Energy + Nutrients Flashcards
What are the 2 essential nutrients?
Macronutrients - fats, carbs, protein
Micronutrients - vitamins, minerals
What makes essential nutrients ‘essential’?
They cannot be produced by our body (not in an adequate amount) so must be provided in diet
What is ‘adequate nutrition’
All essential nutrients are consumed in adequate amounts + correct proportions for…
- energy
- regulate metabolism
- growth + development
- good health
Digestion + Absorption
Describe the Alimentary Canal of Gastrointestinal (GI) system
- Mouth - food is pushed into throat by tongue
- Oesophagus - peristalsis begins, moving food to stomach
- Stomach - food is mixed with digestive juices = chyme
- Small intestine - continued digestions (water + nutrients are reabsorbed)
- Large intestine - absorbs water, forms + moves stool to rectum
- Anus - remaining waste is expelled as stool
What are the accessory organs during digestion + absorption?
- Salivary glands - produce saliva to moisten food, aiding in easy movement to stomach
- Pancreas - produces enzymes that break down carbs, fats, lipids
- Liver - creates bile = breakdown of fats
- Gallbladder - stores bile from liver + releases into small intestine
Describe the 3 main processes that occur in GI tract
Digestion - large -> small molecules via mechanical and chemical breakdown
Absorption - transporting digested molecules across GI tract walls into blood
Elimination - removing undigested food + waste products from body
What does the cephalic phase of digestion refer to?
The stage in which the stomach responds to the mere sight, smell, taste, or thought of food.
What are the 3 responses of cephalic phase of digestion?
- Anticipatory physiological response - sensing or expecting food (uses senses)
- Preparations for food processing - activates GI tract (20% of acid produced before)
- Vagus nerve activation to increase production of… saliva, bile, stomach acids, enzymes, gastric + pancreatic hormones
Describe mechanical digestion (what are the 2 main processes that can occur?)
Involves the contraction of circular + longitudinal muscles = moves food through GI tract
- Peristalsis
- Segmentation
Explain peristalsis
Propels food via contracting longitudinal muscle
- wave-like contractions push food in one direction along tract
- includes oesophagus, stomach + intestines
- when stomach rumbles = peristalsis is occurring
Explain segmentation
Mixing of chyme via contraction of circular muscle
- Small intestine creates alternating forward + back contractions
Describe chemical digestion
- Dietary components - starches, sugars, fats + proteins must be broken down into smaller molecules for absorption + metabolism
- Ezymatic hydrolysis - enzymes break chemical bonds holding food molecules together, transforming them into constituent ‘building blocks’ = then absorbed + utilised by body
What are the constituent ‘building blocks’ of each macronutrient?
Carbs -> monosaccharides
Lipids -> fatty acids + monoglycerides
Protein -> amino acids
Where is the stomach located + explain key structures
Located between oesophagus + small intestine, essential for mechanical digestion
- Gastroesophageal sphincter (at top) - prevent backflow of contents to oesophagus
- Fundus = reservoir for food
- Antrum + pyloric gland area - mechanically breakdown’s semi-digested food into chyme
- Pyloric sphincter (bottom) - releases chyme into duodenum of SI
Small intestine digestion - what’s a key structure of SI and what are the 3 parts of SI?
Has villi that increases the SA of SI where absorption takes place
- Duodenum = C-shaped region extending on from stomach
- Jejunum
- Ileum - runs into cecum of LI
List the enzymes involved in digestion, where are they released + what do they breakdown?
- Salivary amylase - from mouth - carbs
- Pepsin - from stomach - proteins
- Pancreatic amylase - pancreas - carbs
- Bile salts - liver - lipids
- Lipase - pancreas - lipids
- Trypsin, chymotrypsin, carboxypeptidase - pancreas - proteins
- Disaccharidases - SI - carbs
- Peptidases - SI - proteins
What is gastric emptying + its importance?
The contents of stomach are transferred into the duodenum
- important as nutrients passage + indigestible particles through GI tract needs to be regulated
How is gastric emptying regulated?
Determined by coordinated motor activity of stomach + proximal intestine (involves smooth muscle + neural + hormonal factors)
Where are the following hormones produced + what do they do?
- Ghrelin
- Gastric Inhibitory Polypeptide (GIP)
Ghrelin - produced in stomach to accelerate gastric emptying + stimulate appetite
GIP - Produced by intestinal K cells to delay gastric emptying + reduce appetite
How is gastric emptying different for solid vs liquid meals?
Solids - 2 phase process
- Initial delay (lag period of roughly 30mins) before emptying begins (solids-> smaller particles)
- Linear pattern of emptying (30-120mins) - changes depending on volume of meal, consistency + fat content
Liquids - generally empty stomach in exponential matter (much faster process)
What factors slow gastric emptying?
- Solids vs liquids
- Fats vs carbs + protein
- Increased energy density - indigestible foods stay in stomach for longer (high fibre, veg)
- acidity
- Larger volume
How can nutrients influence gastric emptying?
ST nutrient exposure - increased exposure to specific nutrients can alter GE
e.g. dietary supplementation with 400g of glucose per day for 3 days can sig. increase GE compared to normal diet
The SI can rapidly adapt with specific adaptations in regulatory mechanisms for GE in response to increase dietary load
What is the importance of gastric emptying in metabolic health?
- Slower GE rate leads to rise in macronutrients postprandially (after eating)
- this can reduce burden of clearing substances from circulation - Postprandial triacylglycerol conc - if not cleared it is an independent risk factor for CVD
- Impact of glycaemic control - small differences in GE can sig. affect postprandial glycaemia (blood sugar) in healthy + type 2 diabetes people
- Has a role in appetite - GE is associated with satiety + hunger = influences food intake
- Energy homeostasis - crucial role in maintaining chronic food intake + energy balance in body
How is gastric emptying important during exercise performance?
GI tract has role in delivering carbs + fluid during prolonged exercise (not always optimal in endurance conditions)
- Body loses fluid via sweat, so any fluid taken on needs to be efficiently emptied into small intestine to be absorbed into bloodstream (avoid dehydration + impaired thermoregulation)
- Carbs are usually consumed during prolonged exercise - they need to reach small intestine, absorbed + utilised to ensure maintenance of blood sugar levels, delaying onset of fatigue
GE can be influenced by nutritional factors (type of nutrients consumed + previous dietary history)
What are the recommendations of % of energy from macronutrients intake for a balanced diet?
50% from carbs
35% from fats
15% from protein
How do requirements of macronutrients change throughout life?
Young - more energy to grow + be active
Decreases in adulthood - needs depend on activity levels
Older adults - energy requirements decreases as less active + reduction in basal metabolic rate
- pregnant women require can extra 200kcal/day during 3rd trimester
What is energy intake defined as?
The energy content of food + drink ingested as provided by major sources of dietary energy
- different food = different energy for a given weight
How is the energy contribution (calorie density) of foods measured?
Via Atwater General Factor System
- uses single energy value for each macronutrient
Basis of system - avg heats of combustion of each food group
- then adjustments are made for losses during digestion, absorption + urinary excretion of urea
What are the energy contributions of each macronutrients + alcohol?
Carbohydrates = 4kcal/g
Proteins = 4kcal/g
Fat = 9kcal/g
Alcohol = 7kcal/g
What makes up an individuals total energy expenditure?
- Resting / basal metabolic rate
- Activity energy
- Thermic effect of food
Basal metabolic rate
What is it, how much of total EE, factors influencing, differences between young vs old and male vs female
The rate of EE at rest, necessary for bodily functions (70% of total EE)
- determined by fat-free mass, fat mass, sex, age, genetics
Infants - higher due to rapid growth (proportionally) and elderly - lower as decreased muscle mass
Males have higher RMR than females (more muscle mass)
Activity expenditure
How much of total EE, factors influencing
Most variable component (depends on activity levels) - ranges from 15% (highly sedentary) to 50% (highly active)
- Energy cost is determined by activity levels + efficiency
- Muscular work - comprises of spontaneous + voluntary exercise (e.g. sitting upright + running)
Thermic effect of food
What is it, how much of total EE, factors influencing + impacted by
Refers to energy required to digest, absorb + metabolise + store nutrients (approx 10% of EE)
- influenced by - type of nutrients (+ amount) + diet composition
- impacted by - sedentary lifestyle (lower), ageing (lower), activity (enhanced), obesity (altered), insulin resistance (independently impact TEF regardless of food intake)
What is energy balance? If there is energy balance, what would this mean?
Between energy intake + expenditure
- state of energy balance = maintained body weight over a period of time
What occurs if there’s a positive energy imbalance compared to a negative energy imbalance?
Positive…
Energy consumed > energy expended = weight gain
Negative…
Energy consumed < energy expended = weight loss
What is obesity?
An excess accumulation of body energy, in form of fat (adipose tissue)
What are the types of adipose tissue?
- Visceral adipose tissue
- accumulation = risk factor for CMD
- located in abdominal cavity
- Subcutaneous adipose tissue
- just below skin
- considered neutral / protective
What is the body mass index + equation?
A surrogate measure of body fatness - but measures excess weight (not fat)
BMI = Weight / Height (m2)
What are positive of BMI?
+ Simple, inexpensive + non-invasive
+ High BMI is important risk factor for CVD and T2D
+ Good tool for tracking + identifying pop. trends - comparisons across time, countries, pop subgroups etc
What are negatives of BMI?
- surrogate measure of body fatness
- age, sex, ethnicity + muscle mass can influence interpretation
- does not distinguish between excess fat, muscle or bone mass
- does not provide indication of fat distribution
