Energy Requirements of Humans

Food is a basic need of all living things. Food contains nutrients that provide the body with energy. Sixty-five percent of the human body is water. The rest is fat, protein and carbohydrates.

The energy provided by these nutrients is expressed in units called calories. This unit is used to express the heat output of the organism or the energy value of food. You will find that some product labels indicate how many calories their product contain. For example, a cup of dried buttermilk has 465 kilo- calories, a cup of roasted peanuts has 840 kilo calories, and 10 pieces of vanilla and wafer cookies have 185 kilo calories.

There are several factors that influence calorie intake. Nutritionists and dietitians have conducted studies to show how sex, age, physical activity, health, and climatic conditions affect calorie intake.

Generally, growing individuals or those who are engaged in strenuous activities, and those living in warm to hot places should take in food with high calorie value. For individuals with special health concerns, it is suggested that they consult a doctor or a nutritionist.

The Energy Pyramid

In a food web, the producer has the greatest amount of energy. At the consumer level, only 10% of absorbed nutrients are used to make a new body tissues. This represents the food available for the following level. The rest of the energy is lost as heat. Thus, the amount of usuable energy per unti mass decreases as the feeding level goes higher.

Herbivores, primary consumers, acquires only 10% of the total energy of the producers. Only 10% of the hervivores' energy goes to the animal in the next trophic level, so that the latter acquires 1/100th of the total producer's energy.