E5. Macronutrients Flashcards
what are the dietary macronutrients?
-fats
-proteins
-carbohydrates
-they provide different energy values
solubility of a lipid?
Insoluble or poorly soluble in water but soluble in organic solvents
Functions of a lipid?
-Fuel & energy store
-Insulation
-Protection- eg fat around kidneys
-Membrane structures
-Intra/intercellular signalling- phospholipids
-Substrate for hormone and prostaglandin synthesis- eg cholesterol
-Improve flavour perception of foods
-Add texture to foods
-Improve palatability
-Supply of essential nutrients
Absorption of fat soluble vitamins
Essential fatty acids
structure of lipids?
-Over 90% dietary fats are triacylglycerols (also known as triglycerides)
-Triacylglycerols are made up of glycerol and 3 fatty acids
ONE NOTE
Saturation of fatty acid chains?
-Saturated (no double bonds)
-Monounsaturated ( 1 double bond)
-Polyunsaturated (> 1 double bond)
Describe fats and oils
-Dietary fats contain a mixture of saturated and unsaturated FAs
-Fats- mostly from animals.
-Oils- mostly from fish or plants.
what is the ratio of saturated vs unsaturated oils?
-Ratio different depending upon source. eg veg. oil- high in PUFAs, low in SFAs.
-In most veg. oils the omega6 PUFAs predominate.
-Fish oils- low in SFAs, high in PUFAs.
-Omega3 PUFAs predominate
eg Eicosapentanoic Acid (EPA) &
docosahexaenoic acid (DHA)
Describe omega6 and omega3
Omega6 (n-6)
1st double bond 6 carbons from methyl terminal
Omega3 (n-3)
1st double bond 3 carbons from methyl terminal
What other lipids are needed in diet?
-phospholipids
-sterols
-plants-phytosterols
Describe phospholipids
eg. Phosphatidylcholine; phosphatidylinositol
Structural lipids- membranes
Describe sterols
eg. Cholesterol
- Membranes
- precursor to bile salts - fat digestion
- precursor to steroid hormones
- Only found in animal fats
Describe plants-phytosterols
Plants- phytosterols. Similar structure to cholesterol. Inhibits cholesterol uptake. eg benecol
Describe essential fatty acids (EFA)
-Humans can’t insert double bond between any of 1st seven carbons of FAs.
eg Linoleic (omega6) and a-linolenic (omega3)
-Required for e.g prostaglandins, leukotrienes
-Other long chain fatty acids derived from these EFAs
Describe cholesterol
-Primary component of cell membranes
-Substrate for synthesis of bile acids, steroid hormones and vitamin D.
-Dietary cholesterol - little influence on blood cholesterol.
-Increased dietary cholesterol, decreased re-uptake of biliary cholesterol
-Type of fat influences blood cholesterol
-Dietary sources – liver, eggs, shellfish
Describe lipid transport
-Cholesterol and TAGs transported around the body as lipoproteins (composed of lipid and apoprotein):
-VLDL-TAG rich. Transports TAG to adipose/ muscles.
-LDL- cholesterol rich. Transports cholesterol from liver to cells.
-HDL- removal of excess cholesterol from peripheral tissues.
-Raised LDL-cholesterol associated with CVD
-HDL-cholesterol- inversely related to CVD
What are the differences between the saturated, unsaturated and trans fats?
ONE NOTE
Summary of dietary fat requirements in adults?
ONE NOTE
What mixture of proteins is needed?
Need adequate mixture of essential amino acids either animal or plant origin.
Essential proteins?
(can’t be made de novo)
Isoleucine
Leucine
Lysine
Methionine
Phenylalanine
Threonine
Tryptophan
Valine
(Histidine)
Semi essential proteins?
(synthesis dependent on eg another amino acid)
-Cysteine
-Tyrosine
Non-essential proteins?
Glycine
Proline
Glutamic acid
Aspartic acid
Serine
Alanine
Arginine
Protein requirements?
RNI protein is 0.75g/kg body weight per day (DOH 1991)
When are increased protein requirements needed?
-Increased requirements during growth, for repair e.g. post surgery or injury
Also pregnancy (+ 6g/day)
and lactation (+ 11g/day)
-More required for growth eg children.
Describe high biological value (HBV) proteins
-all of the essential amino acids in sufficient amounts for protein synthesis.
eg animal proteins.
Describe low biological value (LBV) proteins
-Low Biological Value (LBV) –lack some essential amino acids
-eg Plant proteins are LBV
-but eaten in combination can make a HBV mix
- Good plant protein sources include beans, pulses, nuts, seeds.
Describe carbohydrates
-Main energy source. ~50% energy.
-Surplus stored as glycogen in the liver (about 70g) and in skeletal muscle (about 450g).
-Blood glucose levels need to be maintained in tight parameters
Describe sugars- carbohydrate sources
-Present in nutrient rich foods such as fruits, vegetables and milk
-A lot from added sources
e.g. sweets, chocolates, soft drinks, cakes, biscuits
-No more than 5% of daily calories should come from added sugar - about seven teaspoons
-Link with obesity & type 2 diabetes
Describe polysaccarides (complex carbohydrates)- starches?
-e.g Bread, potatoes, rice, pasta, cereals, cous cous etc
-Foods also provide other essential nutrients
i.e. B vitamins, minerals, protein and fibre
Describe non-starch polysaccharides (NSP: Fibre)
-NSP – major component of plant cell walls, include cellulose, pectins, glucans, gums etc. Not digestible
-Soluble - fruit, veg, esp pulses and legumes
-Insoluble –tough fibrous parts of plants eg wheat & rye
-Sources – fruits, vegetables, wholegrains, oats, brown rice, bread, nuts, seeds
-Recommended intake 30g per day
Describe insoluble NSP e.g in wholegrains and nuts
-Water attracting properties. Softens stools and increases bulk of faeces.
-Reduces transit time through GIT
eg wheatbran 2-6 g water per gram
Vegetables 18-30g water per gram
-Some fermentation in colon.
Describe soluble NSP
-Fermented in colon
-Delays gastric emptying- feel fuller longer
-blunts postprandial blood glucose response by slowing digestion, slowing uptake
-binds to bile salts, decrease cholesterol reuptake.
-High fibre diet can have hypocholesterolaemic effect
Describe physiological actions of NSP?
-Acts as substrate for bacterial fermentation in the colon
-Bacteria produce short chain fatty acids, absorbed by colonic mucosa.
-Bacteria also produce butyric acid which is important fuel for mucosal cells of the colon.
-Faecal bulk (insoluble fibre)
Epidemiological studies suggest what about fibre?
-A diet high in fibre reduces the risk of colorectal cancer.
-Linear decrease in risk of colorectal cancer with increasing fibre intake.
Source of fibre foods?
-High fibre foods (>6g per 100g)
-Source of fibre foods (3-6g per 100g)
-Pulses, nuts, seeds, berries, wholegrains, broccoli, sweetcorn, cabbage, potatoes plus skins
Role of diet in regulation of blood glucose levels?
-Simple sugars easily digested in GI Tract
-Rapid increase in blood glucose levels
ONE NOTE
What is a Glycaemic index?
relates the concentration of glucose in the plasma after consumption of food
Describe a low and a high glycaemic index
-Low GI- broken down and absorbed slowly (eg complex CHO eg beans/ legumes, bran)
-High GI- broken down and absorbed rapidly eg simple sugars.
-NB complex CHO does not always equal low GI
-Some complex CHO broken down quickly.
what are the macronutrients needed in a balanced diet?
-Carbohydrate- 50-60% of energy intake: Fibre 30g
-Protein- 10-15% of energy intake
-Fat- 30-35% of energy intake
-Saturated fat <11% of energy intake (ideal<7%)
what are the micronutrients needed in a balanced diet?
-Vitamins
-Minerals, trace elements
