Macronutrients: Lipids

"Quirks" of RDA Recommendations for Lipids

Omega 3 and Omega 6 have their own RDA recommendations as they are essential fatty acids

Common Sources of Lipids in Diet

Oils, Seeds/Legumes, Animal Products

Animal products are especially high in cholesterol compared to other types of lipids

Types of Lipids

Fatty Acids - Energy source

Triglycerides - Energy storage

Phospholipids - Membranes

Steroids - Hormones

Fatty Acids

Carboxylic acids with an aliphatic chain (chain consisting of mostly straight C-C bonds) of variable length

Classified into saturated, unsaturated, cis, trans, and omega fatty acids

Role of Fatty Acids

-Energy (via beta oxidation -> krebs)

-Storage (via formation of trigylcerides)

-Component of cell membranes (as a part of phospholipids)

Saturated Fatty Acids

Fatty acids that lack double carbon bonds (C=C), leading to being relatively shelf-stable (due to lack of oxidation) and solid (due to lack of kinks)

Unsaturated Fatty Acids

Fatty acids that have at least one double carbon bond (C=C), leading to them being more likely to be liquid.

Includes cis, trans, and omega fatty acids

Cis Fatty Acids

Unsaturated fatty acids with hydrogen atoms on the same side of the double carbon bond, making their structure kink more

Typically naturally occuring

Trans Fatty Acids

Unsaturated fatty acids with hydrogen atoms on the opposite side of the double carbon bond, making their structure and behavior resemble saturated fats (solid, stable shelf life)

Typically occurs due to partial hydrogenation during processing

Hydrogenation is banned in Canada, however some traces of trans fatty acids still exist in Canadian food sources

Hydrogenation of Fatty Acids

Process of converting unsaturated fatty acids into saturated fatty acids through the removal of the double carbon bond.

Trans fatty acids are often created in this process through partial hydrogenation

Monounsaturated Fatty Acids

Fatty acids with exactly one double carbon bond

Polyunsaturated Fatty Acids

Fatty acids with more than one double carbon bond

Omega 3 Fatty Acids

Aka a-Linoleic acid

Essential unsaturated fatty acids that have their first double carbon bond on the third to fourth carbon from the end (omega) of the fatty acid chain

Has a lower dietary requirement compared to Omega-6 FAs

Omega-6 Fatty Acids

Aka Linoleic acid

Essential unsaturated fatty acids that have their first double carbon bond on the sixth to seventh carbon from the end (omega) of the fatty acid chain

Has a higher dietary requirement compared to Omega-3 FAs

Omega-3 FAs vs Omega-6 FAs Diet Recommendations

Omega 3 FAs have lower RDA recommendations compared to Omega 6 FAs (1 : 5-10 ratio)

Omega 3 FAs are often lacking in a Canadian diet

Eicosanoids

Hormone-like regulatory molecules that are synthesized from omega 3 and omega 6 fatty acids. They regulate processes such as inflammation, clotting, BP, immune function, etc.

Role of Omega-3 and Omega-6 FAs

-Synthesizes eicosanoids, regulatory hormone like molecules

-Helps form phospholipids

Essential nutrients

Nutrients that are required for proper body function but are not synthesized in sufficient quantities by the body and thus must be obtained through diet.

Includes vitamins, Omega 3 + 6 fatty acids, and some amino acids (essential +/- conditionally essential amino acids)

Unsaturated vs Saturated Fat Diet Sources

Saturated Fats - Animal Fat + Tropical Oils

Unsaturated Fat - Vegetable Oils

Triglycerides

A type of lipid consisting of a glycerol molecule attached to three fatty acid tails through ester linkages.

Monoglycerides - 1 fatty acid tail

Diglycerides - 2 fatty acid tails

Triglycerides Role

-Main storage molecule for lipids

-Component of lipoproteins

-Breaks down into fatty acids and glycerol by lipases for energy

Phospholipids

A type of lipid consisting of a glycerol molecule attached to two fatty acid tails through ester linkages, plus a polar phosphate head

Due to the polar phosphate head, they are amphipathic, meaning they have a polar and non-polar region

Amphipathic Lipid

An amphipathic molecule has a non polar and polar region. Phospholipids are amphipathic molecules

Phospholipids Role

-Forms plasma membranes

-Acts as emulsifiers of other lipids as a component of lipoprotein membranes

Sterols

A type of lipid consisting of four fused carbon rings with an OH-group on the C3 group and a functional side chain.

Cholesterol

A type of sterol that is:

- a structural lipid to cell membranes (temp regulation)

- a precursor for many hormones

- involved in bile salt synthesis (-> emulsification of lipids via micelles)

- a major component of LDL

Cholesterol can be synthesized by the body

Lipids and Cardiovascular Disease

Increased cholesterol, saturated fat, and trans fatty acids is associated with increased LDL levels, leading to atherosclerosis and various CVDs

Increased Omega-6, Omega-3, polyunsaturated fats, and monounsaturated fats is associated with decreased LDL levels, increased HDL levels, and increased eicosanoids, leading to decreased risk of CVDs

Lipids and Breast Cancer

Mixed Evidence

Mediterranean + high omega 3 FA diets are associated with a reduced incidence of cancer

High omega 6 FA diets cause tumor proliferation vs high omega 3 FA + saturated fatty acid diets in mice studies

Lipids and Colon Cancer

High saturated fat in diet is associated with increased risk of colon and prostate cancer

High omega-3 fatty acids in diet is associated with reduced risk of colon cancer

Lipids and Obesity

Greater dietary fat intake leading to greater total energy intake is associated with increased risk of obesity

No evidence to support that increased proportion of lipids relative to other nutrients is associated with an increased risk of obesity