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Diet and digestion

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Diet and health

The food you eat has a big effect on your body. A balanced diet from childhood helps keep you healthy all through your life. If too little food is eaten (undernutrition) or too much food is taken in (overnutrition), or if any one element of the diet is lacking then you will suffer from malnutrition. Malnutrition affects the health of millions of people in countries all over the world.

Health authorities have studied the amounts of the major food groups that are required each day in a balanced diet. The Dietary Reference Value (DRV) describes a range of amounts for each food that is required.


Nutrient Amount per day (15-18 year old)
  Vitamin C
  74 g
  277 g
  45 g (female), 55 g (male)
  18 g
  0.015 g
  0.04 g
  0.8 g (female), 1.0 g (male)


This range reflects the natural variation and differences in activity levels of the population. For example, a pregnant woman would have different nutritional needs to a male office worker but confusingly many food labels still quote the Recommended Daily Amount (RDA). This is the amount that would be enough to meet the dietary needs of the majority of the population.


At different life stages, different amounts of energy are required by our body. This energy requirement on average, peaks at 18 years, with 3,200 kcals for males, and 2,500 for females. From there on, fewer calories are needed, stabilising at 75 years with 2,300 kcals for males, and 1,800 for females.

The recommended amount of nutrients such as carbohydrates or fat is expressed as a percentage of the total energy intake required. For example, daily carbohydrate intake should provide 50% of the total daily energy requirement, whereas saturated fat should not exceed 11%.

In the case of fibre, the recommended intake per day remains constant at 30g for people aged 17 and over. For protein, the recommended intake for adults depends on the weight. For adults, 0.75g of protein is required for each kg of weight.

For example, an adult weighting 60 kg will require 0.75 x 60 = 45g of protein per day.

An individual that weights 80kg of weight will require 0.75 x 80 = 60g of protein.

These amounts are, however, averages for the general population. Pregnant or lactating people require more protein for the baby. In a similar case, if you want to build muscle, through weightlifting, running, or cycling, you will need more protein, as protein is needed to build muscle. The average 0.75g would increase to 1.2-1.7g of protein per kg of weight.

For example, 1.5 x 60 = 90g and 1.5 x 80 = 120g for our 60 and 80kg adults, respectively. This is double the amount an average adult needs!


Problems with over-eating

If people take in more energy than they need in their food, the body stores the extra energy as fat. If this continues, they will become obese. This means that the amount of fat they are carrying increases their risk on many different diseases. Obesity can be measured as the BMI (Body Mass Index) or by waist-to-hip ratio. Scientists now think that the waist-to-hip ratio is the best way of measuring obesity and predicting future disease.

Some of the diseases linked to obesity include strokes, angina, heart attackshigh blood pressure and type 2 diabetes.


Problems with lack of food - Deficiency diseases

For large areas of the world the problem is that people do not have enough food. If the diet does not contain enough energy, people will be underweight with reduced resistance to disease and a shortened lifespan.

If food is in short supply, people will also suffer from diseases as a result of deficiencies in certain vitamins, minerals or macronutrients such as proteins.


Mineral and vitamin deficiency diseases include:

Vitamin or Mineral Deficiency disease
  Iron   Anaemia: tiredness, weakness from lack of oxygen
  Calcium   Rickets: weak bones and soft teeth
  Vitamin A   Night blindness, damaged cornea of eye
  Vitamin B1   Beri-beri: wasting of the muscles and paralysis
  Vitamin C   Scurvy: the connective tissue which holds the body together is damaged and destroyed
  Vitamin D   Rickets: weak bones and soft teeth


Scientists have discovered that many people in countries like the UK and US suffer from deficiency of a B vitamin called folic acid. Folic acid is found in leafy green vegetables. Although we have plenty of food, we do not always eat the right things.

A lack of folic acid in the early stages of pregnancy means that the spinal cord of the fetus may not develop properly. This causes spina bifida and other similar problems.

Since extra folic acid started to be added to bread and cereals, the number of babies born with spinal cord problems has decreased.