LipidsIva Řehová

• Like carbohydrate, a lipid molecule is composed of carbon, oxygen, and hydrogen atoms linked together in a specific and unique way.

There are three different functions for lipids in our bodies:

• Energy source• Energy storage • Forming the membranes around our cells. • Hormones and vitamins (facilitate absorption of fat-

soluble vitamins (A, D, E and K) and carotenoids)

• The largest amount of energy is stored in the body as fat.

• Lipids contain a lot of calories in a small space.

• Fats are stored as triglycerides in both the muscle tissue and adipose (fat) tissue.

• Essentially, a lipid molecule consists of one glycerol molecule and three fatty acid molecules to form triglyceride.

• Fatty acids have two unique characteristics:1.the length of their carbon chain

2.the bonding of carbon atoms

The length of carbon chain:

• Short-chain fatty acids (SFA) have 4 to 8 carbons; sources: milk and dairy produce

• Medium-chain fatty acids (MFA) have 9-12 carbons; sources: milk and dairy produce, coconut and palm oil

• Long-chain fatty acids (LFA) have more than 12 carbon; source: many animal fats

• Oils are usually of the short-variety.• The fatty acids with shorter chains are more

easily breakdown during digestion.

The bonds of carbon chain

• saturated fatty acids with only single bonds linking carbons together

H H H H OH

R - C - C - C - C - C = O

H H H H glycerol

• unsaturated fatty acids with at least one double bonds in the carbon chain– monounsaturated– polyunsaturated

H H H H H H OH

R - C = C - C - C = C - C - C = O

H Hglycerol

• There are different types of fatty acids in one molecule of triglyceride.

• Regardless of the degree saturation, all lipid have essentially the same number of calories per unit weight.

The American Heart Association has set guidelines for triglyceride levels in blood:

Level mg/dLLevel mmol/L Interpretation

<150 <1.69 Normal range, lowest risk of CVD

150-199 1.70-2.25 Borderline high

200-498 2.25-5.63 High level, high risk of CVD

>500 >5.65 Very high, increased risk of CVD

Saturated fats• At room temperature, saturated fats are usually solid.• Source: primarily in animal products including beef,

lamb, pork and chicken, egg yolk, dairy fats of cream, milk, cheese, butter; coconut and palm oil; non-dairy creams because they contain coconut oil

• Consumption of saturated fats has been linked with risk of coronary heart disease:– sources of saturated fat are full of cholesterol (except coconut

and palm oil) – diet high in saturated fat facilitates cholesterol synthesis by

the liver (including coconut and palm oil)

Unsaturated fats• At room temperature, unsaturated fats are usually liquid.

• Monosaturated• Sources: olive, peanut, canola, rape oil, almonds, avocado

• Polyunsaturated• Sources: sunflower, soybean, corn, and safflower oil, fish

oil, walnuts, sesame seeds, pumpkin seeds, tofu, lard• Unsaturated fatty acids are sensitive to heat and light

damage – store them in the dark bottles and use for cold or short hot preparations

• Humans and other mammals can synthesize saturated and some monounsaturated fatty acids from carbon groups in carbohydrate and protein.

• Polyunsaturated fatty acids an omega-3 fatty acid and an omega-6 fatty acid are considered essential fatty acids (because they cannot be synthesized by humans).

Essential fatty acids:• omega-3The parent fatty acid of the omega-3 series is alpha-linolenic acid (ALA) ALA- humans can synthesize eicosapentaenoic acid (EPA) and

docosahexaenoic acid (DHA) from ALASources: flaxseed oil, soybean oil and canola oil, nuts, seafish – salmon,

herring, sardine, tuna

• omega-6The parent fatty acid of the omega-6 series is linoleic acid (LA).LA - humans can synthesize dihomo-gamma-linolenic acid (DGLA) and

arachidonic acid (AA) from LASources: olive and sunflower oils, sesame, pecans, pine nuts, freshwater fish –

carp, trout, catfish, eel

• Clinical signs of essential fatty acid deficiency decreased growth in infants and children, increased susceptibility to infection and poor wound healing.

• Omega-6 and omega-3 PUFA are important structural components of cell membranes, they are important to central nervous system function, and they play important roles in vision.

• Typical Western diets tend to be much higher in omega-6 fatty acids than omega-3 fatty acids.

• It has been estimated that the ratio of omega-6 to omega-3 fatty acids in the diet of early humans was 1:1, but the ratio in the typical Western diet is now almost 10:1 due to increased use of vegetable oils rich in LA and declining fish consumption.

• Omega-3 intakes are associated with significant reductions in cardiovascular disease risk, the American Heart Association recommend that all adults eat fish, particularly oily fish, at least twice weekly.

• A large body of scientific research suggests that increasing the relative abundance of dietary omega-3 fatty acids may have a number of health benefits.

• Increasing EPA and DHA intake may be beneficial to individuals with diabetes, especially those with elevated serum triglycerides.

0 20 40 60 80 100

coconut oil

palm oil

butterfat

pork fat (lard)

sunflower oil

soybean oil

olive oil

canola oil (rapeseed)

polyunsaturated monosaturated saturated

Approximate percentage of fatty acids in common fats and oils

Trans-unsaturated fatty acids (TFA)

• TFA are product of hydrogenation which increases the saturation of fatty acids within oils and converts natural cis to trans configuration

• Hydrogenation= industrial process that chemically transforms a low melting point oil into a solid fat with a higher melting point to enhance product taste, stability and shelf life.

• Found in commercially fried foods (French fries, popcorn), commercial baked goods and snacks (cakes, cookies, biscuits), margarine, and cheap vegetable shortenings (not in e.g. Flora, Rama).

• Trans-fatty acids have many adverse metabolic effects including elevation of LDL cholesterol, triglycerides, reduction in HDL cholesterol, and adverse effects on endothelial function, inflammatory markers, and probably insulin resistance.

• The diet in northern European countries has traditionally contained more trans-fatty acids than the diet in Mediterranean countries in which olive oil is commonly used.

• Mean daily intakes of trans-fatty acids in European countries range from minimal values in Italy, Portugal, Greece and Spain to greater values for Germany, Finland, Denmark, Sweden, France, United Kingdom, Belgium, Norway, the Netherlands, and Iceland.

• Recent decreases in the trans content of the diet have been observed, presumably due to modifications of commercially available fats or changes in consumer choices.

• Today, most margarines in the European market have a lower content of trans fatty acids than 5 to 10 years ago and in most cases the change has been carried out without adverse effects for the consumer.

• The technologies used here are now implemented in a number of other industries. New technologies have been adopted to solve specific problems in, for example, the bakery and chocolate confectionery.

Cholesterol

• Cholesterol is non-fat substance vital to human metabolism, and although it may be obtained in the diet only from animal foods, the body can produce its own way.

• The recommended cholesterol intake is less then 300 milligrams per day (the richest source is egg yolk has 220 mg).

• A positive relationship has been established between high blood cholesterol levels and coronary heart disease, reduction of dietary cholesterol has been advocated by a number of health recommendations.

• Fruits, vegetables, grains, and nuts have no cholesterol.

Cholesterol content – egg and meat group

Amount Cholesterol (mg]

Eggs 1 220

Liver, kidney, brains 1 oz 120

Shrimp 1 oz 45

Beef, pork, ham 1 oz 25

Poultry 1 oz 23

Fish 1 oz 21

Cholesterol content – milk group

Amount Cholesterol (mg]

Ice cream 1 cup 85

Milk, whole 1 cup 27

Milk, 2% 1 cup 15

Milk, skim 1 cup 7

Cream cheese 1 tbsp 18

Butter 1 tbsp 12

Type of Fat Dietary Sources Total Cholesterol

LDL-cholesterol

HDL-cholesterol

Triglycerides

Saturated Fat Red meat, cheese, butter, commercially fried foods and baked goods

Increase Increase No effect No effect

Trans Fats Commercially fried foods and commercially prepared snacks and baked goods

Increase Increase Slight Decrease

No effect

Monounsaturated Fats

Nuts, olives, avocados, olive & canola oils

Decrease Decrease No effect No effect

Polyunsaturated Fats : Omega-6

Corn, soybean and safflower margarine & oils

Decrease Decrease Decrease Unknown

Omega-3 Salmon, mackerel, herring, flaxseed, walnuts, walnut oil, soybean and soybean oil

Decrease Decrease No effect Decrease

•Recommendation is that total daily fat intake be limited to < 30% of total daily energy intake

•with no more than 10% provided by saturated and trans fats,

•polyunsaturated fatty acids should be limited to no more than 10% of total daily energy intake (Because polyunsaturated fatty acids may also lower HDL-cholesterol as well as LDL-cholesterol)

•10% provided by monounsaturated fats

Digestion and absorption• Digestion of fats starts in the stomach by the action of linqual

lipase, an enzyme secreted in the mouth. This enzyme digests short- and medium-chain saturated fatty acids.

• The stomach secretes gastric lipase which works with linqual lipase to digest a very small amount of fat.

• The major breakdown of lipid occurs in the small intestine.

• The fat is emulsified into very small droplets by the action of bile (secreted from gallbladder) - it facilitates enzyme action.

• Pancreatic lipase, the main fat-digesting enzyme, degrades some of the triglyceride molecules to monoglycerides and fatty acids.

• In this simpler form, monoglycerides are more easily absorbed by the intestine.

• The absorbed glycerol, fatty acid, and monoglyceride molecules are then free to recombine to reform triglycerides.

• The fatty acids take one of two routes depending on their chain length:– Short- and medium-chain fatty acids

proceed to the portal vein and empty into the liver.

– Long-chain fatty acids and cholesterol is first reconverted to a chylomicron and then transported through the lymphatic system into the systemic vein that empty into the heart.