What are macronutrients? Maybe you’ve heard about counting macros or diets that restrict certain macronutrients for weight loss or muscle gain but don’t totally understand what they are or how your body uses them. This guide explains what macronutrients are, their structure, how they function in the body, and good food sources of each macronutrient.

What are Macronutrients?

Macronutrients are nutrients that the body needs in large amounts. They are the body’s main source of energy and building blocks for many bodily structures and functions. The body cannot make macronutrients in sufficient quantities, therefore they must be obtained through the diet. The three primary macronutrients are:

  • Carbohydrates
  • Protein
  • Fat

Each macronutrient has a different structure and functions differently in the body, but they all provide energy in the form of calories.

  • 1 gram of carbohydrates = 4 calories
  • 1 gram of protein = 4 calories
  • 1 gram of fat = 9 calories


The primary role of carbohydrates is to provide energy to the body in the form of glucose. Once glucose is absorbed it circulates in the blood (i.e., blood sugar) to either be taken up by the cells to be used immediately as fuel or stored as glycogen in muscle and liver cells. 

Carbohydrates are made up of units called saccharides, which are sugar molecules. Depending on the number of saccharide units a carbohydrate contains it’s classified as a monosaccharide, disaccharide, oligosaccharide, or polysaccharide. 

Monosaccharides and disaccharides are collectively known as simple sugars, while oligosaccharides and polysaccharides are known as complex carbohydrates

carbohydrate food source

Simple Sugars

Monosaccharides contain one saccharide unit, which is a sugar molecule. The three most common monosaccharides found in foods are:

  • Glucose, 
  • Fructose
  • Galactose. 

Monosaccharides are the only absorbable form of carbohydrate so all carbohydrates that you eat are ultimately broken down into glucose, fructose, or galactose. 

Glucose is the most common monosaccharide found in food and it’s the major sugar that circulates in the blood. All starch ultimately breaks down into glucose. Glucose is also found in corn syrup, brown rice syrup, and molasses.

Fructose is found primarily in fruits and honey but is also found in cane sugar, brown sugar, and date sugar. Fructose is the sweetest of all simple sugars.

Galactose is the simple sugar naturally occurring in dairy products. 

Disaccharides combine two sugar molecules. The three most common disaccharides are:

  • Sucrose = glucose molecule + fructose molecule
  • Lactose = glucose molecule + galactose molecule
  • Maltose = glucose molecule + glucose molecule

Sucrose is also commonly known as table sugar. It’s generally what people think of when you talk about added sugar.

Lactose is milk sugar. If someone is lactose intolerant it means they are not able to properly digest the disaccharide lactose.

Maltose is produced when starch is being broken down. Grains, sweet potatoes, and even some fruits naturally contain a lot of this disaccharide.  

Complex Carbohydrates

Oligosaccharides are compounds made up of 3 to 10 sugar molecules. They’re found in peas, lentils, beans, and some fruits and vegetables such as cabbage, brussels sprouts, broccoli, asparagus, and soybeans. 

Most oligosaccharides are indigestible because humans lack the enzymes to chemically break them down. This allows oligosaccharides to move into the large intestine where intestinal bacteria feed on them, which can cause gas for some people when they eat legumes and some vegetables. 

The indigestible oligosaccharides that the large intestinal bacteria feed off of are more commonly known as prebiotics because they serve as food for probiotics, which are the “good” bacteria that live in your large intestine and promote health. 

Polysaccharides are complex carbohydrates that include starches, fibers, and glycogen. They are long chains that contain 10 or more sugar molecules. Polysaccharides include both digestible starches and fiber.

There are two forms of fiber: soluble and insoluble.

Soluble fiber dissolves in water to form a gel and includes pectins, gums, and mucilages. It’s associated with better heart health, glucose control, and creates a feeling of fullness by slowing digestion. Soluble fiber is found in oatmeal, beans, some fruits (e.g., apples or pears), and some vegetables (e.g., sweet potatoes, carrots). Most soluble fibers are digested by the bacteria living in the large intestine. 

Insoluble fiber does not dissolve in water and is not easily digested by intestinal bacteria. It adds bulk to waste in the digestive system, which helps prevent constipation and promotes feeling full because it slows down the digestive process. Insoluble fiber comes from the structural parts of plants and includes compounds like cellulose, hemicellulose, and lignin. It’s found in the outermost portion of grains, vegetables, fruits, and seeds (e.g., whole-grain wheat, celery, brown rice, quinoa, apple peels, or broccoli). 

Added Sugars

Added sugars are sugars that are added to foods and do not include sugars that are naturally contained in the food such as fructose in fruit or lactose in milk. All added sugars, regardless of their source, are either monosaccharides or disaccharides.

A World Health Organization guideline recommends that added sugar be less than 10% of your total daily caloric intake. Therefore, if you consumed 2,000 calories in a day, that would correspond to less than 50g of added sugar per day. To put that into perspective, a 12 oz. can of cola contains 40g of added sugar, so if you’re consuming sweetened beverages, candy, cookies, sweetened yogurt, you’re going to hit that limit very quickly.  

Whole Grains vs. Refined Grains

A whole-grain kernel is made up of the following parts:

  • Bran – the outermost layer that contains B vitamins, antioxidants, and fiber.
  • Endosperm – the largest part of the kernel, which contains the starch.
  • Germ – the embryo of the kernel that contains B vitamins, minerals, and some protein. 

When whole grains have their outermost portions removed, this is what produces

A processed starch or a refined grain (e.g., white bread or white rice) is made by removing the bran and germ, leaving the starchy endosperm. The refining process removes most of the fiber and vitamins from the grain, which is why it’s recommended to eat whole grains rather than refined grains.  


Protein is involved in almost all bodily functions and processes. It’s necessary to eat protein to make hormones, neurotransmitters, enzymes, and antibodies. Proteins are also a key component in maintaining fluid balance and pH balance in the body, cell signaling, and muscle contractions. Protein is vital for the body’s structure; the physical structure of muscles and bones are made up of protein.  

It’s harder to digest protein than carbohydrates, therefore eating protein makes you feel fuller longer and can help to stabilize blood sugar levels if you’re eating a high carbohydrate meal. 

Protein can also be used as a backup source of energy if there are not enough carbohydrates to support normal energy production. This occurs during a process called gluconeogenesis, where your body starts to break down your muscle tissue and connective tissue to convert certain amino acids into glucose, which is the preferred fuel source for the body. 

You can get protein from quality meat, poultry, dairy, eggs, or seafood or plant-based sources such as tempeh/tofu, beans, lentils, nuts/seeds, and some whole grains. 


Protein Structure

Amino acids are the building blocks of protein. All protein that you eat is broken down into amino acids, which are then absorbed by the small intestine during digestion. 

There are 20 amino acids, including 9 essential amino acids that the body cannot synthesize on its own therefore they must be obtained from the diet. The body is able to synthesize the 11 non-essential amino acids. 

The 9 essential amino acids are isoleucine, leucine, valine, histidine, lysine, methionine, phenylalanine, threonine, tryptophan. 

Three of the essential amino acids (leucine, isoleucine, and valine) are branched-chain amino acids, named for their branch-like structure. These are abundant in muscle tissue. 


Dietary fat is needed for obtaining essential fatty acids that the body can’t synthesize. Fat is also necessary for metabolizing fat-soluble vitamins (A, D, E, and K), creating cell membranes, and insulating and retaining heat in the body. Fats are the most concentrated form of energy; fat contains 9 kcals/gram compared to 4 kcals/gram for protein and carbohydrates.  

Structure of Fats

Fats are a type of lipid. Lipids are made up of chains of fatty acids.

There are several types of lipids, each with a different function in the body. These include simple lipids such as fatty acids, compound lipids such as phospholipids, and derived lipids such as cholesterol.

Triglycerides are the form of lipids that are stored and transported through the body.  They make up adipose tissue in the body (i.e., body fat). A triglyceride is made of three free fatty acids attached to a glycerol backbone.

Types of Fatty Acids

Fatty acids are either saturated or unsaturated, which is based on the number of hydrogen molecules they contain.

Saturated fatty acids have no double bonds between carbon atoms and have the maximum number of hydrogen molecules, therefore they are saturated with hydrogen. 

Foods high in saturated fatty acids are solid at room temperature and can be found in meat, dairy, egg yolks, coconut oil, palm oil, and dark chocolate. 

Unsaturated fatty acids have one or more double bonds between carbon atoms and are either monounsaturated or polyunsaturated. Unsaturated fats tend to be liquid at room temperature

Monounsaturated fatty acids (MUFAs) are found in avocados, peanut butter, olives, olive oil, and canola oil.

Primary sources of polyunsaturated fatty acids (PUFAs) include vegetable oils, margarine, mayonnaise, and certain nuts.

Trans fat is an artificial fatty acid that occurs when hydrogen is added to liquid vegetable oils to make them more saturated with hydrogen, and therefore more solid at room temperature. Adding trans fat extends a product’s shelf life, however, consuming trans fat is well known to be associated with increased risk for heart disease and stroke. 

Essential Fatty Acids

Dietary fat is necessary for consuming sufficient amounts of essential fatty acids, which are needed for optimal health, however, the body can’t synthesize them so they need to be consumed in the diet.  

Essential fatty acids include linolenic acid (omega-3) and linoleic acid (omega-6), which are both types of polyunsaturated fatty acids.

The 3 most important types of omega-3a are ALA, EPA, and DHA. ALA is found mostly in plant sources including walnuts, flaxseed oil, and chia seeds. EPA and DHA are found in fatty fish and shellfish. EPA and DHA are more biologically active than ALA, therefore they are more important for health.


Related Nutrition Articles

How Protein Boosts Your Metabolism

Basics of a Healthy Metabolism

Nutrition 101: How Your Digestive System Works

Nutrition 101: How to Maintain Blood Sugar Levels





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