(1) What is a healthy balanced diet?

e.g. a good balance of carbohydrates, lipids, vegetable oils, animal fats, protein, mineral ions, vitamins, dietary fibre (roughage), water

This section helps you with questions like ...  What constitutes a healthy balanced diet?  Why do we need protein in our diet?  Why do we need both fats and carbohydrates in our diet?  What is metabolism?  Why is regular exercise good for? What are our energy requirements and why?

• You need to know the content of a healthy human diet: carbohydrates, lipids (fats and oils), proteins, vitamins, minerals, dietary fibre and water, and why each is needed

• Know that a healthy diet contains the right balance of the different foods you need and the right amount of energy and the different food groups are ...

• Carbohydrates

  • These are needed to provide energy for your body chemistry to function correctly, and of course to keep you warm at 37^oC,

  • Carbohydrate sources include bread, potatoes and cereals, all of which contain starch.

  • Carbohydrates are digested and broken down to give sugars such as glucose that are needed for respiration in the mitochondria of cells - powering much of a cell's, tissue or organs chemistry.

  • BUT, not too much, or excessive fats or carbohydrates build up in your body which can lead to obesity.

  • Obesity is a common disorder in developed countries eg in Europe and the US.

  • Obesity is defined as 'having a body mass of at least 20% greater than the maximum recommended body mass.

  • Although the usual causes of obesity are overeating, lack of sufficient exercise and bad diet, hormonal problems can also help cause obesity.

  • Obesity can contribute to other medical problems eg arthritis (joint inflammation), type 2 diabetes (failure to control blood sugar levels), high blood pressure and heart disease and even some types of cancer.

• Lipids (e.g. animal fats and vegetable oils)

  • Sources include butter, vegetable cooking oils and cream.

  • These can act as energy stores which your body can use if insufficient carbohydrates are available.

  • They are also important molecules for the formation of cell membranes.

  • If you have too much saturated fat in your diet, your blood cholesterol levels are raised above what is needed and deposits form on the walls of your blood vessels leading to higher blood pressure.

  • See also medical issues mentioned under carbohydrates.

• Proteins

  • Sources include cheese, meat, eggs and fish.

  • Proteins are used by the body to build cells - growth of new tissue, cell repair and cell replacement.

  • Proteins are important molecules for muscles, tissues and their repair.

  • In digestions, protein is broken down into much smaller amino acid molecules, these are then combined in the ribosomes of cells to synthesise the particular protein molecules are body needs.

• Mineral ions

  • A variety of mineral ions are needed in varying amounts for healthy functioning of the body - organs, skin, bones etc.

  • You do need mineral salts containing e.g. sodium, calcium, potassium and chloride ions BUT too much salt (sodium chloride) can cause high blood pressure and heart problems.

  • You need iron to make haemoglobin molecules that convey oxygen from the lungs through the blood vessel systems to all the cells of your body. Iron is found in red meat and some vegetables.

  • Calcium ions are an important component in bone structure - skeleton and teeth.

  • Sodium ions are important for the functioning of the nervous system, readily obtained from table salt.

  • Besides iron, you also need tiny amounts of other transition metal ions like copper and cobalt ions, which are important for the function of some enzymes and co-enzymes.

  • You need iodine, usually absorbed as the iodide ion, to make the hormone thyroxine.

• Vitamins

  • Vitamins are needed in tiny amounts for healthy functioning of the body - organs, skin, bones etc.

  • They are involved in many important chemical reactions in the complex biochemistry of our body.

  • There are many vitamins important for good health e.g.

    • Vitamin C for healthy skin and avoiding scurvy.

    • Vitamin D helps the body absorb and retain calcium and phosphorus; both are critical for building bone and teeth structure and it also believed to reduce cancer cell growth, help control infections and reduce inflammation..

  • The name 'vitamin' dates from the time early in the 20th century when it was recognised that micro amounts of particular molecules were need for important reactions in maintaining a healthy body.

  • They are mostly obtained from vegetables, fruit and cereals.

• Dietary fibre ('roughage')

  • Dietary fibre keeps everything moving smoothly through the lower part of your digestive system - from the small intestine to the colon.

  • Fibre helps undigested food pass through the gut system.

  • Good sources of fibre include vegetables, fruit, nuts and cereals.

  • Highly processed food tend to be deficient in good quality fibre.

  • It improves the conditions for your gut bacteria and fungi (microbes of the microbiome) to do their job in aiding digestion and synthesising important molecules including some vitamins.

• Water

  • Potable water, fit for drinking and cooking.

  • Water is present in all drinks and you need a few litres per day and water makes up ~75% of your body.

  • It is the great solvent of the body and provides the main medium for transport and the chemical reactions in and out of cells.

  • In other words throughout your body including the contents of cells, circulatory system of the blood and your digestion system.

  • Water is also a reactant molecules in the digesting of food e.g. the hydrolysis of complex carbohydrates into smaller sugar molecules.

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Learning objectives for this section on diet and exercise

What is a healthy balanced diet? Know why are carbohydrates, lipids, vegetable oils, animal fats, protein, mineral ions, vitamins, dietary fibre (roughage) and water are all important in a healthy diet.

• Appreciate that a combination of a balanced diet and regular exercise is needed to help keep the body healthy.

• Be aware that our bodies provide a good environment for many microbes to live and multiply at our expense and can make us ill once they are inside our body.

• Our bodies need to be capable of stopping most microbes from getting in and dealing with any microbes which do get in.

• You are expected to be able to ...

  • ... evaluate information about the effect of food on health,

  • evaluate information about the effect of lifestyle on development of disease,

  • and analyse and evaluate claims made by slimming programmes, and slimming products.

    • There are lots of slimming products on the market eg from special diets ('Atkins Diet'), diet pills, low calorie milkshakes, soups, ready made meals etc. but how do you know which is likely to be effective?

    • BUT has the diet been properly scientifically tested and evaluated?

    • Have different research groups agreed on the effectiveness or otherwise of a particular diet strategy?

    • Is the only information on the diet, that supplied by the manufacturer?, so no independent review of the diet's effects on body weight, just the non-verified company's opinion!

    • In the end for many people the best thing is to take in less calories and eat a smaller better balanced nutritious diet AND take more exercise.

    • In all cases the necessary data and information will be provided in the exam paper.

    • Even a study of food labels is useful eg what energy does a food provide, what is the protein, carbohydrate/sugar, fat, fibre, minerals (salt, calcium, iodine) content etc.

      • See Vitamins E numbers, food additives, cooking chemistry!

      • and Natural vegetable oils, fats, margarine (GCSE chemistry pages)

  • What are the health implications for the content of the food in a meal OR what is the meal deficient in? ie are you having a good balanced diet meal?

  • Note that knowledge and understanding of ...

  • See also Respiration - aerobic and anaerobic  gcse biology revision notes

  • Appreciate the effects of having a balanced diet and regular exercise, as opposed to an unhealthy diet and lack of exercise.

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