Week 1- Nutrition, body weight and homeostasis Flashcards
Energy
Capacity to do work
What do living cells require energy for?
- Biosynthetic work - synthesis of cellular components
- Transport work across cell membranes - maintenance of ion gradients, uptake of nutrients
- Muscle contraction
- Nervous conduction
- Osmotic work - kidney
- Thermogenesis
- Detoxification
SI unit of food energy
Kilojoule
1 kilocalorie equals how many kilojoules?
1 kcal = 4.2 kilojoules
Which type of energy is used to drive the energy-requiring activities of the cells in the human body?
Chemical bond energy: used directly without prior conversion to heat, as the human body is isothermal and under this condition heat energy cannot be used for work
Chemical bond energy
-Form of potential (stored) energy
Exergonic
Energy released is greater than the energy input
Energy is produced by oxidation of which fuel molecules?
- Carbohydrates
- Proteins
- Fat
- Alcohol
Components of daily energy expenditure:
- Energy to support our basal metabolism - Basal metabolic rate
- Energy for voluntary physical activities
- Energy required to process the food we eat (diet-induced thermogenesis)
Basal metabolic rate
Measure of the basal energy required to maintain life - functioning of the various tissues of the body at physical, digestive and emotional rest Major tissues contributing to BMR: 1. Skeletal muscle = 30% 2. Central nervous system = 20% 3. Liver = 20% 4. Heart = 10%
Rough estimate of BMR (kJ/24 hours): multiplying body weight in kg by 100
Factors that affect basal metabolic rate:
- Controlled by thyroid hormones: excessive secretion (hyperthyroidism) increases BMR
- Gender: BMR is lower for women than for men of the same weight as women have more adipose tissue that is less metabolically active than lean tissue
- Temperature: BMR increases by 10% for every 1 degree celcius increase in body temperature
- Pregnancy and lactation increase BMR
Voluntary physical activity
-Energy required by skeletal and cardiac muscle
Rough estimate of total daily energy required for physical activity:
1. BMR + 30% of the BMR: sedentary person
2. BMR + 60-70% of the BMR for a person who engages in approximately 2 hours of moderate exercise a day
3. BMR + 100% of BMR for a person who does several hours of heavy exercise a day
Diet-induced thermogenesis:
- Following the ingestion of our food, our metabolic rate increases because energy is required to digest, absorb, distribute and store nutrients.
- Energy required to process the food is approximately equal to 10% of the energy content of the ingested food
Macronutrients
Nutrients that are required in relatively large amounts
Examples: carbohydrates, fat, protein
Recommended dietary allowance (RDA)
- Quantities of nutrients required to keep the general population in good health
- Considerably higher than the minimum amounts required to prevent deficiency symptoms
Estimated average requirement
For energy or a nutrient is the amount that any stated group of people will on average need
-RDA and EAR: represents an average need over a number of days
Energy content of fat, carbohydrate, proteins and alcohol
- Fat: 37 kJ/g
- Carbohydrate: 17 kJ/g
- Protein: 17 kJ/g
- Alcohol: 29 kJ/g
Which tissues need a constant supply of glucose as a source of energy?
- Brain
2. Red blood cells
Alternate ways that body can produce glucose:
- Gluconeogenesis from certain amino acids
- Glycerol released from the hydrolysis of triacylglycerol
- Can be synthesised from dietary sugars such as galactose and fructose
Importance of fats in the diet:
- Energy yield sometimes 2.2 times greater than carbohydrates or proteins
- Necessary for absorption of fat-soluble vitamins (A,D, E and K) from the gut
- Certain polyunsaturated fatty acids (the essential fatty acids) notably linoleic and linolenic acids, which are structural components of cell membranes and precursors of important regulatory molecules (eicosanoids)
Why protein is required in the diet:
- Amino acids are used in the synthesis of a number of essential N- containing compounds including creatine, purines, pyridimines and haem (part of haemoglobin)
- To remain in zero nitrogen balance (nitrogen intake=nitrogen loss), an adult male has an average daily requirement of about 35 grams
- Growing children and women during pregnancy need more protein and normally show a positive nitrogen balance (nitrogen intake > loss)
- To supply essential amino acids which are not synthesised by the body
Proteins of animal origin: contain a high proportion of the essential amino acids unlike proteins of vegetable origin
Other dietary requirements/essential nutrients:
- Water:
-Adult: 50-60% of body weight is water
-Average water loss is approximately 2.5 litres per day
-Ways water is lost: urine, expired air, through the skin, faeces - Dietary fibre:
Non-digestible plant material such as cellulose is necessary for normal bowel function - Minerals and vitamins: some vitamins and minerals have important antioxidant properties in the body such as vitamin C, E and selenium
Measures of health:
- Body mass index
2. Waist to hip ratio: better measure of obesity and the risk of cardiovascular disease
Obesity
Chronic condition characterised by excess body fat
