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, I’m most intrigued by fat! Today I’m sharing a breakdown of fats function in the human body, how they digest, food sources of fats, and how our bodies store fat. If I haven’t lost you yet, keep reading on to learn the basics of fat from a dietitian’s point of view. Let’s jump in!
fat, part I
What are fats?
Fats are 1 of the 3 macronutrients (protein and carbohydrate being the other two) that make up our food and source of nourishment. Fat is the most calorically dense out of all macronutrients containing about 9 calories / gram of food in comparison to protein giving us 4 calories / gram and carbohydrates that also give us about 4 calories / gram. When we talked about carbohydrates, I shared that carbohydrates are our bodies preferred energy source partially because it’s easier on our bodies (and quicker) to digest and utilize 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 our reserve, our long-term source of energy, the one that sticks around longest. On a technical side, which we’re about to get very technical: fat is three fatty acids + a glycerol molecule = a triglyceride (tri- as in three and glyceride).
What are functions of fat?
Fats are incredibly important, just are carbohydrates and proteins for the human body, yet fats provide our body with a layer of protection, literally insulating our organs and also keeping a normal body core temperature. Fats also help us digest fat-soluble vitamins such as A, D, E, and K and keep our brains, cells, hormones, tissues, hair, skin, and nails healthy. 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 many clients recovering from eating disorders and/or very restrictive diets and they’ve 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!
Digestion of fats
All digestion first takes place 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 almonds for example, 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. Fats actually hang out here 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! 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. But wait, 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. In this grease pan example, though, the fat droplets just don’t disappear, 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,
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 and are 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 metabolizes 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
OOF. That’s a lot right? There’s much more to learn about fat and the use of it in the body, but I’ll leave the rest of this process for part II. But wait! Enter in, coconut oil and 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 super easy to break down the fat before getting rapidly absorbed and used for energy by the body). If you’re curious about digestion overall, check out this post on the Basics of Digestion, Part I.
Storage of fats
Let’s say you just ate 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 we already tap out on glycogen stores? That’s where triglycerides come into play – glycogen is converted to triglycerides and stored as fat. Our bodies are amazing with all these mechanisms, and they’re always efficient at seeking out energy. sS in the case that we need energy, our bodies can actually convert fat back to sugar. Let’s say it’s been a long time in between a meal. Glucose is 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 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.
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 is does for us. Stay tuned for part II where I answer your questions you comment here about- so what else would YOU like to learn about carbohydrates? Let me know so I can get to writing!
Other nutrition topics and Basics you’ll love:
- Carbohydrates, part I and part II
- Protein part I
- Digestion, part I
- Proteins Everyone Should Be Eating
- Nutrient Directory to learn more about every mineral/vitamin!
Check out these Friday favorites from the Nutrition Stripped squad wearing the uniform- tees! Order yours here.