The Complete Guide to Macronutrients

There’s a lot out there about macronutrients (AKA “macros”) these days. I hear a lot about measuring, counting, and limiting them, but not much about what they do! 

So, in effort to make nutrition more accessible, I’m going to outline the three macronutrients, their functions in the body and in meal planning, and what to consider when designing your meals. In the future, I will touch on whether the macronutrient breakdown or ratio really matters for you. 

What are Macronutrients?

The three macronutrients include carbohydrates, proteins, and fats. They provide your body with energy, or calories. Keep in mind that alcohol provides calories as well, but I won’t focus much on it since it is not essential. 

Macronutrients are found in the foods that we eat. That being said, macronutrients are different from food groups. Rarely do we eat a single macronutrient in isolation. Most foods contain a combination of multiple macronutrients, however they are often classified according to their predominant nutrient. Take pasta, for instance: it is often considered a carb, but it does have a few grams of fat and protein in it. See examples of this in the venn diagram below.

venn diagram showing the food groups and which macronutrients they provide

What are Carbohydrates?

Carbohydrates are molecules made up of carbon, hydrogen, and oxygen. They are the body’s main source of fuel, in the form of glucose. 

In our food system, we consume carbohydrates of all different types. In order to be used for energy, carbohydrates must be broken down into glucose during digestion. The most common examples are starch, sucrose (i.e. table sugar), lactose (from milk products) and fructose (from fruit). 

Carbohydrates can be simple, including monosaccharides and disaccharides, or complex, including oligosaccharids and polysaccharides. They are classified according to how many molecules make up the compound. 

Oligosaccharides (e.g. fiber) are indigestible; they provide other benefits for bowel regulation and the gut microbiome. See chart below for an overview of the simple and complex carbohydrates and examples of each. 

SimpleMonosaccharide (i.e. “simple sugars”)Single moleculeGlucose
Disaccharide2 molecules bonded togetherSucrose (table sugar)
Lactose (in milk/dairy)
ComplexOligosaccharide3-10 molecules bonded togetherRaffinose, Stachyose, and verbascose (found in beans, peas, whole grains – good for the gut!)
Polysaccharide10 or more molecules bonded togetherStarch (i.e. bread)

Carbohydrate Functions in the Body

Carbohydrates are the body’s main source of energy. Glucose is the fuel for all cells in the body, particularly brain cells. It maintains a healthy blood glucose, or sugar, level. When blood glucose drops too low, bad things can happen, including seizures, coma, or death. 

Luckily, the body has a mechanism in place to prevent blood glucose from dropping too low. Most healthy people don’t truly suffer from low blood glucose, or hypoglycemia. However, you may notice mild symptoms when you go a long time without eating, such as shakiness, irritability (hanger, anyone?), and trouble concentrating. 

What if you eat a low carbohydrate diet?

Even though hypoglycemia is an urgent risk, most healthy people won’t experience it, even if following a low-carbohydrate diet. In the short-term, the body keeps a back-up supply of glucose (in the form of glycogen) in the liver and muscles. It can access this when you go a long time without eating, such as overnight. 

If you avoid carbohydrates over the long-term, the body can convert certain amino acids to glucose in the event that no glucose is coming in. This will maintain a healthy blood glucose range.

That being said, it is not recommended to completely cut out all carbohydrates, even if you are following a ketogenic (“keto”) or high fat diet. Even though our body can get energy from other sources, it is not the most efficient, and you would be missing out on many vitamins, minerals, fiber, and other beneficial plant compounds. 

Sources of Carbohydrates

Carbohydrates are found in grains and starchy foods, beans/legumes, milk and yogurt, fruits, vegetables (not just potatoes – all kinds!) and sugary foods/sweets. 

Carbohydrates in Meal Planning

Carbohydrates provide fiber and volume to your meals, which is important for fullness and satiation. They provide the energy for your body’s cells and support focus and mood. In this way, they can help prevent cravings for sweets when blood glucose starts to fall. 

What are Proteins?

Protein is having a moment. 

Regardless of diet, pretty much everyone agrees that protein is a pretty big deal. And for good reason! Literally everything in the body if made up of protein. Amino acids, the building blocks of protein, are the foundation of the DNA in your body. 

What are amino acids?

Proteins are big molecules, relatively speaking. Amino acids are the molecules that make up proteins. Like carbohydrates, they are made up of carbon, hydrogen, and oxygen; however, protein also includes nitrogen. 

There are 20 amino acids found in the body. Amino acids are classified according to whether they are essential or non-essential. 

Essential vs nonessential amino acids

Whether an amino acid is essential or non-essential does not actually have anything to do with importance. They are all important for the functioning of the body! 

Non-essential means that your body is able to synthesize these amino acids itself, provided the diet is otherwise balanced. 

Essential amino acids are those that the body cannot synthesize and must be consumed in the diet. 

ThreonineAspartic acid
TryptophanGlutamic acid


Protein Functions in the Body

Frankly, what doesn’t protein do in the body?

First and foremost, proteins are the foundation of the body: they make up your skeleton, muscles, organs, and hormones. 

They are also transporters, meaning they help move other compounds throughout the body. For example, we have glucose transport proteins that allow glucose to move from the bloodstream into our body’s cells where it is used for energy. 

Protein’s Role in the Body
Building blocks of muscle, bone, cartilage, hair, skin, and nails
Enzymes to stimulate chemical reactions
Transporters to move other compounds throughout the body
Hormones and other messengers to transmit messages throughout the body
Antibodies to support the immune system


Sources of Protein

The largest sources of protein are your animal products, including meat, fish, poultry, eggs, milk, yogurt, and cheese. 

That being said, protein is found in a wide variety of foods, including plants. Plant-based sources include nuts and seeds, legumes (including beans), and soy. Grains and vegetables provide small amounts of protein as well. 

Protein in Meal Planning

Protein is the most filling nutrient. The reason for this is that it both reduces ghrelin, the hunger hormone, and increases peptide YY, a powerful fullness hormone. Having a source of protein at each meal promotes satiety, or how soon you feel full while eating. 

Complete vs incomplete proteins

Complete proteins are those that provide all of the essential amino acids. Remember: these are the amino acids that your body cannot synthesize, therefore you must consume them in the diet. Animal protein and soy are complete proteins. 

Incomplete proteins only provide some of the essential amino acids. Most plant-based protein sources are incomplete. These must be consumed alongside a complementary protein. 

Complementary proteins are two or more foods that make a complete protein when consumed together. Their amino acid profiles are incomplete on their own, but complete when combined. Examples are beans and rice, a peanut butter sandwich, and hummus with pita bread. 

Now, you do not necessarily need to consume these complementary proteins at the exact same time to get the benefits, but it is good practice, especially if you are a strict vegetarian or vegan. Doing so can help you ensure that you are meeting your protein needs, particularly for athletes or those with higher protein needs.


Fat has gotten a bad rap over time, but luckily it is having a comeback. Recognize that the fat in food does not automatically become fat on your body! 

There are several important functions in the body that rely on fat. It support the brain and nervous system, provides the foundation for the cell membrane, and helps absorb vitamins and minerals.

Fats, AKA “lipids”, include fatty acids and triglycerides. Likes carbohydrates and proteins, fatty acids are are made up of carbon, hydrogen, and oxygen atoms. The difference is that a fatty acid includes a chain of carbon atoms surrounded by hydrogen atoms that ranges in length.

A triglyceride is a collection of three fatty acid chains. The properties of the chain are important when it comes to understanding the different types of fats found in the food supply (e.g. saturated fat or omega-3). 

A glycerol background with three fatty acids = “triglyceride”

Saturated Fats

The term saturated fat is given to a carbon chain that is saturated, or fully bonded, with hydrogens. 

Chemistry class refresh: chemical bonds can be single, double, or triple. 

Saturated means that there are only single bonds connecting hydrogen to the fatty acid. This then appears that the fatty acid is “saturated” with hydrogen atoms. In the case of a double bond, there are fewer hydrogens (i.e. unsaturated). See image below.

Most saturated fats are solid at room temperature (e.g. butter or bacon grease). A good way to think about this is that, because of the nice “saturated” nature of the fatty acid, it allows perfect “stacking” for a nice solid foundation. It provides the stable structure to allow for the fat to maintain its shape at room temperature. 

Unsaturated Fats

Unsaturated fats are aptly named due to the fact that they are not “saturated” or fully bonded with hydrogen. They have one or more double bonds. Unsaturated fats can be monounsaturated or polyunsaturated. 

Monounsaturated means that there is only one double bond (or, only one carbon atom that is not saturated with hydrogen). Polyunsaturated indicates that there is more than one double bond. 

Unlike saturated fats, unsaturated fats are liquid at room temperature (e.g. olive oil or peanut oil). This double bond changes the way the fatty acid sits, and prevents perfect “stacking”. This reduces the stability of the fatty acid, leaving it liquid. 

Omega-3 and omega-6 fatty acids are two types of polyunsaturated fatty acids. This means they have more than one double bond. The name “omega”, followed by the number, is how the fatty acid is named. It helps identify where the double bond is located in the fatty acid. 

Omega-3 and omega-6 fatty acids are both considered essential. As discussed with amino acids, essential means that the body is incapable of synthesizing these fats, even if the diet is well rounded. These must be consumed in the diet. 

Trans fats

Trans fats are mostly man-made fats that are being phased out of our food supply because of their significant impact on heart disease risk. 

Historically, trans fats were produced because research suggested that saturated fats were bad for our health. So, food scientists tried to make liquid oils work like solid fats (i.e. margarine and shortening). They turn liquid oils into solids by adding hydrogen (AKA hydrogenation). This stabilizes the liquid plant oils and also gives baked goods their perfect, crumbly texture. Really cool, but not great for your heart.

Fat Functions in the Body

Fat has many roles in the body including the production of hormones, assistance in vitamin and mineral absorption, and they play a role in digestion. They also provide a source of energy.

Sources of Fat

Fats are primarily found in all types of oils, nuts and seeds, avocados, and full-fat dairy products and meat/fish. Generally, plant-based oils and those found in fatty fish like salmon and tuna are associated with better health

Fats in Meal Planning

Like protein, fats play a role in satiation and satiety. They increase fullness hormones and decrease hunger hormones. 

Bottom Line

Carbohydrates provide energy and support digestion and a healthy gut microbiome. Protein is the foundation of everything in your body, and helps make a filling meal. Fat promotes satiety and may help keep you full in between meals. 

A balanced diet is one that includes all three macronutrients. The exact breakdown does not really matter for most healthy people. Hitting on all three groups will ensure that your meal is energizing, filling, and satisfying. It will also help you meet your nutrient needs in a given day. There may be advantages to hitting specific targets for some people which I will touch on in the coming articles!

Additional References

Gropper & Smith (2013). Advanced Nutrition and Human Metabolism. 6th Edition. Wadsworth.

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