Dietary Requirements And Reference Values

Question 1

Essential nutrients

Answer 1

• EAA: leucine, isoleucine, valine, lysine, methionine, phenylalanine, threonine, tryptophan, histidine
• nitrogen: to synthesize non essential AA
• lipids: ALA, LA
• energy!!

Question 2

How to determine requirements: body composition analysis

Answer 2

• autopsy studies looking at affects on organs following malnutrition
• can also measure body composition using DXA, potassium 40 counting, protein-neutron activation analysis, anthropometry

Question 3

How to determine requirements: nutrient balance studies

Answer 3

• give dose of nutrient and measure excretion rate

- assumption is that once saturate stores will start coming out in urine

Question 4

How to determine requirements: nutrient deficiency studies

Answer 4

• looking at deficiencies and impact on health

- observational studies such as scurvy and beri-beri amongst sailors

Question 5

Techniques for measuring nitrogen balance

Answer 5

• kjeldaahl method: catalytic oxidation of protein, tedious method. Multiple titrations
• chemiluminescence analysis: protein burnt in furnace with O2 to form NO2, releases photons and analyser reads light
• indicator amino acid oxidation method: give C13 labelled amino acids and looking at degree of oxidation

Question 6

The issue with nitrogen balance studies

Answer 6

• regression analysis: both linear and curved regression usually fit data, making the intercept for positive N balance difficult to accurately assess
• indicator amino acid oxidation method: same amount of Phe indicator given at different levels of amino acid
• pregnant women: do not need the high intakes indicated by efficiency factors, it is toxic
• some populations, such as very old or critically unwell may need more protein

Question 7

Basis of reference requirements

Answer 7

• based on assumption that nutritional requirements in a population follow a gaussian distribution
• EAR: average requirements
• RNI: covers 97% of the population
• LRNI: only appropriate for 3% of the population
• levels much above RNI could result in toxicity- energy is an example where not much over the RNI could cause obesity
• levels below the LRNI could cause deficiency
• give age dependent advice based on standardised weight
• set a safe upper level for vitamins and minerals

Question 8

Energy requirements

Answer 8

• BMR calculations can be based on variety of equations, many are outdated, Henry 2005 often used
• EE for different activities: PAR 1.2 (sedentary), PAR 3.7 (cleaning, bricklaying), PAR 6-7.9 (exercise)

BMR*PAR

Question 9

Uk recommendations for omega 3

Answer 9

• found that the higher the omega 3 index the lower the CVD

- therefore recommend 0.2g per day meaning oily fish 1-2x per week

Question 10

Comparison of low fat versus low cho diets for weight loss

Answer 10

• barely any difference in fat loss
• no metabolic effects or ‘ramping up metabolism’ in the high fat group
• predictable changes in RQ
• more water weight loss in the high fat group