Bio 28: NutritionInstructor: Paul Nagami

Laney College

Feb. 3, 2014

Lipids, pt. 1

Today’s Agenda• Reminders + Administrative Details• What Are Lipids? Chemistry and

Types of Lipids• Fatty Acids• Saturated vs. Unsaturated• cis vs. trans

• Triglycerides• Phospholipids• Sterols and Cholesterol

• Lipoproteins: Moving Lipids through the Body

What Are Lipids?Lipids are energy-dense (9 kcal/gram) macronutrients that do not mix well with water.

Four types of lipids

Fatty Acids

Triglycerides

Phospholipids Sterols

Fatty AcidsFatty acids consist of a hydrophilic (water-loving) acidic head, and a hydrophobic (water-repelling) tail. Because they are mostly made of the tail, they do not mix well with water.

HeadThe tail is made entirely of carbon and hydrogen. The bonds between carbon and hydrogen are easy to “burn,” converting the fatty acid to carbon dioxide and water. This releases a lot of energy!

Fatty Acids Are Energy-Dense!Their tails are similar

to components of gasoline!

Octanoic acid, a fatty acid.

Octane, a component of gasoline.

is almost as energy-dense as….

Saturated vs. Unsaturated Fatty Acids

All of the chemical bonds in the tails of saturated fats are single bonds. This gives the acid the ability to rotate freely and pack together tightly. This is not healthy! The fat can solidify easily.

Unsaturated fats have at least one double bond in their tail. This double bond can be cis or trans in its orientation.

(Black atoms = C, white atoms = H, red atoms = O)

Double bond

cis and trans fatsIn some unsaturated fatty acids such as oleic acid (found in olive oil), the double bond creates a “bend” in the molecule that improves the fluidity of the lipid. These fatty acids, called cis fats, are processed by the body into healthier forms, and can lower cholesterol in moderation.

Other unsaturated fatty acids do not have that “bend” in their tails. This means they pack together more easily in cell membranes, making them less fluid, and are not processed as well by the lipase enzymes. These fats, called trans fats, increase the risk of heart disease.

Essential Omega-3 and Omega-6 Fatty Acids

Our body uses omega-3 and omega-6 fatty acids to make cell membranes and important compounds.

The name scheme tells us where the first double bond in the fatty acid tail is. Omega-3 means that the first double bond is on the third carbon from the end of the tail. Omega-6 means that the first double bond happens at the sixth carbon from the end of the tail. There are other double bonds, too; these fatty acids are polyunsaturated.

TriglyceridesTriglycerides are the form of fat stored in your adipose tissue (fat cells). They consist of three fatty acids stuck to a glycerol head.

Triglycerides can be found in animal fat (with mostly saturated tails) and vegetable oils (with mostly unsaturated tails) – but watch out for coconut oil and palm oil, which have more saturated fat!

Glycerol head 3 fatty acid tails

PhospholipidsPhospholipids are similar to triglycerides, except that one of the fatty acid tails is replaced with a phosphate group and possibly other components.

Our body can make these out of triglycerides, so we don’t really need to get much of them in our diets - though we do need some trace amounts of phosphorus to do that. Fish are high in phosphorus.

Phospholipids in Cell Membranes

All of your cells use two layers of phospholipids to retain their contents! You need fat to make cell membranes!

SterolsUnlike other types of lipid, sterols, such as cholesterol, do not contain long fatty tails. They are made of rings of carbon.

High levels of cholesterol – especially in the form of LDLs (low-density lipoproteins) – are associated with increased risk of heart attack and stroke.

Drugs that reduce cholesterol levels are called statins. Many very effective statins are available as generic drugs.

Steroid HormonesThe body needs to make some sterols in order to produce hormones. While most Americans consume too much cholesterol, it is still a necessary molecule! That said, your liver can make cholesterol from other lipids… so you don’t really need to eat it.

The body’s pathways to convert cholesterol into other hormones are very complicated. You should know we make testosterone, estrogen, and other steroid hormones from cholesterol… but you don’t need to know how!

LipoproteinsBecause lipids and water don’t mix well, your body uses carrier molecules to move fat,cholesterol, and fat-soluble vitamins around your body. These carriers are called lipoproteins (fat + protein), and are like “balls of fat” with carrier proteins that let them move through blood. The carrier proteins work a little like a natural detergent, breaking the oil into small drops!

Protein

Trigylcerides

Different forms of cholesterol

Phospholipids and protein on the outside carry cholesterol and fatty acids on the inside

Types of LipoproteinThere are four types of lipoprotein:

Chylomicrons: These are big lipoprotein spheres that carry fat through your bloodstream right after a meal.Very Low Density Lipoproteins (VLDLs): These lipoproteins are made by the liver to carry fat and cholesterol.

Low Density Lipoproteins (LDLs): These lipoproteins come from VLDLs and can carry cholesterol to your blood vessels. This is the “bad cholesterol.”High Density Lipoproteins (HDLs): These lipoproteins carry cholesterol away from your blood vessels. This is the “good cholesterol!” Exercise and avoidance of saturated fats can improve your HDL/LDL ratio.