Lipids Flashcards
(75 cards)
What are the functions of lipids?
They form part of every cell.
Far from being inert, white adipose tissue (WAT) is a complex, metabolically-active endocrine tissue.
Depending on where it is in the body it behaves in different ways. eg: inflmmatory cytokines in fat around the middle of the body.
1 Energy (ATP) production — each gram of fat supplies the body with about nine calories.
2 Storage of energy reserves — fats are a more efficient form of storage energy than carbohydrates or proteins, so the body stores any excess energy as fat.
3 Cell membrane structure — phospholipids and cholesterol stabilise cell membranes, whilst allowing a degree of fluidity which is crucial to the function of every cell.
4 Thermal insulation in subcutaneous tissue and protection around organs.
5 Steroid hormones — progestogens, androgens, glucocorticoids, mineralocorticoids and oestrogens are derived from cholesterol.
6 Formation of eicosanoids — signalling molecules involved in a range of processes such as blood coagulation and inflammation.
7. Growth and development — the brain is rich in arachidonic acid (AA) and docosahexaenoic acid (DHA).
8. Constituents of nervous tissue structure (sphingomyelin).
9. Aid to cell-signalling processes.
10. Required for the absorption of fat-soluble vitamins.
Name the different types of lipids in the body
- Individual fatty acids.
- Triglycerides.
- Phospholipids — in every cell membrane.
- Cholesterol and steroid-based compounds (e.g. oestrogen).
- Sphingolipids — found in nerve cell membranes, e.g. myelin.
- Glycolipids — involved in cell identity (like a cell ‘passport’).
- Cerebrosides — glycosphingolipids found in the brain.
- Fat-soluble vitamins — A, D, E, K.
Name the four different fatty acid hydrocarbon chains and explain the difference
Fatty acids are hydrocarbon chains with an acid group at one end and a methyl group at the other. The number of carbons in the chain effect the way they behave.
Short-chain fatty acids (up to 5 Cs)
Medium-chain fatty acids (6–12 Cs) (coconut oil)
* Travel directly to the liver where they can be used to create energy or ketones.
* Much more readily converted to energy
Long-chain fatty acids (14–22 Cs)
Very long chain fatty acids (> 22 Cs)
* Used to build cell membranes.
When are SCFA’s produced?
What are the most common types?
What role do they play?
When are SCFA’s produced?
When dietary fibre is fermented in the colon.
Good fibre sources increase SCFA’s
What are the most common types?
Acetate, propionate and butyrate
What role do they play?
Speculated to have a role in the microbiota-gut-brain axis crosstalk.
Butyrate
- important for colon health because it is the primary energy source for colonocyte and supports the intestinal tight junctions.
- thought to have an
anti-inflammatory effect on the colon.
What is the omega system for naming fatty acids?
Uses
1. the number of carbon atoms
2. the number of double bonds
3. the number of carbons from the omega end to the first carbon in the double bond.
The omega-6 fatty acid, arachidonic acid, is referred to as 20:4 w6.
What is hydrogenation?
Fatty acids can be manipulated.
Unsaturated fats can be saturated by the addition of hydrogen
Hydrogenation = additiona of hydrogen
Makes oils into solid spreads.
Hydrogenation turns the natural fatty acid into unnatural forms (i.e. trans fats) which are damaging to health.
What is the difference between saturated and unsaturated fats.
The more double bonds in a fatty acid the less stable it is which means it is more prone to reactivity and thus oxidising
Saturated fatty acids
Contain no C-C double bonds. All the carbons are completely saturated with hydrogen bonds. Solid at room temperature.
Unsaturated fatty acids:
Contain one or more double bonds between carbons. Liquid at room temperature.
- Monounsaturated fatty acids:
Have one double bond in the chain. - Polyunsaturated fatty acids:
Have several double bonds.
Not saying that polyunsaturated fats are bad but they are less stable and more prone to oxidation
How are unnatural trans fats produced?
What foods do we find them in?
Why do they cause a problem in the body?
What problems do they cause?
**How are unnatural trans fats produced? **
High temperatures and hydrogenation.
What foods do we find them in?
margarine, processed foods and refined vegetable oils.
Why do they cause a problem in the body?
They stiffen cell membranes, making them prone to oxidation. This also alters their protective action and permeability, impeding normal cell function.
There are no safe levels of trans fats
What problems do they cause?
* Alter blood triglyceride and cholesterol profiles. Increase LDL and decrease HDL
* Linked to an increased risk of cardiovascular disease, insulin resistance and cancer.
What is a natural ‘TRANS’ fat
One on which the H atoms are on separate sides of the double bond. Conjugated linoleic acid is an example.
Most fatty acids are ‘CIS’ where the H atoms are on the same side as the double bond/
What are triglycerides?
What are they made up of?
What causes high serum tryglycerides?
What are high levels of triglycerides linked to?
What are triglycerides?
The major form of dietary fat, and the form in which fat is stored in the body.
What are they made up of?
One unit of glycerol (the backbone) and three fatty acids which can differ in length and degree of saturation with hydrogen molecules. .
What causes high serum tryglycerides?
1. Refined carbohysrates are the biggest cause
2. Alcohol
3. Obesity
What are high levels of triglycerides linked to?
Atherosclerosis, and hence heart disease and stroke.
Why does lipogenesis happen?
What is lipogenesis?
Whenever caloric intake exceeds energy requirements the excess dietary energy is converted to triglycerides via a process called lipogenesis.
Lipogenesis takes place in adipose tissue and the liver.
Excess ingested fat is taken up by adipose tissue.
Where does it happen?
Key sites are liver and adipocytes.
Also kidneys and lactating mammary glands.
What is lipogenesis?
Where does it happen?
It is the synthesis of fatty acids from non lipid sources, specifically carb rich food.
Excess glucose is converted to Acetyl-CoA which is converted to triglycerides (glycerol backbone + fatty acids) for storage in fat.
It happens when there is an excess of carbohydrates.
What is Lipolysis and when does it happen?
Why would insulin resistance reduce lipolysis?
When dietary energy is limited triglycerides from adipocytes are hydrolysed by lipase into fatty acids and glycerol are are mobilesed into circulation. This is called Lipolysis.
Lipolysis is switched on/stimulated by a number of hormones but insulin antagonises these lipolytic effects meaning it opposes the fat-burning (lipolytic) effects of certain hormones. The fat is not broken down and remains as central adiposity.
When insulin levels are high (e.g., after eating carbohydrates), it blocks fat burning by suppressing the actions of hormones that usually break down fat. This is why conditions like high insulin resistance can make fat loss more difficult.
What is the pathway for fatty acids to be turned into energy?
Which amino acid helps and how?
What is the pathway for fatty acids to be turned into energy?
Fatty acids cross the cell membrane, traverse the cytosol and reach the mitochondria.
Once they reach the mitichondria the fatty acids undergo beta-oxidation and are broken down into 2-carbon blocks as acetyl-CoA, which is oxidised via the Krebs cycle to CO2 and H2O.
Energy is then generated using the electron transport chain.
Which amino acid helps and how?
Carnitine facilitates the transport of fatty acids across the mitochondrial membrane.
What is ketone synthesis and why is it important for the brain?
When glucose are in short supply fat becomes the primary fuel for energy production but the brain cannot metabolise fatty acids so it can’t get its energy this way.
Luckily another fuel known as ketones are also made when glucose is in short supply. They are made overnight, when dieting or fasting.
Ketones can cross the blood-brain-barrier and supply fiel to the brain.
Name the ketones.
Aacetyl-CoA is converted to the ketones
* acetoacetate
* β-hydroxybutyrate (β-OHB).
* Acetoacetate can undergo decarboxylation to another ketone acetone.
How and when might we want to induce ketosis?
To shift the body’s primary fuel source from glucose to fat.
For most adults, this happens when carbohydrates are restricted to less than around 40 g a day.
Ketosis is linked with health benefits including
* Weight loss
* Management of epilepsy
* Parkinson’s and Alzheimer’s disease. (the theory is that a T3D in diseases such as these contribute to neurological degradation and a state of ketosis might help because it supplies energy to the brain)
NOTE: Nutritional ketosis is different from ketoacidosis — an unstable and dangerous condition
What aids the digestion of triglycerides?
- Gastric lipase in the stomach and pancreatic lipase in the duodenum, which act to separate the glycerol and fatty acids.
- This process is facilitated greatly by the emulsifying action of bile, which increases the surface area of fat droplets.
The resulting three fatty acids and monoglyceride are transported into enterocytes, where they are rebuilt in the cell, packaged into chylomicrons and
transported via the lymphatic system to the bloodstream.
The released fatty acids can be used or stored in adipose tissue.
How do we optimise lipid digestion?
- Chew adequately and eat mindfully
- Avoid drinking with meals
- Stress management
- Increase bile production by
(a) optimising stomach acid levels via zinc and B6-rich foods, bitter foods (e.g. chicory, rocket)
(b) Ensure good hydration to support bile flow.
(c) Increase glycine and taurine, which are components of bile.
(d) Olive oil can stimulate bile secretion.
(e) Choleretics (increase bile production) and cholagogues (increase bile flow); e.g. dandelion, artichoke and turmeric.
What are the general recommendations for fat consumption?
What is wrong with government dietary guidlienes regarding fat consumption?
What should we be advising regarding fat?
What is wrong with government dietary guidlienes regarding fat consumption?
- Low fat - often fat being replaced with refined carbohydrates and sugar.
- Recommended unsaturated oils and spreads (may be highly refined and contain trans fats) and eat in small amounts
- Without adequate energy from fat, people struggle to be sufficiently satiated. This has
resulted in the consumption of ultra-processed foods. - No emphasis on healthy fats such as oily fish, avocado, nuts, seeds, extra virgin olive oil, egg yolk and grass-fed meat
What should we be advising regarding fat?
- Love your fats
- Eat fats from natural, unrefined foods
- A mixture of saturated, monounsaturated and polyunsaturated fats, but absent of trans fats.
- Fat-soluble antioxidants, e.g. vitamin E, are important when including fats in the diet.
- Focus on the quality of the fat and combine with foods naturally rich in antioxidants.
- Cold pressed oils as a lot of seed and vegetable oils are highly refined
- Avoid farmed fish due to poor omega 6/3 ratio
Saturated fat:
What type of tryglyceride is Coconut oil?
What are its benefits?
What type of tryglyceride is Coconut oil?
Medium-chain triglycerides
Therefore used as a source of fuel or tunred into ketones
What are its benefits?
* as a MCT
- increases the number of calories burned compared to longer-chain fatty acids.
- Preliminary studies show positive outcomesin epilepsy and Alzheimer’s disease.
- Antibacterial, antiviral and antifungal properties.
- ↑ HDL cholesterol, ↓ LDL cholesterol.
Saturated fat:
Name a SCFA and where you find it
Butyric acid
* in butter and dairy
* Also produced in the gut which is why a good intake of fibre is needed
Saturated fat:
Name two MCFA and where you find them in order of abundance
- Carprylic acid
Coconut
Palm kernel
Breast milk
- Lauric acid
Coconut
