fiber diet. There is also an association between prostate cancer in men and uterine and ovarian cancer in women and high dietary fat consumption, particularly saturated fats found in animal foods.
Obesity is much more likely in people who eat a high-fat diet, which is often a high-calorie diet, since each gram of fat contains nine calories instead of the four calories in each gram of protein or carbohydrate. With obesity comes an increased risk of all the previously mentioned diseases, such as atherosclerosis, hypertension, and certain cancers, besides a variety of other problems, including adult-onset diabetes.
I want to further delineate the role of fats in cardiovascular diseases. Saturated fats and hydrogenated vegetable oils, which contain high amounts of saturated fats in place of their once polyunsaturated oils, both raise serum cholesterol. The liver makes cholesterol from saturated fats. A number of factors can increase the risk of cardiovascular disease. The top three are elevated serum cholesterol, smoking, and high blood pressure. (For cholesterol, the most important factor is elevated LDL.) Anyone who smokes, has high blood pressure, and has a serum cholesterol level of more than 250, especially with a high LDL:HDL ratio, is almost certain to close off his or her arteries relatively rapidly. Other risk factors for the cardiovascular diseases include stress, obesity, gender (the female hormone estrogen is protective for women), heredity (for heart disease or for higher cholesterol levels), lack of exercise, and elevated blood triglyceride levels. We are in a position to reduce most of these risk factors by changing our lifestyles and dietary habits, and doing so will significantly reduce our chances of developing blood vessel and heart disease. Overall, the best way to lower risks of cardiovascular disease is to reduce total and saturated fat intake, keep the blood pressure normal, not smoke, and exercise regularly.
The current theory about the body’s process of forming plaque in the arteries is rather complex. A simple version is as follows: The liver produces cholesterol mainly from the saturated fats. The LDLs are the primary carriers of cholesterol through the blood and to the plaques, so the higher the intake of saturated fats (increasing cholesterol and LDLs), the greater the potential for plaque formation. The smooth muscle cells in the middle layer of the arterial wall invade the inner wall to help form the plaques, which start from some irritation of the inner lining that may come from irritants such as smoking, viruses, chemicals in the diet, and increased stress. High blood pressure also causes increased stress on the artery walls. These irritations attract platelets and LDL cholesterols and thicken the wall with plaque. HDLs carry cholesterol away from plaque and out of the bloodstream back to the liver for reprocessing, so higher HDL levels reduce the likelihood of plaque formation.
An important key to preventing cardiovascular disease is lowering serum cholesterol and LDL levels and raising the HDL cholesterol in ratio to the total cholesterol and to LDL. This can be done by following my repeated suggestion, which is also that of the government and the American Heart Association: lower intake of saturated fats found in meats and animal foods, in milk products, and in hydrogenated oils and increase the proportion of mono- and polyunsaturated vegetable-source fats and oils in the diet. In general, a fat-modified diet can lower serum cholesterol from 20–40 percent, especially if exercise is included. Polyunsaturated fats specifically can lower cholesterol by reducing lipoprotein (LDL) synthesis and increasing lipoprotein breakdown, as well as by the effect of the essential fatty acid linolenic acid. Linolenic acid reduces plaque formation and thrombosis by decreasing platelet aggregation, promoting prostaglandin (E3 series) synthesis (which also influences platelets), and decreasing LDLs. The essential fatty acids also influence the intravascular coagulation as well as energy metabolism within the myocardial muscle of the heart.
One of the main ways to raise HDL levels is exercise—that is, regular, prolonged, aerobic-type exercise. Females normally have higher levels of HDL and thus a reduced cardiovascular disease risk. Smoking lowers HDL, so stopping smoking will help raise it, besides reducing the increased risk caused by the vascular irritation of smoking. Also, the polyunsaturated fat level influences the HDL level, and the omega-3 fatty acids, particularly eicosapentaenoic acid (EPA) found in fish, help to raise HDL levels and reduce the risk of cardiovascular disease.
Factors that help lower LDL levels, besides reducing saturated fat and dietary cholesterol, include eating a relatively higher amount of mono- and polyunsaturated fats compared to the saturated or hydrogenated varieties; adding specific nutrients, such as sufficient dietary vitamin C (a deficiency of vitamin C can raise LDL); avoiding excess copper, sodium, and iron intakes, which can raise LDL; and getting sufficient chromium and natural dietary fluoride, as deficiencies can raise LDL. A diet high in animal protein can raise LDL, whereas eating a higher percentage of vegetable protein helps to lower it. Sufficient fiber in the diet, particularly from the legumes, vegetables, and fruits (such as apples that contain pectin), helps in lowering LDL as well.
With regard to nutrition and cancer (our second most prevalent deadly adult disease), it is likely that more than 50 percent (probably more) of cancer occurrences are related at least in part to diet. The Hunza tribes of Pakistan who are known for their longevity and have the lowest known cancer rates eat an exclusively natural, chemical-free diet of foods they grow themselves. High animal protein intake and low dietary fiber consumption are two important factors increasing cancer incidence, but the one that is being shown to be the most significant is increasingly high intake of fats, particularly the saturated animal fats, in the diet. Many chemicals in foods, used as preservatives or from herbicides and pesticides, may be carcinogenic in the body, especially in the gastrointestinal tract, and many of these chemicals are stored in animal fats. Artificial red dyes, cyclamate, nitrites and nitrates in processed meats, and saccharin have all been implicated in cancer.
The theory of how fat can cause cancer in the colon and rectum is based on the fact that fats in the diet cause release of bile acids from the gallbladder and liver into the intestine to help emulsify the fats. High-fat diets stimulate increased bile acid levels in the colon. Fat in the diet also weakens the metabolism of the normal colon bacteria which, when functioning optimally, may help protect the colon lining from carcinogens. These altered microflora interact with the bile acids to potentially create compounds that may cause cancer. An increased fiber content, even in a higher-fat diet, seems to be protective by increasing bowel motility, by diluting these carcinogenic substances through its bulking action, and by improving bacterial detoxification functions.
More than 100,000 new cases of cancer of the colon are diagnosed each year. The high-fat diet increases the incidence of this cancer, which, if diagnosed early, can usually be cured through major surgery, a drastic measure that could be prevented. The high-fat diet is also commonly associated with a higher fried-food component and lower fiber content, two other important dietary factors in carcinogenesis in the colon.
Numerous studies have shown the relationship of dietary fat to colon cancer. Research with the Seventh-Day Adventists who eat a vegetarian diet reveals that their incidence of colon cancer is much lower than average. They usually consume a diet higher in fiber and lower in fat than the average American. A study of the Mormon high-fiber diet has more clearly isolated dietary fats as the main connection to colon cancer incidence. Other nutritional qualities of the fruit and vegetable fiber foods seem to help inhibit cancer formation as well. Vitamins C and E, beta-carotene, and selenium, plus the plant sterols and antioxidant phenolic compounds like bioflavonoids from foods such as berries and citrus fruits, all seem to be beneficial factors. The cruciferous vegetables, such as broccoli and cabbage, seem to have other factors such as sulfhydryl-containing molecules besides the fiber that may protect against the development of cancer.
Cancer of the breast and a high-fat diet have been shown to be related for some time. It is thought that saturated fats generate more cholesterol and higher estrogen levels in women. This theory supports the dietary fat and breast cancer relationship as estrogen is particularly related to increased incidence of female breast cancer. Although the dietary fat and breast cancer question is not conclusively answered, it is generally agreed that, in regards to this disease, a low-fat, high-complex-carbohydrate diet minimizing alcohol, cigarettes, and preserved and chemical foods is still the best way to live to help prevent breast cancer. Countries, such as Japan, whose people traditionally eat a low-fat diet have a much lower incidence of breast cancer than countries eating higher quantities of animal fat, such as the United States, Australia, New Zealand, and the countries of Western Europe. Japanese who eat more Westernized diets in their own country or who move to a country eating a Western diet have a higher incidence of breast cancer. In the United States, Seventh-Day Adventist women on a vegetarian diet exhibit a lower incidence of this disease.
Not all recent studies correlate higher cancer incidence solely with total fat intake. There is some question as to whether certain fats are more significant than others. Milk fat and dairy foods have been implicated in several studies. The strongest correlation for breast cancer has been with the intake of the trans-fatty acids that are created when vegetable oils are hydrogenated to make margarine and solid vegetable shortening. There is even some concern with the polyunsaturated fats. Since they are less stable, they can go through peroxidation, which can lead to the formation of epoxides that may be cancer causing. This is especially true when these fats are heated. (Vitamin E and beta-carotene are two antioxidants which protect against the peroxidation process.) Because of this, I suggest using polyunsaturates moderately, along with some monosaturates, such as olive oil, which are more stable, while cutting down on the saturated fats.
The specific cancer preventive diet put out in 1984 by the American Cancer Society’s Medical and Scientific Committee includes the following suggestions:
- Avoid Obesity. Obese people have higher incidences of many cancers, particularly of the breast, colon, stomach, gallbladder, and uterus.
- Reduce total fat intake. As we have just discussed, dietary fat is mainly associated with increased risk of colon, breast, and prostate cancer. It also adds to obesity, another risk.
- Eat more high-fiber foods, particularly fresh fruit and vegetables and whole grains. This is not conclusive, but it does seem that these nutrient rich, low-calorie and low-fat foods reduce the likelihood of cancer through a variety of means.
- Include in the diet those foods that are rich in vitamin A and vitamin C. Beta-carotene, the precursor of vitamin A, is found in many fruits and vegetables, such as carrots, spinach, tomatoes, apricots, peaches, and melons. This nutrient is thought to help reduce carcinogenesis. Vitamin C, found in high amounts in citrus fruits and many vegetables, may also prevent cancer. It interferes with production of nitrosamine, a carcinogen formed from dietary nitrites in preserved foods.
- Include the cruciferous vegetables, such as broccoli, Brussels sprouts, cabbage, and cauliflower, in the diet. Their actions are not known exactly, but these foods are thought to help prevent cancer.
- Minimize the consumption of alcoholic beverages. Alcohol increases the risks for certain cancers, which are even more liable to occur in those who smoke.
- Avoid the consumption of salt-cured, smoked, and nitrate-treated foods. Nitrates and nitrites can form nitrosamine, a carcinogen, in the digestive tract. Also, the smoking of foods can cause fats to be converted to polycyclic aromatic hydrocarbons, which are also carcinogenic.
The suggestions for reducing cardiovascular diseases include the following:
- Reduce the amount of total fats in the diet from more than 40 percent (the current average) of total calories to approximately 30 percent or below.
- Specifically reduce the saturated-fat intake by reducing consumption of red meats and whole milk products, such as cheeses and butter.
- Reduce intake of hydrogenated fat (also saturated) found in cooking oils and margarine.
- Raise the ratio of poly-unsaturated fats to saturated fats in the diet by maintaining or slightly increasing the dietary intake of polyunsaturated fats found in vegetable oils such as safflower, corn, and soybean oils and in most seeds and nuts. These also contain high amounts of the essential fatty acids, which are important to healthy body function.
- Eat more cold-water fish (at least twice weekly), rather than red meats, for the omega-3 fatty acid content.
- Keep the blood pressure under control, do not smoke, and exercise regularly.