Download Lipids

LIPIDS
- Fat is an essential nutrient. The term lipid applies to a broad range of organic
molecules that dissolve easily in organic solvents such as alcohol, ether, or
acetone, but are much less soluble in water.
- Lipids generally are hydrophobic (water fearing) and lipophilic (fat loving).
They can be identified as:
a) Visible fats or oils: They account about 40% of the lipids in the diet. (e.g.
butter, margarine, meat fat, vegetable oil).
b) Invisible fats: They account about 60% of the lipids in the diet (e.g. found in
milk, whole grains, cereals, nuts).
- The main classes of lipids found in foods and in the body are triglycerides,
phospholipids, and sterols.
a) Triglycerides are the largest category of lipids. In the body, fat cells
store triglycerides in adipose tissue.
b) Phospholibid is a compound that consists of a glycerol molecule
bonded to two fatty acid molecules and phosphate group with a nitrogencontaining component. About 2 percent of dietary lipids are phospholipids.
They are found in foods of both plant and animal origin, and the body also
makes those that it needs. Unlike other lipids, phospholipids are soluble in both
fat and water. These molecules play crucial roles as major constituents in cell
membranes, and in blood and body fluids where they help keep fats suspended
in these watery fluids.
c) Sterols: a category of lipids that includes cholesterol. Sterols are
hydrocarbons with several rings in their structures. Only a small percentage of
our dietary lipids are sterols (e.g. cholesterol). The body makes cholesterol,
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which is an important component of cell membranes and a precursor in the
synthesis of sex hormones, adrenal hormones (e.g., cortisol), vitamin D, and
bile acids.
- Eicosanoids are a class of hormone-like substances formed in the body from
long-chain fatty acids. They are crucial chemical regulators. They have
profound localized effects through their influence on inflammatory processes,
blood vessel dilation and constriction, blood clotting, and more.
Fatty Acids
- Fatty acids are common components of both triglycerides and phospholipids
and are often attached to cholesterol.
- Fatty acids determine the characteristics of a fat, such as whether it is solid or
liquid at room temperature. Some free fatty acids have their own distinct flavor
(e.g. Butyric acid is the fatty acid that gives butter its flavor).
- Fatty acids are basically chains of carbon atoms with an organic acid
(carboxyl) group (—COOH) at one end and a methyl group (—CH3) at the
other end.
Chain Length
- Fatty acids differ in chain length (the number of carbons in the chain). Foods
contain fatty acids with chain lengths of 4 to 24 carbons, and most have an even
number of carbons. They are grouped as short-chain (< 6 carbons), mediumchain (6-10 carbons), and long-chain (12 or more carbons) fatty acids.
- As chain length increases, fatty acids become more solid at room temperature.
- Each carbon in these chains can be numbered for identification, but it’s
important to know from which end the counting begins. In organic chemistry,
the scientific naming of fatty acids counts from the carbon at the acid (-COOH)
end.
This
carbon
is
the
alpha
carbon,
and
the
carbon
at
the
methyl (—CH3) end is the omega carbon. Named after the first and last letters
of the Greek alphabet, respectively). Nutritionists identify double-bond
locations by their location relative to the omega carbon.
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Saturation
Within a fatty acid chain, each carbon atom has four bonds. When a carbon is
joined to adjacent carbons with single bonds (—C—C—C—), it still has two
bonds available for other atoms, such as hydrogen atoms. If all the carbons in
the chain are joined with single bonds and the remaining bonds are filled with
hydrogen, the fatty acid is called a saturated fatty acid. It is fully loaded
(saturated) with hydrogen.
However, if adjoining carbons are connected by a double bond (C=C), there are
two fewer bonds holding hydrogen, so the chain is not saturated with hydrogen.
This is an unsaturated fatty acid. A fatty acid with one double bond is a
monounsaturated fatty acid (MUFA); one with two or more double bonds is a
polyunsaturated fatty acid ( PUFA).
Saturated fatty acid: A fatty acid completely filled by hydrogen with all
carbons in the chain linked by single bonds.
Unsaturated fatty acid: The carbon chain contains one or more double bonds.
Hydrogen, oxygen, or some other atom can attach easily to a double bond.
a) Monounsaturated fatty acid: The carbon chain contains one double
bond.
b) Polyunsaturated fatty acid: The carbon chain contains two or more
double bonds.
- Foods never contain only unsaturated or only saturated fatty acids.
- Food fats with more unsaturated fatty acids typically have a lower melting
point and are more likely to be liquid at room temperature.
- Foods rich in saturated fatty acids tend to be solid at room temperature and
have a higher melting point.
- For example, the 18-carbon saturated fatty acid, stearic acid, is abundant in
chocolate and meat fats, both of which are solid at room temperature. The major
fatty acid of olive oil is 18-carbon monounsaturated oleic acid. Olive oil is a
thick liquid at room temperature, but may solidify under refrigeration.
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Omega-3, Omega-6, and Omega-9 Fatty Acids
The location of the double bond closest to the omega (methyl) end of the fatty
acid chain identifies a fatty acid’s family. Oleic acid has one double bond, at
carbon 9 (counting from the omega end of the chain) and is classified as an
omega-9 fatty acid. Linoleic acid has double bonds at carbon-6 and carbon-9
but is an omega-6 fatty acid, because the first double bond occurs at carbon 6.
Omega-3 fatty acids such as alpha-linolenic acid have a double bond at carbon
3, plus two or more double bonds.
Sources of Omega-3 Fatty Acid
Generally 18-carbon polyunsaturated fatty acids are found in plant foods.
Soybean oil, canola oil, and walnuts are contributors of alpha-linolenic acid, the
essential omega-3 fatty acid. However, the most generous source is flaxseed,
which is more than 50 percent alpha-linolenic. The longer chain omega-3s, EPA
and DHA are found in fatty fish (e.g., salmon, tuna).
Sources of Omega-6 Fatty Acid
Good sources of the 18-carbon, omega-6 fatty acid linoleic acid include seeds,
nuts, and the richest source, common vegetable oils.
Iinoleic acid: An essential omega-6 fatty acid that contains 18 carbon atoms
and 2 carbon-carbon double bonds (18:2).
alpha-linolenic acid: An essential omega-3 fatty acid that contains 18 carbon
atoms and 3 carbon-carbon double bonds (18:3).
Nonessential and Essential Fatty Acids
- The body synthesizing most fatty acids.
- The liver adds carbons in a process called elongation to build storage and
structural fats, to manufacture the fat in breast milk, or to make fatty acids for
use in other compounds.
- For example, the body synthesizes oleic acid, an omega-9 fatty acid, by
removing hydrogens from carbons 9 and 10 of saturated stearic acid, thus
creating a double bond at carbon 9. This process is called desaturation. Oleic
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acid can be elongated further and desaturated to create other necessary fatty
acids.
- Because the body can make saturated and omega-9 fatty acids, it is not
essential to get them in your diet. We therefore call them nonessential fatty
acids.
- The human body cannot produce carbon-carbon double bonds before the ninth
carbon from the methyl end, so we cannot manufacture certain fatty acids such
as omega-6 linoleic or omega-3 alpha-linolenic acids. They must come from
food, so they’re called essential fatty acids (EFA).
- Nonessential fatty acid: The fatty acids that your body can make when they
are needed. It is not necessary to consume them in the diet.
- Essential fatty acids: Those the body needs but cannot synthesize, and which
must be obtained from diet.
Triglycerides
Triglycerides are the major lipid in both the diet and the body.
Triglyceride Structure
- A triglyceride is three fatty acids attached to a molecule of glycerol. Both in
food and in the body, most fatty acids exist as part of a triglyceride molecule.
- Glycerol: An alcohol that contains 3 carbon atoms, each of which has an
attached hydroxyl group (OH). It forms the backbone of mono-, di-, and
triglycerides.
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Triglyceride Functions
1) Energy Source
- Fat is a rich source of calories. fat is protein-sparing; that is, fat is burned for
energy, sparing valuable proteins for their important roles such as muscle tissue,
enzymes and antibodies.
- Glucose is virtually the sole fuel for the brain except during prolonged
starvation, and fat is the preferred fuel of muscle tissue at rest. During physical
activity, glucose and glycogen join fat in supplying energy.
- High-fat foods are higher in calories than high-protein or high-carbohydrate
foods.
- One gram of fat= 9 kilocalories
- One gram of CHO= 4 kilocalories
- One gram of protein= 4 kilocalories
- One gram of alcohol= 9 kilocalories
2) Energy Reserve
- The body store excess dietary fat as body fat. The fat is stored inside fat cells
called adipocytes, which form body fat tissue.
- Cells break down these lipids to release energy.
3) Protection
- Fat tissue accounts for about 15 to 30 percent of a person’s body weight.
- It serves an important function by cushioning and shielding delicate organs.
Women have extra fat, most noticeably in the breasts and hips, to help shield
reproductive organs and to guarantee adequate calories during pregnancy. Other
fat tissue is subcutaneous, lying under the skin, where it protects the body.
- ~ 60 percent of brain structure is fat.
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4) Carrier of Fat-Soluble Compounds
- Dietary fats dissolve and transport micro-nutrients such as fat-soluble
vitamins.
- Dietary fats carry fat-soluble substances through the digestive process,
improving their intestinal absorption or bioavailability.
- People who suffer from fat malabsorption disorders have a risk of developing
fat-soluble vitamin deficiency.
- removing a food’s lipid portion; for example, removing butterfat from milk
also removes fat-soluble vitamins. Fat-soluble vitamins may be destroyed in fat
processing; for example, some vitamin E is lost in processing vegetable oils.
5) Improving flavor, texture and odor of food
As a food component or as an ingredient, fat contributes greatly to the flavor,
odor, and texture of food… simply, it makes food taste good.
Isomers
Unsaturated fatty acids can exist in different isomers. In most naturally
occurring unsaturated fatty acids, the hydrogens next to double bonds are on the
same side of the carbon chain. This is called a cis formation. The carbon chain
of a cis fatty acid is bent. If the double bond is altered, moving the hydrogens
across from each other, the formation is called trans and the carbon chain is
straighter.
Hydrogenation
- Commercial process of hydrogenation, adding hydrogens where some of the
double bonds are located in the unsaturated fatty acid, creates most of our
dietary trans fatty acids.
- Hydrogenation involves breaking some of the double bonds in unsaturated
fatty acids and adding hydrogen. This process produces a harder, more saturated
fat one that is more effective for making snack foods, and one that spreads like
butter. While hydrogenation protects the fat from oxidation and rancidity, it also
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changes some of the double bonds in the fat’s structure to the trans
configuration.
- Trans fatty acids have become a health concern because they have been
implicated in raising blood cholesterol levels.
Cis fatty acids The hydrogens surrounding a double bond are both on the same
side of the carbon chain, causing a bend in the chain. Most naturally occurring
unsaturated fatty acids are cis fatty acids.
Trans fatty acids In trans fatty acids, the hydrogens surrounding a double bond
are on opposite sides of the carbon chain. The bent carbon chain straightens out,
and the fatty acid becomes more solid.
Hydrogenation A chemical reaction in which hydrogen atoms are added to
carbon-carbon double bonds, converting them to single bonds. Hydrogenation
of monounsaturated and polyunsaturated fatty acids reduces the number of
double bonds they contain, thereby making them more saturated.
Oxidation
When an unsaturated fat comes in contact with air, oxygen atoms can attach at
each of its double-bond sites. The result is oxidative rancidity. Oxidized fats
damage body tissues (e.g. blood vessels).
The more unsaturated oil (the more double bonds it has), the more vulnerable
it is to oxidation. Naturally occurring vitamin E inhibits oxidation.
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Digestion and Absorption
- Lipids generally are not water-soluble and digestive secretions are all water
based, therefore, the body has to treat lipids differently to digest them.
1) Digestion
- Triglycerides are water insoluble, and the enzymes needed to digest them are
found in a watery environment; therefore, preparing triglycerides for digestion
is a more elaborate process than for either carbohydrates or proteins.
- In the mouth, a combination of chewing and the work of lingual lipase get the
digestive process rolling, with the small amount of dietary phospholipid
providing emulsification.
- In the stomach, gastric lipase joins in, and the stomach’s churning and
contractions keep the fat dispersed. After two to four hours in the stomach,
about 30 percent of dietary triglycerides have been broken down to diglycerides
and free fatty acids.
- Fat in the small intestine stimulates the release of the hormones
cholecystokinin (CCK) and secretin from duodenal cells. CCK signals the
gallbladder to contract, sending bile down the bile duct and into the duodenum.
Secretin signals the pancreas to release pancreatic juice rich in pancreatic lipase,
which joins the bile just before entering the duodenum where they mix with the
watery chyme.
- Bile contains a large quantity of bile salts and the phospholipid lecithin. These
components are the key elements that emulsify fat breaking globules into
smaller pieces so that water-soluble pancreatic lipase can attack the surface.
This emulsification process increases the total surface area of fats by as much as
1,000-fold. As bile breaks up clumps of triglycerides into small pieces and
keeps them suspended in solution, pancreatic lipase breaks off one fatty acid at
a time. Pancreatic juice contains enormous amounts of pancreatic lipase—
enough to digest all accessible triglycerides within minutes. When the lipase has
completed its work, most of the dietary triglycerides have been split into
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monoglycerides and free fatty acids.
Bile salts surround the products of fat digestion, forming micelles-water-soluble
globules with a fatty core. The micelles transport the monoglycerides and free
fatty acids through the watery intestinal environment to the brush border of the
intestinal mucosal cells for absorption.
Phospholipid digestion follows a similar pathway, with phospholipases as well
as other lipases participating in the process and with the added release of the
phospholipid’s phosphate and nitrogen components.
Digestibility
Normally, triglyceride digestion and absorption are very efficient. Production of
fatty stools, called steatorrhea, indicates fat malabsorption, a condition that may
follow radiation therapy or digestive surgery and often accompanies diseases of
malabsorption such as cystic fibrosis or Crohn’s disease.
Triglycerides of medium-chain fatty acids (medium-chain triglycerides, or
MCT) often are used in products developed for people with fat malabsorption.
Medium-chain fatty acids—those with 6 to 12 carbons—are more water-soluble
than longer chain fatty acids, and thus more readily emulsified with less need
for bile. Because the fatty acid chains are shorter, MCTs are digested more
easily. They are hydrolyzed more easily and quickly and absorbed more
efficiently.
- Breast milk is easily digestible. It is rich in medium-chain fatty acids and
contains its own lipase, which enhances fat digestion despite the immaturity of
the baby’s digestive system. Some free medium-chain fatty acids released by
hydrolysis are even absorbed directly through the baby’s stomach lining.
Short-chain fatty acids, with the exception of butyric acid in milk fat are almost
never found in foods. Instead, they are produced by bacteria in the colon from
undigested food, especially from soluble fiber. These fatty acids enter the cells
of the large intestine (enterocytes) where they can be used for energy.
Steatorrhea: Production of stools with an abnormally high amount of fat.
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2) Lipid Absorption
Most fat absorption takes place in the duodenum or jejunum of the small
intestine. Micelles carry the monoglycerides and long-chain fatty acids to the
surfaces of the microvilli in the brush border. Then the monoglycerides and
long-chain fatty acids immediately diffuse into the intestinal cells (enterocytes).
The unabsorbed bile salts return to the interior of the small intestine to transport
another load of monoglycerides and fatty acids. In the last section of the small
intestine (the ileum), bile salts are absorbed. They return via the portal vein to
the liver where they are once again secreted into the bile. This bile recycling
pathway—the liver to the intestine and the intestine to the liver—is called
enterohepatic circulation.
As monoglycerides and fatty acids pass into the intestinal cells, they reform into
triglycerides. Most of the triglycerides, as well as cholesterol, and phospholipids
join protein carriers to form a lipoprotein. When this assemblage leaves the
intestinal cell, it is called a chylomicron. The chylomicrons make their way to
the central lacteal of the villi, where they enter the lymph system, to be
propelled through the thoracic duct and emptied into veins in the neck.
Absorption of glycerol and short-chain and medium-chain fatty acids is more
direct. They are absorbed directly into the bloodstream rather than forming
triglycerides and entering the lymph system. These fatty acids can diffuse
directly into the capillaries of the villi because they are more water-soluble than
longer chain fatty acids.
- One or two hours after you eat dietary fat begin to appear in the bloodstream.
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Cholesterol Synthesis
The body can synthesize cholesterol; therefore, it is not needed in the diet.
While the liver manufactures most of the cholesterol in the body, and the
intestine contributes appreciable amounts, all cells are believed to synthesize
some cholesterol.
Cholesterol Functions
The body can synthesize Cholesterol; therefore, it is not needed in the diet.
Cholesterol is the best-known sterol. Cholesterol is important substance in the
body; it becomes a problem only when excessive amounts accumulate in the
blood. Like phospholipids, it is a major structural component of all cell
membranes and is especially abundant in nerve and brain tissue. Most
cholesterol resides in body tissue.
Cholesterol is important not only in cell membranes, but also as a precursor
molecule. For example, vitamin D is synthesized from cholesterol. Cholesterol
is the precursor of five major classes of sterol hormones: progestins,
glucocorticoids, mineralocorticoids, androgens, and estrogens.
Progesterone is essential for maintaining a healthy pregnancy. Glucocorticoids
(such as cortisol) increase the formation of liver glycogen and the breakdown of
fat and protein. Mineralocorticoids (primarily aldosterone) help control blood
pressure. Androgens (such as testosterone) promote the development of male
sex characteristics. Estrogens promote the development of female sex
characteristics.
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- The liver uses cholesterol to manufacture bile acids, which are secreted in
bile. The gallbladder stores and concentrates the bile. On demand, the gallbladder releases the bile into the small intestine where the bile acids emulsify
dietary fats.
Lipids in the Body
To be transported around the body in the bloodstream, lipids must be specially
packaged into lipoprotein carriers.
Lipoproteins have a core of triglycerides and cholesterol esters (cholesterol
linked to fatty acids) surrounded by a shell of phospholipids with embedded
proteins and cholesterol. They can transport water-insoluble (hydrophobic)
lipids through the watery environment of the bloodstream. There are several
main classes of lipoproteins, and many subclasses. These differ mainly by size,
density, and the composition of their lipid cores. In general, as the percentage of
triglyceride drops, the density increases. A lipoprotein with a small core that
contains little triglyceride is much more dense than a lipoprotein with a large
core composed mostly of triglycerides.
Lipoproteins become less dense as they increase in size. LDL is about double
the size of HDL. VLDL is about 60 times larger than HDL. Chylomicrons range
from 500—1000 times larger than HDL.
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Main classes of lipoproteins
1) Chylomicrones: Transport triglycerides from the intestine to the tissues.
Chylomicrons are about 90 percent fat, but as they circulate through the
capillaries, they gradually give up their triglycerides. An enzyme located on the
capillary walls, called lipoprotein lipase, attacks the chylomicrons and removes
triglyceride, breaking it into free fatty acids and glycerol. These components
enter adipose cells, as needed, where they are reassembled into triglycerides.
2) Very-low-density lipoproteins: Liver and intestine synthesis VLDLtransporting triglycerides to the tissue.
3) Low-density lipoprotein: Transport Cholesterol from liver through blood to
tissues (bad cholesterol). Low-density lipoproteins (LDLs) deliver cholesterol to
body cells, which use it to synthesize membranes, hormones, and other vital
compounds. LDL is more than half cholesterol and cholesterol esters;
triglycerides make up only 6 percent.
Low-density lipoprotein binds to a special receptor on the cell wall. The cell
engulfs and ingests the LDL via endocytosis. Inside the cell, LDL is broken into
its triglyceride component parts, releasing its load of cholesterol.
Liver cells also have LDL-receptors that bind LDL and control blood
cholesterol levels. Saturated fats appear to block these receptors, which explain
why saturated fats tend to raise blood cholesterol levels.
A lack of LDL-receptors reduces the uptake of cholesterol, forcing it to remain
in circulation at dangerously high levels.
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4) High-density lipoproteins: Transport cholesterol from blood and tissues to the
liver, where it is metabolized (good cholesterol).
Lipids and Health
When diets are consistently high in fat several problems emerge. High-fat diets
are typically high in calories, and contribute to weight gain and obesity. High
intakes of fat and saturated fat increase risk for heart disease, and high-fat diets
have been weakly linked to several types of cancer.
Obesity
Obesity is defined as the excessive accumulation of body fat leading to a body
weight in relation to height that is substantially greater than some accepted
standard.
Standard advice is to maintain or attain normal weight usually includes cutting
back on fats and fatty foods, along with increasing physical activity and eating
fewer kilocalories.
Heart Disease
In the early 1960s high blood cholesterol, or hypercholesterolemia, was
identified as a principal risk factor for cardiovascular disease, along with
smoking and high blood pressure.
Artery disease and heart attack were often caused by atherosclerosis, the
buildup of fatty plaques inside the artery wall. High blood cholesterol was
associated with atherosclerosis, and diet could affect blood cholesterol levels.
A high blood cholesterol level usually leads to more specific testing for HDL
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and LDL levels. High LDL cholesterol levels are now known to pose a greater
risk than high total cholesterol. Low HDL cholesterol levels are also considered
a risk factor for heart disease, as are high levels of triglycerides. Elevated blood
triglyceride levels are associated with low HDL levels.
One of the first steps in identifying people at high risk for heart disease is to
measure blood cholesterol levels. All adults over the age of 20 should have their
blood cholesterol levels checked.
Reducing Risk of Heart Disease: Lifestyle Factors
Some of the risks for development of atherosclerosis are beyond our control like
being male and/or getting older but we can control many risks such as
a) Avoiding or quitting smoking, which is a positive step toward reducing risk.
B) Managing weight and controlling blood pressure are other steps we can take.
C) Physical activity for keeping weight normal, and for overall heart health.
Reducing Risk of Heart Disease: Dietary Factors
- Today, nutritionists recommend lowering total fat intake, lowering saturated
fat, and keeping body weight normal. Within total fat limits, monounsaturated
oils should be the fat source of choice. Reducing dietary cholesterol is a good
idea for those who do respond to such a change. Eating fruits, vegetables,
legumes, and grains that contain soluble fiber helps lower cholesterol levels,
too. These foods also have antioxidant nutrients and B vitamins such as folic
acid that may also reduce the risk of heart disease.
Since its inception in 1985, the National Cholesterol Education Program
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(NCEP) has made population-wide dietary recommendations.
Latest recommendations:
• Choose foods low in saturated fat.
• Choose foods low in total fat.
• Choose foods high in starch and fiber.
• Choose foods low in cholesterol.
• Be more physically active.
• Maintain a healthy weight and lose weight if you are overweight.
Antioxidants: There is much good evidence for the oxidation theory, which has
become widely accepted. In the blood, oxygen can damage low-density
lipoproteins. Once oxidized, they are deposited in the inner layer of the blood
vessels, and the atherosclerotic process begins. A diet high in vitamin E and
other antioxidants appears to inhibit oxidation and subsequent
Homocysteine: High levels of the amino acid homocysteine may contribute to
heart disease by promoting atherosclerosis, excessive blood clotting, or blood
vessel rigidity. Folic acid and vitamins B 6 and B,, are all important in the
metabolism of homocysteine, reducing destructive levels.
Dietary Omega-3 Fatty Acids: In the 1 970s a study of the Inuits (Creenland
Eskimos) focused attention on the beneficial physiologic influence of EPA and
DHA, the omega-3 fatty acids in fish fats. Here was a population with a high
intake of fat, saturated fat, and cholesterol from marine mammals and fish. Yet
they had little evidence of atherosclerosis. The Inuits were compared to Danes
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among whom atherosclerosis was common, and whose diet was similarly high
in fat, but from meats and dairy products.
Diet high in EPA and DHA content (e.g. fish and fish oil) had a protective
effect, discouraging blood cells from clotting and from sticking to artery walls.
Population studies yielded fairly consistent results. The Japanese, for example,
with their generous fish intake, had low rates of atherosclerosis.
A considerable number of observational and intervention studies have pointed
in the same direction, some showing that as few as two or three servings of fish
weekly can be protective.
Interest in omega-3 fatty acids has expanded recently research shows that
omega-3s can modestly lower blood pressure, and can help lower elevated
blood triglycerides. In addition to their circulatory effects, they may also help
some chronic inflammatory conditions such as rheumatoid arthritis, asthma.
Soluble Fiber: Soluble fibers bind to bile acids in the gastrointestinal tract, so
these bile acids are excreted in the feces rather than recycled and reused.
Additional bile acids then must be made from cholesterol, lowering the total
amount in the body.
In addition, soluble fibers can be fermented by intestinal bacteria, and the
resulting short-chain fatty acids have been linked to reduced cholesterol
synthesis.
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The Mediterranean Diet: How can Greeks, Turks, and others around the
Mediterranean eat a diet high in fat but still have low rates of heart disease? The
focus here is on the source of the fat—olive oil. Their diet pattern—ample fresh
fruits, vegetables, pasta and grains, small amounts of meat and poultry, and
generous use of olive oil.
Phytochemicals: Plant chemicals affect heart disease risk. Two widely studied
phytochemical groups are isoflavones in soybeans and lignans in flax seed,
whole grains, and some fruits. These are also referred to as phytoestrogens
(plant compounds with hormone-like effects).
Cancer
The evidence linking dietary fat to cancer is inconclusive. The case looks strong
when we compare cancer rates of countries: overall cancer rates are generally
higher in countries with high fat intake, and lower in countries where people eat
less fat. But in population studies within those countries, the evidence linking
fat to cancer is weaker.
The Nurses’ Health Study followed more than 121,000 women for 14 years and
found no evidence that higher total fat intake was associated with an increased
risk of breast cancer.
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Diet and Cancer Risk Reduction
Strategies for reducing cancer risk include a moderately low-fat diet and
increased consumption of fruits and vegetables and whole grains.
The report Food, Nutrition and the Prevention of Cancer: A Global Perspective
presents guidelines for reducing the risk of cancer.
Some of The “Advice to Individuals” statements concerning diet includes the
following:
1. Choose predominantly plant-based diets rich in a variety of vegetables and
fruits, legumes, and minimally processed starchy staple foods.
2. Avoid being underweight or overweight and limit weight gain during
adulthood to less than 5 kg (11 lb).
3. If occupational activity is low or moderate, take an hour’s walk or similar
exercise daily and also exercise vigorously for a total of at least one hour
each week.
4. Eat 400 g to 800 g, or five or more portions (servings) a day of a variety of
vegetables and fruits, all year round.
5. Eat 600 g to 800 g, or more than seven portions (servings) a day of a variety
of cereals (grains), legumes, roots, tubers, and plantains. Select minimally
processed foods. Limit consumption of refined sugar.
6. Limit intake of red meat to less than 80 g (3 oz) daily. Fish and poultry are
preferable to red meat.
7. Limit consumption of fatty foods, particularly those of animal origin. Choose
modest amounts of appropriate vegetable oils.
8. Limit consumption of salted foods and use of cooking and table salt.
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