L7 - Dietary Fats and Lipids

What are the essential functions of fat in the body? (5)

• Help brain development and function - 60% of the brain is fat

• Structural component of cells

• Support the absorption of fat soluble vitamins

• Certain types of fat maintain a healthy heart and blood vessels

• Source of energy

How many kcal and kJ is 1 g of fat?

9 kcal and 37 kJ

What is the recommendation for fat intake and does the UK population meet this recommendation?

• Total fat intake should not exceed 35% of daily energy

• The UK population meets this recommendation

What is the main form of fat in the body?

Triglycerides

Describe the 3 categories of triglycerides

• Visible fats - concentrated fats, e.g., butter or vegetable oil, and marbling of fat in meat

• Hidden fat - found in baked goods, dairy products, and fried foods

• Naturally occurring fat - found in avocado, olives, corn, and nuts

Draw the structure of a triglyceride

H O H

H - C - O - C - carbon chain - C - H

H

O H

H - C - O - C - carbon chain - C - H

H

O H

H - C - O - C - carbon chain - C - H

H H

Describe the structure of a fatty acid

• Fatty acids contain a hydrocarbon chain, carbon atoms bonded to hydrogen atoms, usually with an even number of carbons, that is insoluble in water (hydrophobic)

• They contain a carboxyl group (-COOH), the acidic end, and a methyl group (-CH₃)

What features determine the properties of a fatty acid? (3)

• Carbon chain length

• The number of double bonds

• The position of any double bonds

What do structural properties of a fatty acid impact? (2)

• Melting point

• Health effects

What does n-3 mean when labelling a fatty acid?

The 3rd carbon from the methyl group end has the first double bond in the chain

Describe fatty acid classification by hydrocarbon chain length

• Short chain fatty acids contain less than 6 carbons, e.g., cheese and yoghurt

• Medium chain fatty acids contain 6-10 carbons, e.g., coconut oil and some dairy products

• Long chain fatty acids contain 12 or more carbons, e.g., meat and fish, plant oils, avocados, and dairy products

What does hydrocarbon chain length influence?

Digestion and absorption

What are features of saturated fatty acids and give an example of one and where it can be found

• No double bonds

• Straight chains, so they can pack tightly

• Solid at room temperature

• Stearic acid in butter

What are features of unsaturated fatty acids and give an example of one and where it can be found

• One or more double bonds

• Kinks in the chain

• Liquid at room temperature

• Oleic acid in oils

For vegetable/plant oils, animal fats, and tropical oils, indicate if they are saturated or unsaturated, solid or liquid at room temperature and an example

• Vegetable/plant oils - mostly unsaturated and are liquid at room temperature, e.g., sunflower oil

• Animal fats - mostly saturated and are solid at room temperature, e.g., butter

• Tropical oils - mostly saturated but liquid at room temperature due to a medium chain length, e.g., coconut and palm oil

How is the fatty acid chain and double bonds represented numerically?

[number of carbons]:[double bonds]n-[position of the first double bond]

E.g., oleic acid = 18:1n-9

Describe the role of the mouth during digestion of fats

• Chewing and lingual lipase in saliva begin digestion of fats

• Lingual lipase has minimal activity in the mouth due to sub-optimal digestion conditions

Describe the actions at the stomach to digest fats

• Lipase activity helps to start breaking down triglycerides into diglycerides and fatty acids

• Only about 30% of fats are digested by lipase enzymes in adults - greater importance in infants

Describe the actions at the small intestine to digest and absorb fats

• Lipid droplets are broken down into smaller emulsified fat droplets

• Bile salts coat fat droplets to aid digestion as bile salts are hydrophilic and attract water for digestion

• Bile salts help to break down fat droplets

• Pancreatic lipase is secreted from the pancreas into the small intestine to break down diglycerides into monoglycerides and fatty acids

• Micelles deliver fatty acids surrounded by bile salts and monoglycerides to the intestinal membrane

• Fatty acids and monoglycerides cross into enterocytes for absorption

How are short and medium chain fatty acids absorbed?

They are absorbed directly into the portal vein and into the bloodstream

How are long chain fatty acids, monoglycerides, cholesterol, and fat-soluble vitamins absorbed?

• Indirectly absorbed through the lymphatic system

• They are reassembled into triglycerides and packaged into chylomicrons

What are the 2 roles of the liver in fat metabolism

• Synthesis of lipoproteins, cholesterol, and phospholipids

• Direct fat storage or breakdown based on energy needs

Describe what happens at the liver during excess fat intake and if there is low energy or glucose

• Excess fat intake - lipogenesis - conversion of excess fat for storage in adipose tissue

• Low energy or glucose - lipolysis - breaks down stored fat into glycerol and fatty acids for energy

Describe the functions of the fat-soluble vitamins and what foods they can be found in

• Vitamin A - immune and skin health, vision, found in dairy fat, liver, beta-carotene rich fruit and vegetables

• Vitamin D - immune, bone and muscle health, found in oily fish, fortified foods, and the sun

• Vitamin E - antioxidant, protects cells, found in plant oils, nuts, and seeds

• Vitamin K - blood clot formation and bone health, found in leafy greens and fermented foods

What is fat-soluble vitamin absorption dependent on?

Micelle formation with dietary fat and bile salts

What are the SACN recommendations about vitamin D supplementation?

Everyone aged 4+ takes a daily 10 ug supplement of vitamin D from October to April

What are the 2 essential fatty acids?

Linoleic acid (18:2n-6) and alpha-linoleic acid (18:3n-3)

What foods can linoleic acid be found in?

Soybean and corn oils

What foods can alpha-linoleic acid be found in?

flaxseed, walnuts, chia seeds, and rapeseed oil

What are the guidelines for linoleic acid and alpha-linoleic acid consumption and are these guidelines met in the UK?

• Linoleic acid - at least 1% of total daily energy, typically achieved in the UK through omega-6 fats

• Alpha-linoleic acid - at least 0.2% of total daily energy, not currently achieved in the UK

What are the signs of essential fatty acid deficiency? (4)

• A dry scaly rash

• Decreased growth in infants and children

• Increased susceptibility to infection

• Poor wound healing

What are the key roles of essential fatty acids? (3)

• Form structural components of cell membranes

• Precursors for eicosanoids - regulate blood pressure, immunity and inflammation

• Conversion to very long chain fatty acids, e.g., EPA and DHA

What are EPA and DHA found in?

Oily fish and algae

Why are EPA and DHA not classified as essential fatty acids?

They can be synthesised from alpha-linoleic acid

What enzymes are required for synthesis of EPA and DHA from alpha-linoleic acid? (2)

Elongase and desaturase enzymes

Why are direct sources of EPA and DHA important?

Conversion of alpha-linoleic acid to EPA and DHA is limited (<5% for EPA and <0.5% for DHA)

What are the health benefits of EPA and DHA? (5)

• Regulate blood pressure

• Reduce circulating triacylglycerol levels

• Improve brain function

• Support eye and brain development

• Anti-inflammatory

What is the dietary recommendation for consumption of EPA and DHA in sufficient quantities?

2 portions of fish should be consumed per week, one of which should be oily fish

Why are traditional sources of very long chain omega-3 fatty acids unsustainable?

• 34% of the world’s assessed fish resources are overfished, up from 10% in the 1970s

• Current farmed and wild fish supplies cannot meet global nutritional needs

Describe the benefits of 2 replacement foods high in EPA and DHA

• Algae oil - sustainable replacement for fish oil and has a comparable impact on reducing triacylglycerol concentrations to omega-3 PUFAs in fish oils

• Camelina sativa seed oil - as effective as fish oil for increasing EPA and DHA concentrations in humans but is currently unavailable and is a GMO product

What does the 2019 SACN report indicate the effects of reduced saturated fat intake are? (3)

• Reduces risk of cardiovascular disease and coronary heart disease events

• Lowers total and LDL cholesterol levels

• Improved indicators of glycaemic control

What are the SACN recommendations for saturated fats?

• Average intake should not exceed 10% of daily energy intake from 5 years old

• Saturated fats should be replaced by unsaturated fats in small quantities and more evidence is available for supporting substitution with polyunsaturated fats than monounsaturated fats

Describe the impact on coronary heart disease risk by replacing saturated fats with trans fats, MUFAs, PUFAs, carbohydrates from refined starches/added sugars, and carbohydrates from whole grains

• Trans fats - a 2% replacement increases CHD risk by 5%

• MUFAs - a 5% replacement reduced CHD risk by 15%

• PUFAs - a 5% replacement reduces CHD risk by 25%

• Refined starches/added sugard - a 5% replacement increases CHD risk by 2%

• Whole grains - a 5% replacement reduced CHD risk by 9%

What was the dietary intervention in the DIVAs study?

A 16-week intervention where about 10% total energy intake from saturated fatty acids was substituted with either monounsaturated fatty acids of polyunsaturated fatty acids

What were the findings from the DIVAs study?

Replacement of saturated fatty acids with MUFAs or PUFAs lowered total choelsterol (-8.4% and -9.2%), lowered LDL-C (-11.3% and -13.6%), and gave an estimated reduction in cardiovascular disease mortality (-17% and -20%)

Do UK adults currently meet the guidelines for saturated fat intake?

Currently, only 15% of adults meet the guidelines and average intake is 12.6%, which is an excess of about 5g

What is the effect of saturated fatty acids on LDL cholesterol?

• Lauric acid, myristic acid, and palmitic acid all have significant increases to LDL cholesterol

• Stearic acid has a neutral effect on LDL cholesterol

Draw the food matrix effect

Dietary components + physical form and structure —> food matric —> bioavailability —> physiological and overall health effects

How does the food matrix effect change beliefs about saturated fat consumption?

• Previous advice was to restrict saturated fat to reduce risk of cardiovascular diseases

• Current evidence suggests that health effects of saturated fatty acids depend on the interacting effects from naturally occurring food components and from unhealthy compounds introduced during processing

• E.g., whole-fat dairy, unprocessed red meat, and dark chocolate all have a complex food matrix with high saturated fat content, but also other nutrients and non-nutritive components, leading to no increased CVD or diabetes risk

What is the EatWell guide recommendation for saturated fat?

Consume reduced fat or fat-free dairy products to lower saturated fat consumption

How are the EatWell guidelines challenged by current research? (3)

• Studies indicate that total dairy intake is either not associated or is positively associated with CVD risk

• Pooled analyses of 7 RCTs indicated that cheese intake significantly reduced total and LDL cholesterol levels in comparison to energy and fat-matched intake of butter

• Cheese and milk diets lowered circulating total ad LDL cholesterol in comparison to butter and that higher calcium levels led to greater faecal fat excretion - calcium could bind to fatty acids to produce insoluble soaps, so more fat is excreted