Wednesday, August 4, 2010

More skinny on fats - the good, the bad, the ugly

While we're on the topic of fat...Yesterday the U.S. Centers for Disease Control (CDC) released statistics on obesity. First, what defines obesity?  In determining overweight or obesity for adults, a tool called the Body Mass Index (BMI) is used.  According to the CDC:
  • an adult that has a BMI between 25 and 29.9 is considered overweight
  • an adult that has a BMI of 30 or more is considered obese
Check out the CDC's BMI tool in the right hand column of this blog. As you can see, it uses height and weight, and for most people this correlates with their amount of body fat. If the tool isn't working for you (it requires Flash Player 9) you can go directly to the CDC's website here and use their interactive BMI calculator. Children and teens have their own BMI calculator that also uses height and weight, but this data is then plotted on a BMI-for-age growth chart in order to obtain a BMI percentile. You can find that tool here.

So, back to the obesity statistics.  This may not be all that surprising to some, but it's a sad fact that recent data released by the Weight Control Information Network (WIN) shows that over one third (33.8%) of American adults (age > 20) are obese and over two thirds (68%) are overweight. After checking your BMI, you might even be realizing that you're among these statistics.

Okay, enough of the depressing news. Let's talk about what can be done to make a positive change in these obesity trends.   The last post mentioned the 1990's low-fat/no-fat diet craze. Then the pendulum swung the other way and low carbohydrate eating became the next fad. Regardless of how or what you're eating, the most important information to keep in mind when you're trying to lose weight is calorie consumption. If the calories being consumed are greater than the calories being burned, weight gain occurs. It's as simple as that.

Most experts agree that 20-35% of our daily calories should come from fat  This amounts to about 44 to 78 grams of total fat a day, based on a 2,000 calorie a day diet (Mayo Clinic). Even though all fats contain the same number of calories (9 calories per gram), it's the foods we eat and the types of fat they provide that is vitally important. In addition, the ratio of certain fats in our diet is being recognized as significant for good health as well.

Plant Oils
Perhaps you've seen the classic spaghetti western starring Clint Eastwood called The Good, the Bad and the Ugly. The title of this film might be a helpful way to remember the reputation, so to speak, of the different dietary fats. They are:

Unsaturated fats - the good
These fats are called unsaturated because of their chemical structure, where most of the fatty acids are not saturated with hydrogens. You may recall that unsaturated fats can be mono- or polyunsaturated fatty acids (also known as MUFA's and PUFA's respectively).  Major sources of MUFA's are:
  • plants oils ( olive oil, peanut oil, canola oil)
  • avocados, nuts and seeds 
Major sources of PUFA's are:
  • plant oils (safflower, sesame, soy, corn and sunflower) 
  • nuts and seeds
  • high in omega 3 - Fatty, cold-water fish (such as salmon, mackerel and herring), flax seeds, flax oil and walnuts
Saturated fats - the bad
In addition to fats that are unsaturated, there are also fats that are saturated.  They are called saturated fatty acids because their chemical structure has all the hydrogens it can hold, so it is said to be saturated. Later in the post the significance of the hydrogen saturation/unsaturation will become clearer, but for now it's important to note that saturated fats should be limited in the diet.  Consuming saturated fat is one of the main dietary factors linked to increased blood (serum) cholesterol levels.  Major sources of saturated fats are:
  • whole milk, cream, butter, cheese,
  • fatty cuts of beef and pork, sausage
  • coconut, palm and palm kernel oils and products containing them like prepackaged cakes, cookies, pies, doughnuts and pastries
Trans fats - the ugly
The fact that a fat is saturated, or mono/polyunsaturated influences its firmness at room temperature and also its stability. Generally speaking, an example would be that polyunsaturated vegetable oils are liquid, whereas saturated fats like that found in beef or butter are more solid. All fats eventually become spoiled (rancid) when exposed to oxygen (oxidation), but polyunsaturated fats are the most unstable, so they're the most susceptible.

Back in the early 1900's a chemist figured out a way to alter the chemical structure of fats through a process called hydrogenation. This is the chemical process of taking a mono- or polyunsaturated fat and partially saturating it with more hydrogen atoms. Why bother? Well, one reason behind hydrogenation is that it makes a liquid fat more solid.  It also increases the stability of the fat. This helps to prevent spoilage and extends the shelf life of prepackaged foods containing partially hydrogenated oils. Unfortunately, the downside of this process results in what are called trans-fatty acids, which are also known as trans-fats. Major sources of trans-fats are:
  • Commercial baked goods — such as crackers, cookies and cakes 
  • Fried foods, such as doughnuts and french fries
  • Shortenings and some margarine can be high in trans fat (Mayo Clinic)
What's so "ugly" about trans-fats? Well, it turns out that when it comes to cholesterol, these fats pack a deadly one, two punch. Not only does consuming trans-fat lower the "good" cholesterol called high density lipoprotein (HDL), it raises the bad cholesterol called low density lipoprotein (LDL). In brief, lipoproteins are clusters of lipids and proteins and they transport fat through the bloodstream. LDL is loaded with cholesterol whereas HDL has the job of carrying cholesterol to the liver for recycling or disposal. A high HDL level represents better elimination of cholesterol.  As a result it is considered the good cholesterol. This is why high LDL and low HDL levels are risk factors for heart disease and stroke. You can find much more detailed information on cholesterol levels at the American Heart Association's website here.

So, now that we're familiar with the types of fat, and a few of the food sources, how can we apply this knowledge? How can we consume more of the good fats and in the proper ratios? The next and final post on fats will cover these questions. In the meantime, one suggestion is to avoid or eliminate processed, prepackaged (short for prepared and packaged) and fast foods which contain the bad and ugly fats. Replace these with whole foods, which are in their natural state, or have been processed or refined as little as possible. Start by trying to make small dietary changes, like substituting a serving of omega 3 rich fish for meat once a week. Taking small steps does make a difference and can eventually lead to lifestyle changes and healthier nutrition. 

Image source: Merriam Webster


  1. I don't like the BMI calculator!

  2. Mike, Try to keep in mind that this is just a tool to give you a general idea of your body mass. Also, it's important to keep in mind that the BMI calculator correlates height and weight to body fat and works for most people. However, an exception is for very fit people with more muscle mass in which case the calculator may be off.

    The most accurate way to measure body fat is with hydrostatic weighing. Another option is body fat calibration where a person skilled in using calipers measures specific sites on the body to assess a fat:lean ratio. A third option is using a bio-impedance device. Thanks for your comment.