Just as Dunkin’ is the favored fuel source among New Englanders, the body also has a go-to fix: carbohydrates.
“Carbohydrates are the body’s preferred source of energy,” says registered dietitian nutritionist Katie Whitson, R.D., L.D., expert with Health Loft Co. “The brain, central nervous system, and red blood cells all rely heavily on carbohydrates to function properly,” she explains.
Carbs also help power your workouts. A quick hit gives your body readily available fuel to draw from. This makes your body less likely to break down lean body mass for fuel, explains Whitson. That’s a major bonus if your goals include building muscle, getting stronger, supporting recovery, or shifting body composition.
Given this macronutrient’s importance from head to toe, getting too little—or relying too heavily on low-quality sources—can leave your entire system feeling sluggish. That doesn’t necessarily mean eating more healthy carbs will suddenly make you feel like you mainlined espresso. But it does mean your body may run more smoothly and efficiently.
More specifically, you might find yourself reaping these unexpected benefits of consuming carbs.
- ABOUT OUR EXPERTS: Katie Whitson, R.D., L.D., is a dietitian with Health Loft Co. in Naperville, Illinois. Amanda Rossetti, R.D., is a registered dietitian and founder of Fuel First Nutrition. Mallory Aldred, R.D., is a registered dietitian and founder of What Mallory Eats.
1. Less Brain Fog
Even more than gym bros love a shaker bottle, the brain loves carbohydrates. While it can adapt to using other sources of fuel in certain situations—such as following a ketogenic diet—the glucose from carbohydrate sources remains its number one go-to. So, “consuming too little carbohydrate may also negatively impact mental performance,” says Whitson.
As far as your noodle is concerned, not all carbohydrates are created equal. High intake of refined, or simple, carbohydrates can exacerbate brain fog, according to Whitson. These include white bread, sugary drinks, candy, pastries, and other heavily processed foods.
Particularly when eaten without fats or proteins, refined carbohydrates can cause your blood sugar and energy to rise rapidly before nosediving. This rollercoaster, per Whitson, can contribute to fatigue, irritability, difficulty concentrating, and mental sluggishness. In fact, a 2023 review published in Nutrients found that inadequate carbohydrates intake can impair reaction time, as well as other measures of cognition.
Conversely, consuming carbohydrates with a higher fiber content (think: oats, lentils, beans) can help support steadier blood sugar levels. This, in turn, can translate to more mental clarity, says Whitson.
Including complex carbs in your morning meal can be a particular game-changer. Doing so may help support more stable energy and concentration throughout the day, she says. Oatmeal topped with berries and chia seeds, whole-grain toast with nut butter or eggs, or Greek yogurt with fruit and granola are all good choices.
2. Faster Gym Progress
If you feel like you’ve been hitting a wall during training, consider your carbs. “Endurance athletes and individuals who are regularly exercising definitely need more daily carbohydrates to support their training demands,” says registered dietitian Amanda Rossetti, R.D., and founder of Fuel First Nutrition.
A quick hit of simple carbs pre-workout gives the body energy it can use lickety split during a sweat sesh, she explains. (Buddy up with a banana, pre-workout carb powder, a shot of honey, or a slice of bread, for example.) Meanwhile, during slow-and-go cardio, the body can draw on carbs previously stored as glycogen. These carbohydrates support steady energy during longer training bouts, and reduce the risk of bonking, or abruptly hitting a wall mid-session, she explains.
“Carbs are key for recovery as well,” Rossetti adds. Consuming them after exercise replenishes those now-depleted stores. This way, you support recovery from your last workout and prep for future ones, she says. Pairing carbohydrates with protein might be especially beneficial, as carbohydrates help shuttle nutrients (including amino acids) into your muscles, she says.
Wondering if your workouts need more carb fuel? Consider how your body has been feeling lately. Decreased athletic performance, hitting a “training plateau,” and niggling injuries are common signs you’re not eating enough calories and carbs for your training needs, says Rossetti. If these sound familiar, she suggests gradually increasing the percentage of your daily calories from carbs, especially before and after exercise.
3. Better Poops
Your probiotic supplement and squatty potty won’t do squat for your GI system if you’re not eating adequate fiber. And fiber, as it turns out, is present in the highest quantities in complex carbohydrates, says registered dietitian Mallory Aldred, R.D., founder of What Mallory Eats.
Read More: How To Make Fibermaxxing Work For You: The Dos And Don’ts
Healthy intake of fiber is about 14 grams for every 1,000 calories. Reaching this target can support healthy stools as well as feelings of fullness, says Aldred. Certain fibers from complex carbs also act as prebiotics—AKA food for healthy gut bacteria. Ultimately, prebiotics help reduce inflammation, improve gut motility, and regulate bowel movements, adds Rosetti. Win!
If better poops are your primary motive, Aldred suggests upping intake of high-fiber picks, such as legumes, whole grains, and veggies. But don’t increase intake of fiber-rich complex carbs overnight. Adding too much too quickly, especially without increasing daily fluid intake, can land you with bloating and constipation.
4. Improved Mood
Candy bars, cookies, and mountains of ice cream are often touted as feel-good foods. But in reality, refined carbs like these don’t actually benefit mood in the long term. Instead, “a diet rich in complex, high-quality carbs—like whole grains, fruits, and vegetables—can improve mood,” says Aldred. One 2025 study published in BMC Geriatrics found that higher-quality carbohydrates were associated with better mood outcomes and lower odds of anxiety and stress.
Read More: Is Your Cranky Mood A Metabolic Issue?
The reason for the complex carb-mood connection? To start, intake can ward off certain issues like constipation, fatigue, and brain fog, all of which can make you feel pretty darn crummy. Plus, recent research in Advances in Nutrition suggests that carbohydrates also help increase the availability of tryptophan. This amino acid supports the production of mood-boosting serotonin.
To be clear: Not all carbs can improve mood equally. But swapping refined carbs (like that aforementioned candy bar) for higher-quality options like oats, quinoa, and sweet potatoes may support mental and emotional well-being.
5. More Balanced Hormones
The benefits of eating enough carbs even extend to your hormones. When the body is consistently denied adequate fuel—particularly carbohydrates—it can trigger so-called “survival mode.” In this metabolic state, the stress hormone cortisol can spike, says Whitson.
The entire endocrine system is interconnected, so inadequate carb intake may also suppress the production of other hormones. That includes those involved in metabolism, recovery, and reproduction, such as estrogen and testosterone. A 2022 review published in Nutrition and Health found that men on very low-carb diets had elevated cortisol levels during and after exercise, as well as low resting testosterone levels. Other research shows that female athletes who don’t consume enough carbohydrates for their activity levels have higher risk of low estrogen output and menstrual irregularities.
At the same time, overdoing it on simple and refined carbohydrates can nudge blood sugar up and insulin resistance down, says Rossetti. “This can disrupt reproductive hormones and increase risk for ovulatory infertility,” she says. (This is when irregular ovulation makes conception more difficult.)
With that, the best way to support hormone balance is to find the carbohydrate sweet spot. You want to consume enough to support energy needs, recovery, blood sugar regulation, and overall hormonal health—without relying too heavily on ultra-processed, refined options, says Whitson.
6. A Nicer Scent
There’s eating too few carbs for optimal function… and then there’s going full-blown keto. A keto diet limits carbs to the point where the body has to rely on fat as its primary fuel, explains Whitson.
Read More: No, Low-Carb And Keto Are Not The Same Thing
The switch to using fat for energy can come with some unpleasant side effects (nicknamed the “keto flu”). “Common symptoms of keto flu include fatigue, headaches, irritability, digestion changes (such as constipation, diarrhea, or bloating), nausea, clamminess, muscle cramps, and even changes to smell to the breath or body odor,” says Whitson.
Why the change in scent? As the body breaks down fat for energy, compounds called ketones are released into your system. Some of these ketones get released through the breath and sweat, which can create a fruity, metallic, or acetone-like odor, she explains.
So will eating carbs suddenly make your B.O. smell like sandalwood or spice? Eh, that’s a stretch. Still, those who were previously on a keto diet might notice the pungent odor associated with ketosis begin to fade with a higher-carb diet.
Exactly How Many Carbs Should You Consume?
Considering all the benefits of eating enough carbs, it’s not surprising that the Academy of Nutrition and Dietetics recommends getting 45 to 65% of your total daily calories from them. But your macronutrient breakdown should be individualized, based on factors such as your age, overall health, life stage, activity level, and more, Rosetti says.
Physically active people, for example, generally require the higher end of that range, per Aldred. “Athletes such as endurance runners, swimmers, and bodybuilders need to keep muscle glycogen stored to prevent fatigue and support recovery,” she says. Laborers, construction workers, and other people with physically demanding jobs often need a higher intake of healthy carbs, too, she says.
If you’re having symptoms associated with inadequate carbohydrate intake—such as persistent fatigue, brain fog, poor workout recovery, low mood, poor sleep, or frequent, intense cravings—you may also benefit from taking a closer look at your intake, says Aldred. Measuring and tracking your food intake for a short period can help you determine whether overall calorie and carbohydrate needs are being met, she says.