Note

  Lecture 22- 2 March 2017 Lipids

Definition   Broad range of organic compounds that dissolve in organic solvents such as alcohol, ether, acetone but are much less soluble in water Hydrophobic (lipophilic) vs hydrophilic (lipophobic) Lipids are hydrophobic

Definition continued Some lipids are more hydrophilic than others (eg phospholipids)   The degree of hydrophilicity depends on molecular charge Water is charged Remember that like likes like- what does this mean

Classes of lipids in foods Fatty acids- chains (of varying length) of carbon with hydrogens and oxygens attached to the carbons

Classes of lipids in foods fatty acids are: saturated (no double bonds)-more in animal fats -monounsaturated (one double bond)-olive oil -omega 9 (eg major monounsaturated in olive oil)

Classes of lipids in foods fatty acids are: -polyunsaturated (2 or more double bonds) more of these in plant oils than animals   -omega 6 (major polyunsaturated fatty acids in many plant oils) -omega 3- major polyunsaturated fatty acids in fish and some plant oils (eg flax, canola oil)

Classes of lipids in foods Triglycerides –3 fatty acids attached to glycerol   -very hydrophobic -interestingly glycerol is not very hydrophobic – rather leans toward hydrophilic

Classes of lipids in foods Phospholipids- one or 2 fatty acids attached to a glycerol backbone -third carbon of glycerol has a phosphate group attached to it -most famous of these is lecithin   -somewhat water soluble

Classes of lipids in foods Sterols- molecules made up of rings - one of the rings can have a fatty acid attached   -cholesterol is the most famous (infamous?) of these- Michael Brown has described cholesterol as being the most highly decorated little molecule in the world   -plant sterols = phytosterols -sterols are quite hydrophobic

In foods -most of lipid is in the form of triglycerides   -fats and oils- all triglyceride -fats are generally considered to be solid at room temperature -oils are generally considered to be liquid at room temperature -though fats are sometimes used interchangeably with oils

In foods   - to make an oil more saturated one can bubble hydrogen gas through it -unfortunately this produces trans fatty acids-for example in margarine- this makes the margarine solid at room temperature (about 20 degrees celsius)

In foods -get cholesterol in foods from animals and phytosterols in plant foods   -these are in foods in small amounts (less than triglycerides but more than phospholipids) -phospholipids occur in plant and animal food sources but these are a minor component of our nutritional lipid load

Digestion -little chemically in mouth or stomach- why? -issue of mechanical digestion   -small intestine enzymes break down triglycerides and phospholipid generating fatty acids -fatty acids and sterols not broken down further in stomach or intestine but are absorbed whole into small intestinal wall

Absorption -occurs in small intestine -absorption of fatty acids and sterols   -chylomicrons are made in the intestinal wall

Transport - chylomicrons converted to very low density lipoproteins which are converted to low density lipoproteins   -all of these conversions happen in liver -high density lipoproteins are made in the liver from various lipids and proteins some of which are left over from liver conversions of lower density lipoproteins

Transport lipoproteins- lipids cannot be transported easily in the blood (why?)   -to overcome this solubility issue must wrap lipids in protein and phospholipid coat to get a lipoprotein -once the lipids are in this coat they are easily transported to where they are needed

Transport -lipids are used for -energy -fat soluble vitamin transport -building cell membranes -acting as cellular messengers (one part of the cell telling another part of the cell or other cells what to do and when to do and how much to do it).

-however lipids can also cause problems in the body -weight problems- arthritis -type II diabetes -heart disease -stroke -high blood pressure -kidney failure -a number of other problems

Note World Health Organisation indicated on 5 March 2014 that keeping one’s simple sugar (mono and disaccharides) consumption to less than 5 % of daily calories (ie less than about 6 teaspoons of sugar) has added health benefits compared to keeping one’s simple sugar (mono and disaccharides) consumption than 10 % of calories. This refers to all simple sugars whether they are added (pop, cakes) or naturally (e.g. honey, fruit) occurring.

Fats   Why are lipids important from a nutritional perspective ? Blood free fatty acids-if elevated concentration then greater risk of type 2 diabetes Blood triglycerides – if elevated concentration then greater risk of heart disease Blood cholesterol- if elevated concentration then greater risk of heart disease

Lipoproteins -lipids are insoluble in water -need protein and phospholipid coat to be transported around in body blood (water a problem)

Lipoproteins continued -good cholesterol-high density lipoprotein cholesterol -bad cholesterol –low density lipoprotein cholesterol -very low density lipoprotein- carry mostly triglyceride in fasting state -chylomicrons-carry triglyceride - only post-prandially

Atherosclerosis- how does it work ? LDL- pumps cholesterol into arterial wall HDL- pumps cholesterol out of arterial wall Triglycerides make the LDL more aggressive in pumping cholesterol into the arterial wall

Eating lipids -it’s a good news/bad news story   -saturated fats (12, 14 and 16 carbon fatty acids are the really bad ones in terms of raising concentrations of bad cholesterol)

Eating lipids -it’s a good news/bad news story   -trans fats-lower good cholesterol and raise bad cholesterol in the blood plasma

Eating lipids -it’s a good news/bad news story replacing saturated fats with monounsaturated fats lower concentrations of blood plasma triglycerides, cholesterol and bad cholesterol  

Eating lipids -it’s a good news/bad news story replacing saturated fats with polyunsaturated fats lowers concentrations of blood plasma triglycerides, cholesterol and bad cholesterol

Eating lipids -it’s a good news/bad news story Omega 3s- lower platelet stickiness -lower triglycerides in blood plasma -oily fish (eg salmon, trout, arctic char) two –three servings a week -too much- bleed out - no more than 3 grams a day of fish omega 3 fatty acids without medical supervision

Eating lipids -it’s a good news/bad news story Keep lipids to 20-35 % or less of total dietary energy intake -this means ? kcal of fat per day for a 2000 kcal diet-why?   Keep saturated fatty acids to less than 10 % or less of total dietary energy intake- why? To accomplish these fat goals follow Canada’s food guide

Fats in foods and other sources Saturated fat foods   -meats (especially red meats and pork) -fried foods -dairy products

Fats in foods and other sources Monounsaturated fat foods Omega 9 –oleic acid is the major fatty acid of interest nutritionally at this point in time -olives -olive oil -canola oil  

Polyunsaturated foods -corn -corn oil -most plant products Fats in foods and other sources Polyunsaturated foods -corn -corn oil -most plant products -deep sea or cold water fish-why? -arctic char -salmon -trout

Fats in foods and other sources Omega 3 -alpha-linolenic acid (ALA) -flax seed oil -canola seed oil -black currant seed oil   -humans make eicosapentaenoic acid and docosahexaenoic acid from alpha-linolenic acid-but SLOWLY -eicosapentaenoic acid-fish and algae -docosahexaenoic acid- fish and algae

Concept of functional foods versus a nutraceutical   -a functional food is a food that contains one or more molecules that do not have a traditional nutrient role but yet confer a therapeutic advantage -a therapeutic advantage means preventing or partially preventing or curing or partially curing a disease -eg flax bread fish garlic (not used for lipid composition to date)

-a nutraceutical is a concentrate of one or more molecules of a plant or animal -these one or more molecules may not have a traditional nutrient role but yet confer a therapeutic advantage   -eg fish oil canola oil allicin (not a lipid) –allicin found in garlic

Thus the lipids can be found in food, a functional food or a nutraceutical

When we get to diseases we will talk more about lipids and their role in specific diseases -arthritis -heart disease (atherosclerosis) -stroke -type I diabetes -type II diabetes -cancer