Understanding Dietary Fats

Contributed by Dr. Steven T. Devor – Director of Performance Physiology for MIT and OhioHealth, and Associate Professor of Exercise Physiology, Department of Human Sciences, and Department of Physiology and Cell Biology, The Ohio State University

Dietary fat is the most calorically dense of all the macronutrients. One gram of fat contains 9 calories, while carbohydrate and protein contain only 4 calories per gram. There are four different types of dietary fats, and they have significant and important differences. Make no mistake, in order to function properly and maintain overall health, fat must be a part of your daily dietary intake. Fat is used an energy source and is necessary to help your body absorb vitamins, minerals, and other nutrients from food.  

My goal is to help you understand all four of the dietary fat types, and how they are either good or bad for your body. While some fats, like trans fat, are completely inconsistent with a healthy diet and lifestyle, other fat types are absolutely necessary and essential to have in your daily diet.

Recently, the Food and Drug Administration (FDA) made the decision to ban all trans fat in all processed food products. The FDA has declared the only safe level of trans fat in the American diet is zero trans fat, and further labeled trans fats a major public health concern. Trans fat has been shown in numerous published scientific studies to contribute to diabetes, high cholesterol, and heart disease.

Many, many food manufacturers and restaurants have already removed trans fats from their recipes, but the FDA-ordered elimination is another very positive step in a healthier direction for all Americans. The Centers for Disease Control and Prevention has estimated that further decreasing the amount of trans fats consumed every day may potentially prevent as many as 20,000 heart attacks and 7,000 deaths per year. In spite of the FDA-mandated trans fat ban being phased in, it will be several years before it is completely eliminated from all processed food products at your average grocery market.   


Trans Fat

 Trans fat is a solidified form of partially hydrogenated vegetable oil. Many processed food manufacturers began utilizing this synthetic fat in the 1950s because it is very inexpensive and can greatly extend the shelf life of a processed food product. But over the last few decades, numerous scientific studies have shown that dietary trans fat has serious adverse health effects, including raising LDL (the “bad” cholesterol), lowering HDL (the “good” cholesterol), and contributing to the risk for development of heart disease.

However, in spite of the ban, trans fat will never fully vanish from the food supply. Trace amounts of trans fat occur naturally in meat, dairy products, and a few vegetable oils. But the processed food products where trans fats are most frequently found include many convenience foods like frozen pizzas, TV dinners, highly processed baked goods, many snack chips, and margarine, which can contain unnaturally high amounts of trans fat. So the consumer knows what they are buying, the FDA mandates that all trans fat be clearly listed on the Nutrition Facts panel on every food label. The more difficult problem is when you purchase a pastry at a coffee shop or nachos at your favorite bar. In those sorts of situations, there is simply no way of knowing how much trans fat is in the product you are consuming.

The truly tricky part is that due to a loophole in the food labeling law even processed food products where the labels claim no trans fat may be misleading. According to a recent FDA Consumer Update, food manufacturers may legally indicate "zero trans fat" if the product has less than 0.5 grams of trans fat per serving. However, the serving sizes on these products are frequently quite small, so in reality you may be consuming more trans fat than you think. Additionally, if the food label indicates the processed food product contains a "partially hydrogenated" oil of any kind you should avoid making a purchase or consuming. The FDA considers partially hydrogenated oils to be trans fat.

So, even though the FDA mandated trans fat ban has begun, it will be years until all trans fats are out of our food chain. As with many food industry claims the onus is on the consumer to be self-educated about trans fats. My advice is to read food labels carefully, be wary of unmarked pastries and other baked goods, and until restaurants can no longer cook with products that contain trans fat choose wisely where you enjoy meals when you are dining out.


Saturated Fat

Unlike most trans fat, saturated fats are naturally occurring in meat and dairy products. And even though they are not as unhealthy as trans fat, saturated fat is generally not recommended in a heart healthy diet. Saturated fat raises LDL (the “bad” cholesterol), which is a known risk factor for cardiovascular disease, heart attacks, and strokes. Many food products that are high in saturated fat also contain high levels of cholesterol, which most people need to watch. Additionally, there is an increasingly large amount of research that demonstrates an increased intake of saturated fat also increases the risk for development of diabetes.

Consuming a small amount of saturated fat is not a disaster for your health, and since it is almost unavoidable (unless you are a vegan) that is good news. Recommendations from the American Heart Association for saturated fat indicate that as much as 7 percent of daily calories are allowable. Assuming you consume approximately 2,000 calories per day, which for many active men is a bit low, that would equate to approximately 16 grams of saturated fat per day.

Most of the saturated fat in the American diet comes from animal products, such as red meat, chicken with the skin on, butter, cheese, and animal milks (cow or goat, for example). Additionally, any foods prepared with animal products such as cream-based sauces or soups, many salad dressings, ice cream, many baked goods and nearly all fried foods contain saturated fat. Also be advised that most restaurants and bakeries cook with saturated fats and they are ubiquitous in processed and packaged snack foods.

Keep your intake low by screening the nutrition label on prepared food products and select foods that either contain no, or very low amounts, of saturated fat. Choose the leanest cuts of red meat possible, look for minimal marbling and cuts with the fat around the edges so that it can be easily removed. Choose poultry products that have had the skin removed. In general, fish tend to have less overall saturated fat.


Monounsaturated Fats

Fats that unsaturated permit your body to attain the necessary health benefits associated with fat without as many of the unhealthy pitfalls associated with trans fat and saturated fats.

Monounsaturated fats are found in and derived from many plant-based foods, including nuts, seeds, olives, avocados, and sunflower and canola oils. Research indicates that consumption of monounsaturated fats improves cholesterol profiles and helps to moderate blood glucose. However, it is important to remember that monounsaturated fats are still fats, which means that they are as calorically dense as any other fat type. All fats carry 9 calories per gram (compared with carbohydrate and protein, which are both 4 calories per gram). So even though monounsaturated fats are considered to be helpful in the prevention of cardiovascular disease, you still need to be aware of how much you are eating to keep overall daily calories in check.

Currently, there are no specific recommendations for how much monounsaturated fat one should consume daily. However, given the current guidelines that fat intake should comprise approximately 20 to 35 percent of your daily calories, this would equate to 44 – 78 grams of fat; assuming a 2,000 calorie a day diet. And most of those fat calories should come from either monounsaturated or polyunsaturated sources.


Polyunsaturated Fats

Like monounsaturated fats, polyunsaturated fats are found in several plant food sources. And they also help to maintain blood glucose and keep overall cholesterol under control. The human body requires polyunsaturated fats, but is not able to produce them on its own as it can with other types of fats. Accordingly, they need to be obtained exclusively from dietary food sources.

Polyunsaturated fats exist in two forms: 1.) omega-6 fatty acids; and, 2.) omega-3 fatty acids. Soybean, safflower, and corn oils contain high amounts of omega-6 fatty acids, and because many processed foods are produced with these types of oils the diets of many Americans generally contain enough of the omega-6 polyunsaturated fats. There was controversy regarding the benefit of omega-6 fats and that they may lead to inflammation. But most health experts and scientists now agree that they are beneficial in your diet.  

Great sources of omega-3 fatty acids include many cold-water fish like salmon, herring, and mackerel, and flaxseeds and walnuts. Unfortunately, omega-3 fats are not as common in the diets of most Americans. Physicians and scientists are now realizing that the benefits of omega-3 fats extend well beyond the protection they afford your heart. It has been shown that these fats are beneficial for helping to prevent many autoimmune diseases, some forms of cancer, and Alzheimers disease as well.

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