Why Are Carbohydrates Important? According to a Dietitian.

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As dietitians, we understand how important carbs are for overall health and function. (And, as human beings, we know they’re delicious!) But often, our clients don’t have the same understanding. They’ll ask us why carbohydrates are important, because they’ve heard from an influencer or a friend that carbs aren’t necessary.

Because we work primarily with eating disorders and disordered eating, we do a lot of myth-busting and pushing back against diet culture‘s restrictive food rules. If you’re here, it’s probably because you’ve also been fed (pun intended) some bad information about carbs. Maybe you’re scared to eat them. Maybe you just don’t think they’re necessary. Either way, let’s set the record straight on what carbs are and why they’re so, so important.

What are carbohydrates, exactly?

Carbohydrates (AKA carbs) are one of our three main sources of energy, along with protein and fat. These three nutrients are called “macronutrients,” because our body needs them in large amounts every day. In addition to providing the energy (AKA calories) that our bodies need, each macronutrient plays a unique role in supporting various bodily functions and our overall health.

All carbs are broken down during digestion into glucose molecules, which is their simplest form. Glucose is absorbed, transported around the body, and converted by our cells into energy. 

When you hear “carbs,” you might only think of starchy carbs like bread, tortillas, rice, and potatoes. But actually, most of the foods that we eat contain at least some carbs. 

There are 3 main types of carbs:

–  Sugar, which tastes sweet and is found in table sugar, fruit, candy, honey, syrup, etc. Sugar is the easiest type of carb for our bodies to break down, which means it absorbs fast and quickly gives us some energy.

Starch, which includes things like bread, tortillas, rice, potatoes, pasta, oatmeal, and cereal. Starch takes a bit longer than sugar for our bodies to break down, which means it absorbs more slowly and can give more sustained energy.

∙  Dietary fiber, which is found in fruits, vegetables, whole grains, nuts, seeds, beans, and legumes (typically alongside sugar, starch, or both). Dietary fiber can’t be broken down and absorbed by our bodies, which means it doesn’t provide any energy. But it’s not useless! In fact, fiber is great for helping us feel satisfied, keeping our bowel movements regular, and supporting our heart health.

What is the Glycemic Index — and does it matter?

The glycemic index (GI) tells us how fast or slow a particular type of carbohydrate is broken down and absorbed in our bodies. Low GI foods are digested more slowly and don’t cause such big shifts in blood sugar and insulin levels. High GI foods digest quickly and can lead to bigger swings in blood sugar and insulin.

Generally speaking, carb-rich foods that contain mostly sugar have a higher GI (because sugar digests fast), and carb-rich foods that contain mostly starch have a lower GI (because starch digests more slowly). Dietary fiber typically lowers a food’s GI, since fiber slows digestion and isn’t broken down by the body. Foods that also contain fat and protein will have a lower GI than foods that are all carbs, since these other macronutrients slow down digestion as well.

All that said, we take the glycemic index with a huge grain of salt. When researchers measure a food’s GI, they look at how your body digests the food when you eat it all by itself. For example, they measure what happens to your blood sugar when you eat an apple all by itself, or when you eat a piece of bread with nothing on it. The problem? We rarely eat foods by themselves. Eating an apple with peanut butter or yogurt will lower the overall GI of the snack, since these other foods contain fat, protein, and fiber. Likewise, a slice of white bread might have a high GI when you eat it alone, but a lower GI when you eat it with cream cheese, and an even lower GI when you eat two slices as part of a sandwich with meat, cheese, and some sliced vegetables (since these things add fat, protein, and fiber). 

So, while we might talk a bit about glycemic index sometimes, it’s not always the best way to talk about carbs. The same carb-rich food will impact your blood sugar and insulin levels differently depending on what other foods you eat it with.

Why do we need carbs? 

Fuel for our body and brain

Carbohydrates are the body’s main and most efficient energy source, because they’re easier for the body to convert into glucose than proteins or fats. (Although, little known fact: Protein and fats can also be turned into glucose when needed!) Carbohydrates are an essential fuel  source for our muscles, central nervous system and brain. Some of our body cells (particularly in our brain) prefer to run on glucose, but our brains can’t store a supply of extra glucose the way other muscles and organs can. To keep our brains running at full-tilt, we need a regular supply of carbohydrates from food. It’s a bit like putting gas in your car — but unlike filling up at the gas station every few weeks, your body needs a fresh supply of carbs several times a day for optimal functioning. Not eating enough carbs, or having long gaps in the day without carbs, can make it difficult for us to concentrate properly, make decisions, plan ahead, and regulate our emotions. 

Muscle growth and maintenance

In addition to providing our  body with energy, carbs have a ‘protein sparing effect’. Eating enough carbs at regular intervals protects your muscle tissue from being broken down and used  for energy. Since muscle tissue supports our health and takes a lot of work to build back, you really don’t want it being wasted as an energy source! Eating adequate carbs also ensures that any protein you eat is used for its primary purpose (muscle growth and maintenance), rather than being “stolen” from the muscle maintenance process and used for energy. Plus, muscle breakdown (which happens when your body is short on carbs) releases toxins into your bloodstream. These toxins are OK sometimes and in small amounts, but too much of them too often puts pressure on your kidneys. 

Digestion

Certain types of dietary fiber encourage the growth of healthy bacteria in the intestines, which helps digestion and ensures long term gastrointestinal health. You’ve probably heard of probiotics, a type of “healthy” bacteria that supports digestive health. The truth is that while probiotics are important (we recommend getting them from fermented foods like yogurt and kimchi, which are more likely to stick around and support your digestive system than probiotic supplements), certain types of fiber (called prebiotic fiber, found in many carb-rich foods) are crucial for keeping these probiotics alive. (I wrote an article for Outside Magazine that goes over probiotics, prebiotics, and why it’s better to get these things from food than supplements.)

Fiber has other digestive benefits as well. Insoluble fiber adds bulk to your stool, while soluble fiber holds moisture in your stool. Both help prevent constipation, and keep your bowel movements normal and regular. 

Hydration and immune function

Carbs help our muscles and organs hold onto water and stay hydrated — this helps muscles work for longer without getting fatigued, and keeps our organs working properly.

Getting adequate carbohydrates also supports various immune functions in our body, which keeps us healthy and can help ward off sickness.

Mood, sleep and appetite 

Carb intake is directly linked to the release of serotonin (a neurotransmitter) in the brain. Serotonin is important, because it helps improve mood and  regulate both our sleep/wake cycle and our appetite. Having enough serotonin helps prevent low mood/depression. It also helps you to sleep well and feel more alert when you’re awake. Serotonin plays a role in regulating our hunger and fullness signals, which allows you to experience that ‘satisfied’ feeling following a meal and stop eating when you’re full. 

How many carbs do you need?

Carbohydrates should make up the majority of our food intake each day — about 45-60% of your daily energy should be in the form of carbs. All carbs give you energy and help your body perform the important functions listed above, so there’s no reason to totally avoid a particular type of carb. In order to reap all the benefits of carbs and keep your energy levels steady, try to include a variety of carb sources in your meals and snacks every day. 

Fiber-rich carbs like fruits, starchy vegetables, whole grains, beans, and legumes will give you sustained energy and support good digestion, so they’re a great choice.

Carbs with little or no fiber, like candy, sugar, and white bread can and should be part of your overall diet, since they provide energy and taste delicious. Try pairing these types of carbs with other foods that are high in protein, fat, or fiber, so that they digest a little more slowly and  

Myths About carbs

Some people believe carbohydrates make you gain weight, or that low-carb diets help you lose weight. These beliefs are usually based on dumbed-down nutrition science, or straight-up pseudoscience lacking a true scientific research basis. Reducing your carb intake may initially result in some rapid weight loss, since you’ll also lose some of the water that’s being held by  your muscles and organs. Low-carb diets often lower your overall energy intake as well — and research shows that eating less can lead to weight loss in the first several months, but that this weight typically comes back within a year even if you stick to the diet. Worst of all, low-carb diets (and other types of diets) can lead to a loss of muscle tissue, which has a negative impact on your health overall. 

Another myth is that eating carbs at night will lead to weight gain. There’s no significant evidence supporting this, since your body metabolizes carbs the same way whether it’s 8 AM or 8 PM.

Negative side-effects of eating too few carbs

  • Constipation due to lack of dietary fiber  
  • Bad breath due to the release of ketones (which are created when your body lacks carbs and needs to turn fat and protein into glucose instead)
  • Fatigue, low energy, and tiredness  
  • Mood swings, low/depressed mood, and trouble concentrating
  • Worse sleep
  • Poor immune response  

TL;DR: Carbs are the best!

You not avoid carbohydrates if your goal is to be happy and healthy. In fact, most of the energy you eat in a day should be in the form of carbohydrates. Instead of feeling guilty about your morning bagel or your favorite pasta dinner, remind yourself that these foods give you the carbohydrates that your body and brain need to function at their best.


If you’re ready to stop obsessing about food, feeling guilty about what you eat, and succumbing to disordered thoughts, we can help. We’re a group of dietitians who specializes in eating disorders, disordered eating, fertility, pregnancy, and pediatric nutrition. We take a weight-inclusive, gender-affirming, patient-centered approach. Learn more about nutrition counseling, offered in Raleigh and Durham, NC, and virtually to clients in several states. (We’re in-network with most Blue Cross Blue Shield plans as of October 2022, which means you might be able to work with a non-diet dietitian at little or no cost!)

If you’re not ready to commit to counseling but want more information about the anti-diet approach, subscribe to my weekly newsletter.


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