There are two broad ways to classify fat: there is dietary fat and there is body fat. We consume dietary fat through our daily meals and body fat is found throughout our bodies and can accumulate, expand and contract depending upon our genetics, gender, diet and activity levels. The focus of today’s post is dietary fats; what they are and how they work. In a future post, I will focus on body fat and its role in health and disease.
Dietary fats, also called lipids or triglycerides, consist of carbon and hydrogen molecules. Triglycerides specifically consist of 3 fatty acids stuck to a glycerol backbone (3 fatty acids + glycerol backbone = triglyceride). The chemical bonds holding the fat together contain a significant amount of energy. Therefore, fats are rich sources of energy (9 kcal per gram versus 4 kcal per gram for protein or carbohydrate). When we eat fat, the fatty acid portion gets used for energy by our mitochondria helping to sustain work in places like our skeletal muscle. But big picture question: is eating fat good for us? To answer this, we need to consider the two main categories dietary fat: unsaturated versus saturated. Historically, the medical community has prescribed eating unsaturated over saturated fats due to reportedly beneficial effects on metabolic health, cholesterol levels and inflammation. There are two main types of unsaturated fats (mono- and poly-) found primarily in plant and vegetable oils.
- Monounsaturated fats are found in peanut, canola and olive oils, avocados, nuts (almonds, pecans, etc.) and seeds (chia, sesame, etc.). Monounsaturated means the fat has one double bond present between carbon molecules meaning the fat is typically liquid at room temperature.
- Polyunsaturated fats are found in flaxseed, sunflower, and corn oils, walnuts, flaxseed, fish and again, canola oil. Polyunsaturated fats simply have multiple double bonds between several carbon molecules.
Saturated fats have no double bonds between carbon molecules. Therefore, they are saturated with hydrogen molecules and typically solid at room temperature. Saturated fats are found in many foods primarily animal based such as fatty beef, pork, lamb, butter, cheese, etc. Fried foods and baked goods also contain significant levels of saturated fat. Saturated fats reportedly raise LDL and lower HDL cholesterol and therefore intake should be limited (~13 grams/day for a 2,000-calorie diet).
- Trans fats are naturally occurring (milk, meat) and manufactured as artificial trans-fatty acids by hydrogenating liquid vegetable oil resulting in “partially hydrogenated oils” which are used in cooking. These fats are reported to have detrimental effects on cholesterol, increase risk of heart disease and are associated with diabetes. Trans fat is found in food items like donuts, baked goods, cookies, stick butter, basically anything moist and delicious with a long shelf life!
While it is important limit intake of saturated and trans fats, it is equally important to incorporate mono- and poly-unsaturated into a healthful eating plan. However, just be conscious of the number of calories we are adding! Since foods containing these healthful fats are nutrient dense, consuming a little bit goes a long way. For example, noshing on some raw almonds is a great afternoon snack and will provide a serving of monounsaturated fat. However, a single serving containing 23 almonds has 162 calories. So, if we are not mindful, and end up eating a few “handfuls” of almonds we could be taking in an extra 300-500 calories! Another reason to consume healthy unsaturated fats, is that they will impart a feeling of satiety or fullness. For example, swap out mayo on your turkey sandwich for a few slices of avocado. You’ll be replacing the empty calories of the mayo with the energy and satiating effects of the monounsaturated containing avocado. So, the next time you purchase groceries, include several foods containing these healthy fats and then slowly work them into your daily meals. Don’t be afraid to try different things, just be mindful of the serving size so that you are reaping the benefits of healthy dietary fats and not unknowingly adding extra calories.