B1b: Human health and diet

Balanced Diet

What is a balanced diet?A balanced diet gives the body all the essential nutrients it needs. There are 6 essential nutrients: Carbohydrates - provides energy Fats - provides energy, acts as an energy store and provides insulation Proteins - needed for growth and repair of tissue, and provides energy during emergency Vitamins and Minerals - eg. Vitamin C prevents scurvy, iron (a mineral) used to make haemoglobin for healthy blood Water - prevent dehydration

What are they made of? Carbohydrates are made up of long chains of simple sugars like glucose. They are stored in the liver as glycogen or converted to fats. Fats are made up of 3 fatty acids linked to a molecule of glycerol. They can be stored under the skin and around organs as adipose tissue. Proteins are made up of amino acids. There are 22 amino acids. They don't get stored. Some amino acids can't be made by the body so it is obtained from a diet - these are called essential amino acids.Animal proteins (found in meat) contain all essential amino acids - plant proteins don't.This means that vegetarians need to eat a wide variety of plant sources to make sure they have a complete range of amino acids in their diet.Animal proteins - first class proteinsPlant proteins - second class proteins

Different Diets

Why is there a variation of energy and nutrients between people?A balanced diet is not a fixed thing - it is different for everyone. It depends on: Age - Children and teenagers need more protein for growth. Older people need more calcium to protect against degenerative bone diseases like osteoporosis. Gender - Females need more iron to replace the iron lost in menstrual blood. Physical activity - Active people need more protein for muscle development, and more carbohydrate for energy.

Why do some people choose to eat a different diet?Some people choose not to eat certain foods for all sorts of reasons: Religious - eg. Hindus don't eat cows as they believe that they're sacred. Personal - vegetarians don't eat meat as some think it's cruel to animals, some don't like the taste, some think it's healthier and others think it's trendy. Vegans don't eat anything that are products of animals. Medical - some people are intolerant to certain foods, eg. wheat and dairy products. Eating these foods can make the person feel ill or bloated. This is because they can't make the enzyme needed to digest that food properly. Some others are allergic to foods and can get serve reaction which can sometimes be fatal.

Diet Problems

What problems can be caused by eating too little protein?It can cause a condition called kwashiorkor. A common symptom is a swollen stomach.This condition is common in developing countries because of: Overpopulation - the demand for protein rich food is greater than what is available Lack of money - there is little money to invest in agriculture meaning it is difficult to produce enough protein rich food for everyone.

How to calculate a person's Estimated Average daily Requirement (EAR) of protein?Using the formula: EAR (g) = 0.6 x body mass (kg)EAR is just an estimate. It shows how much protein the average person of a particular body mass should eat a day.It can vary with age, eg. teenagers need more protein for growth.It can also change during and after pregnancy. Pregnant women need extra protein to help their baby grow. A woman who is breast feeding also needs protein to produce milk.

What eating disorders can cause problems?Some psychological disorders, eg. anorexia nervosa and bulimia nervosa, can cause under-nutrition.Anorexia nervosa leads to self-starving. Bulimia nervosa involves binge eating, followed by self-induced vomiting.They are usually caused by low self esteem and a desire to be 'perfect' - sufferers tend to heave poor self-image.These disorders result in a poor diet, which can cause a host of other illnesses. e.g. liver failure, kidneyfailure, heart attacks, muscle wastage, low blood pressure and mineral deficiencies. Bulimia can lead to tooth decay (the acid in vomit eats away the tooth enamel). Both disorders can be fatal.Also, being overweight or obese is linked to increased health risks such as arthritis, heart disease, diabetes and breast cancer.

Under- or Overweight?

The Body Mass Index (BMI) is used as a guide to help decide whether someone is underweight, normal, overweight or obese. It is calculated using this formula:

This table shows how BMI is used to classify people's weight:

BMI isn't always reliable. Athletes have lots of muscle, which weighs more than fat, so they can have a high BMI even though they’re not overweight. An alternative to BMI is measuring % body fat.