"Some antiquated diet books will tell you to shun all fats if you want to lose weight, but in reality, it's not healthy to eliminate fat from our diets altogether." - Harley Pasternak
When it comes to healthy eating, fats have long been public enemy number one. The idea was that fat begot fat. The more fat you ate, the more fat you would store. Thus, advertisements and food labels made it very clear when something was low-fat or fat-free. What the food manufacturers failed to mention was that they used other strategies to maintain the flavor of these fat-free foods by increasing salt or sugar. Only recently has the dialogue moved away from eliminating fat in diet and toward replacing unhealthy fats with healthy fats. Now we talk about fats as saturated and mono- or polyunsaturated, trans fats, and omega-3 fats. But what does all of this mean? What makes one fat healthier than another? But before we delve into that, it’s important to discuss why fats are important, not only in cooking, but for our health.
Fat's Role in the Kitchen
It goes without saying that a majority of the foods we love are high in fat. As mentioned in Macronutrients & Metabolism, because fats are the most energy-dense of the macronutrients with 9 kcal per gram, our brains are wired to seek these out, a biological homage to our hunter-gatherer days when there was no guarantee when your next meal would be. But fats provide more than just energy and flavor.
- Enhance mouthfeel – Fats add a smooth and creamy component to mouthfeel, which refers to the physical sensation we get from food, separate from the flavor. This is what makes ice cream so creamy, ensures salad dressings provide moisture without being too watery, and ensures juicy hamburgers aren’t like eating a piece of cardboard.
- Retain moisture – Fats help foods retain moisture which not only adds to the foods mouthfeel, but it also ensures texture and consistency. Fats in baked goods prevent them from drying out, which can result in an overly crumbly cookie or cake. Meats with higher fat contents also tend to be more moist, such as the juicy steak that was marbled with fat or the prime rib roast with its fat cap.
- Aid in browning proteins – Fats aid in the Maillard reaction or browning that leads to the flavorful brown crust you will see on meats that are seared in fat. Maillard browning is a chemical reaction between the amino acids and sugars found within the meat that result in a distinctive flavor.
- Prevents sticking – Fats create a protective layer between the food and the cooking vessel that prevents food from sticking to baking pans and skillets. Sautéing, grilling, and roasting are all cooking techniques that rely on fats to prevent foods from sticking during the cooking process.
- Promotes even cooking – Because most fats are stable at higher temperatures relative to the food that is being cooked, it aids in conducting heat more evenly when cooking. This is best seen with techniques such as roasting and sautéing.
- Separates starch – While starches can be used as a thickener for soups and sauces, adding it directly to a dish will lead to the starches clumping together. A roux, equal parts fat and starch, allows the starches to be coated by the fats, separating them, leading to a smooth consistency when added as a thickener. Mashed potatoes and some pastas also incorporate fats and starches together for a smoother consistency.
Fat's Role in the Body
Fats aren’t all bad. In fact, they have many important roles throughout our body and our development. The brain, for instance, is mostly fat. All of our the nerves within our brain and nervous system are coated in fat which insulates them and increases the speed at which they are able to transmit signals. Here are some of the other roles that fats play in our bodies.
- Fuel – Lipids are rapidly made available for energy. Because they have fewer hydrogen atoms, they have a lower weight, which leads to fats having having more energy dense (9 kcal/gram) than their carbohydrate counterparts (4 kcal/gram). Energy stored as fat can provide a source of energy for weeks, compared to energy stored as glycogen which will last for only hours.
- Insulation – Fat provides insulation to keep our bodies warm, which comes in handy for those who live in more temperate climates.
- Protection – We might not always think of fat as protective, but it does serve to provide some cushion from external forces or just the usual jostling of organs that occurs when we do something as simple as walking. Most of our vital organs have a bit of fat around them to make the ride a little less bumpy.
- Vitamin transport – The fat-soluble vitamins (Vitamins A, D, E, and K) and the carotenoid antioxidants are both absorbed by and transported throughout the body by fats. People can become deficient in this vitamins if they have problems absorbing fats due to some malabsorptive disorder, such as Crohn’s disease.
- Infant thermogensis – Babies have a special kind of fat tissue called brown fat. This type of fat is integral in keeping babies warm. Instead of metabolizing macronutrients into chemical energy (ATP), brown fat metabolizes them into heat, keeping babies warm.
What's In a Fat?
Now that we know what fats do, let’s spend a moment to talk about what they really are. When we talk about fats, we tend to think of two categories: fats and oils. Examples include lard (animal fat), butter, shortening, margarine, and oils, such as olive and vegetable. Chemically speaking, fats or lipids, are molecules composed mainly of carbon and hydrogen. These include triglycerides, phospholipids, and cholesterol. From a dietary standpoint, the primary focus is on fatty acids, triglycerides, and cholesterol.
Just like carbohydrates and proteins, fats can be broken down into single subunits, called fatty acids. Generally speaking, a fatty acid is just that, an acid “head” and a fatty “tail”. The acidic head interacts well with water, but the fatty tail, which is a long chain of carbons with hydrogens, is hydrophobic, or water-fearing. This means it repels water molecules, and because these tails are so long, making up the majority of the fatty acid, substances that are made up of a lot of these subunits are themselves also hydrophobic. Hence why we might say two things “are like oil and water,” meaning they don’t have a tendency to mix at all. However, fats do dissolve in organic solvents, such as benzene and acetone.
The acidic head of these fatty acids are generally the same, but it is the fatty tail that defines one fatty acid from another. These can vary in three general ways: 1) the number of carbons, 2) the number and location of double bonds, and 3) the configuration of these double bonds (cis vs trans). Using these defining traits, fatty acids can be subdivided into categories based on their level of saturation, saturated vs unsaturated. For those that are unsaturated, they can be further subdivided into monounsaturated and polyunsaturated. Let’s take a look at these groups of fats.
Fatty Acid Length
The number of carbons in the fatty acid chain is the first way that fatty acids can vary. this is also generally how they get their name. For example, as seen above, four carbons is butyric acid. Five carbons? Valeric acid. Twelve carbons? Lauric acid. Eighteen? Stearic acid. Fatty acids can also be classified by their length.
- Short-chain fatty acids – 5 and fewer carbons in length
- Medium-chain fatty acids – 6-12 carbons
- Long-chain fatty acids – 13-21 carbons
- Very long-chain fatty acids – 22 or more carbons
Unsaturated Fats
Unsaturated fats contain at least one double bond. Carbon atoms like to have bonds with four other atoms, but sometimes instead of having four separate bonds, carbons can share two bonds with another atom, such as another carbon or oxygen. That’s why the C and the O in the acidic head are connected by two lines instead of one. These are called double bonds. In the case of unsaturated fats, two adjacent carbons in the chain have a double bond with one another. Because there is an extra bond between these two carbons, they each lose a bond with a hydrogen. Thus they are called unsaturated, because they are not saturated with hydrogens. This change in bond not only alters the number of hydrogens in the fatty acid tail, but changes the shape. The double bond creates a kink of sorts in the chain. This kink makes it difficult for the fatty acids to stack. This inability to stack together easily leads to an increase in fluidity, making unsaturated fats more often liquids at room temperature, what we would normally consider to be an oil.
Monounsaturated
Monounsaturated fats are those that only have one double bond. Oleic acid is a monounsaturated fatty acid found in olive oil. Oleic comes from the Latin oleum, which means oil. Other foods that are high in monounsaturated fatty acids are canola oil, sesame oil, sunflower oil, peanut oil, peanut butter, avocado, and nuts and seeds, including almonds, walnuts, pecans, and sesame seeds. A diet high in monounsaturated fats has been shown to decrease the risk of heart disease, LDL (bad cholesterol) levels, and improvement in blood pressure, as well as regulating insulin levels.
Polyunsaturated
Polyunsaturated fats, as you might guess, have more than one double bonds. The increasing number of double bonds increases their fluidity at room temperature. Examples of these oils include soybean, corn, and safflower. Other foods rich in polyunsaturated fats are grains, seafood, fish oils, walnuts, and sunflower seeds. The location of the double bond along the chain also plays a key role. There are two important types of polyunsaturated fats: omega-6 and omega-3. Omega is the last letter of the Greek alphabet, so the number tells us where the first double bond is, counting from the end of the fatty acid tail. Thus omega-3 fatty acids have the first double bond between the 3rd and 4th carbon from the end of the tail, and omega-6 fatty acids are between the 6th and 7th carbon.
Linoleic acid is an 18-carbon omega-6 polyunsaturated fatty acid with two double bonds. This is one of the two essential fatty acids (the other being ALA), as our bodies do not have the ability to synthesize this. It derives its name from the Latin linon (flax) and oleic acid (again, oleum is Latin for oil), as the result of saturating the omega-6 bond results in the formation of oleic acid. It can be converted into GLA and then arachidonic acid. Some great sources of linoleic acid are avocado, safflower oil, eggs, and nuts.
Gamma-linolenic acid (GLA) is an 18-carbon omega-6 polyunsaturated fatty acid with three double bonds, derived from linoleic acid, and precursor of arachidonic acid. It was first isolated from evening primrose seed oil, known as “king’s cure all” in the 17th century as a popular folk remedy. Dietary sources beyond evening primrose oil include hemp oil, oats, barley, and durian.
Arachidonic acid (AA) is a 20-carbon omega-6 polyunsaturated fatty acid with four double bonds. It serves as the precursor to both anti-inflammatory and inflammatory signals, such as prostaglandins, thromboxanes, and leukotrienes. These signals are considered pro-inflammatory as they promote inflammation and are important in disease states that activate the immune system, such as asthma. However, they are also important for promoting growth and are seen elevated in healthy individuals during physical activity. Whether arachidonic acid is inflammatory or anti-inflammatory is dependent on how it is metabolized. Arachidonic acid is also one of the most abundant fatty acids in the brain, and important for neurological health. Dietary sources are primarily from meats, such as chicken, beef, pork, and fish.
Alpha-linolenic acid (ALA) is an 18-carbon omega-3 polyunsaturated fatty acid with three double bonds. This is one of two essential fatty acids (the other being linoleic acid). While many seeds contain ALA, flax and chia seeds contain more than other seeds. Flax seeds must be ground in order to gain its nutritional benefits. Other good sources include walnuts and many common vegetable oils.
Eicosapentaenoic acid (EPA) is a 20-carbon omega-3 polyunsaturated fatty acid with five double bonds. Derived from ALA, EPA can also be found in oily fish, such as salmon, cod liver, herring, mackerel, and sardines. While our body can convert ALA to EPA, we absorb it from our diet much more efficiently, so it is still an important part of our diet. Moderate amounts can also be found in mussels, oysters, shrimp, crab, and scallops. Along with DHA, it has an integral role for growth and inflammatory response and may decrease the risk of coronary artery disease, hypertension, and stroke.
Docosahexaenoic acid (DHA) is a 22-carbon omega-3 polyunsaturated fatty acid with six double bonds. Derived from EPA, it has similar effects and is also important in growth and inflammatory responses and may potentially decrease the risk of heart disease, hypertension, and stroke. It is one of the most abundant fatty acids found in the brain. Breast milk has high levels of DHA, providing babies’ developing brains with this important fatty acid, and can be found in most infant formulas. Adults mainly get dietary DHA from oily fish, such as salmon, tuna, sardines, anchovies, and rainbow trout. Moderate amounts can also be found in shellfish, such as shrimp, crab, scallops, mussels, and oysters.
Saturated Fats
Saturated fats are those that contain no double bonds, meaning it is a long string of carbons with two hydrogens bonded to each carbon. Because the the carbons are full of hydrogen bonds, they are said to be saturated. Saturated fats are typically a solid at room temperature. This is because the long chains are straight and therefore easily stack with one another, which results in a solid at room temperature. Examples include coconut oil, butter, palm oil, lard, and cocoa butter. The various saturated fatty acids really only vary in the number of carbons that they contain in their tail. Below are some examples of common examples.
Butyric acid (as mentioned above) is a 4-carbon short-chain saturated fatty acid. Found in animal fats like butter, this fatty acid gets its name from Latin for butter, butyrum.
Lauric acid is a 12-carbon medium-chain saturated fatty acid. From the Latin word laurus for laurel, which is fitting as it is found in oil extracted from leaves of the plant Laurus nobilis or bay tree. Bay leaves are used frequently in cooking as a seasoning, especially in Mediterranean cuisine. Bay leaves and laurel oil were thought to have medicinal properties and used by the Romans to treat a variety of ailments including paralysis, spasms, headaches, and rheumatism. Lauric acid is also the predominant fatty acid in coconut oil and milk. It can also be found in breast milk.
Myrisitic acid is a 14-carbon long-chain saturated fatty acid. Its name refers to the genus Myristica, which includes the nutmeg tree. It is the predominant fatty acid of nutmeg butter, but can also be found in cow’s milk and other dairy products, especially butter. It can also be found in breast milk.
Palmitic acid is a 16-carbon long-chain saturated fatty acid. Its name is derived from the Latin for palm, palma, as it is found most predominantly in palm oil, extracted from the pulp of the palm fruit. This is the most common saturated fatty acid found in nature as it is the first fatty acid created when carbohydrates are converted into fatty acids and serves as the precursor to longer fatty acids synthesized in animals. Thus it can be found in animal fats in many types of meat. Processed foods are high in palmitic acid from the addition of palm oil as it is an inexpensive way to add texture to these foods. Palmitic acid has also been implicated in increasing one’s risk of cardiovascular disease and raising LDL (bad cholesterol).
Stearic acid is an 18-carbon long-chain saturated fatty acid. From the Greek stear for tallow, it is found predominantly in animal fat. Although most vegetable fats contain very little stearic acid, cocoa and shea butters are the exceptions, containing high levels of this saturated fat. It is the second most common saturated fatty acid found in nature.
Arachidic acid is a 20-carbon long-chain saturated fatty acid. From the Latin arachis for peanut, it is found predominantly in peanut oil, corn oil, and cocoa butter. It is the end product of hydrogenation of the polyunsaturated fatty acid arachidonic acid.
Behenic acid is a 22-carbon very-long-chain saturated fatty acid found predominantly in ben oil (also known as moringa oil) from the horseradish or ben oil tree. Ben oil has a long shelf-life and pleasant flavor. It can be used for frying or sauteing due to its high smoke point but also is used as a salad oil in dressings. Behenic acid gets its name from the Persian month of Bahman when the ben oil tree roots are harvested.
A diet high in saturated fat is associated with atherosclerosis, stroke, and coronary artery disease, which is the leading cause of heart attacks. These fats also tend to have a negative effect on one’s cholesterol level, meaning a diet high in saturated fat can lead to a higher cholesterol level, which can also increase the risk of atherosclerosis.
Hydrogenated Oils
You may have also heard the term hydrogenated oil. This is a processed oil in which manufacturers saturate the double bonds with hydrogens through a process called hydrogenation, effectively turning an unsaturated fat into a saturated one. When you eliminate those double bonds, you eliminate the kinks in the molecule that increase its fluidity. Thus, you end up turning the liquid oil into a solid one. This is done as it increases the shelf life and is therefore used in a lot of processed foods. This process can also change the configuration of double bonds from cis to trans.
Trans Fats
Double bonds can take one of two configurations: cis and trans. Most naturally occurring oils have cis double bonds. This means that the pieces of the carbon tail are on the same side of the double bond as pictured to the left. This is where the kink arises that leads to the increase in fluidity. Trans double bonds, on the other hand, can occur naturally, though they are mainly the result of processing oils. As you can see on the left, trans double bonds have the pieces of the carbon tail on opposite sides of the double bond. This leads to a more linear fat, which decreases its fluidity. Trans fats are high in fried foods, many packaged snack items, and processed foods. Research has shown that consuming a diet with 2-7 grams of trans fats per day leads to an increase in LDL (“bad cholesterol”), a decrease in HDL (“good cholesterol”), as well as increases the risk of coronary artery disease.
Triglycerides
Triglycerides are something that you may have seen on a lab report or heard your doctor or other health professional talk about. But what exactly are they and how do they differ from fatty acids? The three fatty acids that are attached to a glycerol backbone put the tri- (Greek for three) in triglyceride (-glyceride of course referring to the glycerol backbone these fatty acids are attached to. Adipose or fat cells that make up fat tissue are packed full of droplets of triglycerides as this is the simplest means of storing fatty acids.
While some triglycerides do exist that have three identical fatty acids attached to the glycerol backbone, most triglycerides are made up of a mixture of fatty acids. For instance, the triglyceride pictured above is made up of three different saturated fatty acids: lauric acid, palmitic acid, and myristic acid. You can see then how this varies greatly from the triglyceride to the right. Although the first fatty acid (lauric acid) is the same in both, the one on the right has linolenic acid in the second position and EPA in the third, both of which are polyunsaturated fatty acids.
Cholesterol
Cholesterol is a waxy-like substance found primarily in animal products. Diet is one of the main sources of cholesterol, however another source is our liver, which produces cholesterol so that it can synthesize bile salts, which are stored in the gallbladder. These bile salts along with an enzyme secreted by the pancreas called lipase are crucial for fat digestion. Lipase breaks apart triglycerides into fatty acids and bile salts act to emulsify these hydrophobic molecules, allowing them to be dissolved for absorption. Although Americans consume close to 500 mg of cholesterol per day, the recommended goal is 300 mg per day. Only about half of dietary cholesterol is absorbed in the intestines and the rest is excreted in your stool.
Total
Total Cholesterol
HDL
"Good" Cholesterol
LDL
"Bad" Cholesterol
Dietary cholesterol and its role in the levels of cholesterol measured in our blood is still undergoing a great deal of research. However, this research suggests that the amount of dietary cholesterol only greatly impacts about 8% of the population’s blood levels of cholesterol. So what leads to an increase in cholesterol levels for the other 92%? Well, it appears that saturated and trans fats play a larger role in increasing LDL, although how and why this happens is still unknown.
Cholesterol fulfills many important roles in our body. While some of this comes from dietary cholesterol intake, the majority of the functions of cholesterol in the body are carried out by hepatic cholesterol that is synthesized by the liver.
- Hepatic cellular membrane stability and permeability – Cholesterol increases the stability of the cells outer layer, but also decreases its permeability, making it less leaky.
- Exports cholesterol and triglycerides – Packets of hepatic cholesterol called very low density lipoproteins (VLDL) carry triglycerides and cholesterol throughout the body to deliver these to other cells throughout the body.
- Bile salts – The liver uses cholesterol as a base to synthesize bile salts, which are important in fat digestion and absorption.
- Steroid hormones – Cholesterol serves as the precursor for many hormones, such as progestins (progesterone), androgens (testosterone), estrogens (estradiol), glucocorticoids (cortisol), and mineralcorticoids (aldosterone).
- Vitamin D – Cholesterol also serves as the precursor to vitamin D which is made in the skin.
Using Fat Wisely
Great, so now you’re an expert in lipid biochemistry. How do we use this to eat healthier? It starts with recognizing that various foods have a ratio or mixture of several fatty acids, but this mixture is not created equal and so foods will have a predominance of polyunsaturated fats, omega-6 or omega-3 fatty acids, monounsaturated, or saturated fats. So the goal is to eat more of the foods that are higher in unsaturated fats and especially those that are omega-3 fatty acids. Below are some ratios to keep in mind.
- Total fat – It is recommended that 10-35% of your daily calories come from fat with less than 10% coming from saturated fats.
- Saturated vs unsaturated – We should strive to eat a diet that has about 1.5 times more unsaturated fat than saturated fat.
- Omega-6 vs omega-3 – The ideal ratio of these polyunsaturated fats should be about twice as many omega-3 rich foods compared to those with a predominance of omega-6. However, the typical Western diet is on the order of 10-30 times more omega-6 than omega-3.
Saturated Fats
Butter
Cheese
Cream, half-and-half, & whole milk
Bacon, bacon fat, & ham
Beef
Animal fats
Coconut oil & coconut milk
Unsaturated Fats
Olive oil
Canola oil
Vegetable oil
Fish & seafood
Nuts
Seeds
Smoke Point
Since we want to steer away from saturated fats, which tend to be solids at room temperature, we are presented with the dilemma of picking an oil to cook with. With so many choices of oils, it can seem a bit overwhelming. One thing to help in selecting cooking oils is its smoke point. The smoke point is the temperature at which the oil begins to smoke. It isn’t really necessary to know the exact smoke point, as this will vary based on the ratios of various fatty acids in the oils, but generally knowing if it has a high or low smoke point will help.
- High smoke point – Grapeseed, safflower, vegetable blends, and non-virgin olive oil all have high smoke points. These are the perfect choice when you are planning to saute something, as they will handle high heat without burning.
- Low smoke point – Examples of fats with a low smoke point are sesame, nut oils, and extra virgin olive oil. Butter is another fat with a low smoke point. These fats may not be able to handle high heat, but they can still be used to add a tremendous amount of flavor. Oils and butter (in moderation) are best used for finishing dishes once the cooking is nearly done. This adds a great deal of flavor and also adds to the food’s texture without burning the oil with high heat. These also add flavor to baking and salad dressings. Canola oil is a great oil to use in baking as it has the functionality of the fat without adding flavor, allowing you to either eliminate saturated fats or use a small proportion of them to still get some of the flavor.
Storing
Something worth noting is how to store oils. The reason this is important is that when oils interact with oxygen they can undergo oxidation. This is a similar process that leads to apples or avocados from turning brown. However, when oil undergoes oxidation it goes rancid, leading to a bad taste, change in color, and bad odor. To slow this process, store oils in airtight containers, away from light, in a cool place. Ever wonder why many olive oil bottles are green? It’s to help the oil last longer. These strategies are also true for oil-containing foods, especially nuts, which can also go rancid.
It is worth mentioning here that another factor that plays into oils going rancid is time. Oils should really be thought of like a perishable item and shouldn’t be kept on your shelf for extended periods of time. I made the mistake once of keeping a nice bottle of olive oil in my pantry. I was hesitant to use it just for everyday cooking, because I thought it should be reserved for special dinner. But what ended up happening was this nice oil that I had received went rancid and I didn’t get to use it at all. Moral of the story: if someone gives you a nice bottle of olive oil, use it or lose it.
Substitutions
I think fat substitution is one place where you can get really creative. Keeping in mind the main functions that the fat plays in your dish is important, as this will help guide you to pick fat substitutes that will serve that same function. Substitutes from fats can come from some very unlikely sources. Check out some interesting and practical substitutions below.
| Fat Substitutes | |
|---|---|
|
Ripe bananas or applesauce |
Baked goods and desserts, can be used as a one-to-one replacement for butter |
|
Prune/raisin paste |
Baked goods and desserts (especially those that are chocolate), adds moisture to ground meats |
|
Legumes |
Baked goods (think black bean brownies), desserts, dressings, sauces, and spreads |
|
Avocado |
Works well in baked goods and desserts; can be used as a one-to-one replacement for butter |
|
Plain low-fat yogurt |
Mayo and sour cream |
|
Olive/vegetable oil |
Baked goods, desserts, entrees with reduced-fat meats |
|
Nuts or seeds |
Puree in sauces or dressings, add to rice or grains, top salads |
|
Vegetables |
Add to ground meats (meatloaf, meatballs, burgers) to add moisture, flavor and texture; pasta sauces, grains, rice, or pastas |
|
Grains |
Mix in sauces, baked falafel, whole grains added to soups |
|
Liquids and condiments |
Add to reduced-fat meats to add moisture; examples include tomato paste or mashed sweet potatoes |