Fats are 1 the macronutrients, alongside protein and carbohydrates that make up our food and source of nourishment. Fat is the most calorifically dense out of all macronutrients, and it contains around 9 calories / gram of food in comparison to protein and carbohydrates which both give us around 4 calories / gram.
When I explained about carbohydrates, I shared that they are our bodies preferred energy source partially because it’s easier for our bodies (and quicker) to digest and utilise that energy. On the other hand, fat is insoluble in our blood and takes a different route before we can use it as energy. Think of fat as being your reserve, your long-term source of energy, the one that sticks around longest. On the technical side, fat is three fatty acids + a glycerol molecule = a triglyceride (tri- as in three and glyceride).
WHAT ARE FUNCTIONS OF FAT?
All of the macronutrients are incredibly important for the human body, but fats also provide our body with a layer of protection, and literally insulates our organs and keeps a normal core body temperature. Fats also help us digest the fat-soluble vitamins A, D, E, and K; which are essential for keeping our brain, cells, hormones, all tissues, and hair, skin and nails healthy (now you might be understanding why a low fat diet is so bad). Fat provides the structural component to many cell membranes which are essential for cellular development and carrying various messages (hormones) through our body quickly. I’ve worked with several clients who are recovering from very restrictive diets and they’ve been years without periods due to their low body fat % - there’s a fine line between wanting to be toned and being a healthy woman able to provide your body with enough fat reserves for healthy hormones and hormonal production. Don't underestimate how crucial Fat is!
DIGESTION OF FATS
All digestion starts in the mouth, carbohydrates more so than fat, because fat needs a little bit more attention and energy to digest. After you eat a fat containing food, let’s use nuts for example, you first break down the food in your mouth, then it goes to your stomach where those solid pieces of the nuts are further broken down; fats actually hang out here for quite a bit which is one reason for why fat keeps you feeling fuller longer, even longer depending on the volume of food and components of food.
Fat droplets then 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). They act like soap, breaking and emulsifying the fat droplets 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. Bile isn’t the only thing added in here, our pancreas also adds pancreatic digestive juices (lipase) to the duodenum which helps break down triglycerides into two fatty acids and a monoglyceride. Going back to the greasy pan visual, the fat droplets just don’t disappear, the fatty acids and monoglycerides are absorbed in the microvilli (remember these from All About Digestion?), reassembled into triglycerides. Have I confused you yet? Why would your 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, basically a way to get released into the lymphatic system and eventually in the blood for circulation. When chylomicrons reach the capillaries of muscle and fat tissue it activates 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 the liver metabolises them. The liver is key at 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 → GALL BLADDER → cycles back to bile acids
There is so much more to learn about fat and the use of it in the body, but I'm going to leave the rest of this process for part II. I don't want to completely overwhelm you ! However .... before we move on I just want to introduce a slightly different fat... coconut oil (which is a medium chain triglyceride). The difference between medium chain triglycerides and long-chain fatty acids. In a nutshell, medium chain triglycerides are passively diffused from our gastrointestinal tract to the portal system (i.e. our bodies find it far easier to break down the fat before getting rapidly absorbed and used for energy by the body). Curious about digestion overall, check out my post All About Digestion
STORAGE OF FATSImagine that you have just eaten a meal, during and after meals when glucose (remember this from our carbohydrate chat?) is high or we have plenty of it to go around, it can supply more than enough for what our body needs to do. The muscles and liver convert excess glucose (sugars) into glycogen (storage/reserve). But what if you have already filled up your glycogen stores? ENTER: triglycerides - glycogen is converted to triglycerides and stored as fat. Our bodies are amazing, with all these mechanisms, it’s always efficient at seeking out energy; so in the case that we need energy, our bodies can actually convert fat back to sugar - for example if there has been a long time in between a meal, glucose will then be obtained from the glycogen stores and other molecules I won’t go in depth about here. Then the triglycerides are broken down into glycerol, which converts to glucose, + fatty acids for energy.
HOW MUCH DO WE NEED?This will always be the most popular question I recieve 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 too many/excess than your body needs of carbohydrates or protein.
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Your guide to living whole and well. Emma Olliff is a Registered Nutritional Therapist, wellness expert, food lover, and advocate for healthy living!