Which nutrient has the least amount of energy, and which nutrient can be considered to have the maximum energy density?
There are six types of nutrients that are generally listed as nutrients that the body needs. Those six are carbohydrates, proteins, fats, minerals, vitamins, and water.
If the question is asking about calories per gram of intake, then water, vitamins, and minerals offer the least amount of energy. They have zero calories. That doesn't mean they are useless though. Your body needs those nutrients in order to maintain optimal health and wellness.
Of the calorie providing nutrients, carbohydrates and proteins both provide four calories per gram. They are equal in energy density. Fats provide nine calories per gram; therefore, fats have more than twice the energy density of carbohydrates and proteins. That definitely doesn't mean that a person should only eat fats though. A balanced diet that contains the proper amounts of all six nutrients is the most beneficial to overall health.
The nutrients our body can get energy for the various metabolic processes are carbohydrates, proteins and fats. Carbohydrates can be substituted as energy sources by proteins and fats and this makes it possible for a person to survive even if no carbohydrates are consumed.
Carbohydrates which can be digested provide 3.75 kilocalories of energy per gram, proteins that our body is able to digest provide 4 kilocalories per gram and fats contain 9 kilocalories per gram.
This would make carbohydrates the nutrient which provide the body the least amount of energy per gram and fats the nutrient which provide the body with the maximum amount of energy per gram.