Why is nutrition important?
High values indicate excessive fat stores and low values indicate insufficient fat stores. Your BMI can therefore be used like a diagnostic tool for both over-nutrition and under-nutrition. If your BMI is between 25.0 and 29.9 you’re classisfied as overweight. If it is above 30.0, you are classified as obese. The healthy BMI range is 18.5-24.9. However, the BMI is best used together with waist circumference.
BMI calculations will overestimate the total amount of body fat for:
Body builders;Some high performance athletes;Pregnant women.BMI calculations will underestimate the amount of body fat for:
The elderly;Those with a physical disability who are unable to walk and may have muscle wasting.BMI isn’t the perfect measure of weight and health risk. A person’s waist circumference is a better predictor of health risk than BMI.
BMI and kids
The healthy weight range for adults of the BMI of 20 to 25 isn’t an appropriate measure for children.
For adults who’ve stopped growing, a rise in BMI is often caused by a rise in body fat. But as children grow, their amount of body fat changes and so will their BMI. for example, BMI usually decreases over the preschool years and then increases into adulthood.
For this reason, a BMI calculation for a child or a teenager must be compared against age and gender percentile charts. These charts needs to be used only by health professionals for instance your general practitioner, child health nurse, or dietitian.
Body fat distribution and health riskAnyone’s waist circumference is a better predictor of health risk than BMI. Having fat across the abdomen or even a ‘pot belly’, regardless of the body size, means you are more likely to develop certain obesity-related health conditions. Fat predominantly deposited around the hips and buttocks doesn’t appear to own a similar risk. Men, in particular, often deposit weight inside the waist region.
Studies have shown of the fact that distribution of body fat is related to an increased prevalence of diabetes, hypertension, high cholesterol and cardiovascular disease.
Generally, the association between health risks and body fat distribution is as follows:
Least risk – slim (no pot belly);Moderate risk – overweight with no pot belly;Moderate to high risk – slim with pot belly;High risk – overweight with pot belly.
Waist circumference and health risks
Waist circumference can be used to indicate health risk.
For men:
94 cm or more – increased risk;102 cm or more – substantially increased risk.For girls:
80 cm or more – increased risk;88 cm or more – substantially increased risk.Being physically active, avoiding smoking and eating unsaturated fat instead of saturated fat have been shown to decrease the risk of developing abdominal obesity.
When there is an imbalance between your nutrient requirements plus your intake, malnutrition sets in. There are a couple of forms of malnutrition – under-nutrition and over-nutrition. Over-nutrition is common in many developed countries, including Australia.
Associated health conditions
Dietary factors are associated with some leading causes of death, for instance:
Coronary heart disease;Some kinds of cancer;Stroke;Type 2 diabetes mellitus.
Essential nutrient requirements
Nutrients can be described because the chemical components of food and can be classified into six broad groups: carbohydrates, proteins, fats, vitamins, minerals and water. Water is not technically a nutrient, but it is important for the utilisation of nutrients. Nutrients perform various functions in our bodies, including energy provision and maintaining vital processes such as digestion, breathing, growth and development.
Energy balance
Your energy requirement is dependent upon your age, size and activity level. If your energy intake equals the amount of energy you expend, you then are in energy balance. If your intake exceeds your expenditure, the excess energy is converted to body fat and you gain weight. On the other hand, if your intake is less than your expenditure, the body uses up fat stores and you lose weight. Therefore, for weight to remain stable, the total quantity of calories which can be consumed must not exceed the total that is used up through metabolic processes (e.g. exercising, sweating, breathing). Energy intake must match energy output. The common energy intake is about 2800 kcal/day for men and 1800 kcal/day for women, although this varies with body size and activity level.
Carbohydrates
Carbohydrates can be classified as monosaccharide (e.g. glucose, fructose, galactose), disaccharide (e.g. sucrose,lactose, maltose) and polysaccharide (e.g. starch, fibre). Carbohydrates must be reduced to the simplest form of glucose (through digestion) before your body can make use of them. Carbohydrates should structure a minimum of 55% of your total energy intake. The brain is often a special part of your body that depends primarily on glucose for its energy and requires about 100 g/day of glucose for fuel. In some situations, the body can compensate for decreased levels of carbohydrates by using alternative energy pathways for instance burning fatty acids.
Protein
Protein is important for the production, maintenance and repair of tissues in the body. When energy intake is insufficient, protein intake must be raised. It’s because ingested proteins are preferentially directed towards glucose (sugar) synthesis and oxidation. The tissues and organs in your body are made up of protein and protein compounds. Enzymes (biological catalysts), antibodies and hormones also consist of protein. The building blocks of protein are called amino acids. the body can make all of this 20 amino acids except eight, which are termed essential amino acids. These are isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine. Histidine is important only for infants. The number and nature of amino acids present in a particular protein determines that protein’s characteristics.
For adults, the recommended dietary allowance of protein is about 0.75 g/kg body weight per day. Animal products tend to have the highest quantity of proteins, followed by legumes (beans), cereals (rice, wheat, corn) and roots. Animal protein (from meat, eggs, fish, milk) contains all the essential amino acids and is generally referred to as ‘complete’ or ‘high biological value’ protein. Protein derived from plants lack one or two essential amino acids. However, a good combination of plant-based protein can be of equal value to animal protein. for instance, legumes lack methionine but have adequate amounts of lysine. Cereals, on the other hand, lack lysine but have a lot of methionine. Therefore, a mixture of rice and beans will supply all the essential amino acids.
Excess protein cannot be stored in the body, so we need to consume protein daily. Consuming too much protein is not recommended because it promotes increased calcium excretion through urine, which increases the risk of developing osteoporosis. Additionally, too much protein intake may lead to a greater concentration of this amino acid homocysteinein the blood, and the subsequent conversion to thiolactone. Thiolactone is associated with increased levels of atherosclerosis and endothelial damage.
Fats and oilsMost of the fats we consume occur in foods as triglycerides. A triglyceride is comprised of three fatty acid molecules attached to a glycerol molecule. Fatty acids are made up of carbon and hydrogen atoms which enable it to be either saturated or unsaturated. Saturated fatty acids (SFA) have the most number of hydrogen atoms attached to the carbon chain, while unsaturated fatty acids have lower than the specified hydrogen atoms. for example, monounsaturated fatty acids (e.g. oleic acid) have two hydrogen atoms missing. Monounsaturated fats are found mainly in nuts, avocados, olive oil, canola oil, grapeseed oil, peanut oil, flaxseed oil, sesame oil, corn oil, safflower oil, sunflower oil, etc.
Polyunsaturated fatty acids (PUFA) have more than two hydrogen atoms missing (e.g. linoleic acid and linolenic acid). Linoleic and linolenic acids are regarded as essential fatty acids (EFAs) because the body cannot make them. There are two categories of EFAs: omega-3 and omega-6. The number that comes after “omega-” represents the position of the first double bond, counting from the terminal methyl group on the molecule. Omega-3 fatty acids are derived from linolenic acid and omega-6 from linoleic acid. Alpha linolenic acid (ALA) is converted into eicosapentaenoic acid (EPA), and later into docosahexaenoic acid (DHA) in the body. Sources of omega-3 fats include salmon, mackerel, sardines, anchovies, tuna, flaxseed oil, walnuts, etc. Sources of omega-6 fats include palm oil, soybean oil, canola oil, sunflower oil, nuts, etc. Evidence from research indicates that omega-3 fatty acids reduceinflammation and help prevent certain chronic diseases for instance cardiovascular disease and arthritis. Omega-3 fatty acids are highly concentrated during the brain and appear to be crucial to brain function as well as normal growth and development. Infants who do not get enough omega-3 fatty acids from their mothers during pregnancy are at risk of mental impairment.
Generally, saturated fatty acids raise blood cholesterol levels, whereas unsaturated fatty acids lower them. Saturated fats are found in foods for instance butter, meat and dairy fats. Trans fats are artificially created during food processing. In your body, trans fats act in a similar way to saturated fats and may raise cholesterol levels. These fats are considered to be harmful to your health. Trans fats are found mainly in deep-fried fast foods and processed foods made with margarine.
Fats are a concentrated and rich source of energy. It is strongly recommended that your total fat intake is no more than 30% of the energy (calorie/kilojoule) intake. Polyunsaturated fat needs to be lower than 10% of energy, and saturated fat and trans fat together should be less than 10%. The rest of your fat intake should consist of monounsaturated fat.
Vitamins
Vitamins constitute a group of nutrients which can be needed in small quantities. Like amino and fatty acids, most vitamins cannot be made in the body and must be obtained from dietary sources. Only vitamin D can be manufactured by the body. Essential vitamins are grouped into two families: water soluble and fat soluble. Water soluble vitamins can dissolve in water (thiamine, riboflavin, niacin, vitamin C, folic acid). These cannot be stored by the body and should be consumed every day. Fat soluble vitamins can dissolve in a fat medium (vitamins A, D, E, K). These are taken into our bodies when we consume fat-containing foods. Vitamins are needed for various reasons, including the formation of hormones and blood cells. They typically act as coenzymes. An inadequate supply of vitamins in our diet leads to the development of diseases.
Vitamin A: Derived from carotene, vitamin A affects vision, reproduction, and the formation and maintenance ofskin, mucous membranes, bones and teeth. Deficiency ends in night blindness (difficulty in adapting to darkness). the body obtains vitamin A from either carotene (vitamin A precursor) or by absorbing ready-made vitamin A from plant-eating organisms. Carotene is obtained in dark green leafy vegetables and yellow-orange fruit/vegetables. Pre formed vitamin A is found in milk, butter, cheese, egg yolk, liver, and fish-liver oil.Vitamin B complex: The vitamin B complex is a mix of eight essential vitamins necessary to enhanceimmune and nervous system function, and promote cell growth and division. Pregnant or lactating women,alcoholics and the elderly are more likely to suffer from vitamin B deficiency.Vitamin B1 (thiamine): Thiamine, or vitamin B1, acts as a catalyst in carbohydrate metabolism. Thiamine deficiency causes beriberi, a vitamin deficiency disorder characterised by muscular weakness, swelling of the heart and leg cramps. In severe cases, beriberi may result in heart failure and death. The richest dietary sources of thiamine are pork, organ meats (liver, heart, and kidney), brewer’s yeast, lean meats, eggs, leafy green vegetables, whole or enriched cereals, wheat germ, berries, nuts, and legumes.Vitamin B2 (riboflavin): Riboflavin, or vitamin B2, acts like a coenzyme in the metabolism of carbohydrates, fats, and respiratory proteins. One of the best sources of riboflavin are liver, milk, meat, dark green vegetables, whole grain and enriched cereals, pasta, bread and mushrooms.Vitamin B6 (pyroxidine): Pyridoxine, or vitamin B6, is critical for the absorption and metabolism of amino acids. It also plays a role in the body’s use of fats and in the formation of red blood cells. The top sources of pyridoxine are whole grains, cereals, bread, liver, avocados, spinach, green beans and bananas.Folic acid (vitamin B9 or folacin): Folic acid is a coenzyme needed for forming body protein and haemoglobin. Folic acid deficiency is related to neural tube defects. Dietary sources are organ meats, leafy green vegetables, legumes, nuts, whole grains and brewer’s yeast. Folic acid is lost in foods stored at room temperature and during cooking.Minerals
Minerals are essential, acting as cofactors of enzymes (i.e. enzymes would not exist or function without minerals). Some of the minerals necessary for health are:
Calcium: Calcium is an important mineral in the diet, especially for women at menopause. The major function of calcium is to build and help maintain strong bones. It can stop the onset of osteoporosis and reduce bone loss and fragility. It is involved in blood clotting. Calcium deficiency can develop when there is a lack of vitamin D.Iron: Iron in food exists as haem and non-haem iron. Haem iron, found in white meat, is relatively well (20-30%) absorbed. Non-haem iron, found mostly in cereals, pulses, certain vegetables (e.g. spinach) and eggs, is generally less well absorbed. Non-haem iron absorption depends on other factors inside the diet. for example, vitamin C and animal protein enhance non-haem iron absorption, while tea, coffee and phytates inhibit it.Zinc: Zinc represents only 0.003% of the human body, but is important for synthesising protein, DNA and RNA. It is required for growth in all stages of life. Sources include meats, oysters and other seafood, milk, and egg yolk.Water
For adults, 1-1.5 mL water per kcal of energy expenditure is often sufficient to allow for normal changes in physical activity, sweating, and dietary solute load. Water losses consist of 50-100 mL/day through faeces (stools), 500-1000 mL/day by evaporation, and approximately 1000 mL/day through urine. If external losses increase, we must increase the amount of water we ingest. In special circumstances for instance diarrhoea and vomiting, water requirements further increase.
It is critical that nutrients in our body are available in sufficient amounts and in the right proportions. This can be achieved by eating a balanced diet. We must eat a variety of foods, since different foods contain different nutrients in varying amounts. In stressing the importance of variety in our diet, Nutrition Australia encourages all Australians to make sure that their daily diet includes 30 individual foods. This may appear impossible at first thought, but in reality can easily be attained by eating typical diets based on carefully selected foods. Food selection based on the ‘Healthy Eating Pyramid’ can assist you in planning your meals for a balanced and healthy diet.
A healthy diet consists mainly of plant foods (e.g. fruits and vegetables, potatoes, cereals, etc.) and moderate amounts of animal products (e.g. milk, fish, lean red meat and poultry). Fats and oils should normally provide less than 30% of our energy, and less than 10% of this should be saturated fat. Lean white meat, poultry and fish, eggs and dairy foods are rich sources of animal protein. Dairy foods, aside from supplying quality protein, are good sources of calcium. Good vegetable sources of protein include legumes (e.g. peanuts, lentils, kidney beans), soya products (e.g. tofu), grains, nuts and seeds.
Healthy eating pyramid
The food pyramid is often a simple practical guide to selecting varied foods for meals. The Australian Nutrition Foundation Inc. (Nutrition Australia) has developed its own food pyramid. The rationale behind the food pyramid emphasises the need to include generous amounts of plant-based foods (cereals, legumes, fruits and vegetables) and moderate amounts of animal products (meat, fish, milk, eggs) in our diets. Furthermore, our diet should contain only small amounts of energy-dense foods (e.g. sugar, fats and oils). The base of the pyramid (plant-based foods) is broad, and the top (animal products) is narrow. Eating according to the structure of the meals pyramid ensures we consume a healthy diet. With care the food pyramid can also assist vegetarians and vegans to consume a nutritionally balanced diet, although some people will require dietary supplements (e.g. vegans will require vitamin B12).
Glycaemic index and glycaemic load
Carbohydrates should structure a minimum of 55% of our total daily energy intake. The quality and quantity of these carbohydrates are important in blood sugar and appetite control. After you consume carbohydrate-containing foods, your pancreas secretes insulin to break the carbohydrates down into their building blocks. Insulin acts to reduce blood glucose levels. When your blood glucose levels decrease to a particular level, your brain is shipped a sign and you become hungry again.
Though different foods may contain exactly the same amounts of carbohydrate, their effects on blood glucose control may be very different. This has lead to the development of measures for instance the glycaemic index (GI) and glycaemic load(GL) of your food product. The concept of GI was formulated by Jenkins and colleagues in 1984. They found that blood glucose response to carbohydrate foods is independent of the amount of carbohydrates they contain. The limitation of the GI lies in the difficulty of translating the concept into practice, since the glycaemic effect of foods isn’t constant which enable it to vary depending on the way the meals is cooked.
Low GI and GL foods are shown to be connected to health advantages such as decreased blood sugar levels. Foods with a low GI (lower than 55) cause a slower and lower rise in blood glucose levels. These include breads for instance mixed-grain and oat breads, barley, pasta, noodles, beans, sweet potatoes, green peas and milk. Foods with an increased GI (greater than 70) cause a faster and higher rise in blood glucose levels. High GI foods include white bread, steamed white rice and chips.
By incorporating low GI foods into your diet, you will bring down the average GI of the meal, have a lower, slower blood sugar response to the meal and feel ‘full’ for extended. By consuming low GI foods, you tend to be more more likely to be satisfied and feel full for longer periods of time. This helps you to maintain a healthy weight and avoid diseases for instance heart problems, diabetes and many cancers.
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