Exam 3 March Winter 2017, questions PDF

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Energy is not a nutrient – but it is released from food via chemical reactions during digestion. The macronutrients (carbohydrates, proteins and fats) are also known as the energy nutrients since they contribute energy to the body. Alcohol also contributes energy to the body – but it is not a nutrient as it does not provide any nutrition, hence it is often referred to as “empty calories”. The metric unit of energy is Joules (the old measure was calories). 1000 joules (J) = 1 kilojoule (kJ) Calories are more confusing. 1 kilocalorie = 1000 calories = 1 Calorie (note the capitalisation). 1 Calorie = 4.18 kJ Energy in each macronutrient and alcohol: Nutrient

kcal/g

kJ/g

Carbohydrate

4

17

Protein

4

17

Fat

9

37

(Alcohol)

(7)

(29)

Carbohydrates are chemical compounds made up of carbon, hydrogen and oxygen atoms. They can be divided into 2 categories – complex carbohydrates (such as starches) and simple carbohydrates (sugars). Carbohydrates are broken down during digestion to glucose which is the body’s (especially the brain’s) main source of fuel. Examples include: bread, rice, pasta, potatoes and sugar.

There are 6 simple carbohydrates: Monosaccharides (“mono” meaning one sugar unit)   Glucose (Blood Sugar)  Fructose (Fruit and Honey Sugar)  Galactose (Part of Milk Sugar) Disaccharides (“di” meaning two sugar units, formed by the combination of 2 monosaccharides) 

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Sucrose (Table Sugar) Lactose (Milk Sugar) Maltose (Malt Sugar, used in brewing)

The important disaccharides in nutrition are sucrose, lactose and maltose. All contain glucose. Sucrose (Glucose + Fructose) – Table Sugar Lactose (Glucose + Galactose) – Milk Sugar Maltose (Glucose + Glucose) – Malt Sugar Once digested into monosaccharides and absorbed, the fructose and galactose are converted to glucose by the liver. Complex carbohydrates are also known as polysaccharides. Poly is Greek for “many” since they contain many monosaccharide units joined together. Glycogen, starch and dietary fibre are the three most important complex carbohydrates in nutrition. Glycogen is a storage molecule found in the muscles and liver. Starch usually consists of around 3000 glucose molecules joined together and is a good energy source for the body. Dietary fibre is indigestible plant material. It can be divided into insoluble (such as cellulose) and soluble fibre (such as the fibre found in fruit, vegetables, gums, and psyllium). Proteins are chemical compounds made up of carbon, hydrogen, oxygen and nitrogen atoms. Some sulfur is also found in proteins. Examples of proteins include: meat, fish, eggs, milk and nuts. Protein accounts for around 17% of body weight. Proteins are made of units called amino acids. There are 20 amino acids and 9 are considered “essential”. This means that they cannot be manufactured by the body and must come via diet. Essential AA

Nonessential AA

Histidine

Alanine

Isoleucine

Arginine

Leucine

Asparagine

Lysine

Aspartic Acid

Methionine

Cysteine

Phenylalanine

Glutamic acid

Threonine

Glutamine

Tryptophan

Glycine

Valine

Proline

Serine

Tyrosine

• • • •

Proteins containing all essential amino acids in the correct proportions for use by the body are known as complete proteins or “high quality” proteins. Complete proteins are only found in animal proteins (meat, milk, eggs), soy and quinoa. Incomplete (or “low quality”) protein is deficient (i.e. it may be present but in low amounts) in at least one essential amino acid. By eating a variety of foods, a full complement of amino acids can be attained through the diet. Plant protein can be of low quality – even staple foods are deficient: Wheat in lysine Rice in threonine Corn in tryptophan Legumes in methionine, cysteine, tryptophan Therefore, this is an important issue in vegetarian diets, especially vegans, who do not eat milk and eggs. Some animal proteins are also incomplete, e.g. gelatine – an incomplete animal protein no tryptophan at all and low in isoleucine, threonine and methionine. Protein has varied roles in the body including - regulating body processes (hormones, neurotransmitters and enzymes), promoting growth and development (muscles and other tissues), fighting infections (antibodies), transporting nutrients (haemoglobin carries oxygen to cells), fluid balance (albumins and globulins in blood), acid-base balance (protein buffers) - rather than being used for energy. Using protein as an energy source places a large stress on the liver and kidneys and is generally avoided by the body unless there is limited supply of carbohydrates. Most individuals eating a standard Western diet consume more protein than is required each day. The amount of protein needed each day is 0.8 g of protein / kg of healthy body weight for an average person. Excess protein is stored in the body as fat. Individuals who undertake regular vigorous exercise have higher protein requirements (1.5 – 2 g / kg). Pregnant and breastfeeding women also have higher protein requirements. Scientifically, fats are known as lipids. They are chemical compounds made up of carbon, hydrogen and oxygen atoms. Many fats are known as triglycerides and consist of a glycerol unit and 3 fatty acids. There are two essential fatty acids – these must be consumed in the diet. They are linoleic acid (“omega-6”) and linolenic acid (“omega-3”). The balance between the omega-3 and 6 compounds is important for conditions involving inflammation like arthritis. The ratio should between 5:1 and 10:1. Age

Adequate Intake (AI) Linoleic acid (ω-6)

a-linolenic acid (ω-3)

Total fish LC ω-3 (DHA+EPA+DPA)

1-3 yr

5 g/day

0.5 g/day

40 mg/day

4-8 yr

8 g/day

0.8 g/day

55 mg/day

Boys and girls

Boys

9-13 yr

10 g/day

1.0 g/day

70 mg/day

14-18 yr

12 g/day

1.2 g/day

125 mg/day

9-13 yr

8 g/day

0.8 g/day

70 mg/day

14-18 yr

8 g/day

0.8 g/day

85 mg/day

Men

13 g/day

1.3 g/day

160 mg/day

Women

8 g/day

0.8 g/day

90 mg/day

Girls

Adults 19+ yr

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These are needed for immune function, vision, and for the production of hormone-like compounds and are a structural component of cell membranes. The hormone-like compounds made from the essential fatty acids are important for regulating blood pressure, body temperature, pain, childbirth, clotting, stomach secretions, the immune system defence against infections and allergic and inflammatory reactions. Triglycerides are the main form of energy storage in the body. If a lipid is a solid at room temperature, it is called a fat and if it is a liquid at room temperature, it is called an oil. Triglyceride properties differ due to differences in the length of the fatty acids (more or less atoms in the chain) and due to the type of chemical bonding (single or double carbon bonds). If a lipid has double bonds in its chains, it is called “unsaturated”. If it has one double bond, it is called “monounsaturated” (such as olive oil and avocado oil) and if it has multiple double bonds then it is called “polyunsaturated” (such as sunflower oil, safflower oil, canola oil and linseed oil). These all tend to be liquids at room temperature (i.e. oils). If a lipid has single bonds in its chains then it is known as a saturated fat and tends to be solid and room temperature. Animal fats are high in saturated fat, as are palm oil and coconut oil. Trans fatty acids have a slightly different chemical structure to most fatty acids (which are known as cis fatty acids). Due to this structure, they are treated differently by the body and can raise blood cholesterol, like saturated fatty acids. Trans fatty acids occur naturally in low levels but are found in much higher concentrations in manufactured fats and oils, such as margarines, shortening and many commercially prepared baked goods. They are often labelled as “hydrogenated oils”. Cholesterol is also a lipid. It is an essential component of cell membranes (with phospholipids – allows fat soluble compounds in and out). Produced by the liver Found only in animal products Forms important hormones (oestrogen, testosterone, vitamin D) Precursor to bile acids (made by liver – emulsifiers) Aids with transport of lipids/triglycerides in the bloodstream Sources of cholesterol: foods of animal origin only We obtain one third of our cholesterol from the diet, unless you are a complete vegetarian (vegan), The rest (two thirds) we make ourselves, therefore cholesterol is not an essential nutrient 40-60% of dietary cholesterol is absorbed Plant sterols (phytosterols) – in plant foods and margarine (e.g. ProActive) reduce body’s absorption of cholesterol and lower blood cholesterol Saturated fatty acids and trans monounsaturated fatty acids raise blood cholesterol Polyunsaturated and cis monounsaturated fatty acids decrease blood cholesterol The “Standard Adult” dietary requirement is 8700 kJ per day. This is defined by our government law in the Food Standards for Australia and New Zealand (FSANZ) Code 1.1.1

Nutrient

Quantity per day

Energy

kJ (calculated)

% of total kJ

8700

Carbohydrates

310 grams

5180

~60%

Fat

70 grams

2640

~30%

Protein

50 grams

835

~10%

The 60:30:10 rule comes from the calculated nutrient requirements for a standard adult.  55-65% of energy from Carbohydrates (with ≤10% from refined sugar)  ≤30% of energy from Fats (with...