The word Macro means large or exceptionally prominent. Nutrients are substances vital for an organism to stay alive, grow, and maintain bodily functions.

It is important to understand that nutrients (and toxins) are chemical compounds, not food itself.

The three main macronutrients are carbohydrates, proteins, and fats. Macronutrients are the nutrients from food that the body can use in large amounts to provide energy (all three) and build/repair tissues (primarily protein and fat).

Essential in nutrition means 'Must come from the diet; the body cannot fabricate from other sources'. Carbs may be considered by many to be desirable, but are not essential. Protein and fat are essential.

Water can be considered a macronutrient because it is needed in large quantities, although it doesn't provide energy.

Alcohol also sometimes makes the list because it provides energy, but it is not generally considered to be a nutrient.

Fiber is a non-digestible carb, considered by some nutritionists to be a macronutrient due to its large quantity in standard, carb-heavy diets. Most scientists, however, categorize fiber as a subset of carbs.

All of the three main macronutrients have sub-categorizations:

• Carbs are simple (sugars) or complex (starches, fiber).
  
• Fats are saturated, unsaturated, or trans fats.
  
• Proteins are categorized by the completeness of amino acid content - incomplete proteins that lack some; complete proteins contain all essential amino acids.