HUBI - Section 6: An Introduction to Dietary Fat

Why do we need dietary fat

• Important source of food energy (needs change through the life-cycle)

• Provides and enables the absorption of fat soluble vitamins (A, D, E & K)

• Provides the essential fatty acids

• Makes food palatable - dissolves flavors and has a characteristic mouth-feel

Setting recommendations (for dietary fats)

Amounts required to meet needs for:

– Energy

– Fat-soluble vitamins

– Essential fatty acids requirements.

• Amounts required to decrease risk of chronic disease

Saturated vs unsaturated (Degree of saturation)

– Affects the temperature at which the fat melts

• In general, the more unsaturated the fatty acids, the more liquid the fat is at room temperature

• In general, the more saturated the fatty acids, the firmer the fat is at room temperature

Hydrogenation

Adding hydrogen. Yeilds hydrogenated fatty acids, now fully saturated, and trans fatty acids.

Alternatives to partial hydrogenation (replacing the trans fats)

• Full hydrogenation

• Fractionation

• Highly saturated traditional fats

Replacing trans fats (interesterification)

Interesterification of blends of fractionated and/or fully hydrogenated fats

• Replacement of the partial hydrogenation process

• Specific positional composition and/or functionality

• Use to produce hard stock fats

Interesterification benefit

• Change the melting properties of a fat without generation of trans fatty acids

• Can reduce the saturated fat content by ~10%

• Higher proportion of SFA in sn-2 position

Fat or lipid

Class of naturally occurring organic compounds which are generally hydrophobic in nature. Various type of lipids include fatty acids, triacylglycerides, sterols and phospholipids.

Fatty acids

Carboxylic acid with aliphatic carbon chain. Methyl group and carboxyl group on each end. Common lengths: C4 – C28

Triglycerides

Most abundant dietary lipid. Consist of 3 fatty acids and 1 glycerol molecule

Phospholipids

Amphipathic and major lipid found in biological membranes. Consists of 2 fatty acids, glycerol, phosphate group and organic molecule

Sterols

Amphipathic lipids with hydroxyl group – alcohols. Conserved 4 ring structure

Classifying lipids

Unique structures, Unique biological functions, Different sources, Different implications on health

Fat as a source of energy

Fat provides 9 kcal/g (37kJ/g) compared with ~4 kcal/g for protein (18kJ/g) and carbohydrate (17kJ/g)

% energy from fat = ((fat in g x 9) / total energy intake in kcal)*100

– eg 90g of fat consumed by a man consuming 2400 kcal/d is approximately 34% of the energy

• The higher % energy from fat the more energy dense the diet:

-Breast milk 52%

-Asian and African rural diet 10-15%

-Japanese diet 25-30%

-Traditional Inuit diet 40-60%

-European and American diet 35-42%

Essential fatty acids (omega-6)

Double bond on 6th carbon.

• Linoleic Acid.

• leafy vegetables, seeds, nuts, grains, vegetable oils (corn, safflower, soybean, canola, cottonseed, sunflower)

Essential fatty acids (omega-3)

Double bond on 3rd carbon

• α Linolenic acid (ALA)

 Fats and oils (canola, soybean, walnut, wheat germ, margarine and shortening made from canola and soybean oil).

 Nuts and seeds (walnuts, soybean kernels)

 Vegetables

• EPA (Eicosapentaenoic acid) and DHA (Docosahexaenoic acid)

 Human Milk

 Shellfish and fish (mackerel, salmon, bluefish, menhaden, herring, trout, sardines, tuna -all except tuna provide at least 1 g of omega 3 fatty acids per 100 g of fish), Seal blubber

 Not essential because they can be made from linolenic acid

Cholesterol source

Cholesterol is only found in animal products

• Eggs, 30%

• Beef, 16%

• Poultry, 12%

• Cheese, 6%

• Milk, 5%

Effects of different fats on cholesterol

Raising LDL cholesterol is bad (risk for heart disease). Raising HDL cholesterol is good (protects from heart disease).

Dietary fat recommendations

< 30% of energy from fat (2000 kcal diet this is > 65 g / day).

≤ 7% of energy from saturated (+ trans).

≥ 10% polyunsaturated.

≥ 13% monounsaturated.

< 300 mg cholesterol / day

How to meet recommendations

• Choose foods with lower fat

• Eat less animal fat, particularly those from red meats, replace

with poultry and fish.

• Eat less hydrogenated fat, less processed foods

Calories, fat, and saturated fat in cooked ground meat patties

• Regular ground beef, 23% fat

• Ground chuck, 16% fat

• Commercial ground turkey, 15% fat

• Ground round, 10% fat

Food feature: defensive dining

At home: Avoid adding saturated fat to foods