Nutrition Flashcards
What is nutrition?
sum of processes involving: - growth - maintenance -repair of the body as a whole or its constituent parts
“effects of food on the body in health and disease”
What 6 main processes are involved in proper nutrition?
ingestion digestions absorption transport assimilation excretion
What is diet?
sum of food consumed by a person
What is the difference between food and nutrients?
Food = substances we take into our body. Classified into groups Nutrient = components of food
What are the types of macronutrients?
Fat
Carbohydrates
Protein
Alcohol
What are the types of micronutrients?
Vitamins (water- vs fat-soluble)
Trace minerals
Which vitamins are water soluble?
Vitamin B and C
Which vitamins are fat-soluble?
Vitamins A, D, E, K
How many calories do each of the macronutrients carry?
Fat: 9 kcal/g
Carbs: 4 kcal/g
Protein: 4 kcal/g
EtOH: 7 kcal/g
Why is nutrition important?
prevent deficiency and disease
safeguard against toxicity
How are nutrient requirements calculated?
Observational: average intake amongst healthy groups
Experimental:
- vary nutrient intake and estimate minimum amount needed to prevent deficiency
- identify biochemical markers to detect depletion of nutrient stores prior to presentation of symptomatic deficiency (e.g. ferritin as a proxy for iron)
How is ferritin used as a maker of nutrient status?
iron stored as ferritin
small amounts of ferritin secreted into plasma
serum [ferritin] correlates with size of total body iron stores
low serum ferritin = depleted iron stores
What is the caveat when using ferritin as a marker of iron stores?
Ferritin = +ve acute phase protein
[ferritin] increase during inflammation
It is then no longer an accurate estimation of the iron stores
What is total energy expenditure?
= basal metabolic rate + diet-induced thermogenesis + activity ± stress
where stress = illness ± inflammation ± surgery
How is total energy expenditure measured?
direct or indirect calorimetry
usually in research
How is total energy expenditure estimated in the clinical situation?
use predictive equations and adjust for clinical situation
- 23-35 kcal/kg
- Schofield equations
- Harris-Benedict equation
- Ireton Jones
What affects nutrient requirements?
age gender body size physical activity state of health physiological status (e.g. pregnancy and lactation) growth
What are dietary reference values (DRV)?
estimates of the amount of energy and nutrients needed by different groups of HEALTHY people in UK population
Which situations are dietary reference values irrelevant?
in individuals
in illness/injury
outside UK
Which regulatory bodies generate dietary reference values?
was COMA
now superseded by SACN
What are the different types of DRVs?
EAR = estimated average requirement RNI = reference nutrient intake LRNI = lower reference nutrient intake SI = safe intake
How is RNI calculated?
reference nutrient intake (RNI)
= amount of that nutrient that is sufficient for 97.5% of the group or population
How is LRNI calculated?
lower reference nutrient intake (LRNI)
= amount of nutrient that is enough for only 2.5% (lower) of a group
i.e. the majority of people need more than LRNI
How is EAR calculated?
estimated average requirement (EAR)
= intake level for a nutrient at which 50% of the group/population will be met
this means that 50% will need less than the EAR
and 50% will need more than the EAR
Which DRV is used as a measure of energy intake?
EAR
Which DRV is used as a measure for protein, vitamin and mineral intake?
RNI
Also used as a reference amount for population groups
What is LRNI a useful measure of?
nutritional inadequacy
i.e. the amount(s) at which deficiency or symptoms may appear as intake is too low for that nutrient
Why do we estimate nutritional requirements?
Benchmark to evaluate dietary adequacy/demands in HEALTHY GROUPS
Plan what to provide - hospital menus, school meals, rations
How can DRVs be used in clinical situations?
Can distinguish underlying pathology from a low intake of a nutrient
e.g. if intake > RNI, deficiency is unlikely to be due to inadequate intake
BUT if intake < LRNI, then they are not consuming enough of that nutrient to meet their requirements
What are the main caveats of using DRVs?
- Bioavailability of nutrient
- assumes that requirements for other nutrients are met (i.e. cannot look at multiple nutrients at once)
- DRVs have differences between countries
- DRVs reflect needs of healthy people not unwell people
Why do deficiencies develop?
- inadequate intake
- reduced absorption (e.g. Coeliac)
- increased losses (e.g. D+V)
- increased demand (e.g. pregnancy)
What are the stages of nutrient deficiency?
= supply < demand Stages: - health - subclinical deficiency - deficiency - death
What are the main symptoms of vitamin A excess?
toxicity
What are the main features of vitamin A deficiency?
LEAST DEFICIENT Health Depleted vitamin A stores in liver Low blood levels Increased infection risk Xerophthalmia (blinding vs. non-blinding) MOST DEFICIENT
What is Xerophthalmia?
abnormal dryness of conductive and cornea
+ inflammation
mostly associated with vitamin A deficiency
What nutrients are absorbed in the stomach?
water ethyl EtOH Copper iodide Fluoride molybdenum
What nutrients are absorbed in the terminal duodenum and jejunum?
lipids
monosaccharides
amino acids
small peptides
What nutrients are absorbed in the ileum?
vitamin C folate Vit B12 Vit D Vit K Magnesium
What is absorbed in the terminal ileum?
bile salts and acids
enterohepatic circulation to feed back to liver
What is absorbed in the large intestine?
water Vit K Biotin Na+ Cl- K+
What is the function of Calcium? In which foods, is it found?
Foods: dairy, sardines, green leafy veg (not spinach), fortified flour
Function: build strong bones + teeth, regulates muscle contractions, blood clotting, cardiac function
What is the function of iron (HAEM)? In which foods, is it found?
Foods: liver, black pudding meat
- well absorbed and not affected by other dietary components
Function = O2 carrier
haemaglobin in blood
myoglobin in muscle
What is the function of iron (NON-HAEM)? In which foods, is it found?
Foods: beans, nuts, dried fruit, wholegrains etc
Function: Function = O2 carrier
haemaglobin in blood
myoglobin in muscle
Which dietary components affect the absorption of NON-HAEM iron?
REDUCED by tannins and phyates
INCREASED by vitamin C
What is the function and dietary source of K+?
foods: bananas, broccoli, parsnips, seeds, fish, beef
function: major intracellular cation, role in acid-base balance, muscle contraction and nerve conduction
What is the function and dietary source of Mg2+?
Foods: dairy, meat, fish, wholegrain bread, brown rice and green leafy veg
Functions: cofactor in enzymatic reactions (e.g. respiration), skeletal development, protein synthesis, muscle contraction,
Metabolically associated with Calcium
What is the function and dietary source of Na+?
foods: salted foods
function: major extracellular cation, fluid balance, BP maintenance, transmembrane gradients
What is the function and dietary source of phosphorus?
foods: meat, dairy, cereal, meat and fish
function: strong bones/teeth, release energy from food and O2 release (via ATP and NADP)
What is the function and dietary source of Selenium?
foods: bread, meat, poultry, offal, nuts and eggs
function: antioxidant, immune function and thyroid hormone metabolism
What affects selenium content?
the soil on which the crops are grown or animals are grazed
UK soil has low Se content
What is the function and dietary source of Zn2+?
foods: meat, shellfish, dairy, bread, pulses, eggs
function: cofactor for >100 metalloenzymes, wound healing
What is the function and dietary source of vitamin A?
foods: dairy, eggs, oily fish, liver products
function: night vision, development of tissues, reproduction, embryonic development and growth
What is the function and dietary source of beta-carotene?
foods: yellow, red and green veg, yellow fruit e.g. mango, papaya
function: night vision, development of tissues, reproduction, embryonic development and growth
What is the difference between vitamin A and beta-carotene?
Vitamin A = retinol
beta carotene is a precursor to vitamin A
Body converts beta-carotene into vitamin A
What is the function and dietary source of vitamin B1?
Vitamin B1 = thiamine
foods: peas, fresh/dried fruit, fortified bread, cereals, eggs
function: release of energy from food, nervous system health
What is the function and dietary source of vitamin B2?
vitamin B2 = riboflavin
foods: milk, eggs, fortified cereals, rice
functions: normal growth, integrity of mucous membranes, skin, eyes and nervous system
What can affect riboflavin content?
Riboflavin = vitamin B2
UV light can destroy riboflavin so these foods should be stored out of direct sunlight
What is the function and dietary source of vitamin B3?
vitamin B3 = niacin
foods: meat, fish, eggs, milk, wheat flour
function: metabolic pathways = REDOX in respiration, lipid metabolism
What is the function and dietary source of pantothenic acid?
precursor to coenzyme A
foods: yeast, offal, meat, eggs, green leafy veg, fortified cereals
function: coenzyme A has central role in energy metabolism
What is the function and dietary source of vitamin B6?
Vitamin B6 = pyridoxine
foods: pork, poultry, fish, eggs, milk, bread, oatmeal, wheatgerm, soya, peanuts, cereals
functions: storing energy from protein and carbs, haemoglobin synthesis
What is the function and dietary source of vitamin B7?
vitamin B7 = biotin
foods: wide range but only in small levels
functions: coenzyme in many reactions e.g. lipolysis, lipogenesis and gluconeogenesis
Why is it unclear whether exogenous biotin from diet is needed?
Commensal gut bacterial synthesise biotin
this may be sufficient for the requirements we have for biotin
What is the function and dietary source of folate?
foods: liver (but avoid in pregnancy), yeast extract, pulses, green veg, dairy, fortified cereals
functions: folate coenzymes needed for methylation (cell division), erythropoiesis, prevention of neural tube defects in utero (e.g. spina bifida)
What is the function and dietary source of vitamin B12?
vitamin B12 = cobalamin
foods: meat, salmon, cod, dairy, fortified cereals
functions: amino acid metabolism, conversion of homocysteine to methionine (in which vitamin B12 is a cofactor)
What is the function and dietary source of vitamin C?
vitamin C = ascorbic acid
foods: fruits (esp. citrus), kiwi, green and red peppers
functions: antioxidant (esp in aqueous tissues), reduced Fe3+ to Fe2+ (latter is used in absorption of non-haem iron), collagen synthesis, vascular and cartilage maintenance,
What is the function and dietary source of vitamin D?
vitamin D3 = cholecalciferol
vitamin D4 = ergocalciferol
foods: oily fish, red meat, egg yolks, cereals
function: Ca2+ homeostasis and absorption, regulates Ca2+ and phosphate absorption in small intestine, plasma Ca2+ levels via bone reabsorption
What is the function and dietary source of vitamin E?
vitamin E = alpha tocopherol (highest bioavailability) and gamma-tocopherol (found mainly in plants)
foods: plant oils, nuts and seeds, cereals
functions: antioxidant (esp in preventing ROS damage in cell membranes and other lipid structures)
What is the function and dietary source of vitamin K?
vitamin K1 = found in plant foods
vitamin K2 = synthesised by colonic bacteria
foods: green leafy veg, veg oils, cereal grains, smaller amounts in meat and eggs
functions: prothrombin formation, blood coagulation
What is malnutrition?
nutritional imbalance
UNDER-nutrition vs OVER-nutrition
What is over-nutrition?
excess nutrient and energy intake over time
malnutrition when over-nutrition leads to morbid obesity
number of complications linked to obesity
What are the ranges for BMI?
healthy 18.5-24.9 overweight 25-29.9 obesity I 30-34.9 obesity II 35-39.9 obesity III 40+
What measures are used to classify obesity?
BMI
waist-to-hip ratio
waist circumference
waist-to-height ratio
What are the complications of obesity?
stroke heart disease liver disease cancer reproductive complications depression and anxiety sleep apnoea T2DM asthma osteoarthritis
What is the prevalence of obesity in children?
1: 10 children in reception are obese
1: 5 children in year 6 is obese
What is under-nutrition?
state in which there is a deficiency of nutrients such as energy, protein, vitamins and minerals
adverse effects on body composition, function or clinical outcome
What are the main causes of under-nutrition?
starvation-related
- inadequate intake
disease related
- malabsorption of micro/macronutrients
- increased demand
What are the demographics of malnutrition in the UK?
> 3 million people
~ 1.3 million are >65yo
25-34% of patients admitted to hospital are at risk of malnutrition
What are the consequences of malnutrition?
- weakened immune system
- impaired wound healing
- loss of muscle mass
- kidney injury
- infertility
- apathy, depression
- hypothermia
- micronutrient deficiency (e.g. rickets)
- increased hospital stay and mortality
What screening tools are available for malnutrition?
- malnutrition universal screening tool (MUST)
- subjective global assessment (SGA)
What does the MUST score take into account?
MUST = malnutrition universal screening tool
- BMI score
- weight loss score
- acute disease score
- overall risk of malnutrition
total score of >2 is HIGH RISK
How are the different MUST scores manages clinically?
Low risk (MUST = 0) routine clinical care
Medium risk (MUST = 1) observe
High risk (MUST >=2) treat
What does the subjective global assessment consider?
Medical history:
- weight change
- dietary intake
- GI symptoms
- functional impairment
Physical examination:
- muscle wasting
- subcutaneous fat loss
- oedema
3 categories of SGA score:
1) well nourished
2) mild/moderate under-nutrition
3) severe under-nutrition
What clinical signs are indicative of malnutrition?
sunken eyes skin pinch (also dehydration) loose clothing, loose jewellery indicating weight loss pressure sores diarrhoea, vomiting, pain
What tests can be used to make a nutritional assessment for malnutrition?
anthropometry
biochemical and haematological markers
clinical state and physical condition
diet
What is anthropometry?
= external measurement of body composition
- weight
- BMI
- weight loss
What are the limitations of anthropometry?
difficult to obtain wright in bed bound patients
affected by oedema and ascites (fluid is not taken into consideration)
What are the dry weight estimates for ascites?
tense = 14kg moderate = 6kg minimal = 2.2kg
What are the dry weight estimates for oedema?
severe (up to sacrum) = 10kg
moderate (up to ankle) = 5kg
mild (up to ankle) = 1kg
How is hand grip strength used?
index of muscle function
measured over time
can respond more rapidly to nutritional support than other parameters
mean value is compared to reference data
<85% is cause for concern and is linked to significant morbidity
What are the limitations of using hand grip strength?
- affected by motivational status
- improves with repeated use (accuracy of measure reduces)
- arthritis and confusion will affect it
What biochemical markers can be used to detect malnutrition?
Albumin (35-55 g/L)
levels fall when protein absorption is reduced)
Urea (6-20 mg/dL)
formed from proteolysis
low levels indicate poor protein intake
Why are albumin levels a poor measure of nutritional status?
- long half life ~ 21 days
- levels increase during dehydration
- levels fall during stress/infection (important to consider albumin levels with CRP)
- poorly correlated with nutritional status
What is the metabolic response to starvation?
adaptive response
prolonged starvation = BMR reduces by 30%
reduction in mass of metabolically active tissues (e.g. liver and GI tract)
protein loss minimised
glucose supply maintained
In which order are macronutrients used following starvation?
(FIRST) carbohydrates (hepatic glycogen stores run out after days) fats + ketones protein (LAST)
What is the metabolic response to injury, trauma or sepsis?
different to starvation
need to mobile energy for immune defence and repair
What are the 3 stages of metabolic response to injury/trauma/sepsis?
- Ebb phase
- Flow phase
- Anabolic phase (recovery phase)
What is the Ebb phase following injury/trauma/sepsis?
shock
occurs within hours
- energy reserves are mobilised, but body is shocked and struggles to use it
- BMR falls
- body temp falls (hypothermia)
What is the flow phase following injury/trauma/sepsis?
Catabolism
occurs within days
- breakdown of energy stores
- BMR rises
- body temp increase (fever)
- acute insulin resistance
- visceral and skeletal muscle breakdown
What is the recovery phase following injury/trauma/sepsis?
anabolism
occurs within weeks
- building up energy stores
- nutritional therapy: increase protein synthesis and restore lean body mass
Which injuries/trauma cause the biggest spikes in energy expenditure?
highest EE - major burns - sepsis/peritonitis - skeletal trauma - elective surgery - starvation least EE
What are the main metabolic processes that occur in response to starvation?
- reduced BMR
- slow weight loss (almost all from fat)
- nitrogen loss reduced
- early small increase in catecholamines, cortisol and GH
- slow fall in glucagon and cortisol
- insulin reduced
- initial loss of water and sodium
What are the main metabolic processes that occur in response to injury?
- increased BMR
- rapid loss of weight (80% from fat stores, 20% from body protein)
- nitrogen losses increased
- increased catecholamine, glucagon, cortisol and GH
- insulin increased but with resistance (hyperinsulinaemia with IR)
- retention of water and sodium
What is rickets caused by?
Vitamin D deficiency
either due to poor diet or inadequate sunlight
