Dietary Fat: Friend or Foe?

History of the Low Fat Diet

In 1980, science came to the consensus that a low-fat diet needed to be followed in order to prevent coronary heart disease and cancer. Due to this promotion of a low fat diet, the food industry saw a money-making opportunity, and began replacing fat with sugar in processed foods. This was known as the "Snackwell's phenomenon" because low fat foods had just as many calories as their full-fat counterparts. This trend grew and grocery store shelves were littered with low-fat food options. In 1992, the Food Guide Pyramid was released which also promoted the idea of "low-fat" needed for optimal health. In 1988, the "heart healthy" seal of approval was created by the American Heart Association and companies could pay to have this stamped on their food products. However, this backfired when the public realized no fresh foods included this seal of approval, and began to believe that processed foods were the only heart-healthy options. 

In the 1990's food moved from being low fat to being no fat and ads filled magazines and promoted low to no fat was the key to weight loss, not calories. Throughout the 1990's, scientists, the government, and writers declared that low fat, high carbohydrate diets were the optimal way to prevent heart disease. Americans believed they could eat as much as they wanted as long as it was low fat. Despite all of this effort to reduce the risk of heart disease, yet there was no evidence to support low fat diets preventing heart disease.

So what is the deal with fat? Does fat make us fat? Is it required for a healthy diet?

Fat is an energy-dense nutrient at 9 calories per 1 gram. Fat is required for the digestion, absorption, and transportation of fat soluble vitamins, which include A, D, E, and K. Fat makes up our cell membranes, helps to slow down gastric emptying, and increases the palpability of our foods (aka, makes them taste good!). While dietary fat is an essential nutrient in our diet, we must consider the types of fats we are eating in regards to health outcomes.

Fat can be categorized into two main groups; saturated and unsaturated fats. These are based upon the chemical structure of the fat molecule. A saturated fat has no double bonds in the molecule and is solid at room temperature, example: animal fat, coconut oil, butter, lard. An unsaturated fat has one or more double bonds and is typically liquid at room temperature, example: oils. Unsaturated fat can further be categorized as monounsaturated or polyunsaturated. This nomenclature has to do with the number of double bonds within that unsaturated fat. Furthermore, there is a third category known as trans fat which has to do with the positioning of a double bond within an unsaturated fat. 

We will not go any further in depth about structure of bonds, but we will discuss the benefit and the risks of each type of dietary fat and what current recommendations are.

Saturated Fat

As stated above, saturated fat is solid at room temperature and includes animal fat, coconut oil, butter, lard, etc. Intake of saturated fat is associated with an increased level of LDL cholesterol concentrations (aka our "bad" cholesterol), therefore recommendations are to limit saturated fat to less than 10% of total calories. 

While intake of saturated fat has been associated with increased risk of coronary heart disease (CHD), it is important to note that CHD is a multi-factorial disease and cannot be boiled down to one single factor. Replacing saturated fat with refined carbohydrates is not associated with a decrease of CHD risk. One study even indicated that replacing saturated fats with refined starch or added sugars actually increased risk of CHD. However, replacing saturated fats with polyunsaturated fats or complex carbohydrates did show a decrease risk of CHD.  A publication from the Nurses' Health Study showed an association between replacing carbohydrates with unsaturated fats and reduction in CHD death.

Unsaturated Fat

Monounsaturated fats and polyunsaturatd fats both fall into the category of unsaturated fats.  Consumption of polyunsaturated fat is associated with a decreased risk of CHD. Studies showed that PUFA consumption resulted in a 19% decrease in CHD risk. Polyunsaturated fats include omega-3 and omega-6 which are essential fatty acids that are strongly associated with health outcomes. Omega 6 help to clot blood, promote inflammation, and increase blood pressure. While chronically these are body responses that are not favored, they are required short-term in some instances. Omega-3 counteracts omega-6 and decreases inflammation, blood pressure, and clotting abilities. The ratio of omega-6 to omega-3 is extremely important. Current recommendations are a 1-4:1 ratio of omega 6 to omega 3. However, currently, the ratio is about 10:1 which may be exacerbating inflammatory diseases. 

Omega 6's are found heavily in processed foods and omega-3's are found heavily in fish.

Recommendations are not necessarily to increase omega-3 intake, but to decrease omega-6 intake in order to be in the correct ratio.

In conclusion, consuming more whole, minimally processed foods is recommended! Fats should come from nuts, seeds, avocados, olive oil, and fatty fish. To decrease risk of cardiovascular disease saturated fat should be limited, and polyunsaturated fats should be increased.

Resources:

Patterson, E., Wall, R., Fitzgerald, G. F., Ross, R. P., & Stanton, C. (2012). Health implications of high dietary omega-6 polyunsaturated Fatty acids. Journal of nutrition and metabolism, 2012, 539426. Liu, A. G., Ford, N. A., Hu, F. B., Zelman, K. M., Mozaffarian, D., & Kris-Etherton, P. M. (2017). A healthy approach to dietary fats: understanding the science and taking action to reduce consumer confusion. Nutrition journal, 16(1), 53. doi:10.1186/s12937-017-0271-4 Ann F. La Berge; How the Ideology of Low Fat Conquered America, Journal of the History of Medicine and Allied Sciences, Volume 63, Issue 2, 1 April 2008, Pages 139–177, https://doi.org/10.1093/jhmas/jrn001 SR