Balanced Diet
- Energy Balance
- Energy is obtained from food
- Main energy from carbohydrates (glucose) and fats
- Proteins are used for growth and repair first
- Excess proteins is converted to energy
- Out of balance
- More energy/food than required → obesity
- Less energy/food than required → starvation
- Types of carbohydrates
- Intrinsic sugars: found within cells (fruits)
- Extrinsic sugars: sugars that have been added to food (processed food)
- Milk sugars: found in milk products
- Basal Metabolic Rate (BMR)
- Energy needed at rest (not when asleep!) for routine tasks of cells (excrete waste)
- Factors that influence BMR
- Age
- Young > Old
- Growth requires more energy → children, pregnant women (fetus)
- Young and active people have more muscles than older people
- Sex
- Male > Female
- Women have more adipose than muscle tissue
- Muscles (work out) require more energy than fat cells (storage)
- Body size
- Tall and thin > short and obese
- Tall and thin people have a large surface area but small volume
- Loose heat quicker
- Need more energy to maintain body temp
- High body mass > Low body mass
- High body mass → more cells that require energy
- Starvation
- No carbohydrates and fats are available in the diet
- Body starts to break down its own proteins (muscles)
Function of
Fibres
- Polysaccharides (cellulose) that cannot be broken down by enzymes in the gut
- Reduce absorption of carbohydrates
- Reduce hunger
- Prevent constipation (need plenty of water)
- Speed up passage of food through intestine
- Less time for toxins to accumulate
- This reduces risk for colon cancer
Water
- Makes up 65% of our body weight/body mass
- Requirements depend on
- Intake of water by food
- Body size
- Physical activity
- Environment (hot? cold?)
- In normal conditions, 2L of water per day is recommended
- Dehydration causes reactions inside cells to slow down
- Overhydration causes dangerously low sodium levels []
- How is water lost?
- Breathing
- Sweating
- Excretions (urine, faeces)
- Diuretics (alcohol, caffeine), which increase the amount of water in the urine
Carbohydrates
- Starch and sugar
- Provide ≈80% of total chemical P.E.
- Breast-fed infants obtain ≈40% of their chemical P.E. from lactose
- Non-starch polysaccharides (e.g. glycogen)
- Control appetite
- Prevent appendicitis, colon cancer, haemorrhoids, constipation
- Store and transport energy
- Glucose is the main energy source in the brain
Lipids
- Source of chemical P.E. (energy reserve)
- Phospholipids are essential for plasma membranes
- Essential fatty acids are precursors of other important substances
- Needed to absorb fat-soluble vitamins
- Maintain body temperature
Proteins
- Required for growth and repair in cells and tissues (children require more!)
- Carrier (change shape for different molecules) for water-soluble molecules such as glucose
- Ion channels (sodium and chloride ions)
- Pumps use energy to move water-soluble molecules and ions
- Enzymes, which speed up chemical reactions at the edge of the membrane
- Receptors enable hormones and nerve transmitters to bind to specific cells
- Recognition sites, which identify a cell as being of a particular type
- Adhesion molecules for holding cells to extracellular matrix
Vitamins
- Often interact with enzymes to speed up metabolic reactions
- Most are essential (must be absorbed from food)
- Only vitamin D (skin) and vitamin K (gut bacteria) are non-essential (produced by body)
- Fat soluble
- Vitamin A: vision, growth, reproduction
- Vitamin D: regulates calcium levels, bone formation
- Vitamin E: antioxidant (prevent cancer, Alzheimer)
- Vitamin K: blood clotting
- Water soluble
- Vitamin C: antioxidant, wound healing, synthesis of adrenaline, bone formation
- Vitamin B12 and folic acid: cell division (low levels cause anaemia)
- Supplements
- Vitamins A and D (fat soluble)
- Cannot be excreted from body
- Only small amounts are needed, rest stored within liver
- Excessive intake from supplements can cause liver damage
- Vitamin C (and other water soluble vitamins)
- Not stored - regular intake required for good health
- Excess excreted in urine
- In the UK, supplements are only useful for
- Pregnant women (growth)
- Elderly (less efficient absorption, less appetite)
Mineral Ions
- Sodium: water balance (maintain osmotic pressure)
- Chloride: maintain osmotic pressure, required for acid production in stomach
- Potassium: abnormal levels cause abnormal heart rhythms
- Calcium: bones and teeth, regulation of heartbeat, muscle contraction, blood clotting, nerve and brain function (important for synapses)
- Phosphate: nucleic acids, ATP, phospholipids, bones and teeth
- Iron: haemoglobin (low levels cause anaemia) and myoglobin formation
Healthy diet
- EAT fruit and vegetables
- 5 portions of fruit each day
- Contain fibres (prevent constipation)
- Contain vitamins (antioxidants)
- MORE starch than sugar
- Starch (pasta, rice, brown bread) releases glucose more slowly
- Food with a high GI (food rich in sugar) is linked to obesity
- RESTRICT salt and fats
- Heart disease is caused by a diet
- High in fat - increases cholesterol
- High in saturated fats
- High in salt - increases BP in hypertension (not in people with normal blood pressure)
- Replace saturated with polyunsaturated fats
- Omega 3 fatty acids (oily fish) protect from heart disease
- Alcohol is not a risk factor for coronary heart disease (CHD)!
- In fact, one glass wine per day reduces the risk of CHD
Gut Bacteria (Intestinal Flora)
- Healthy gut flora
- Harmless gut bacteria (symbiotic relationship)
- Compete with harmful gut bacteria and reduce their disease-causing ability
- Produce most of vitamin K
- Strengthen the immune system
- Babies are born without a gut flora
- Pick up bacteria from surroundings
- Breastfeeding helps to establish a healthy gut flora
- Balance between harmless and harmful gut bacteria
- Overgrowth of harmful bacteria or loss of harmless bacteria disturbs this balance
- Can cause malabsorption and abdominal discomfort
Vitamin K
- Used by E. coli for their respiration
- Released into and absorbed from the gut after E. coli die
- Deficiency is common in newborn (sterile gut flora!) → haemorrhagic disease of the newborn
- Impaired blood clotting
- Babies bleed easily from
- Mucous membranes, such as nose
- Intestines
- Cuts in the skin
- Treated with vitamin K (by mouth or injection)
- Formula milk contains vitamin K
- Vitamin K deficiency is more likely in babies who are breastfed
- Takes time for E. coli to settle down within the gut
Probiotic Drinks
- Contain "good" bacteria
- Help to restore the balance of a healthy gut flora
- Modify the immune system and reduce hay fever (1)
- Only useful with an impaired gut flora caused by
- Unbalanced diet
- Inflammatory bowel disease (IBD)
- Some antibiotics, which eradicate (kill) bacteria in the gut
Glycaemic Index (GI)
- Effect of 50g carbohydrates on blood glucose levels
- Thus, how much and how quickly glucose is released from food
- 50g of glucose → GI = 100
- Low GI (<55) - slow release of glucose/energy from food
- High GI (>70)
- Factors that affect GI
- Branching of starch (more bonds → takes longer to digest → lower GI)
- Fibres and vinegar (lowers pH) slow down absorption of starch
- Low GI food (fruit, vegetables, pasta, rice)
- Complex/intrinsic sugars
- Contain large carbohydrates (starch)
- Made up of many bonds that need to be broken
- Blood glucose levels rise and fall slowly
- Glucose is converted to glycogen (storage compound) in the liver
- Keeps blood glucose levels constant
- Prevents disease and improves control of blood glucose in diabetics
- High GI food (Lucozade, white bread, croissants, candy)
- Simple/extrinsic sugars
- Contain small carbohydrates (glucose)
- Easy to digest and quickly absorbed from the gut
- Rapid and prolonged rise of blood glucose levels
- This releases large amounts of insulin from the pancreas
- Not enough time to convert all glucose to glycogen
- Glucose is stored as fat instead (→obesity)
- High glucose levels can damage arteries (atherosclerosis)
- Sharp rise of insulin may cause sudden drop of blood glucose
- Stimulates hunger (→obesity)
- Tiredness
- Loss of concentration
Glycaemic Load (GL)
- Better indicator than GI alone
- Small amount of high GI food has same effect as high amount of low GI food
- Takes into account complexity (GI) and amount of sugar in food
- GL = grams of carbohydrates x [GI / 100]
- High GL (>20)
- Low GL (<10)
Diet and Disease
Processed Foods
- Raw food (bread, cereals, biscuits, cakes, pastries) is altered to improve its taste
- Account for 75% of children’s salt intake
- Rich in salt, simple sugars and fat (→obesity)
- Food labels identify unhealthy food
- Traffic light system
- Red = high amount
- Yellow = medium amount
- Green = low amount
- Guideline daily amounts (GDAs) system
- Labels show amounts in one serving
- Those are compared to guideline daily amounts
Food Additives
- Given an E number when it has passed safety tests
- Make food
- Taste nicer (flavour enhancers, such as glutamate)
- Look nicer (colourings, such as caramel)
- Last longer (antioxidants, such as vitamin C)
- Prevent bacterial growth (preservatives, such as sulphur dioxide)
- Some people are intolerant to glutamate and, hence, most food products!
Obesity
- BMI > 30 // BMI = body mass (kg) / height² (m²)
- Eat more energy/food than required
- Lack of exercise
- Unhealthy diet
- Risk factor for type 2 diabetes
- Obesity and diabetes → strong risk factor for heart disease, stroke, hypertension
- Risk for cancer
- Obese patients suffer from more inflammation than the normal population
- Inflammation increases cell turnover
- Higher chance for mutations that can cause cancer
- Risk for fatty liver disease
- Fat may deposit within the liver - can be reversible!
- In 1%, this may progress to inflammation of the liver (risk for liver cancer!)
- Can cause osteoarthritis and rheumatoid arthritis
- Weight damages joints and bones over time
Type 2 Diabetes
- Failure of blood glucose regulation
- Cells have become insensitive to insulin
- Prolonged, high blood glucose levels causes
- Heart disease
- Blindness
- Nerve damage
- Foot ulcers
Isotonic Sports Drinks (Lucozade)
- Isotonic means same water potential as blood plasma
- Heavy exercise for prolonged time
- Higher sweat production → loss of inorganic ions and water
- Higher rate of respiration → loss of glucose
- Body reserves are lost and performance decreases
- Isotonic drinks replenish ions (electrolytes), water and glucose (energy)
- Increase performance
- Prevent dehydration
- Drinks are beneficial in moderate amounts after heavy exercise
- Contain high levels of glucose - dangerous in diabetes!
- Drinking more water OR sports drinks than fluid lost during heavy exercise
- Can cause dangerously low sodium levels! (2)
- Water starts to move into cells
- Brain cells swell but cannot expand due to bony skull
- This causes vomiting, headache, confusion, coma, or even death
Large Molecules
- Monomer (-OH) + monomer (-H) ⇋ polymer + H2O(l)
- Condensation: monomers join to form polymers
- Amino acids join to form a dipeptide (protein)
- Two amino acids release -H and -OH groups (H2O)
- Peptide bond forms between the alpha-carbon and nitrogen
- Monosaccharides join to form disaccharides
- Glycosidic bond forms between both monomers
- Hydrolysis: break down of a polymer
- Reverse of the condensation reaction
- This is the process of digestion
Carbohydrates
- Organic molecules which contain C, H and O
- Bind together in the ratio Cx(H2O)y
- Monosaccharides → single sugar (monomer)
- Ribose found in RNA and DNA
- Deoxyribose part of nucleic acids
- Glucose is the main energy source in brain
- Fructose is found in sweet-tasting fruits
- Disaccharides → two sugar residues (2 monomers)
- Sucrose (glucose + fructose) → transport carbohydrates in plants
- Maltose (glucose + glucose) → formed from digestion of starch
- Lactose (glucose + galactose) → found in milk
- Polysaccharides → many sugar residues (polymer)
- Starch (alpha-glucose) → main storage of carbohydrates in plants
- Glycogen (alpha-glucose) → main storage of carbohydrates in humans
- Cellulose (beta-glucose) → component of plant cell wall, important for digestion
Starch
- Consists of amylopectin and amylose (both are made of α-glucose)
- Amylopectin is branched via 1,6-glycosidic bonds
- Amylose forms a stiff helical structure via 1,4-glycosidic bonds
- Both are compact molecules → starch can be stored in small space
- The ends are easily broken down to glucose for respiration
- Does not affect water potential as it is insoluble
- Readily hydrolysed by the enzyme amylase found in the gut and saliva
- Found in corn (maize), wheat, potato, rice
Glycogen
- Found in skeletal muscle and liver
- Insoluble, branched polymer, made of α-glucose linked via glycosidic bonds
- Glycogen is broken down to glucose by glycogenolysis (glycogen phosphorylase)
- Major site of daily glucose consumption (75%) is the brain via aerobic pathways
- Most of the remainder is utilized by erythrocytes, skeletal muscle, and heart muscle
- Glucose is obtained from diets or from amino acids and lactate via gluconeogenesis
- Storage of glycogen in liver are considered to be main buffer of blood glucose levels
