Macronutrients Flashcards
How are nutrients classed?
macronutrients (carbohydrates, proteins, lipids), micronutrients (vitamins, minerals), water and alcohol
Function of macronutrients
provide chemical energy that can be converted into electrical (ionic gradients), mechanical (contraction), thermal and chemical energy (protein synthesis)
How is energy measured?
Calorie (1 Cal = 1kcal = 1000 calories) and Joule (J)
What nutrients provide energy (calories)?
macronutrients and alcohol
Which macronutrient has the greatest energy density?
Fat (9kcal/g) compared to protein (4kcal/g) and CHO (3.75kcal/g)
What 3 components make up the Total Energy Expenditure (TEE)?
Basal Metabolic Rate (BMR 60-75% of TEE), physical activity (10-40%), thermogenesis (10-20%)
What are the forms of energy storage?
- fat
- glycogen
- protein
Factors that affect energy requirements
body size, age, activity, pregnancy/lactation, disease, trauma and treatments
How can energy expenditure be measured?
direct calorimetry (metabolic chamber), indirect calorimetry (O2/CO2 measurements), doubly labelled water
How is energy intake measured?
data from National Diet Nutrition Survey
What are carbohydrates?
compounds made of C, H, O
Role of carbohydrates in the body
provide energy (40-80% of total energy intake)
How can carbohydrates be classified based on their chemical structure?
monosaccharides, disaccharides, polysaccharides
What is the nutritional classification of carbohydrates?
- sugars (mono/disaccharides)
- starches
- non-starch polysaccharide (dietary fibre)
Why are complex carbohydrates better for health?
not in a readily available form for absorption (e.g. starch, other polysaccharides, resistant oligosaccharides)
What is the difference between available and unavailable carbohydrates?
available CHO are glycaemic and can be digested e.g. starch and sugars. Unavailable carbohydrates are non-glycaemic (fermented by bacteria to produce short-chain FAs and gases) e.g. cellulose and hemicellulose
What are polyols?
sugar alcohols
Examples of polysaccharides
starch, glycogen, non-starch polysaccharides (NSP)
What is the difference between extrinsic and intrinsic sugar?
extrinsic sugars can be milk and milk products (e.g. lactose) or non-milk (e.g. sucrose), and intrinsic sugars are in fruit and vegetables (e.g. fructose and glucose)
Which type of sugar is most cariogenic?
extrinsic, non-milk sugars
What are added sugars?
sugars and syrups added by manufacturer (does not include sugars in fruit juice or honey)
What are free sugars?
added sugars plus sugars naturally present in honey, syrups and unsweetened fruit juice (not including milk and sugars contained in cellular structure)
What are total sugars?
total amount of sugars from all sources (free sugars plus those from milk and in structure of foods e.g. fruit and vegetables
Which sugars are used in diabetic products?
sugar alcohols (absorbed from gut more slowly)
What are oligosaccharides?
short chain CHO (3-6 monosaccharides) found in plant seeds and legumes
How are oligosaccharides broken down?
cannot be broken down by digestive enzymes, instead is fermented in large intestine
What are dextrins?
short chains of glucose formed by partial hydrolysis of starch
What is the carbohydrate store in humans?
glycogen
What is the storage carbohydrate in plants?
starch
What are the 2 types of starch?
amylose and amylopectin
Structure of amylose
unbranched chain of glucose with a1-4 glycosidic bonds
Structure of amylopectin
long, highly branched polymer of glucose linked by a1,4 glycosidic bonds and branching every 15-30 glucose units via a1,6 glycosidic bonds
In what form is starch digestible?
indigestible when raw, digestible when cooked
How is starch broken down?
pancreatic amylase
Dietary fibre definition
portion of food derived from cellular walls of plants which is poorly digested in humans
3 categories of dietary fibre
non-starch polysaccharide (NSP) e.g. cellulose, and non-cellulose polysaccharides (pectins, glucans), resistant oligosaccharides (FOS, GOS), resistant starch
What is resistant starch?
a form of dietary fibre composed of starch and starch degradation products not fully digested in small intestine
What are oligosaccharides commonly known as?
prebiotics
What happens to food not digested in the small intestine?
fermented by colonic microflora to short chain fatty acids and gases
3 basic types of short chain fatty acids (SCFAs)
acetic acid, propionic acid, butyric acid
Function of short chain fatty acids
health benefits (e.g. propionic acid lowers cholesterol) and act as an energy source
What is the maximum percentage of daily energy intake that free sugars should account for?
5%
Recommended fibre daily intake
30 g/day
What are fats?
compounds made of carbon, hydrogen and oxygen
Role of dietary fats
energy, essential fatty acids, fat-soluble vitamins
What fats are found in food?
mainly triacylglycerols. Also cholesterol, plant sterols, phospholipids, fat soluble vitamins
Structure of triacylglycerol
1 glycerol + 3 FAs
Structure of a phospholipid
1 glycerol + 1 phosphate + 2 FAs
Structure of a sterol
1 FA
What is the basic structure of a fatty acid
CH3(CH2)nCOOH
Which structural factors affect properties of fatty acids?
number of C atoms (chain length), presence of double bonds (saturated or unsaturated)
Term given to fatty acid with one double bond
monounsaturated
Term given to fatty acid with more than one double bond
polyunsaturated
What is the configuration of double bonds in unsaturated fats e.g. vegetable oils?
cis (kink created)
Which type of isomer of fatty acids is industrially produced?
trans (hydrogenated vegetable oils)
Examples of essential fatty acids (EFA)
linoleic acid (LA), alpha-linolenic acid (ALA), LC PUFA AA, EPA, DHA
Roles of essential fatty acids (EFA)
cell membranes, biologically active compounds e.g. eicosanoids, growth and development
Examples of eicosanoids
prostacyclins (vasodilation, inhibit platelet aggregation), thromboxane (vasoconstriction, stimulate platelet aggregation), leukotrienes (promotes inflammation)
Which aspects of growth and development require essential fatty acids?
brain, nervous tissue membrane, photoreceptors in retina
Functions of proteins
structural and functional components of cells, provide 10-15% of dietary energy supply
How can amino acids be classified by essentiality?
essential, non-essential, conditionally essential amino acids
What are essential amino acids?
aa that cannot be synthesised in body
What are non-essential amino acids?
can be synthesised from precursors in sufficient amounts
What are conditionally essential amino acids?
precursor for aa may be insufficient in certain situations (e.g. during growth/childhood)
Examples of essential/indispensable amino acids
isoleucine, leucine, threonine, lysine, valine
Examples of non-essential/dispensable amino acids
alanine, arginine, aspartic acid, asparagine, cysteine
Examples of conditionally essential amino acids
cysteine, tyrosine, arginine
What determines protein structure?
sequence of the amino acid chain and arrangement of amino acid chains
Example of a fibrous protein that is elastic (single alpha-helix)
keratin
Example of a fibrous protein that is inelastic (more than one alpha-helix)
collagen
Example of a globular protein made up of a single folded chain
myoglobin
Example of a globular protein made up of more than one folded chain
haemoglobin
What bond joins adjacent amino acids?
peptide bond (NH-CO)
What is a dipeptide?
2 amino acids joined by peptide linkages
What is a polypeptide?
more than 2 amino acids joined by peptide linkages
What does protein quality refer to?
which amino acids are present (no just quantity of protein consumed)
What is the RNI of protein?
0.75g/kg body weight/day
