Carbohydrates are often misunderstood and vilified, yet they’re the body’s main energy source, fueling everything from brain function to athletic performance. Understanding the science behind carbs can help you make smarter dietary choices and enjoy sustained energy.
What Are Carbohydrates?
Carbohydrates were first discovered in the 19th century, when scientists first began understanding these compounds. The term “carbohydrate” comes from “hydrate de carbone,” which reflects their chemical composition of carbon, hydrogen, and oxygen. In 1838 chemist Jean Baptiste Dumas invented the term “glucose” from the Greek word “gleukos,” meaning sweet wine, for the sugar found in honey, grapes, and starch. From the cellulose that gives plants their structure to the glycogen that stores energy in your muscles, carbohydrates take many forms and serve numerous functions in nature. The human body processes carbohydrates by breaking them down into glucose, which then travels through your bloodstream to provide energy for every cell in your body. For example, your brain alone consumes about 120 grams of glucose daily, roughly equivalent to eating 30 teaspoons of sugar, though obviously not in that form.
Simple vs Complex Carbohydrates
Simple carbohydrates, or simple sugars, are a group that includes monosaccharides like glucose and fructose, and disaccharides like sucrose (table sugar) and lactose (milk sugar). These are found naturally in fruits and milk, but they’re also added to countless processed foods. Your body can break down simple carbs quickly, leading to rapid spikes in blood sugar levels. This is why eating candy or drinking soda gives you that immediate energy boost followed by a crash.
Complex carbohydrates, on the other hand, are made up of long chains of sugar molecules linked together. These include starches found in grains, potatoes, and beans, as well as fiber found in vegetables, fruits, and whole grains. Because of their more complex structure, your body takes longer to break them down, resulting in a more gradual and sustained release of energy. This is why a bowl of oatmeal keeps you satisfied longer than a candy bar with the same number of calories.
Unlike other carbs, the fiber component of complex carbohydrates cannot be fully digested by our enzymes. Instead, it travels through your digestive system largely intact, helping food move through your intestines and serving as food for beneficial gut bacteria. That’s the reason whole grain bread makes you feel fuller than white bread, even when the calorie content is similar.
Why Your Brain Runs on Glucose
Perhaps the most compelling argument for including carbohydrates in your diet comes from neuroscience. Your brain requires an incredible amount of energy, accounting for only 2% of your body weight but consuming roughly 20% of your daily energy expenditure. Unlike muscles, which can burn fat for fuel during exercise, your brain utilizes almost exclusively glucose. This glucose dependency directly impacts your cognitive abilities. Glucose levels in the brain are correlated to thinking, memory formation, and learning capacity. When glucose levels drop too low, neurotransmitter production decreases, leading to brain fog, difficulty concentrating, and mental fatigue that many people experience on very low-carb diets.
The brain stores very little glucose on its own (3-4 minute supply at any given time). Instead, it relies on the supply from the bloodstream, which also depends on either recent carbohydrate consumption or the body’s ability to create glucose from other sources through a process called gluconeogenesis. Even though your body can make glucose from proteins and fats, the process is metabolically expensive and isn’t as quick and efficient as dietary carbohydrates. Certain areas of the brain are more glucose-dependent than others. The prefrontal cortex, responsible for executive functions like decision-making and impulse control, is particularly sensitive.
Debunking the Biggest Carbohydrate Myths
– Carbs make you fat
This is perhaps the most pervasive myth about carbohydrates. Weight gain occurs when you consume more calories than you burn, regardless of whether those calories come from carbs, proteins, or fats. The confusion is often caused from the initial water weight loss people experience when starting low-carb diets. When you drastically reduce carbohydrate intake, your body depletes its glycogen stores and since glycogen binds water, you lose several pounds quickly. You aren’t losing fat, you are losing water weight that will return when you resume normal eating habits.
– Fruit is too high in sugar
While fruits do contain natural sugars, they also provide fiber, antioxidants, vitamins and minerals that refined sugar sources lack. The fiber in fruit slows sugar absorption, preventing the blood sugar spikes that typically come with processed sweets.
– You shouldn’t eat carbs at night
Your body processes carbohydrates the same way regardless of when you eat them. This myth likely persists because people often choose less nutritious, more caloric carb sources for evening snacking, but there’s no metabolic reason why eating a sweet potato at dinner would be different from eating it at lunch.
Carbohydrates in Athletic Performance and Recovery
Carbohydrates are essential for optimal physical performance. This is because of the complex physiological processes that affect everything from endurance to strength to recovery speed.
During exercise, your muscles primarily rely on stored carbohydrates (glycogen) for fuel, especially during high-intensity activities. In fact, fat requires oxygen to be converted to energy, while carbohydrates can be used both aerobically and anaerobically, making them essential for activities that push your cardiovascular system to its limits.
The concept of “hitting the wall” in endurance sports is literally the experience of glycogen depletion. When muscle glycogen stores are exhausted, the body must rely more heavily on fat metabolism and gluconeogenesis, both of which are slower processes that can’t maintain high-intensity output.
Recovery is another reason why carbohydrates are essential. After intense exercise, your muscles are prepared to rapidly absorb glucose and convert it back to glycogen through a process called supercompensation. This process can last for several hours after exercise, which is why post-workout nutrition recommendations typically include carbohydrate consumption alongside protein.
The protein-sparing effect of carbohydrates is particularly important for athletes trying to maintain or build muscle mass. When there are enough carbohydrates available, the body prefers to use them for energy, allowing dietary and muscle proteins to be used for tissue repair and growth rather than being broken down for fuel.
The gut health connection
Fiber, a type of carbohydrate that humans cannot fully digest, serves as food for the beneficial bacteria living in your intestines. These bacteria ferment fiber into short-chain fatty acids that provide energy for the cells lining your colon and have anti-inflammatory effects throughout the body. Different types of fiber feed different bacterial species, which is why dietary diversity is important for gut health. That’s why people following very low-carb diets often experience digestive issues: they’re essentially starving the beneficial bacteria that help maintain gut health. Prebiotics, for instance, are found in foods like garlic, onions, asparagus, bananas, and oats. These foods, other than providing energy, actively support the health of your intestinal ecosystem. The bacteria in your intestines also produce neurotransmitters and communicate with your brain through various pathways, influencing mood, appetite, and even cognitive function. Some researchers now believe that gut health may play a role in mental health conditions like depression and anxiety, though this research is still in its early stages.
Making smart carbohydrate choices
The concept of nutrient density is crucial when evaluating carbohydrate sources. A medium sweet potato and a candy bar might contain similar amounts of carbohydrates, but the sweet potato also provides vitamin A, potassium, fiber and various other nutrients, while the candy bar has low nutritional value. Timing can also influence how your body responds to different carbohydrates. Eating higher-glycemic carbs around exercise can provide quick energy and support recovery, while lower-glycemic options might be better when you want sustained energy and satiety.
The Mediterranean diet is an example of healthy carbohydrate inclusion. This type of diet includes plenty of carbs from sources like whole grains, legumes, fruits, and vegetables, while limiting refined and processed options. Rather than following rigid rules about carbohydrate consumption, focus on choosing mostly whole food sources, paying attention to how different carbs make you feel, and adjusting intake based on your activity level and health goals. Following this approach, you’ll be able to enjoy the energy and health benefits that carbohydrates provide while avoiding the extremes that often lead to nutritional deficiencies or unsustainable eating patterns.
