While many nutrients can be produced by the body, other nutrients – called essential nutrients – cannot. Therefore, we must supply them through our diet: the foods we eat and drink.

Essential nutrients include 9 of the 20 amino acids found in proteins, certain fatty acids found in fats and oils, and a number of minerals and vitamins. Nutrients are generally divided into 2 categories: macronutrients and micronutrients.

Macronutrients include fats, proteins, carbohydrates, and some minerals, and our bodies need these in large quantities on a daily basis. They make up the bulk of our diet and supply the energy and building blocks we need for growth, activity, and maintenance. When these foods are digested they are turned into their basic units, namely sugars from carbohydrates, fatty acids and glycerol from fats, and amino acids from proteins. The energy content derived from each is measured in calories.

Typically, our individual calorie intakes vary greatly depending on the availability of food and on our physical activity, age, and sex. In general:

• older adults, children, and sedentary women need roughly 1,600 calories per day;
• active women, older children, and sedentary men need roughly 2,000 calories per day;
• young men and active adolescent boys need roughly 2,400 calories per day.

Macrominerals include calcium, phosphorus, sodium, chloride, potassium, and magnesium, and our bodies need roughly 1 to 2 grams of each per day. Water is also a macronutrient and we need 1 mL for each calorie of energy we expend, or about 2,500 mL (2.6 quarts) per day.

Essential fatty acids include linoleic acid, linolenic acid, arachidonic acid, eicosapentaenoic acid, and docosahexaenoic acid. Linoleic acid and linolenic acid are found in vegetable oils. Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are essential for brain development and are found in fish oils.

Micronutrients include vitamins and trace minerals, and our bodies need them to metabolize the macronutrients. Micronutrients are usually required in small amounts – from milligrams to micrograms. Essential trace minerals include iron, zinc, copper, manganese, molybdenum, selenium, iodide, and fluoride. With the exception of fluoride, all these minerals activate enzymes that help our bodies metabolize food.