 For decades, the relationship between dietary fats and health was at the center of our attempts to understand the underlying cause of the obesity epidemic. The debates over nutrition that you will hear, should we worry about fat? Should we worry about carbohydrates? Is the problem lack of fiber? All these are attempts to understand what's the problem in the Western diet that is the culprit. Because people would like to figure that out because then you can just adjust that one thing and go on your merry way. But we haven't gotten that down yet. We don't know the answer to that question with any real confidence. Despite the important roles that fats play in our bodies, this entire category of food was shunned for much of the 20th century. This led to an enormous increase in the availability of fat-free and reduced fat foods. But in spite of this, obesity rates continued to rise. Today, rising awareness about the difference between the so-called good fats and bad fats have allowed this important part of our food supply to make a comeback. But once again, the pendulum threatens to swing too far in the opposite direction. Dietary fats can be divided into two families, the saturated and the unsaturated fats. Saturated fats get their name from the fact that their fatty acids are saturated with hydrogen molecules. This means that they can lie flat and packed together densely so that saturated fats tend to be solids at room temperature. Animal fats, like lard and butter, are good examples. In contrast, the fatty acids that make up unsaturated fats are kinked in places where double bonds between the carbon atoms cause the chains to be less saturated with hydrogen. This also means that these fatty acids don't pack together as tightly, leaving most unsaturated fats in the liquid state at room temperature. Omega-3 fatty acids are a special kind of unsaturated fatty acid with double bonds in specific positions of the hydrocarbon chain. They're found in high concentrations in fish oil and also to some degree in nuts, flax seeds and other vegetable oils. Omega-3 fatty acids are the only kind of fatty acid that the human body can't make, so they're essential for our health and they need to be consumed via the food we eat. Unsaturated fats can be naturally occurring like the fats found in olive oil, nuts and avocados, or they can be man-made or chemically manipulated to become unsaturated. These are the fats found in some margarines and in the kinds of oils that are often used for repeated cooling and reheating in deep frying machines like the ones used in many fast food restaurants. The problem with chemically engineered unsaturated fats is that the chemical bonds between the carbon atoms are less stable, so they easily flip into a trans-orientation rather than a cis-orientation. And this is where we get the name trans fats. Trans fats are problematic for our health because they increase the amount of LDL cholesterol in the blood and they lower the amount of HDL cholesterol, the good cholesterol in the blood. By doing this, trans fats promote the formation of arterial plaques and increase the risk of heart disease. While saturated fats have also been shown to contribute to increases in LDL cholesterol, they haven't been shown to lower HDL cholesterol or to contribute to the development of arterial plaques as significantly as trans fats. So what's the bottom line when it comes to foods that contain fat? Probably the most sensible food recommendation is this. Enjoy reasonable amounts of foods that contain mostly naturally occurring unsaturated fats like those found in olive oil, nuts and avocados. Avoid all foods containing trans fats and limit your intake of foods like red meats that are high in saturated fats.