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LIPIDS: OILS AND FATS
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Sources of dietary fats
• Animal sources: meat, cheese, dairy
• Plant sources: vegetable oils, nuts, avocados
• “Hidden” dietary fat: French fries, pizza, pasta dishes,
baked goods, salad dressings
Types of lipids
• Lipids: a group of organic molecules, most of which do
not dissolve in water
• Lipids include:
• Triglycerides: made up of fatty acids and glycerol
• Fatty acids are chains of carbon atoms with an acid group at one
end of the chain
• They determine the triglyceride’s function in the body
• Phospholipids: their structure includes a phosphorus atom
• Sterols: structure composed of multiple rings
Triglycerides and fatty acids
a. A triglyceride contains glycerol and three fatty acids. The
carbon chains of the fatty acids vary in length from short-chain
fatty acids (4 to 7 carbons) to medium-chain (8 to 12 carbons)
and long-chain fatty acids (more than 12 carbons). The types of
fatty acids in triglycerides determine their texture, taste, physical
characteristics, and actions in the body.
Triglycerides and fatty acids
© Can Stock Photo Inc./ angelsimon
Oils are fats that are
liquid at room
temperature. The
properties of the fatty
acids in vegetable oil
allow it to remain a liquid.
The amounts and types of fatty
acids in the triglycerides of
chocolate allow it to remain
brittle at room temperature,
snap when bitten into, and
then melt quickly and smoothly
in your mouth.
© iStockphoto.com/peepo
Triglycerides and fatty acids
• Saturated fats: carbon atoms are bonded to as many
hydrogen atoms as possible; no carbon to carbon
double bonds
• Plentiful in animal foods, such as meat and dairy products
• Plant oils are generally low in saturated fatty acids
• Long-chain saturated fats:
• implicated in the development of cardiovascular disease
• associated with increased levels of LDL (“bad”) cholesterol in the
blood
Triglycerides and fatty acids
• Medium-chain saturated fats:
• behave differently
• may have more beneficial effects
•
•
•
•
shorter, relatively water-soluble
quickly digested and absorbed into the blood stream
bypass peripheral fat tissue
less likely to be stored as fat
Triglycerides and fatty acids
• Unsaturated fatty acids: contain one or more
carbon-carbon double bonds
• Monounsaturated fatty acids: one double bond
• Found in a variety of foods such as meat, olive oil, avocados,
and nuts
• Historically have been thought to be cardioprotective
• Believed to lower LDL cholesterol
• More research required to clear health effects
Triglycerides and fatty acids
• Polyunsaturated fatty acids: more than one double
bond
• Found mainly in plant sources
Triglycerides and fatty acids
Essential fatty acids
Fatty acid
composition of food
Essential fatty acids
• Humans are unable to synthesize fatty acids that have
double bonds in the omega-6 and omega-3 positions
• Therefore linoleic acid (LA) (omega-6) and alphalinolenic acid (ALA) (omega-3) are considered
essential fatty acids (EFAs) and must be consumed in
the diet
Essential fatty acids
• Important for the formation of membrane
phospholipids, for fertility, red blood cell structure,
metabolism, etc.
• Used to make regulatory proteins called eicosanoids
• Omega-3 eicosanoids reduce inflammation, lower blood
pressure and have other health benefits
Trans-fat (trans-fatty acids)
• Small amounts occur naturally in dairy products
• Created when unsaturated fatty acids are partially
converted to saturated fatty acids by the industrialized
process of hydrogenation
• Some double bonds converted from cis to trans configuration
• Decrease the rancidity and increase shelf life
• Most health endangering dietary fats
Trans fatty acids
a. The orientation of
hydrogen atoms
around the double
bond distinguishes cis
fatty acids from trans
fatty acids. Most
unsaturated fatty acids
found in nature have
double bonds in the
cis configuration.
Trans fatty acids
b. Small amounts of trans
fatty acids occur naturally,
and larger amounts are
generated by
hydrogenation. In 2007,
Health Canada called on
food manufacturers to
voluntarily reduce the
amount of trans fat in their
products to less than 5% of
total fat, which the majority
of manufacturers have now
complied with.
Dietary lipid recommendations
• The dietary reference intake (DRIs):
• Total fat: 20%–35% of total calories
• 30–40% for ages 1–3 & 25–35% for ages 3–18
• Adequate intake for linoleic acid = 12 g per day for women
and 17 g per day for men
• Adequate intake for alpha linolenic acid = 1.1.g per day for
women and 1.6 g per day for men
• Cholesterol, saturated fat, and trans fats: keep intake to
minimum
Dietary fat and cancer
• Cancer is a leading cause of death in Canada
• Research indicates that the risk of cancer may be
decreased by choosing diets:
• high in fruits, vegetables, antioxidants and omega-3 fatty acids
• low in trans fats (more studies needed to determine the
association between trans fats and some cancers)
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