Cambridge O Level Biology · Syllabus 5090 · Human Nutrition
Balanced Diet
What is Balanced Diet?
A diet that supplies all the nutrients the body requires, together with dietary fibre and water, in the proportions and quantities needed to maintain health. The required quantities are not fixed: they vary with age, biological sex, activity level, pregnancy, state of health and body size, so two balanced diets can look entirely different.
This definition is part of the Human Nutrition chapter in Cambridge O Level Biology.
Balanced Diet in context
Human nutrition is the study of how food is taken in, broken down and used. A balanced diet supplies every required nutrient, plus fibre, water and energy, in suitable proportions. Digestion converts large, usually insoluble food molecules into small soluble ones. Absorption moves those small molecules through the wall of the intestine into the blood or lymph. Assimilation is what the body's cells then do with them. Material that was never digested leaves the body unchanged as faeces — that is egestion, and it is not excretion.
Common mistakes with Balanced Diet
- “A balanced diet is the same for everyone.” Why it is wrong Requirements change with age, biological sex, activity level, pregnancy, state of health and body size. A balanced diet for a six-year-old is not a balanced diet for an adult doing heavy manual work. Write instead "A balanced diet supplies all the required nutrients, plus fibre and water, in suitable proportions for that person."
Questions students ask about Balanced Diet
Is fibre a nutrient?
Not in the strict sense: fibre is not digested, not absorbed and supplies no energy. It is still required in the diet, because it adds bulk that the muscles of the gut can grip, keeping material moving and preventing constipation. A definition of a balanced diet that leaves out fibre and water is incomplete.