Friday, July 30, 2010

The skinny on fat

What comes to mind when you think of dietary fat? More than likely you're not thinking of the word skinny. Most often eating fat is thought of as being bad for us. Fat became the villain nutrient in the 90's, and was responsible for the low-fat diet craze which spawned countless low fat and fat free food products.

For a number of reasons, the accepted wisdom at that time was if you cut the amount of fat in your diet you'd lose weight, lower cholesterol and reduce the risk for heart disease, among other things. The thinking about weight loss isn't totally out of line, considering there are a little over twice as many calories in one gram of fat as there are in one gram of carbohydrate. Ironically though, the backlash of the no fat/low fat campaign resulted in even greater numbers of overweight Americans, with elevated cholesterol levels and at risk for or diagnosed with heart disease.

Fast forward to a new millennium. We're older, wiser and still a country with an obesity problem. In addition, heart disease is now the number one cause of death (CDC). Fortunately, some interesting information about fat has been learned over the last twenty years. Dr. Walter Willett, of the Harvard School of Public Health, states that he and his colleagues began examining data from studies which shows that "the percentage of calories from fat in a diet has not been related to any important health outcome." Really? How can that be? Well, they realized what is especially significant is the type of fat in the diet. This was the critical factor impacting our health.

So, what type of fat and how much of it should we eat for positive health effects? First, perhaps a little background on fat will aid in understanding. Fat actually refers to a class of nutrients called lipids. Lipids include triglycerides, which are fats (solid form) and oils (liquid form), phospholipids (like lecithin) and sterols (the most well known of these is cholesterol). For now, let's look a little more closely at the triglycerides, in particular.

Just a tiny bit of chemistry is helpful here and, although it may seem a bit tedious, it will become clear why it's important once you've finished reading. Triglycerides are made up of one molecule of glycerol and a chain of fatty acids.  Fatty acids may be saturated or unsaturated. For now I'm focusing on the unsaturated fatty acids. Depending on how many points of unsaturation the fatty acid contains, they can be monounsaturated (mono meaning one) or polyunsaturated (poly meaning many).

Are you still with me? Good because this next part is key. The location of the first point of unsaturation on a polyunsaturated fatty acid's (PUFA's) chain determines whether that PUFA is an omega 3 or an omega 6 fatty acid. We're all relatively familiar with the omega terminology. It's important to note, however, that the terms omega 3 and omega 6 are actually a classification for a group of PUFA's and include, among others, alphalinoleic acid (ALA), EPA and DHA, which are all omega 3's, and linolenic acid (LA), eicosadienoic acid (EA), and GLA, which are all omega 6's. There's also an omega 9 group. The human body can make sufficient amounts of all fatty acids except for the omegas. As a result, omega 3 and omega 6 are considered essential fatty acids (EFA's) because they must be supplied by the foods we eat. The body can manufacture modest amounts of the omega 9's.

Now that you  have  slugged through all of that science, why is it important?  Well, research has clearly shown that omega 3 and 6 fats have health benefits when consumed in the right amounts and ratios. Interestingly, a large body of scientific research suggests that adding more dietary omega-3 fatty acids may have an even greater benefit. This is because, according to the Linus Pauling Institute, "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 as well as reduced fish consumption."Other experts believe we get as much as 25 times more omega 6 than omega 3 (Black).

So, what do you think? Can we eat fat and at the same time not gain weight or have our cholesterol levels increase? The research suggests it's possible IF we eat the right kinds and amounts of fat. I don't know about you, but all this has made me hungry.  I'm going to go grab a healthy omega 3 snack of a few walnuts. Next post will look at the other types of fats, as well as the recommended intakes, which fats to avoid, what foods will provide the fats we need and the many health benefits of eating good fats. Stay tuned for more skinny on fat.


Sources
http://www.pbs.org/wgbh/pages/frontline/shows/diet/themes/lowfat.html
Whitney, E. and Rolfes, Sharon, Understanding Nutrition, 11th edition,  Thomson 2008.
http://www.cdc.gov/features/heartmonth/
http://lpi.oregonstate.edu/infocenter/othernuts/omega3fa/#intro
Black, Jessica, ND, The Anti-inflammation book, Berkeley 2006.

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