Dietitian nutritionist McKel answers what are healthy fats and explains why you need them in your diet.
Today’s Basics topic is all about fat! We’ve covered other macronutrients here on the Nutrition Stripped blog such as carbohydrates, protein, and digestion, and now the list is growing! Out of all the macronutrients, people have the most misconceptions about by fat! Today I’m sharing a breakdown of food sources of healthy fats, the function of fat in the human body, how fats are digested, and how our bodies store fat. If I haven’t lost you yet, keep reading on to learn the basics of healthy fat from a dietitian’s point of view. Let’s jump in!
What is fat?
Fats are one of the three macronutrients that make up our food and source of nourishment (protein and carbohydrates are the other two macronutrients). Fat is the most calorically dense out of all macronutrients and contains about nine calories per gram. In comparison, protein and carbohydrates both contain about four calories per gram.
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).
Do you need fat in your diet?
Yes, you need fat in your diet! All three macronutrients – fats, carbohydrates, and protein – are incredibly important for the human body’s functioning. Fats are important for cellular and hormonal health, and unlike carbohydrates and protein, fats also provide our bodies with a layer of protection, literally insulating our organs and also helping keep a normal body core temperature.
Fats also help us digest important fat-soluble vitamins such as vitamins A, D, E, and K that keep our brains, cells, hormones, tissues, hair, skin, and nails healthy (1). Fat provides the structural component to many cell membranes which are essential for cellular development and carrying various messages through our body quickly via hormones. In fact, fats are vital to hormonal health. I’ve worked with many clients recovering from eating disorders or very restrictive diets who have gone years without periods due to their low body fat percentage. There’s a fine line between wanting to be “toned” and “ripped” and being a healthy woman able to provide your body with enough fat reserves for healthy hormones and hormonal production. Fat is crucial for our bodies!
How are fats used in our body?
All digestion first takes place in the mouth from chewing and saliva beginning to break down food. After you eat a fat-containing food, such as almonds, you first break down the food in your mouth. Next, it goes to your stomach where those solid pieces of almond are further broken down via stomach acid (2). Fats actually hang out in the stomach for quite a bit which is one reason for why fat keeps you feeling fuller longer. Depending on the volume of food and components of food, healthy fats may keep you feeling full for hours.
Fat droplets start to pass through the duodenum where bile acids are added (bile acids are from cholesterol in the liver and stored in the gall bladder). Bile acids are really cool because they act like soap breaking and emulsifying the fat droplets and making them into even smaller droplets. I like to use the visual of washing a pan with grease on it with soap, at first the grease barely comes off, but with a little muscle and scrubbing with soap the detergent breaks up the fat and grease into very small particles until it’s gone.
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.
Confused yet? Why would our body break something down to just put it back together? Long-chain fatty acids are insoluble in blood and in order to transport these across, triglycerides are packaged into chylomicrons that are basically a vehicle that gets released into the lymphatic system and eventually in the blood for circulation. When chylomicrons reach the capillaries of muscle and fat tissue, they activate lipoprotein lipase (stay with me here).
Remember pancreatic lipase from earlier in the duodenum? Well, lipoprotein lipase breaks down triglycerides for absorption which goes into the fat tissue for storage, or it’ll be absorbed in muscle tissue for energy. Where do the chylomicrons go? Basically, they shrink so much that they just become tiny little particles that used to be. They’re absorbed into the liver and then the liver metabolizes them. The liver is key for fat metabolism! Liver health = fat digestion efficiency = healthy fat burning potential.
So quick recap: FOOD → STOMACH → PANCREAS → DUODENUM (BILE ACIDS) → SMALL INTESTINE → CHYLOMICRON → MUSCLE OR FAT TISSUE → CHYLOMICRON PARTICLES (REMNANT) → LIVER → GALLBLADDER → cycles back to bile acids
What are healthy fats?
There are two basic kinds of fat, saturated and unsaturated. Unsaturated fats are considered “healthy fats” include both polyunsaturated and monounsaturated fats. These types of fats are typically found in vegetable oils that are liquid at room temperature, fatty fish, (salmon, trout, catfish, mackerel), and nuts and seeds. Polyunsaturated fats include Omega-3’s that are the building blocks of cell membranes I mentioned earlier. Omega-3’s also give your body energy and help support your hormones and immune system (3).
Wild-caught salmon, olive oil, avocados, walnuts, flaxseeds, chia seeds and hemp seeds are packed with omega-3 fatty acids. Ideally, it’s best to get omega-3 fatty acids from fish sources which contain better converting and more bioavailable forms of DHA and EPA. Plant-based omega-3 rich foods like flax seeds, chia seeds, and hemp seeds must be converted in the body from ALA to DHA and EPA, that conversion doesn’t yield as optimal levels of omega-3 compared to food sources like salmon, mackerel, and other fish.
Monounsaturated fats are considered a healthy fat that is also a good source of vitamin E. Monounsaturated fats include olives, avocados, hazelnuts, almonds, Brazil nuts, cashews, sesame seeds, pumpkin seeds, and olive oil.
Saturated fats are typically what are considered “unhealthy fats” and include animal fats (meat, poultry, dairy) and plant oils that are solid at room temperature like coconut and palm oil.
Whenever I mention coconut oil as a healthy fat I always get the reaction of “But McKel, that’s a saturated fat!”. It sure is. Coconut oil is comprised of about 90% saturated fat. So why do I personally use and recommend this oil in cooking?
The type of fatty acids that make up coconut oil’s saturated fat content is medium chain triglycerides (MCT) and are about 65% of its fat content. Unlike long chain fatty acids (the majority of fats in our diet) which must go through modification prior to being digested and absorbed in our bodies, medium chain triglycerides are passively diffused from our gastrointestinal tract to the portal system. In other words, our bodies find it super easy to break down the fat before getting rapidly absorbed and used for energy by the body. Coming from a clinical background, MCT’s are very commonly used in treating people who have malabsorption issues, are on ketogenic diets, or are increasing calories without much volume.
Several studies explore and show the this type of saturated fat in coconut does not negatively affect cholesterol levels nor overall heart health like we were once told. Some studies have shown coconut oil moderately increases metabolic rate, which is often a “selling” point that it helps boost your metabolism and contribute to fat loss or weight control. I’ll let these studies here, here, and here tell you what we do know.
Additionally, coconut and the different varieties of coconut may have antimicrobial properties, provide benefits to gut and digestive health (here and here), as well as help increase skin moisture and integrity (here, here, and here). For even more studies to read the science behind coconut oil/medium chain triglycerides, feel free to check out one of my favorite resources here.
So a recap:
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.
How much fat should you eat in a day?
This will always be the most popular question I receive after writing these Basic posts and my answer each time is, it depends! It depends on your lifestyle, your health and fitness goals, your digestion, activity level, and genetics. Good thing, though, that I really love figuring all that out for you so you don’t have to! Just email me and we’ll set up a consultation about your goals and how you can meet your needs without eating too much or too little for optimal health.
Can I gain weight if I eat too much fat?
Yes, just like you can gain weight when you eat more than your body’s needs of carbohydrates or protein. While you should be including healthy fats in your diet, keep in mind that they are very calorically dense and offer over twice the calories per gram as protein and carbohydrates.
More resources for your reading pleasure on all things fats:
Krause Nutrition textbooks, Basic Medical Biochemistry, Nutrition Therapy and Pathophysiology (the newest edition contains my food photography), and Advanced Nutrition and Human Metabolism. I hope after reading this you have a better understanding of what fat is and what it does for our bodies.
Other nutrition topics and Basics you’ll love:
- Carbohydrates, part I and part II
- Protein part I
- Digestion, part I
- Plant-Based Proteins Everyone Should Be Eating
- “Fat-Soluble Vitamins”. Diet and Health: Implications for Reducing Chronic Disease Risk. https://www.ncbi.nlm.nih.gov/books/NBK218749/
- “Fat digestion in the stomach: stability of lingual lipase in the gastric environment.” https://www.ncbi.nlm.nih.gov/pubmed/6427744
- “Omega-3 Fatty Acids”. https://ods.od.nih.gov/factsheets/Omega3FattyAcids-Consumer/