Nutrients and a Balanced Diet
Nutrients are the substances in food that the body needs for energy, growth and repair, and a balanced diet supplies all of them in the right amounts. In brief: the seven main nutrient groups are carbohydrates, proteins, lipids (fats), vitamins, minerals, water and dietary fiber. Carbohydrates and fats mainly provide energy, proteins build and repair tissue, and vitamins and minerals help regulate body processes.
What we eat affects growth, energy, disease risk and mental performance. This guide describes each nutrient group and its role, explains what a balanced diet means and how energy needs vary, shows how to calculate the energy in a meal, covers malnutrition and corrects common mistakes.
What are nutrients?
A nutrient is a chemical substance in food that the body uses. Nutrients needed in large amounts, measured in grams, are called macronutrients: carbohydrates, proteins and lipids. Those needed in small amounts, such as vitamins and many minerals, are called micronutrients. Water and fiber are also essential for health.
What do carbohydrates, proteins and lipids do?
Carbohydrates
Carbohydrates are the main source of energy. Starch, found in bread, rice and potatoes, is digested to glucose. Sugars are found in fruit, milk and sweets. One gram of carbohydrate provides about 17 kilojoules (kJ) of energy, or about 4 kilocalories.
Proteins
Proteins are made of amino acids. They are needed for growth and repair, and they form enzymes, hormones, antibodies and parts of muscle and skin. Good sources are meat, fish, eggs, dairy, beans and nuts. About 17 kJ are released per gram when proteins are used for energy, but this is not their main role. Of the 20 amino acids, nine are essential for adults, which means the body cannot make them.
Lipids
Lipids include fats and oils. They are the most concentrated energy source, providing about 37 kJ (9 kilocalories) per gram, more than twice as much as carbohydrates or proteins. They also insulate the body, protect organs, form cell membranes and carry fat-soluble vitamins (A, D, E and K). Sources are oils, butter, nuts, oily fish and meat. Unsaturated fats are generally considered healthier than saturated fats in excess.
What do vitamins and minerals do?
Vitamins are organic compounds needed in small amounts. Minerals are inorganic elements. Both help body processes, and a shortage leads to deficiency diseases.
| Nutrient | Main function | Sources | Deficiency |
|---|---|---|---|
| Vitamin A | Vision, skin | Carrots, liver, eggs | Night blindness |
| Vitamin C | Connective tissue, healing | Citrus fruit, peppers | Scurvy |
| Vitamin D | Calcium absorption | Oily fish, sunlight on skin | Rickets |
| Calcium | Bones, teeth, muscles | Milk, cheese, greens | Weak bones |
| Iron | Hemoglobin in blood | Red meat, lentils | Anemia |
| Iodine | Thyroid hormones | Seafood, iodized salt | Goiter |
Why do we need water and fiber?
Water makes up about 60 percent of adult body mass. It is the solvent for chemical reactions, it transports substances in blood, helps regulate temperature through sweating and removes waste in urine. People can survive weeks without food but only a few days without water.
Dietary fiber, mostly cellulose from plant cell walls, is not digested by human enzymes. It adds bulk to the contents of the intestine, helps food to move through and prevents constipation. Whole grains, vegetables, fruit and legumes are rich in fiber.
What is a balanced diet?
A balanced diet contains the right proportions of all the nutrients, provides the energy needed and avoids too much of any one kind. It varies with age, sex, size, activity and health. Many national guidelines recommend a base of vegetables, fruit and whole grains, moderate amounts of protein foods and dairy, and limited sugar, salt and saturated fat.
Children and teenagers need more protein and calcium for growth. Pregnant women need extra iron and folic acid. Older adults often need fewer calories but still need most nutrients. Because needs differ, recommendations are given as ranges, and individual advice may come from a dietitian or doctor.
How much energy does the body need?
Energy needs depend on the basal metabolic rate (BMR), which is the energy used at rest to keep the body functioning, plus the energy for activity and digestion. Typical estimates for adults are about 8 000 to 11 000 kJ per day (roughly 1 900 to 2 600 kilocalories), with higher values for large, active people. These are approximate, since individual needs vary.
If energy intake is higher than expenditure for a long time, the surplus is stored as fat, and the person gains mass. If it is lower, stored energy is used, and mass falls.
Worked example: energy in a meal
A lunch contains 60 g of carbohydrate, 25 g of protein and 20 g of fat. Use 17 kJ per gram for carbohydrate and protein, and 37 kJ per gram for fat.
- Carbohydrate: 60 × 17 = 1 020 kJ.
- Protein: 25 × 17 = 425 kJ.
- Fat: 20 × 37 = 740 kJ.
- Total: 1 020 + 425 + 740 = 2 185 kJ.
The fat is only 20 g of the 105 g of nutrient mass, but it provides 740 ÷ 2 185 ≈ 34 percent of the energy. If a person needs 9 000 kJ per day, this lunch supplies about 2 185 ÷ 9 000 ≈ 24 percent of the daily requirement. The calculation ignores fiber and water, which provide no usable energy, and it uses rounded values.
What is malnutrition?
Malnutrition means an imbalance of nutrients, and it includes both too little and too much. Undernutrition includes starvation, protein deficiency (kwashiorkor) and shortages of vitamins and minerals. Overnutrition leads to overweight and obesity, which increase the risk of type 2 diabetes, heart disease and some cancers.
Both forms can occur in the same country, or even in the same family. A person can be overweight and still lack iron or vitamin D if the diet is poor in those nutrients.
How was nutrition science discovered?
In 1747 the Scottish naval surgeon James Lind conducted a famous trial on sailors with scurvy and found that oranges and lemons cured the disease, although the reason, vitamin C, was identified only in the 1930s. Casimir Funk coined the word “vitamine” in 1912. The study of vitamins, minerals and amino acids developed rapidly in the early twentieth century and led to the prevention of diseases such as rickets and goiter.
Which mistakes are common?
Mistake 1: Thinking all fats are bad
Fats are essential. The issue is the type and the amount, not their presence.
Mistake 2: Saying that fiber provides energy
Humans cannot digest most fiber, so it provides little or no usable energy. Its role is to support digestion.
Mistake 3: Mixing up kilojoules and kilocalories
One kilocalorie equals about 4.2 kilojoules. Check the unit in a table before comparing values.
Mistake 4: Believing that vitamins give energy
Vitamins help the body use energy, but they contain no usable energy themselves.