good v. bad fat

fat marbling in this Kobe beef is an example of visible fat

Fat is confusing.  There are good fats, bad fats, soft fats, hard fats, visible fats and fats we can't see (...sneaky fats?).  

Fats are useful in many ways:

• Fats are the body’s chief storage form of energy
• It pads internal organs
• It insulates the body against temperature extremes
• It is the major material for cell membranes (phospholipids)
• Essential nutrients stored in fat (...remember the fat-soluble vitamins)

 

Fats are useful in food because it gives enticing aromas and flavors, and it leads to tenderness in meats and baked goods! (yum!)  The problem with fat is that it is extremely high in calories and can "pack" well.  Fat has 9 cal/g as compared with proteins and carbs that have only 4 cal/g, and the body has unlimited storage capabilities for fat  (unlike protein and carbs!).  

Fats are tricky because of their chemical structure.  Fats are generally composed of a glycerol and 3 fatty acid chains varying in length and saturation.  What makes a fat saturated or unsaturated is how many double bonds are formed on that fatty acid chain (the unsaturated fats have more double bonds... they are not saturated!).  Unsaturated fats are further classified by how many points of unsaturation there are: mono (=1) or poly (=2+).  All fats are a mixture of all 3 types, but we classify a fat as the fatty acid that predominates. 

 (A trick to help you know which is which is that unsaturated fats are generally liquid at room temperature, while saturated fats are solids at room temperature).

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So what??

The reason why some fats are labelled unhealthy and some healthy is because of their ability to combine with certain proteins in the body and complete regulatory functions.  To understand, you must realize that fatty acids are hydrophobic.  They will not normally float along through your circulatory system (which is composed of water = hydrophillic).  In order to be transported throughout the body system, fatty acids need to bind with special proteins (called lipoproteins; lipo= fat).  You have heard of some of these lipoproteins before- low-density lipoprotein (LDL) and high-density lipoprotein (HDL).  LDLs and HDLs have an extremely important role in heart health by transporting cholesterol to and from body tissues.  Here is a quick summary:

HDL	LDL
Both carry lipids (cholesterol) in blood
Smaller, denser, packed with protein	Larger, lighter, and richer in cholesterol
Scavenge excess cholesterol and other lipids from tissues to liver for disposal	Deliver triglycerides and cholesterol to tissues
Oppose inflammatory process and protect against heart attack	Carry lipids that trigger inflammation that may contribute to heart disease
High levels point to reduced risk of heart attack	High concentrations warn of increased risk of heart attack
“Good”	“Bad”
Remember H= healthy	Remember L= large, unhealthy

You want to keep your HDL levels as high as possible and keep you LDL levels as low as possible.  Because you want HDL levels high- you need fat in your diet.  But what is the right fat?? 

Certain fats increase LDL (bad) levels and decrease HDL (good) levels.  These fats are the saturated and trans fats. (Note: a trans or hydrogenated fat is a fat that is generally man-made.  An unsaturated fat is hydrogenated to become more saturated and thus stable- increasing the products shelf-life.  This is why you see some cookies, like original oreos, that can last for 10 years!)  Because of their ability to increase LDLs, these are considered "unhealthy" fats.  The majority of these fats come from animals- especially meat and dairy products, and the skin on poultry.

Andrew Scrivani for The New York Times

There are other fats that do not increase LDL levels, and these are the unsaturated fats.  In fact, unsaturated fats are extremely important in the diet, as they provide essential fatty acids to help regulate important body functions. Two polyunsaturated fatty acids are essential and must be supplied by diet: Linoleic acid and Linolenic acid.  These are the omega-6 and omega-3 fatty acid building blocks, respectively.  They are both supplied in the diets through oils and seeds, and omega-3 fatty acids are supplied by fish oils. (note- you cannot increase your HDLs by eating unsaturated fats.  HDL levels are affected by exercise, alcohol (wine is said to help increase!), higher levels of estrogen, and less LDLs). 

Healthy fatty acids*:

Monounsaturated	Omega-6 polyunsaturated	Omega-3 polyunsaturated
Avocados	Margarine (non-hydrogenated)	Fatty fish
Nuts (almonds, cashews, hazelnuts, macadamia nuts, peanuts, pistachios)	Mayonnaise	Flaxseed
Oils (canola, peanut, safflower, sesame)	Nuts (walnuts)	Nuts
Peanut butter (old-fashioned)	Oils (corn, cottonseed, soybean)
Seeds (sesame)	Salad dressing
	Seeds (pumpkin, sunflower)

Harmful fatty acids*:

Saturated		Trans
Bacon	Lard	Commercially baked goods (cookies, cakes, pies- made with margarine or vegetable shortening)
Butter	Meat	Fried foods
Cheese	Milk fat (whole milk products)	Processed snack foods
Chocolate	Oils (coconut, palm)	Margarine- hydrogenated or partially hydrogenated
Coconut	Shortening	Nondairy creamer
Cream, half- and-half	Shortening	Shortening
Cream cheese	Sour cream

 

Don't be scared- there are simple ways that you can substitute ingredients to lower saturated fat intakes:

Andrew Scrivani for The New York Times

• use fat-free milk products instead of whole milk
• use soft or liquid margirines or olive oil instead of butter
• use fruit butter instead of butter
• use toasted nuts or seeds instead of fried onions or potato chips
• use lean ground beef instead of regular
• use herbs, spices, fruits, liquid smoke, olive oil, or bouillon cubes instead of butter, bacon or bacon fat
• use bake tortilla or potato chips (or pretzels) instead of regular potato chips

*Charts and tables for this post are take from: Webb, Frances Sizer., and Eleanor Noss. Whitney. Nutrition: Concepts and Controversies. 2nd ed. Vol. 12. Australia: Wadsworth Cengage Learning, 2011. Print.