Food manufacturers flooded the market with processed foods containing hydrogenated fats and processed sugar. The replacement of saturated fats in the diet with trans fats and sugar resulted in epidemic rates of obesity and its related health complications (2). Rates of diabetes, heart disease and cancer have risen since Americans adopted the low-fat, high-carbohydrate diet.
Of the three macronutrients, carbohydrates are our body’s preferred energy source because they are easier and quicker for our bodies to digest and use for energy. On the other hand, fat takes a different route before we can use it as energy because it is insoluble in our blood. Think of fat as being a reserve or our long-term source of energy that sticks around the longest. On the technical side, which we’re about to get very technical: fat is three fatty acids + a glycerol molecule, or a triglyceride (tri- as in three and glyceride).
But wait, bile isn’t the only thing added in here, our pancreas also adds pancreatic digestive juices called lipase to the duodenum which helps break down triglycerides into two fatty acids and a monoglyceride. After this step, though, the fat droplets don’t just disappear. Instead the fatty acids and monoglycerides are absorbed in the microvilli (remember these from Digestion, part I?) and reassembled into triglycerides.
Trans fats are unsaturated fats that have been processed and as a result, behave like saturated fats. Eating trans fats increases the levels of ‘bad’ cholesterol and decreases the levels of ‘good’ cholesterol in the body which is a major risk factor for heart disease. It is important to lower the amounts of trans fats you eat to help you stay healthy.
Along with nuts, seeds get high marks as healthy fats to improve good cholesterol. And flaxseeds are especially popular among nutritionists because of their versatility in a heart-healthy diet. “Sprinkle flaxseeds onto whatever you like,” says Haisley. “My favorite is with Greek yogurt or on my oatmeal. It is a great addition to salads or whisked into your favorite homemade salad dressing. You can even bake with it, too; try using 3 tablespoons of flaxseed in place of 1 tablespoon of oil or margarine in your muffins.” Try these cranberry-nut mini loaves with flaxseeds.
Healthy fats are unsaturated fats that are found in fatty fish like salmon, avocados, nuts and seeds, plant oils that are liquid at room temperature like olive oil, and coconut oil. Coconut oil is contested as a healthy fat because it is a saturated fat, but because the majority of its fat content is medium-chain triglycerides (MCT), I consider them an exception.
Polyunsaturated fats are required for some of the normal body functions listed above, but the body can’t produce them so they must be obtained from foods. Omega 3 fatty acids are a type of polyunsaturated fat and can be found in cold-water high-fat fish like salmon, mackerel, and sardines, and in flaxseeds, chia seeds, walnuts, canola oil (again look for non-GMO or organic), and unhydrogenated soybean oil (also look for non-GMO or organic as most soy products in the US are GMO unless they specifically state non-GMO or organic.)  Omega 3’s are also found in some greens, including romaine, spinach, and arugula.  Note that the body only partially converts plant-based omega 3’s to DHA and EPA, which are found in cold-water fish
Eating foods with fat is definitely part of a healthy diet. Just remember to choose foods that provide good fats (monounsaturated and polyunsaturated fats) and balance the amount of calories you eat from all foods with the amount of calories you burn. Aim to eat a dietary pattern that emphasizes intake of vegetables, fruits, and whole grains; includes low-fat dairy products, poultry, fish, legumes, non-tropical vegetable oils and nuts; and limits intake of sodium, sweets, sugar sweetened beverages and red meats. Doing so means that your diet will be low in both saturated fats and trans fats.
The fact that many Americans still haven’t shaken off the decades-long notion that fat—and particularly saturated fat—is bad for you, isn’t even the biggest issue we face in adopting more fats into our diets. Many of us struggle to determine which fats we should be eating because the U.S. Dietary Guidelines (and nutrition labels) are both generalizing and misleading.
Since sources of fat are more calorie-dense, it is important to understand what a serving of a fat is equivalent to. For example, one teaspoon of butter, margarine or mayonnaise is one fat serving. For times when you may not have a measuring spoon available, a visual equivalent of one teaspoon is the tip of your thumb. See below for examples of serving sizes for added fats.
Although fat is an essential part of the diet, keep in mind that most high-fat foods are also considered calorie-dense foods. When increasing your intake of healthy fats, it’s important to account for this by making modifications to your diet, such as decreasing your intake of refined carbs or sweets. Without making a few simple swaps to your diet, adding high-fat, high-calorie foods can lead to weight gain.
Healthy fats are unsaturated fats that are found in fatty fish like salmon, avocados, nuts and seeds, plant oils that are liquid at room temperature like olive oil, and coconut oil. Coconut oil is contested as a healthy fat because it is a saturated fat, but because the majority of its fat content is medium-chain triglycerides (MCT), I consider them an exception.
All fats and oils contain fatty acids. You may be most familiar with Omega 3 fatty acids, found in fish oil. When you eat healthy fats and oils, the digestion process enables the fatty acids to be absorbed into the blood. Fatty acids are a component of fats and oils that become the building blocks of your body, helping to create cells membranes and nerve sheathing among other body functions.

Polyunsaturated fats can primarily be found in plant-based foods and oils. Similar to monounsaturated fats, polyunsaturated fats can decrease the risk of heart disease by lowering levels of blood cholesterol (9). A certain type of polyunsaturated fat, omega-3 fatty acids have been found to be particularly beneficial for heart health. They not only lower the risk of coronary artery disease but can also lower blood pressure and protect against irregular heartbeats (9). Omega-3 fatty acids can be easily consumed by eating fatty fish such as salmon, sardines and trout.
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