The Fat Facts: Everything You Need to Know About Dietary Fat
What do you think of when you think about “dietary fat”?
Butter? Fried foods? Weight gain? Heart disease? Diabetes? Or maybe nuts and avocados? Coconut oil? Weight-loss?
There is a lot of information about dietary fat out there, and people have all kinds of different impressions and understandings of what dietary fat is.
Just as I did for protein in my article The Meat Fallacy, here, I want to go back to the basics of fat and give you all the fat facts you need to sort fa(c)t from fiction when you read or hear something about fat in your food!
Dietary Fat: What Is it?
Dietary fat refers to a huge group of hydrogen-carbon based compounds found in food. Though there are a few categories of fat, the overwhelming majority of all the fats you can find in food belong to a class called glycerides.
Glycerides are made up of two basic parts: a glycerol molecule and one or more fatty acid(s). Let’s look each part individually.
Glycerol is a simple three-carbon long alcohol that looks like this:
It serves as a kind of “backbone” for the glyceride molecule. Each of the OH groups in the glycerol can bond with a long chain of carbons and hydrogens, called a fatty acid. If one OH group is bound by a fatty acid, the molecule is called a monoglyceride. If two are bound, it is called a diglyceride and if all three are bound, it is called a triglyceride. Nearly all glycerides in food are triglycerides.
As mentioned above, fatty acids are long chains of carbons and hydrogens. Each fatty acid also has an acidic group (COOH) on one end, which allows it to bind to the glycerol backbone. The generic structure of a fatty acid looks something like this (each point represents a carbon atom and two hydrogen atoms):
Any molecule with this basic structure -- a COOH group followed by carbons and hydrogens -- is considered a fatty acid. Within this basic structure, though, there is a lot of flexibility. Fatty acids can differ from one another in:
The number of carbons in their chain
Based solely on the definition of a fatty acid, any length carbon chain longer than 2 atoms is possible. In nature, though, not every length is really seen. In fact, most fatty acids contain one of just six carbon-chain lengths: 14, 16, 18, 20, 22 or 24 carbon atoms. Though other lengths exist, they are relatively rare.
The presence or absence of double bonds in their chain
Normally, each carbon in a fatty acid has four bonds - one to the carbon in front of it, one to the carbon behind it, and two to two hydrogen atoms like this:
In some cases, though, a carbon loses one of its hydrogen atoms and makes two bonds to one of its neighboring carbon atoms (which is also missing a hydrogen) instead.
This is called a double bond.
Fatty acids are grouped into categories based on the number of double bonds they have in their chains. Those with zero double bonds are called saturated fatty acids (because they are saturated with hydrogen atoms -- every spot that can hold a hydrogen has one).
Fatty acids with a single double bond are referred to as monounsaturated fatty acids and those with more than one double bond are called polyunsaturated fatty acids. An example of each is shown below.
The location of their double bonds
In addition to the number of double bonds in the fatty acid, the position of the double bonds in the chain can vary. For example, a fatty acid with 14 carbon atoms and a single double bond has 13 possible positions for that double bond, and each position is technically a unique molecule.
To help prevent confusing fatty acids with the same length chain and same number of double bonds, just in different positions, fatty acid names include a marker for the location of their first double bond.
Counting from the end that does not have the acidic group attached (the omega-end), the carbon that comes directly before the double bond is noted. So, for example, this fatty acid:
has its first double bond directly after carbon 3 and it would be called an omega-3 fatty acid.
The orientation of their double bonds
Each double bond, regardless of its position in the chain, can be oriented two different
Remember that each carbon atom in a double bond has lost one of its hydrogens, leaving only one attached? Well, the orientation of these two remaining hydrogens to the rest of the carbon chain determines the so-called orientation of the double bond.
If both hydrogens are on the same side of the carbon chain, like this:
it is referred to as a cis double bond or cis fatty acid. Cis double bonds put a bend into the carbon chain, that looks something like this.
If, on the other hand, the hydrogen atoms are on different sides of the carbon chain, like this:
it is called a trans double bond or a trans fatty acid. Trans double bonds don’t put kinks into the chain the way cis bonds do. They look more like this:
As you can imagine, there are millions of possible combinations of these four parameters. Fatty acids can look wildly different from one another and behave in wildly different ways.
For example, polyunsaturated fatty acids with cis double bonds are zig-zaggy. They take up a huge amount of space and can’t stack together well. This keeps them a liquid, even at cooler temperatures.
Saturated fatty acids, on the other hand, are smooth and straight and can stack together neatly, kind of like Lincoln Logs. This lets them become a solid mass at cooler temperatures. For many, this occurs even at room temperature.
Building a triglyceride
Once three fatty acids are bound to the glycerol molecule, they become a triglyceride. A fully-formed triglyceride looks something like this:
As the picture above shows, the three fatty acids in a single triglyceride don’t all have to be identical. All three can be completely different. That means there are millions of possible triglycerides with unique combinations of different fatty acids of varying shapes, lengths and number of double bonds!
All that variety, all those millions of molecules, are what we are referring to when we say “dietary fat”.
What happens to dietary fat in our bodies?
Okay, so now we know what fat actually is. What does it do in our bodies?
After being digested and absorbed along with fat-soluble vitamins (which you can read more about here) fat is packaged by the liver and transported to your body’s cells.
What do triglycerides do once they get to your body’s cells? The exact effects depend largely on the exact combination of fatty acids in the triglycerides and the type of cell it entered.
Generally, however, the basic effects of triglycerides on our cells can be summarized in four broad categories:
Provide building blocks for cell and organ structures
Regulate cell processes and hormone levels
Let's look at each of these in greater detail.
Fat is a macronutrient, which means it provides energy to fuel your body.
Importantly, fat is the best calorie-providing macronutrient in food. Compared to the other three macronutrients that provide calories -- carbohydrates, protein and alcohol -- fat provides the greatest bang for your buck. If you were to consume the exact same amount of carbohydrate, protein, alcohol and fat, your body would get four totally different amounts of calories.
Let’s take 100 grams as an example. If you were to eat 100 grams of pure:
Carbohydrate, you would get 400 calories
Protein, you would get 400 calories
Alcohol, you would get 700 calories
Fat, you would get 900 calories
Why this is the case is a bit complicated. Basically, though, it comes down to the fact that triglycerides are such large molecules and contain so many carbons. Pairs of carbons bound to a special transport molecule (called acetyl CoA) are the fuel your cells ultimately burn for calories, regardless of the type of calorie-providing nutrients you ate. The chains of the three average fatty acids from a single triglyceride molecule can theoretically provide over 30 pairs of carbons! Each sugar molecule can only provide 2. Alcohol can only provide 1. Some amino acids molecules (the building blocks of proteins) can provide a single pair of carbons, but others cannot provide any (they can be used to make calories via a slightly different mechanism if need be, though).
Fat providing such a concentrated source of calories can be useful in times of famine or extreme physical exercise, stress or illness. It allows you to consume enough calories to keep your body functioning properly, without having to eat continually!
Since triglycerides hold so many calories in a single molecule, they are also ideal candidates for storing calories. By choosing to use fat as a storage molecule, your body can hold on to a lot of calories in a lot less space.
Interestingly, your body can store calories in the form of triglycerides whether or not you consumed the calories as fat or as another calorie-providing nutrient. Naturally, it’s a bit easier to just pack triglycerides from your food straight into storage (into cells that are earmarked to do nothing but hold onto triglycerides until your body needs the calories -- fat cells). However, your body has no problem making triglycerides out of sugars, alcohol and some amino acids.
Remember that two-carbon-acetyl-CoA unit made from all calorie-providing nutrients (except some amino acids)? Your body can take the two carbons from this molecule, regardless of their original source, and fuse them back together into long, fatty-acid chains that can be bound to a glycerol backbone and stored as a triglyceride.
Having the ability to store calories in this way is extremely important for long-term health and survival. It provides energy during times when you can’t eat -- when you are sleeping, super busy at work, going for a long hike or are too sick to eat!
Membranes are some of the most important structures in your entire membrane, and they are made from fats! Comprised almost entirely of modified triglyceride molecules, membranes create individual, living cells out of blobs of organic material and separate areas in your cell’s off from one another. This lets you have a nice neutral nucleus to store your DNA and a super acidic lysosome to break down proteins in the same cell!
So, how are triglycerides transformed into membranes? First, they are converted to diglycerides by removing one of the three fatty acid chains. Then, a phosphate group (PO42-) is added in its place, resulting in something that looks like this:
Done! This structure, called a phospholipid, is the basis for building all membranes. By lining phospholipids up so that all their phosphate groups face one way and their fatty acid groups face another, you get a sheet of molecules that looks like this:
Doubling the sheet so that the fatty acid ends are pointed toward one another creates a membrane.
Unlike with energy production and energy storage, the structure of the fatty acids used for producing membranes is really important. Fatty acids with lots of bends (cis-double bonds) keep the fatty acids in the membrane from becoming too tightly stacked together, which would make the membrane too stiff and rigid for the cell to grow normally. Straight, easily stacked fatty acids (trans and saturated fats) keep the fatty acids in the membrane from getting too loosely packed, keeping the membrane from becoming too liquid and losing all its structure. A perfect balance between these types of fatty acids is needed to keep your membranes (and, in turn, cells!) healthy!
Triglycerides and their fatty acids are also responsible for helping control how cells communicate with one another.
Much of this has to do with their essential role as building blocks for all the cell membranes. Cell membranes determine what molecules get into and out of the cell. They can even transfer signals from hormones that never enter the cell across the membrane so the cell knows they are there! carry signals from hormones that bind outside the cell into the cell
As was the case with building membranes, which specific fatty acids are present is important. Different fatty acids transmit different signals more efficiently and can even switch the meaning of a signal. For example, the presence of saturated fatty acids can tell immune cells to mount an immune response, producing pro-inflammatory chemicals that should help protect your body. Polyunsaturated fatty acids can tell immune cells the exact opposite -- that they should stop making pro-inflammatory chemicals!
And, if all that weren’t enough, fatty acids are the starting point for the production for many of your hormones. Hormones, of course, regulate the function of every organ system in your body, influencing everything from metabolism and cognition to mood and reproduction.
Modified triglycerides provide the building blocks for a very important electric insulating substance called myelin. Myelin wraps around the outside of nerve cells, coating them just like wax on a wire, preventing your nerves from short-circuiting.
This is, of course, extremely important in your brain, where many nerves are all packed into one area and need to send signals quickly, efficiently and correctly!
It is also important for sending signals to and from your brain efficiently, though. It’s a long distance between your brain and your feet and hands, for example, and without insulation to ease the flow of the electric signal, the signals can get muddled. This can cause numbness, tingling, weakness or paralysis. Too little fat and too little myelin production can have serious effects on the function of your nervous system.
Fat also serves to hold heat in your body. Fat is much better at keeping heat from escaping than water (the main component of our bodies!), so you have a thin layer of fat just under your skin to help keep heat inside.
Cushioning For Muscles and Organs
The fat under your skin also serves a cushioning, protecting your muscles and bone from impact. There are also deposits of fat in your abdomen that serve the same purpose. They keep your organs from bashing into each other if you get bumped.
Making Mucus and Oils
Fat rich in polyunsaturated fatty acids containing cis-bonds -- fatty acids that are always in liquid form -- are used to make useful oils throughout your body. These oils provide protection, trap water in your body and ease movement of tissues past one another.
How Much Fat Do You Need?
Clearly, dietary fat is really important to our health! Getting the right amounts of all the fatty acids your body needs boosts your health, right down to the cellular level!
But what are the right amounts? What types of fatty acids do you need to consume each day? How much do you need of each? What are the specific consequences of getting the wrong amounts or even the wrong ratios of fatty acids?
Though technically we could go down to the individual fatty acid level and work out exactly how much of each specific acid we need, it doesn’t seem to be necessary. Fatty acids with similar length chains, similar numbers of double bonds, similar locations of those double bonds and similar orientation of those bonds seem to behave similarly enough in your body that they can be grouped together! Based on their effects on your body, researchers have created three categories of fatty acids. Each of these groups should be treated differently in your diet.
1. Essential fatty acids
Essential fatty acids are fatty acids that your body cannot make itself but you absolutely require to be healthy. You have to get all the essential fatty acids you need from your diet.
There are actually two essential fatty acids and we know exactly how much of each you need to consume each day for optimal health.
Linoleic acid is the first. This fatty acid has 18 carbons in its chain. It polyunsaturated with two double bonds, the first located after its sixth carbon. Based on the location of this double bond, linoleic acid is classified as an omega-6 and it is used to make all the other types of omega-6 fatty acids your body needs (if you don’t get them from your diet). Depending on your age and gender, you need between 11 and 17 g of linoleic acid each day.
Linolenic acid is the second essential fatty acid. It has 18 carbons in its chain and is also polyunsaturated. It has three double bonds, the first located after the third carbon atom, making it an omega-3 fatty acid. Linolenic acid is used to make all the other omega-3 fatty acids your body needs. Depending on your age and your gender, you need between 1 and 1.6 g of linolenic acid each day.
Not getting enough of either of these fatty acids can lead to symptoms of a deficiency. This can include dry scaly skin, changes in your hair, increased risk of lung infections, changes in your heart rhythm, brain function, immune function and damage to your kidneys, liver and ovaries/testes.
In addition to a flatout deficiency, you can have an imbalance between these two essential fatty acids. While you are supposed to get more linoleic acid than linolenic acid, too great of an imbalance can lead to an overproduction of inflammatory chemicals by your immune system. This is because some of the omega-6 fatty acids made from linoleic acid are responsible for helping immune cells make inflammatory chemicals. Normally, the pro-inflammatory signals from omega-6 fatty acids are balanced out by anti-inflammatory signals from omega-3 fatty acids. It doesn’t take many omega-3s to keep production under control, but if far too many omega-6s are around, they can overwhelm the anti-inflammatory signals.
Why is this important? Too many pro-inflammatory signals in the body has been associated with the development of heart disease, diabetes, dementia and cancer.
2. Other unsaturated fatty acids
All other unsaturated fatty acids, both monounsaturated and polyunsaturated, belong to this group.
These fatty acids are generally believed to have positive effects on your health. They promote healthy membrane, nerve, artery, heart and immune function. While your body can make all the individual members of this group from other fatty acids, you do need enough raw material available to help your body do so efficiently.
It is generally recommended that you get between 22 and 100 grams of unsaturated fatty acids in your diet each day, depending on your age, gender and calorie intake.
In recent years, there has been special attention given to two specific members of this group: eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Both of these fatty acids are categorized as omega-3 fatty acids. They have extremely long chains (20 and 22 carbons, respectively) and they are highly unsaturated. EPA has five double bonds and DHA has six.
EPA and DHA have been shown to be particularly healthy. Even for omega-3 fatty acids, they provide powerful signals for the immune system not to produce inflammatory chemicals. They also appear to be particularly helpful protecting brain health throughout life, helping prevent dementia and Alzheimer's.
While your body can make both EPA and DHA from linolenic acid, it’s not very good at it, putting some people at risk for having very low levels of both of these health-boosting fatty acids. This has lead to the suggestions by many researchers that many people, especially those not getting large amounts of linolenic acid, may benefit from getting at least 250 mg pre-formed EPA and DHA directly from their diets or supplements.
3. Saturated and trans fatty acids
The final group of fatty acids are the saturated and trans fatty acids. Though small amounts of these types of fatty acids are a normal part of a healthy diet, even relatively small increases in their concentrations can be harmful to your health.
These straight-chain fatty acids are strong inducers of pro-inflammatory chemicals by the immune system. They also appear to be able to make the immune system respond differently to oxidized cholesterol -- the molecule responsible for causing heart disease to develop. Saturated fat makes it more likely that the immune system will help oxidized cholesterol build up in your arteries.
At high concentrations, saturated and trans fats also appear to be directly toxic to your cells. They have been shown to be able to damage your liver cells and your pancreatic cells, both of which can ultimately cause you to develop diabetes.
Based on decades of study, researchers believe that consuming between 0 and 22 g of saturated fat per day can be safe. This depends on your age, gender and the number of calories you eat in a day. The fewer calories you eat, the less saturated fat you should consume (aim for no more than 10% of your calories coming from saturated fat).
Trans fat intake, on the other hand, should be kept as low as humanly possible. The recommended amount of trans fat per day is 0 g.
How Can You Get the Right Ratio of Fats in Your Diet?
The healthiest ratios of fats in your diet would be plenty of healthy fats (22-100 g/10-35% of your daily calories), no unhealthy fats, and a small amount of in-between fats (less than 22 g/10% of your daily calories).
Luckily, unhealthy fats and in-between fats usually come packaged together in the same foods, so a few simple dietary swaps can help you reach the optimal intake levels!
Meat, dairy and junk food all contain both saturated and trans-fats, while fat-rich nuts, seeds, avocados and coconuts are rich in unsaturated fatty acid. By dropping meat, milk and processed junk from your diet and replacing them with whole, unprocessed fat-rich plant foods, you can naturally shift your fat intake to healthy ratios!
And there you have it: the skinny on fat! From its biochemistry, to its roles in your body, to the amounts you should eat from which foods, we’ve covered it all?
Did you learn anything about fat in this article you didn’t already know? Let me know in the comments below! I’d love to hear about it!
© 2018 Miranda Poenicke