Metabolism refers to the complex chemical reactions that occur in the body and are associated with taking food, breaking it down into nutrients and how the body uses those nutrients.
Metabolism is subdivided into anabolism and catabolism.
Anabolism builds up tissue from nutrients. It uses raw nutrients to build up complex molecules in the body, using body reactions, body enzymes to make the raw nutrients required to build up tissue.
Catabolism is breaking food nutrients down in order to gain energy. We use that energy to drive reactions in the body and generate waste.
We constantly need to replenish cells that are lost and to repair damage to the body. Macro-nutrients provide energy and are used in the process of catabolism, where we break down complex molecules and generate energy.
The energy currency of a cell is ATP (adenosine triphosphate).
A molecule of phosphate is added to adenosine diphosphate to create ATP.
Energy is measured in calories (imperial) or joules (international standard).
1 calorie = 4.1868 joules.
A 75 kg person will use 875 joules (209 calories) when walking at 5kph for 60 minutes. To lose 500 grams of weight, you must burn 15 kj or 3.6 kcal more than you take in as food.
That’s 17 hours of walking.
Catabolism and Energy
Aerobic Metabolism generates energy with oxygen, using the Krebs cycle (or citric acid cycle).
Krebs was a biochemist and pharmacologist who, in 1957, worked out that these very complex series of reactions in the body take place in every cell within the mitochondria (that generate ATP) which is the energy currency of the cell. It’s the process that’s used in aerobic respiration to produce energy.
The Krebs cycle takes place in the mitochondria within cells using up nutrients and oxygen, and producing carbon dioxide and water as waste products. In the process, adenosine diphosphate is converted to energy-rich ATP.
The body cannot store ATP. It has to be constantly made when the body needs energy.
The cycle turns twice for every glucose oxidised and two molecules of ATP are produced as a result. The Krebs Cycle is only part of how nutrients are used and how energy is generated in the cells. There are many other complex cellular mechanisms where bits of nutrients are pushed to different parts of the cell.
From there, everything becomes break-down products, to utilise the Krebs cycle and the electron transport chain in order to generate even more ATP. ATP is a molecule full of energy and from this molecule, the cell uses the energy stored chemically to drive all the reactions, including the reaction that builds up nutrients.
The three classes of nutrient available to cells (carbohydrates, lipids [fats] and proteins) are used in catabolic (energy producing and releasing reactions) and anabolic (energy storage and cell-building) ways.
Food is pushed into the citric acid or Krebs cycle, followed by the electron transport chain, which generates even more ATP. In order for cells to utilise aerobic metabolism, they require a good supply in order to deliver the nutrients to the cell, as well as oxygen.
Oxygen and nutrients allow aerobic metabolism to occur.
There are some situations where the body is forced to use anaerobic metabolism (without oxygen). This is similar to a fermentation reaction, forcing the cells to use a different series of reactions. This can only occur in limited degrees and not all tissues can do it. The heart and muscle tissue can for a limited time but the brain requires oxygen and cannot use anaerobic metabolism.
Anaerobic metabolism is very inefficient. It yields only 1/15th of the energy that aerobic metabolism can but is good as a short term generator in muscles during bursts of activity.
It is not possible for humans to use fermentation as their sole metabolic strategy – we don’t work well without oxygen.
Factors that Influence Intake.
There are many factors that influence general dietary intake:
- Ethnicity – cultural and national factors, often influenced by religion or tradition.
- Religion – influences what and when we eat, e.g. Kosher food or fasting for Lent.
- Geographical – location and accessibility to food
Ethnic groups share genes which is seen as similar facial features. Isolated ethnic groups such as Australian aborigines led to certain genes becoming common in the population which influenced their diet. Their response to dietary items after the introduction of white colonisers had a huge impact. Once adopting “white man’s” food, aboriginals became susceptible to certain diseases they have never experienced before, such as diabetes mellitus.
Factors for INDIVIDUAL dietary intake analysis
- Religion (practising or non-participating)
- Socio-economic status
- Dietary Acculturation
- Food Knowledge
- Cooking Skills
- Cooking Time
With modern technology, transportation and population mobility, people’s diets are levelling and becoming more uniform globally.
Recommended Daily Intake (RDI) centres around catabolism and anabolism.
Catabolism are all the reactions that our cells undertake to turn nutrients into energy. The other part is anabolism, which is the building up of tissue. We use nutrients and energy to build cellular components in cells and to grow and repair tissues.
An adult’s energy intake is about 8700kj
Fat should be less than 70 grams
Saturated Fat should be less than 24 grams
Sugar should be less than 90 grams
Carbohydrates (both complex and simple) is around 330 grams
Protein should be around 50 grams
Sodium (salt) should be less than 2.3 grams
Food Labels help us to identify nutrition and energy information.
Malnutrition is when the body doesn’t have enough nutrients or energy to carry out the chemical reactions that it needs. to. Instead it breaks down its own tissues and muscles and fat to maintain life.
Malnutrition is defined as a lack of proper nutrition, caused by not having enough to eat, not eating enough of the right things or being unable to use the food that is eaten.
Lack of nutrition may not always manifest to the whole body and cause extreme thinning. Lack of specific nutrients can lead to specific disorders or deficiencies in the body.
Iodine deficiency leads to thyroid disease with goitre. It can also lead to myxoedema (oedema means fluid retention). Myxoedema has a decreased metabolic rate, generalised oedema, mental dullness, heart and skin problems.
Protein deficiency leads to marasmus or wasting away.
Iron deficiency causes anaemia.
Vitamin D deficiency causes rickets in children and osteomalacia in adults.
Vitamin C deficiency causes scurvy.
Over nutrition is too much food coming into the body and is also known as hyperalimentation. Hyper meaning too much, alimentation meaning eating.
Common over nutrition occurs with
Obese, meaning extremely fat, means an overload of too many joules, too much energy and too many nutrients.
Hyperalimentation with protein
- commonly used by body builders
- builds up tissue mass
- results in hypertrophy of muscles
- commonly used with anabolic steroids
- are hormones like testosterone
- help the body incorporate nutrients into muscle
- lead to health issues like aggression, mania, suicide and liver tumours.
Hypervitaminosis of Vitamin A can build to toxic levels in the body and cause death.
- Calcium causes kidney disease and kidney stone and can impair the uptake of other minerals into the body.
- Iron can harm tissue, especially the heart.
- Copper causes high toxicity and damage to tissues.
Overweight and obese are two different degrees of the same thing. Weigh over what you should and you are overweight; you grossly overweight, you are obese.
Obesity can affect your lifespan.
In 2005, 20% of Australian adults were obese. Today is 30% and increasing.
To calculate Body Mass Index (BMI) use the following formula
If the result is 30kg per m² or more, you are obese.
BMI is an indicator only – you must also consider the physique of a person, their muscle mass and how much fat they have on their body.
Bariactrics is the medical speciality for the causes, prevention, and treatment of obesity. Various diseases affect obese people.
Metabolic, glandular and hormonal causes of obesity are rare cases. Most obesity cases are caused by the intake of too much food.
- is a persistent rise in the systemic blood pressure due to a variety of causes – obesity is one of them.
- occurs in obese people three times as much as in healthy adults.
- can cause heart enlargement, heart failure and strokes.
Coronary Heart Disease
- is the narrowing or blocking of artieries that supply the heart muscle with blood and oxygen. This is called atherosclerosis.
- Causes pain in the chest during stress or exertion
- obese people can get narrowing of other arteries as well, not just the heart muscle.
Gall Bladder Disease
- causes infections, inflammations and gall stones
- creates blockages to the biliary tract, which can be fatal
- is twice as likely in obese people
- causes chronic pain
- is on the rise in Australia due to obesity
- affects almost every organ in the body
- can be fatal
- is caused by a deficiency of insulin, which means a failure to metabolise starch and sugar which accumulate in the blood and urine.
The by-products of alternative fat metabolism disturb the acid base balance of the blood, risking convulsions and coma.
Excess body fat contributes to insulin resistance which is type two diabetes.
Diabetics have to monitor their diet, exercise regularly and may require regular insulin injections.
Glycemic Index (Gi)
- is a measure of how quickly sugar levels rise, and fall, after eating certain foods.
- eating food with a low Gi is considered beneficial
- diabetics especially need to be aware of Gi levels in food.
- different foods cause blood sugar levels to rise at different rates and levels.
- is often now shown on food labels
Gi estimates how much each gram of available carbohydrate (carbohydrates less fibre) raises a blood glucose level, relative to eating pure glucose. Pure glucose has a Gi of 100.
Low Gi foods release energy in a slower, more sustained way over a longer period of time.
High Gi foods are suitable for giving very short bursts of energy (eg, sprinters) and the blood sugar levels raise and fall rapidly.
A low Gi is 55 grams or less
A high Gi is 70 grams or more
- Wholegrain Pumpernickel Bread – Gi of 46
- Oatmeal Gi of 61
- Dates Gi of 105
- Lowfat yoghurt – Gi of 33