The six classes of nutrients are carbohydrates, proteins, fats, vitamins, minerals, and water. Every food you eat delivers some combination of these six, and your body needs all of them to function. Three of them (carbohydrates, proteins, and fats) provide calories and are called macronutrients. The other three (vitamins, minerals, and water) don’t supply calories but are equally essential.
Carbohydrates: Your Body’s Preferred Fuel
Carbohydrates are the body’s primary energy source. When you eat them, your digestive system breaks them down into glucose, which your cells, tissues, and organs use immediately or store in the liver and muscles for later. Each gram of carbohydrate provides about 4 calories, and current dietary guidelines recommend that 45 to 65 percent of your daily calories come from carbohydrates.
There are three main forms. Simple carbohydrates, or sugars, are already in their most basic form and enter the bloodstream quickly. You find them in fruit, honey, and table sugar. Complex carbohydrates, or starches, are chains of simple sugars strung together. Your body takes longer to break them apart, so they provide a steadier supply of energy. Whole grains, legumes, and starchy vegetables are good sources.
Fiber is technically a complex carbohydrate, but your body can’t break most of it down. That’s actually useful: fiber helps you feel full, supports regular digestion, and may help lower cholesterol and blood sugar levels. Most adults fall short on fiber, which is one reason nutrition guidance consistently emphasizes whole grains, vegetables, and legumes over refined carbohydrates.
Proteins: Building and Repair
Proteins are the structural workhorses of the body. They build and repair tissues, form antibodies that fight off viruses and bacteria, and make up enzymes that carry out thousands of chemical reactions inside your cells. Like carbohydrates, protein provides about 4 calories per gram.
Your body assembles proteins from 20 different amino acids. Nine of those are considered essential because your body can’t make them on its own; they have to come from food. Animal sources like meat, fish, eggs, and dairy contain all nine, which is why they’re called complete proteins. Most plant foods are missing one or two, but eating a variety of plant proteins throughout the day (beans, grains, nuts, soy) covers the full set.
The recommended range for protein is 10 to 35 percent of daily calories for adults. That’s a wide range because protein needs vary with age, activity level, and health goals. Active people and older adults generally benefit from the higher end.
Fats: Energy Storage and Hormone Production
Fat is the most calorie-dense nutrient at 9 calories per gram, more than double what carbohydrates or protein provide. That density makes fat an efficient way to store energy, but it also means high-fat foods add up quickly.
Beyond energy, fats serve several roles you might not expect. They help your body absorb fat-soluble vitamins (A, D, E, and K), cushion and protect your organs, insulate your body against temperature changes, and serve as raw material for hormones. Cholesterol, a type of fat in your blood, is essential for making both hormones and vitamin D.
Not all fats affect the body the same way. Unsaturated fats, found in olive oil, nuts, avocados, and fatty fish, support heart health. Saturated fats from animal products and tropical oils are fine in moderate amounts. Trans fats, mostly from partially hydrogenated oils, are the type worth actively avoiding. For adults, the recommended range is 20 to 35 percent of daily calories from total fat.
Vitamins: Chemical Regulators
Vitamins don’t supply energy, but they regulate nearly every process that does. There are 13 essential vitamins, and they split into two categories based on how your body handles them.
Four vitamins are fat-soluble: A, D, E, and K. Your body stores these in the liver, fatty tissue, and muscles, so you don’t need to consume them every single day. Vitamin A maintains healthy skin, vision, and mucous membranes. Vitamin D helps you absorb calcium for strong bones and teeth. Vitamin E acts as an antioxidant, protecting cells from damage. Vitamin K is necessary for normal blood clotting and plays a role in bone health.
The remaining nine are water-soluble: vitamin C and the eight B vitamins. Your body doesn’t store these well. Excess amounts leave through urine, which means you need a regular supply from food. Vitamin C promotes wound healing, helps absorb iron, and maintains healthy gums and skin. The B vitamins collectively keep your metabolism running. B12 supports your nervous system and red blood cell production. Folate is essential for DNA production and cell growth. B1 (thiamine) helps cells convert carbohydrates into energy and supports heart and nerve function. B6 helps form red blood cells and maintain brain function.
Because water-soluble vitamins aren’t stored, shortages can develop relatively quickly if your diet lacks variety. Fat-soluble vitamins, on the other hand, can accumulate to harmful levels if you take excessive supplements.
Minerals: Structural and Functional Support
Minerals keep your bones, muscles, heart, and brain working properly, and they’re involved in making enzymes and hormones. Like vitamins, they don’t provide calories but are essential in specific amounts.
Minerals fall into two groups based on how much you need. Macrominerals are required in larger quantities: calcium, phosphorus, magnesium, sodium, potassium, chloride, and sulfur. Calcium and phosphorus are the primary building blocks of bones and teeth. Magnesium supports hundreds of enzyme reactions. Sodium and potassium regulate fluid balance and nerve signaling.
Trace minerals are needed in much smaller amounts but are no less important. These include iron, zinc, iodine, selenium, copper, manganese, fluoride, and cobalt. Iron carries oxygen in your blood. Zinc supports immune function and wound healing. Iodine is essential for thyroid hormones that control metabolism. Selenium acts as an antioxidant partner alongside vitamin E.
Most people can get adequate minerals from a varied diet that includes dairy or calcium-fortified alternatives, leafy greens, lean meats or legumes, nuts, and whole grains. Iron deficiency is one of the most common mineral shortfalls worldwide, particularly among women of reproductive age.
Water: The Overlooked Essential Nutrient
Water makes up roughly 60 percent of your body weight and is involved in virtually every bodily function. It regulates internal temperature through sweating and respiration, transports nutrients through the bloodstream, cushions joints, and flushes waste products out through urine. Without adequate water, none of the other five nutrient classes can do their jobs effectively.
The National Academies set adequate intake levels at about 3.7 liters (roughly 125 ounces) per day for men and 2.7 liters (about 91 ounces) per day for women. That total includes water from all sources: plain water, other beverages, and the moisture in food. Most people get about 20 percent of their daily water from food alone, so you don’t necessarily need to drink that full amount.
Your needs increase with exercise, heat exposure, illness, and pregnancy or breastfeeding. Thirst is a reasonable guide for most healthy adults, though it becomes less reliable with age.
How Macronutrients and Micronutrients Differ
The simplest way to think about these six classes is in two tiers. Macronutrients (carbohydrates, proteins, and fats) are needed in large amounts because they provide the energy your body runs on. The current recommended balance for adults is 45 to 65 percent of calories from carbohydrates, 10 to 35 percent from protein, and 20 to 35 percent from fat.
Micronutrients (vitamins and minerals) are needed in far smaller quantities, often measured in milligrams or micrograms, but deficiencies can cause serious health problems. Water stands apart from both groups. It provides no calories and no micronutrients, yet you’d survive only days without it, compared to weeks without food. Together, all six classes work as a system: fats help absorb vitamins, water transports minerals, proteins build the enzymes that metabolize carbohydrates. No single class works in isolation.