Research & Education Science Update

How Protein, Fat, and Carbohydrates Fuel Your Body

Macronutrients (also known as macros) are nutrients that the body uses in relatively large amounts and therefore needs to receive daily. There are three macronutrients: proteins, carbohydrates, and fats.

Your body also requires micronutrients (such as vitamins and minerals) in smaller amounts, but the macronutrients provide your body with calories (energy) and the building blocks of cellular growth, immune function, and overall repair.

Here’s what you need to know about macronutrients and why a balanced intake of these vital nutrients are necessary for optimum health and wellness.

The 3 Primary Macronutrients

Each of the three primary macronutrients affects the body differently. To make sure that you’re getting the right amount of each macronutrient in your diet, it will help to understand the role each macro plays in your body.


Carbohydrates are the body’s preferred fuel source. Converting carbohydrates into immediately usable energy is easier for the body than converting fat or protein into fuel. Your brain, muscles, and cells all need carbohydrates to function.

When you consume carbohydrates, the food is converted into sugars that enter the bloodstream. These sugars (in the form of glucose) can be an immediate source of energy or stored in the body’s cells to be used at another time.

Carbohydrates provide the body with fuel. The body breaks carbs down into sugar (glucose) which either provides immediate energy or gets stored for later use.

Carbohydrates can either be complex or simple.

  • Complex carbohydrates (polysaccharides and oligosaccharides) are made up of long strings of sugar units that take longer for the body to break down and use. Complex carbs have a more steady impact on blood glucose levels.
  • Simple carbohydrates (monosaccharides and disaccharides) are made up of either one or two sugar units and can be broken down fairly quickly in the body. Simple carbs have a fleeting impact on blood sugar levels. Blood sugar (and energy) levels typically rise quickly and drop after consuming simple carbs.

In addition to providing fuel to the body, complex carbohydrates (particularly fiber) help the body maintain healthy digestive function and cholesterol levels.

Examples of foods that are high in carbohydrates include starchy foods like grain products (such as bread, cereal, and pasta), potatoes, and rice. Fruits, vegetables, and dairy products also provide carbohydrates.Complex Carbs

  • Peas, beans, and other legumes
  • Whole grains
  • Breads and cereals
  • Rice
  • Starchy vegetables
  • Pasta

Simple Carbs

  • Table sugar
  • Honey
  • Maple and other syrups
  • Candy
  • Fruit juice, sweetened tea, and soda
  • Milk

The United States Department of Agriculture (USDA) suggests that carbohydrates make up 45% to 65% of our daily caloric intake.1 However, some people follow lower carbohydrate diets to manage a medical condition or for weight loss.

The department’s Dietary Guidelines for Americans 2020-2025 also recommend that sugar intake be limited to less than 10% of daily calories while the Dietary Guidelines Advisory Committee and the American Heart Association (AHA) recommend an even lower limit of less than 6%.


Protein provides the body with amino acids, which are the building blocks for muscle and other important structures such as the brain, nervous system, blood, skin, and hair. Protein also transports oxygen and other important nutrients. In the absence of glucose or carbohydrate, the body can reverse-process protein (a conversion called gluconeogenesis) to use as energy.

Your body makes 11 amino acids on its own. There are 9 amino acids that your body cannot make (known as “essential amino acids”), which means you need to consume them through your diet.

You can consume different types of protein to get these amino acids.

  • Complete proteins provide all of the amino acids that your body needs in appropriate amounts. The most common sources of complete protein are meat, poultry, and seafood products. Eggs and milk also provide complete proteins.
  • Incomplete proteins provide some, but not all, of the amino acids you need. Many plant-based proteins are incomplete proteins. However, when they are consumed together as complementary proteins, you can get all the amino acids that your body needs. Nuts, seeds, and (most) grains are examples of incomplete proteins.

The daily requirements for protein vary. The USDA recommends that we consume anywhere from 10% to 35% of our daily calories from protein sources.1 More specific protein guidelines are based on age, sex, and activity level. Some people will consume more protein to reach certain fitness or wellness goals.

Protein Supplements

Many Americans get more than enough protein from the food they eat. While protein supplements are popular and widely used, in many cases, they are unnecessary.


People might try to avoid fat in their diets, but dietary fat plays an important role in the body. Fat provides an important source of energy in times of starvation or caloric deprivation. It is also necessary for insulation, proper cell function, and protection of our vital organs.

While fat is necessary for a healthy body, fat can also contribute to obesity. Fat provides more energy (9 calories per gram) than carbohydrates or protein (4 calories per gram). The macronutrient must be consumed in moderation to maintain a healthy weight.

There are different types of fat that can be part of your daily diet. Specifically, dietary fats might be saturated or unsaturated:

  • Saturated fats mostly come from meat and dairy sources. These fats are generally solid at room temperature and tend to be shelf-stable for a long time.
  • Unsaturated fats include two other types of fats: monounsaturated and polyunsaturated fats. Unsaturated fats come from plant-sources and provide the body with many health benefits. These fats are generally liquid even when refrigerated and have a shorter shelf life than saturated fats.

Studies have shown that when saturated fats in a person’s diet are replaced with poly or monounsaturated fats, it can decrease their risk of certain diseases including heart disease, stroke, and type 2 diabetes.Sources of Saturated Fats

  • Butter
  • Lard
  • Fatty meats
  • Cheese
  • Full fat dairy products

Sources of Unsaturated Fats

  • Nuts
  • Seeds
  • Plant-based oils, such as olive oil
  • Fatty seafood (e.g., salmon and tuna)
  • Avocado

Another type of fat, called trans fat, is slowly getting eliminated from foods. Trans fat is a polyunsaturated fat that is processed to become shelf-stable. Processed foods like crackers, cookies, cakes, and other baked goods typically contain these hydrogenated fats.

Most dietary guidelines suggest that roughly 20% to 35% of your daily calories should come from fats.1 However, no more than 10% of your daily calories should come from saturated fats.

Health experts have advised against the consumption of trans fats. As a result, food manufacturers have started to remove them from their products.

How to Balance Macronutrients

It is important to include each macronutrient in your daily diet. This will be easier if you build each meal around a combination of protein, carbs, and healthy fats. That said, finding the exact balance of macros that’s right for you can be tricky.

The large range of percentages recommended for each macronutrient leaves room for experimentation. Everyone’s body functions differently when various ratios are consumed.

An easy way to plan your meals is to use the USDA’s MyPlate system which simply encourages you to use a divided plate icon to plan your meals. Roughly one-quarter of the plate is designated for fruits, vegetables, grains, and proteins. There is also a small icon for dairy.

There is a similar system called the Healthy Eating Plate that is provided by Harvard Health. Each plate image can serve as a reminder to get your nutrition from different sources to ensure that your macro and micronutrient needs are met.

When you first begin to balance your macros, the goal is to keep each range within its boundaries, but ensure you get enough of each nutrient.

Tracking Macros vs. Tracking Calories

Some people—particularly athletes—track their macronutrient intake rather than their calorie intake because they are trying to reach certain fitness or performance goals. A person might also manage a medical condition by watching their macro intake. For example, people with type 2 diabetes often count carbs to manage and limit intake.

There are pros and cons to tracking calories and pros and cons to tracking macros; the best method for you will depend on your goals.

Why Track Calories?

If your goal is weight management, the success or failure of your program will ultimately rest on your overall calorie intake. You won’t lose weight unless you create a substantial calorie deficit on a regular basis. To maintain your weight, you will likely need to consume a modified version of your weight loss calorie goal.

People who are trying to reach or maintain weight loss often choose to track the calories they consume. Tracking calories is simple and requires little time or effort. The calorie counts for most foods and beverages can be found directly on the Nutrition Facts label. If it’s not available there, there are nutrition databases that provide accurate numbers online or even in smartphone apps.

Why Track Macronutrients?

Even though tracking calories is easy (requiring you to manage just one number), some people choose to track macros instead. Tracking macronutrients is more complex because you need to set goals for three intake numbers instead of just one. For people trying to reach fitness goals or lose weight, these numbers can be helpful.

For example, people who are trying to lose weight might discover that they can reach their calorie goal more easily if they get more of their daily calories from protein. When included at every meal, protein might help you eat less because it generally provides greater satiety than carbohydrates.

People who are managing heart disease or a related condition might track their intake of fat—particularly saturated fat—to reduce their risk for a cardiac event.

People who are trying to reach fitness goals often track their macros. For example, endurance runners might target a particular carb intake to ensure that they are properly fueled for a race. Strength-trained athletes might watch their intake of protein to help them reach their performance goals.

Tools and Tips to Track Macros

If you choose to track your macros, there are different methods you might use to manage your intake.

One of the easiest ways is to use a smartphone app. Many health and wellness apps provide calorie and macro data for countless foods. These apps help you to input each food you consume and then provide updated charts and other graphics to let you see where you’re at throughout the day. Examples of popular apps include LoseIt, MyMacros+, and MyFitnessPal, and Fitbit.

Another method is to use the old-fashioned pen and paper approach. You can either plan meals in advance according to the macro balance that you require, or you can use online resources or apps to get your numbers and keep them in a notebook.

A Word From Verywell

Each macronutrient provides an important role in the body. While some trendy diets severely restrict or even eliminate some macros, each is essential to your body’s ability to function optimally. You need to consume each of them in balance (unless your healthcare provider has advised you otherwise—for example, because you are managing a health condition).

Once you’ve figured out how to balance your macros, you can learn to make healthy choices within each group. To reach your fitness goals and maintain your wellness, choose lean proteins, complex carbohydrates, and healthy fats.

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