Fats vs CHO Flashcards
What are the types of fats?
Mono, poly, saturated and trans.
What are the degrees of polymerisation of CHO?
Sugars 1-2 DP
Oligosaccharides 3-9 DP
Polysaccharides >9 DP
What is the recommended amount of Fats?
2000mg combined with EPA and DHA (optimal omega-3 index, reduce CVD risk)
560g oily fish/week
What is the recommended amount of CHO?
50% total energy intake
25g (<10%) free sugars
30g fibre
What are the health effects of fats?
- Provision of energy
- Effects on satiety/gastric emptying
- Fat-soluble vitamin utilisation
- Cellular integrity
- Storage as adipose (insulation)
- Effect on cholesterol levels
- Brain function
Inflammation (n3 dampens)
What are the health effects of CHO?
- Provision of energy
- Effects on satiety
- Control of blood glucose and insulin metabolism
- Protein glycosylation
- Cholesterol and triglyceride metabolism
- Fermentation
- Bile-acid dehydroxylation
Explain the fatty acid structure
- Varying chain lengths: 4 carbons shortest
- Carboxylic acid (COOH) at one on (alpha carbon); methyl (CH3) on the other end (omega carbon)
- Double bonds = primary structural difference in types of fat
- Count from the omega end and note the ‘position’ of double bonds
- Nomenclature: C(n):n (double bonds)
Structure of Omega 3
1st double bond on 3rd carbon from omega
Structure of Omega 6
1st double bond on 6th carbon from omega
Explain phospholipids
3rd carbon attached to phosphorus
Hydrophilic head
Hydrophobic tail
Create a bilipid semipermeable membrane, 2 distinct aqueous compartments either side separation essential for several functions (incl. metabolism)
Fat metabolism facts (phospholipids)
- Vital part of cell membranes
- Selective permeability
- Intermediates in metabolism
Phosphatidylcholine (PC) helps improve metabolic health.
Acetylcholine (neurotransmitter involved in metabolism)
Regulatory molecules: phosphatidylserine - cell signalling/apoptosis
Explain Beta-oxidation
- Occurs in the mitochondria of the cell.
- Two carbon acetyl fragments split from the fatty acid chain (repeats until degraded to Acetyl-CoA and enter the Krebs cycle.
- Energy yield from fatty acids alters depending on chain length (much greater than from glucose).
- Ketone formation: inadequate CHO oxaloacetate - cannot form citrate (by combining with Acetyl-CoA), so cannot enter Kreb cycle.
- Liver converts Acetyl-CoA to ketone bodies acetoacetate, Beta-hydroxybutyrate and acetone
Explain fatty acid synthesis
Cytosol of the cell (facilitated by several enzymes)
Reverse of beta-oxidation: two-carbon units added to Acetyl CoA
Acetyl-CoA comes from pyruvate (from glycolysis & carbon skeletons of amino acids breaking down)
This explains how we can gain body fat by eating excessive amounts of CHO/Protein
Chylomicrons: Deliver TG to adipose
Lipoprotein Lipase: enzyme on the surface of adipose cells, cardiac and skeletal muscle cells. Break down TG into Glycerol/fa’s - stored or used by muscle cells
Chylomicron remnants return to the liver
What are the metabolic pathways for energy release (CHO)?
Digestion: Break down into monosaccharides for absorption
Metabolic fate: Depends on body’s energy needs
-Glycogenesis
-Glycolysis
-Glycogenolysis
-Gluconeogenesis
Facts about Glycogen
Storage and creation occur in the liver and skeletal muscle
Small amounts stored elsewhere (e.g. kidney)
Liver weight: Up to 7%, approx 10g
Muscle weight,1% approx 500g
Loss of glycogen stores = weight loss at the start of a low CHO diet
Muscle glycogen stores cannot contribute to glucose homeostasis
What is Glycogenin?
Initiates glycogenesis (creating short-chain glycogen primer)
What is Glycogen synthase?
Adds glucose units to the ends of glycogen chains
What is a Branching enzyme?
Attaches branch points for 6 carbon chains
What is Glycogen phosphorylase?
breaks bonds between glucose molecules
Debranching enzymes: breaks the branch points of the molecule
Number of ATP in Glycolysis
2 ATP (anaerobic in the cytosol)
What happens when there is no oxygen available?
Pyruvate becomes lactate.
Lactate is converted back into pyruvate via gluconeogenesis
What is gluconeogenesis?
Glucose Homeostasis.
When CHO intakes are low, blood glucose levels drop. Non-CHO sources are used to create glucose.
Provides about 1/3 of the glucose used for glycogen synthesis.
What are the sources that create glucose in gluconeogenesis?
Glucogenic amino acids (C skeletons), lactate (continually produced by RBCs/skeletal muscle in exercise), glycerol.
What is insulin?
It is a pancreatic hormone released in response to hyperglycaemia. Promotes glycogenesis/uptake of glucose into muscle/adipose.
What is Glucagon?
It is a pancreatic hormone released in response to hypoglycaemia. Promotes glycogenolysis and gluconeogenesis.
What is glycogenesis?
It is the process through which glycogen is synthesised, and glucose molecules are added to the glycogen chains for storage purposes.
Explain the breakdown of a food with CHO and Fats at dinner
CHO is digested to form glucose, absorbed in the small intestine, and transported into the bloodstream.
Rising blood glucose stimulates insulin release and fuel to use (cellular uptake) or storage (glycogenesis) for later use.
Dietary fat will slow absorption (prevent glucose spike).
Bedtime! Glucose is all used, and levels drop.
The pancreas releases glucagon, stimulates glycogenesis and gluconeogenesis, and increases blood sugar levels.
Cellular uptake from Fats
Emulsified with bile salts
Hydrolysed by pancreatic lipases
Generate free fatty acids and glycerol
Uptake by enterocytes (various transporters aided by plasma albumin)
Utilisation within cells with mitochondria
Endoplasmic reticulum - synthesis of triacylglycerols
Cellular uptake from CHO
GLUT4 - uptake of glucose to muscle/adipose
Insulin binds to receptors (surface of the cell)
GLUT4 moves to intracellular storage (cell membrane)
Allows entry of glucose into the cell
Resistance/low insulin levels: low GLUT4 on cell membrane, low permeability to glucose, low glucose uptake
Exercise raises GLUT4 expression
How many grams of CHO are needed to prevent ketosis?
50g
Percentage of energy from CHO and Fat in a healthy diet
55% energy from CHO (non-essential) and no more than 35% from fat (essential)
Which foods are sources of fructose, a monosaccharide?
Fruit juices and honey
What is a form of dietary fibre?
Cellulose
Several (3-9) units of sugar units joined together
Oligosaccharide
The form of carbohydrate stored in the human body
Glycogen
A disaccharide found in milk
Lactose
Definition of Glycaemic load
The glycaemic load (GL) is obtained by multiplying the quality of CHO in a given food (GI) by the amount of CHO in a serving of that food
Definition of dietary fibre
It is a group of compounds in plants that cannot be fully digested in our gut
Statements about polyunsaturated fatty acids
They contain more than 1 double bond
They are made up of carbon atoms, hydrogen atoms and oxygen atoms
Structure of saturated fatty acids
They contain no carbon to carbon double bonds
The ratio of n-3 to n-6 fatty acids
1(n-3) :2(n-6)
Statements about triglycerides
They are made up structurally of a glycerol molecule and 3 fatty acids.
Low levels of blood triglycerides are associated with a lower risk of Cardio Vascular Disease (CVD).
Structure of monosaturated fats
one double bond
Structure of polyunsaturated fats
more than one double bond between carbon atoms
What do we mean by a trans-fat? What are sources of trans fats in the diet?
Trans fats are stereoisomers of fats; the carbons occupy a different place in physical space than those of a cis isomer, and oils are liquid at room temperature.
Food chemists and scientists use a catalyst to hydrogenate the vegetable oils. They are found in baked products, confectionary, cakes, biscuits, etc.
What is the definition of an omega-3 fatty acid?
This is a fatty acid with at least one double bond. The double bond occurs at the 6th carbon from the methyl group end of the fatty acid.
What are the two essential fatty acids for humans?
alpha-linolenic acid (omega-3 fatty acid) and linoleic acid (omega-6 fatty acid)
What is the meaning/definition of eicosanoid?
Eicosanoids are a class of molecules derived from 20-carbon polyunsaturated fatty acid, most frequently arachidonic acid, an n-6 fatty acid.
The eicosanoids include prostaglandins (PG), thromboxanes (TX), leukotrienes (LT), and lipoxins (LX).
Examples of monosaccharides
glucose, fructose and galactose
Examples of disaccharides
lactose, sucrose and maltose
Example of oligosaccharides
3-9 small number of sugar units found in vegetables (Raffinose)
What are non-starch polysaccharides NSP?
Complex carbohydrates other than starches. Part of dietary fibre: includes cellulose, pectins, glucans, gums, mucilages, inulin and chitin (and exclude lignin)
How is fructose metabolised differently from glucose?
When consuming glucose, the liver is initially bypassed, and the glucose reaches systemic circulation to be used by tissues such as the brain and muscles. If excess glucose is consumed in the diet, it will first be stored as glycogen and secondarily as fat. When fructose is consumed, it is metabolised in the liver, where fructokinase will allow for fructose uptake. Fructose metabolism lacks many of the cellular controls that are present in glucose metabolism, which allows for unrestrained lipid synthesis. This can result in raised blood triglyceride levels and non-alcoholic fatty liver disease.
The importance of different dietary fibre in the diet
Dietary fibre generally has properties such as:
- Decrease intestinal transit time and increase stools bulk fermentable by colonic microflora
- Reduce blood total and /or LDL cholesterol levels
- Reduce post-prandial blood glucose and/or insulin levels
Fibre recommendation intake
30g per day
What is the glycaemic index?
It is a number from 0 to 100 assigned to a food with pure glucose arbitrarily given the value of 100, representing the relative rise in the blood glucose level 2 hours after consuming that food. Adding fat will delay the release of the digested sugars due to slower gut transit times.
