IB Biology/Option A - Diet and Human Nutrition

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This page was deleted, so was partially recreated by an IB student with the aid of "Biology for the IB Diploma Standard and Higher Level" textbook by Andrew Allott, published by Oxford. It is not copied directly from the textbook, but some of the information was obtained from it, so you know it is correct. I don't know how to do referencing, hence all this being written here instead of in a reference! Unfortunately this page is not in the usual style (nicely ordered with points from the syllabus followed by the necessary information) so is not as helpful as it probably was before someone deleted the original version! Still, it's better than nothing! Hope it's helpful :) - Hope it helps, Mike den Hartog


The diet is all the food taken in by an individual over a period of time. Food provides us with energy for metabolic functions and all the chemicals needed for life (nutrients).

Below is a list of the 5 major nutrients included in the diet, some examples of here to find them, and what they are needed for:

Carbohydrates are found in honey, grapes, cane sugar, milk, bread and liver. The main function of carbohydrates is to provide energy that can be released rapidly in cell respiration.

Proteins are found in beef, salmon, seeds, peanuts and tofu. Proteins are used for protein synthesis - for cell and tissue growth, regeneration of hair, skin and red blood cells.

Lipids are found in oily fish, nuts and fatty meats. Lipids contain more energy per gram than carbohydrates and form the body's main energy stores in adipose tissue. Fats act as a thermal insulator to the body. Phospholipids are the main constituents of the membranes.

Nutrients are chemical substances (elements or compounds) found in foods that are needed by the human body. All nutrients including essential fatty acids, essential amino acids, minerals, vitamins, water must be obtained from the food consumed because these substances cannot be synthesized by the human body. Non-essential fatty and amino acids can both be synthesized from essential fatty and amino acids by the human body. Carbohydrates are a source of energy, however lipids and proteins can be used for energy and therefore carbohydrates are not classified as nutrients.

Minerals are found in a range of fresh foods. Apart from C, H and O at least 20 minerals are essential in the diet, each with specific use. Deficiencies cause ill health.

Vitamins are found in a range of fresh foods, and vitamin D is manufactured by the body when sunlight hits the skin. 13 different compunds have been identified, each with a specific use. Definciencies cause ill health.


Vitamins and minerals are sometimes called micronutrients because they are needed in very small quantities compared to the three macronutrients. However, they cannot be synthesised by the body and a definciency can cause ill health.

In addition to the macro- and micronutrients, water is essential in the diet.


A balanced diet supplies the energy and nutrients the body needs and no more. Supplying a balanced diet is achieving an equilibrium (balance) between energy intake and expenditure.

Individuals vary in their energy requirements. Factors influencing how much energy is needed by an individual are:

Age: more energy is needed up with increasing age up to adulthood as the body grows larger.

Gender: females use less energy than males.

Activity: physical activity involves energy expenditure.

Condition: extra energy is needed during growth spurts, pregnancy, breast-feeding, illnesses and some other conditions.


Diets containing excessive amounts of energy cause obesity.

Nutrient requirements also vary with age, gender and other factors (pregnancy, diet etc).