Lipids

• Essential nutrients• Provide energy• Help transport fat-

soluble nutrients• Contribute to flavor

and texture of food

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Lipids

• What are lipids?– Triglycerides

• Stored in adipose tissue• Fats and oils in food

– Phospholipids• Plant and animal origin• Body can make them• Soluble in fat and water

– Sterols• Cholesterol

Fatty Acids Are Key Building Blocks• Fatty acid

– Determines solid or liquid at room temp– Basic structure: (-COOH); (-CH3)

• Chain length– 4 to 24 carbon length

Fatty Acids Are Key Building Blocks• Saturation

– Saturated fatty acid• All single bonds

– Unsaturated fatty acid• One or more double bond

– Monounsaturated fatty acid• One double bond

– Polyunsaturated fatty acid• More than one double

bond

Fatty Acids Are Key Building Blocks

• Cis vs. trans– Cis fatty acids

• Occur naturally• Chain is bent

– Trans fatty acids• Produced by

hydrogenation • Chain is

straighter

Fatty Acids Are Key Building Blocks

• Nonessential and essential fatty acids– Nonessential fatty acids

• Can be made in the body

Fatty Acids Are Key Building Blocks

• Nonessential and essential fatty acids– Essential fatty acids

• Can’t be made in body• Must come from food• Omega-3 (alpha-linolenic

acid) and omega-6 (linoleic acid)

• Used to make eicosanoids

Triglycerides• Structure

– Glycerol + three fatty acids• Functions

– Energy source• 9 kcal/g

– Energy reserve• Form of stored energy in adipose tissue

– Insulation and protection• Visceral fat

– Carrier of fat-soluble vitamins– Sensory qualities in food

Triglycerides in Food

• Sources of omega-3 fatty acids– Soybean, canola, walnut, flaxseed oils– Salmon, tuna, mackerel, fish oil

supplements• Sources of omega-6 fatty acids

– Seeds, nuts, vegetable oils– Meat, poultry, eggs

• Commercial processing– Oxidation

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A healthy diet contains a balance of omega-3 and omega-6 fatty acids. Omega-3 help reduce inflammation.

Some omega-6 tend to promote inflammation.

The typical American diet contains 14 - 25 times more omega-6 than omega-3.

The ratio should be in the range of 2:1 - 4:1, omega-6 to omega-3.

Phospholipids

– Glycerol + two fatty acids + phosphate group

• Phospholipid functions– Emulsifiers

• Keeps fat suspended in water• Keep oil and water mixed

– Cell membranes

Phospholipids

• Cell membrane– Double layer of

phospholipids– Important role in

nerve cells

Phospholipids

• Lipid transport– Stomach

• Break fats into tiny particles for digestion

– Intestine• Continue emulsifying fat

– Blood• Surface of lipoproteins that carry lipid particles

in the body

Phospholipids• Emulsifiers (lecithin)

– In body• Phospholipid with

choline– In food

• Used as emulsifiers

Sterols• Cholesterol functions

– In cell membranes– Precursor:

• Vitamin D• Sterol hormones• Bile salts

• Cholesterol synthesis in liver– Found only in animal foods

Lipid Digestion and Absorption

– Mouth• Chewing + lingual lipase

– Stomach• Triglycerides to diglycerides and free fatty

acids (FFA)– Small intestine

• Emulsified by Bile• Digested by pancreatic lipase

• Lipid absorption– Micelles

• Carry monoglycerides and fatty acids to microvilli

• Bile salts absorbed = enterohepatic circulation

• Lipoprotein• Cylomicron

–Deliver dietary lipids from intestines to cells and liver

• Digestion and absorption of sterols– 50% of dietary cholesterol is absorbed

• Fat increases absorption• Plant sterols and dietary fiber decrease

absorption

Lipids in the Body

– Very-low-density lipoproteins (VLDL)• Deliver triglycerides to cells

– Intermediate-density lipoproteins• Converted to LDL

– Low-density lipoproteins (LDL)• Deliver cholesterol

– High-density lipoproteins (HDL)• Pick up cholesterol for removal

Lipids in the Diet

• Recommended intake– Reduce saturated fat, trans fat,

and cholesterol– Total fat: 20–35% of calories– Less than 10% of calories from

saturated fat– Less than 300 mg per day of

cholesterol

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Lipids in the Diet

• Role of fat replacers– Olestra

• Sucrose + fatty acids

• Indigestible— provides no calories

• Reduces absorption of fat-soluble vitamins

Lipids and Health

• Obesity– High-fat diets promote wt gain

• Heart disease– Major risk factors

• High blood cholesterol–High LDL and low HDL

• Smoking• High blood pressure

Lipids and Health

• Atherosclerosis– Slow, progressive hardening and narrowing

of arteries– Promoted by high blood cholesterol – Lipoprotein a [Lp(a)]

• Inflammation and atherosclerosis– C-reactive protein

Lipids and Health

• Reducing heart disease risk– AHA diet and lifestyle recommendations

• Consume an overall healthy diet• Aim for a healthy body weight• Aim for a desirable lipid profile• Aim for normal blood pressure• Aim for normal blood glucose levels• Be physically active• Avoid use of and exposure to tobacco

products

Lipids and Health

• Reduce heart disease risk– AHA recommendations

• Balance calorie intake and physical activity to achieve or maintain a healthy body weight

• Consume a diet rich in fruits and vegetables• Choose whole-grain, high-fiber foods• Consume fish, especially oily fish, at least

twice a week• Limit your intake of saturated and trans fat

and cholesterol

Lipids and Health

• Cancer– Stages of development

• Initiation• Promotion• Progression

– Role of nutrition and diet• Factors that promote or protect

Lipids and Health

• Cancer– Dietary and lifestyle factors for reducing

cancer risk• Maintain a healthful weight• Adopt a physically active lifestyle• Consume a healthy diet• If you drink alcohol, limit consumption