Monday, February 2, 2009

Expert Opinion: Fat

(This month's expert opinion is from Jason Miller. Jason Miller is an MD/PhD student at UCSF doing research on Huntington's and other neurological diseases.)

For those who keep up on the latest about healthy eating, the last decade of nutrition research may feel like a whirlwind of confusion and contradiction. The confusion started in the last part of the 20th century, which saw a trend towards low-fat food consumption. Low-fat alternatives to just about any packaged product began appearing on our grocery store shelves. In the extreme case, we had products like Olestra, which tasted like fat but were indigestible, thereby rendering any food product fried in Olestra as low-fat or fat-free. The US government's "food pyramid" showed fats as part of the "peak" of the pyramid, to be consumed in only sparing amounts. On the heels of this low-fat consensus came the Atkins diet, which emphasized the minimization of carbohydrates. Because the Atkins diet allowed consumption of large quantities of fat (and protein), the diet directly contradicted the mantra that low-fat eating was healthy eating - Atkins dieters were really losing weight eating high-fat food. As the Atkins diet settled in as a way of life for many people, news about trans-fats then hit the national conscience. Trans-fats, which are unsaturated fats that have been partly hydrogenated (no need to understand this technical mumbo-jumbo right now, but just know that partially hydrogenated fats and trans-fats are essentially equivalent), seemed to be especially unhealthy for people - so unhealthy that many cities have banned or are considering banning the fat from being used in restaurants.

So what the heck does one make of all this confusion? Unfortunately, the putative healthiness of a low-fat diet or an Atkins diet (or other diets) were often based on assumptions rather than rigorous and carefully controlled scientific studies. But things seem to be changing. In the past several years, numerous clinical trials have been conducted and a much clearer consensus about what constitutes healthy eating has emerged. While there are lots of new findings from these studies, I am going to focus on those findings related to fat consumption.

First, an introduction to fat. There are three basic categories of fat (but many more subcategories) - saturated fats, unsaturated fats, and trans-fats (which are man-made). Fats are made up of long chains of carbon with hydrogens attached to them. For a fat to be "saturated," each carbon in the chain has to be totally saturated with hydrogens. In contrast, an "unsaturated" fat is one in which there are fewer hydrogens attached to the carbon chain. To create "trans-fats", one takes an unsaturated fat and chemically attaches some (but not too many) extra hydrogens on it - hence the term "partially hydrogenated."

With that introduction, one may naturally wonder why fats were originally thought to be so unhealthy, thereby sparking the low-fat trend of the late 20th century. Part of the answer is simply that people saw fat that you consume as somehow equating to the fat that hangs on your belly. But the body can and does make fat from anything you consume. The real magic rule for how much fat you have on your belly is a simple formula: If you consume more calories than you burn, it will be turned to fat - it doesn't matter what type of calories you consume. To be fair, there was a more legitimate reason to think that fat might be bad, and that has to do with how many calories are in a gram of fat. First, let me remind everyone that essentially all of the calories you consume from food come from either proteins, carbohydrates, or fats. Proteins and carbohydrates each have about 4 calories per gram. But fats actually contain 9 calories per gram. So if you consume a 1/2 pound meal that is all protein and your buddy consumes a 1/2 pound meal that is all fat, your buddy would have consumed more than two times the number of calories as you consumed. Assuming you both eat roughly the same mass of food each day and expend the same number of calories per day, your buddy will soon become a lot fatter than you! The problem with this logic is that it turns out that certain foods tend to make you feel more full than other foods. For example, carbohydrates make you feel full immediately but also make you hungry much earlier than proteins and fats. Fats actually cause a sustained feeling of fullness, and this helps temper how much fat people consume, thereby preventing the high caloric content of fats from actually making people that much fatter.

So now that we know fats don't necessarily make you fat (and can actually cause you to feel more satiated than other food types), is there any real difference between unsaturated fats, saturated fats, and trans-fats? A lot of recent research has provided one clear answer: YES!! I'll cut to the chase and tell you that unsaturated fats are oftentimes really good for you, especially the omega3 and omega6 unsaturated fats, while saturated fats and trans-fats are unhealthy. If all fats have the same property of making you feel satiated (and none of them really make you inherently fat), why is there a health difference between unsaturated, saturated, and trans-fats? The answer lies in how the body utilizes these different types of fat. When the body sees saturated fats, it tends to combine these fats with cholesterol into packages that circulate in the blood and deposit into the walls of our arteries. As these "fat plaques" build up, they clog our arteries, predisposing us to heart disease, stroke, and a slew of other health problems. In contrast, when the body sees unsaturated fats, it tends to put these fats into packages that actually scavenge cholesterol from arteries and brings it back to the liver for proper disposal. Certain types of unsaturated fats, like omega fats, are particularly good at triggering this process. Because these types of fats are promoting the removal of "fat plaques" from our arteries (and proper disposal of the "fat plaque" components in the liver), it isn't surprising that they are associated with a reduced risk of heart disease and stroke. Finally, there are trans-fats. It's not exactly understood why our bodies react so poorly to trans-fats, but some people postulate that because trans-fats are manmade and not seen in unprocessed food, our body has difficulty understanding what to do with these fats. Like saturated fats, they seem to increase our risk of heart disease and other vascular problems.

So what types of foods contain saturated fats, trans-fats, and unsaturated fats?

Saturated fats - almost all fat that comes from animals is largely saturated (EXCEPT for fish!); certain non-animal fats are also high in saturated fats - coconut oil or milk, palm kernel oil, cocoa butter oil, and, to a lesser degree, cottonseed oil. Butter is also comprised almost exclusively of saturated fat.

Unsaturated fats - a good number of vegetable oils are unsaturated, including olive oil, canola oil, sunflowerseed oil, etc.; almost all nuts are high in unsaturated fats as well; fish also contain primarily unsaturated fats. The really really good unsaturated fats (omega3, omega6, and other related fats) are especially high in fish, walnuts, and flaxseeds.

Trans-fats - food has to be processed in order for it to have trans-fats. Most candybars have some trans-fats. Margarine and many butter-substitute spreads are also trans-fats. Anytime the ingredient list for a product says "partially hydrogenated," there are trans-fats in the product.

So after experiencing more than a decade of confusion about what constitutes healthy eating, we finally have some concrete answers that are almost assuredly going to stand up over time:

Avoid saturated fats and trans-fats, while being sure that your diet contains an adequate (not too little, but not too much either) amount of unsaturated fats. Within the unsaturated fats, try to be especially aware of consuming fats like omega3 and omega6 that have been shown to have substantial health benefits.

You can get your fill of omega fats by requesting an omega boost with your Element Bar or packing your bar with walnuts and flaxseeds.