XNN001 Nutrition assessment in individuals and populations


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  • The skinfold estimation methods are based on a skinfold test, whereby a pinch of skin is precisely measured by calipers at several standardized points on the body to determine the subcutaneous fat layer thickness. These measurements are converted to an estimated body fat percentage by an equation. Some formulas require as few as three measurements, others as many as seven. The accuracy of these estimates is more dependent on a person's unique body fat distribution than on the number of sites measured. As well, it is of utmost importance to test in a precise location with a fixed pressure. Although it may not give an accurate reading of real body fat percentage, it is a reliable measure of body composition change over a period of time, provided the test is carried out by the same person with the same technique.Skinfold-based body fat estimation is sensitive to the type of caliper used, and technique. This method also only measures one type of fat: subcutaneous adipose tissue (fat under the skin). Two individuals might have nearly identical measurements at all of the skin fold sites, yet differ greatly in their body fat levels due to differences in other body fat deposits such as visceral adipose tissue: fat in the abdominal cavity. Some models partially address this problem by including age as a variable in the statistics and the resulting formula. Older individuals are found to have a lower body density for the same skinfoldmeasurements, which is assumed to signify a higher body fat percentage. However, older, highly athletic individuals might not fit this assumption, causing the formulas to underestimate their body densityAdvantages: simple, quickDisadvantages: requires training, 5 – 10% error
  • The general principle behind BIA: two conductors are attached to a person's body and a small electric current is sent through the body. The resistance between the conductors will provide a measure of body fat, since the resistance to electricity varies between adipose, muscular and skeletal tissue. Fat-free mass (muscles) is a good conductor as it contains a large amount of water (approximately 73%) and electrolytes, while fat is anhydrous and a poor conductor of electric current.Advantages: simple to useDisadvantages: Altered hydration status will affect results
  • Dual energy X-ray absorptiometry, or DXA (formerly DEXA), is a newer method for estimating body fat percentage, and is a very efficient and advantageous method of determining body composition and bone mineral density.X-rays of two different energies are used to scan the body, one of which is absorbed more strongly by fat than the other. A computer can subtract one image from the other, and the difference indicates the amount of fat relative to other tissues at each point. A sum over the entire image enables calculation of the overall body compositionAdvantages: High precision, measures fat directlyDisadvantages: Expensive
  • Whole body counting, refers to the measurement of radioactivity within the human body. The technique is only applicable to radioactive material that emit gamma rays. A gamma ray is emitted from a radioactive element within the human body. If its energy is sufficient that it can escape the body before being absorbed or have any other interaction where it can lose energy, it can be detected. Usually either a scintillation detector or a semiconductor detector would be used for such purposes.There are many ways a person can be positioned for this measurement: sitting, lying, standing. The detectors can be single or multiple and can either be stationary or moving.Advantages: Direct measure of intracellular K, 3 – 4% errorDisadvantages: Availability and expense (research only)
  • XNN001 Nutrition assessment in individuals and populations

    1. 1. XNN001 Semester 2 2013
    2. 2.  The first step before planning and evaluating the nutritional care of individuals or groups  Determined on the basis of multiple kinds of information  A systematic method for obtaining, verifying & interpreting information
    3. 3. Individual Nutrition Assessment Anthropometry Biochemistry (Laboratory analysis) Clinical Dietary Energy Requirements Population Assessment & Monitoring Food Supply Data Food Prices Household & Dietary Surveys Mortality & Morbidity Data Anthropom etric Data Birth wt, infant feeding & mortality Monitoring & Surveillanc e System
    4. 4. Four main components 1. Anthropometry 2. Biochemistry (Laboratory assessment) 3. Clinical assessment 4. Dietary intake 5. Energy requirements
    5. 5.  Study of physical dimensions of the body  Standardised equipment & procedures essential  Body size  direct measurements  height, weight, circumferences  derived values  Body shape  Waist hip ratio, body weight distribution  Body composition  size of lean tissue and fat compartments
    6. 6.  One of the most commonly used measurements for assessing nutritional status  Ratio of weight to height  Caution – BMI not ideal for determining health risk as it does not reflect amount of muscle compared to fat
    7. 7. # WHO 2000, AIHW (2004) * Ideal body wt (IBW) or desirable wt for ht (US Metropolitan Life Insurance data) 9 Classification # BMI (kg/m2) IBW % * Risk of Chronic Disease Underweight <18.5 >10% below* Low (but other risks) Normal range 18.5-24.9 desirable Average Overweight >25 pre-obese 25.0-29.9 (10-19% above*) Increased obese class I 30.0-34.9 (>20% above*) Moderate obese class II 35.0-39.9 Severe obese class III >40 Very severe
    8. 8. BMI classification in kg/m2 10 Asian Pacific Is. <18.5 <19.9 Underweight 18.5-23.9 20.0 - 26.9 Normal weight 24.0-26.0 27.0-32.9 Overweight 27.0-39.0 33.0-39.9 Obesity
    9. 9.  The International Obesity TaskForce (IOTF) published BMI thresholds defining paediatric overweight and obesity in 2000.  Centile equivalents for children aged 2–18 were derived statistically by extrapolation from adult cutoffs at BMI 25 and 30 kg/m2, respectively.  They were not intended for clinical use but to assess trends and to compare populations.
    10. 10.  Height requires a stadiometer – a ruler calibrated in cm and m, which is fixed to the wall and has a movable head plate
    11. 11.  Infants up to 36 months should be measured in cm, using recumbent length if they are unable to stand
    12. 12.  Chumlea has developed formula to estimate knee height in those who are unable to stand  Men = 64.19 – (0.04 X age) + (0.02 X knee height)  Women = 84.88 – (0.24 X age) + (1.83 X knee height) Chumlea WC, Steinbaugh ML, Roche AF, Mukherjee D, Gopalaswamy N. (1985) Nutritional anthropometric assessment in elderly persons 65 to 90 years of age. Journal of Nutrition for the Elderly. 4:39-51.
    13. 13.  Is measured on scales which are on a hard, firm surface and calibrated daily  Weight is usually measured to the nearest 0.5kg
    14. 14. 1. Waist circumference (AIHW, 2005) > 18 y  >94 cm (M) >80 cm (F) – abdominal overweight  >102 cm (M) >88 cm (F) – abdominal obesity 2. Waist: hip ratio  visceral fat around organs vs. subcutaneous fat on hips  optimal WHR is < 1 (M) or < 0.8 (F)  varies with: genes, age, ethnicity, sex  increased by 'stress', smoking, alcohol  decreased by physical activity 19
    15. 15. NHMRC Obesity guidelines
    16. 16.  Metabolically active tissue determines energy requirements  Lean body mass or muscle mass is the most metabolically active tissue  Bodies are made up of water and fluids, bone, muscle and fat  80% of energy requirements are determined by height, weight, sex and age
    17. 17.  Body fat – skinfold thicknesses and Dual X ray Absorptiometry (DEXA)  Body water – Bioelectrical impedance (BIA)  Body cell mass – Total body potassium, DEXA (bone, muscle)
    18. 18. Fat Fat-free Mass (FFM) Fat Water (TBW) Protein Mineral Fat Ex-cellular fluid Body Cell Mass Ex-cellular solids Adapted from Wang et al (1992) and Heymsfield et al (1996), cited K Campbell, PhD thesis Skinfold DXA BIA TBK Body Composition Assessment Weight
    19. 19. DEXA
    20. 20.  Blood tests  Readily obtained (so often used)  Vary little (homeostatic control)  Should be used in conjunction with nutrient and supplementation history  Tissue testing  May include hair & nails for information about trace elements  Other tissues only acceptable under exceptional circumstances (invasive)  Urine testing  Varies between nutrients and influenced by variety of factors (including volume of urine)  Multiple samples required  Functional tests  Ability to perform specific functions (e.g. muscle response, immunological response)
    21. 21.  Advantages:  Provide the earliest indications of some nutrient deficiencies & excesses  Can confirm a nutritional diagnosis made on the basis of signs & symptoms  Can be used to assess the effect of nutritional therapy
    22. 22.  Information obtained includes:  Socio-demographic details (age, gender, occupation)  Medical history (including family history)  Dietary intakes  To help identify patients at risk of nutritional deficiency  Signs & symptoms important
    23. 23. Assessment of populations
    24. 24.  Infant birth weight  Provides information on:  maternal health & nutritional status  risk of infant mortality  Is influenced by:  maternal body size, infection, smoking, alcohol consumption, maternal nutrition during pregnancy  Infant mortality data  % related to prevalence of low birth weight (populations with high rates of low birth weight usually have high rates of infant mortality) e.g. Indigenous Australians Also affects
    25. 25.  Inappropriate infant feeding practices influences growth & development esp. in the 1st 4 to 6 mths  Decrease in breastfeeding since 1945 (21% 1971, above 50% since 1985)  Breastfeeding or correctly prepared infant formula  infant morbidity & mortality
    26. 26.  Provide information on:  the diseases & conditions that are reported as causes of death/hospital admissions  possibly on chronic conditions such as cancer & diabetes  Reflect:  the major social & health problems of the community  And can be used as:  clues to the most likely causes of mortality & morbidity  measures of the prevalence of specific nutrition related conditions
    27. 27.  Only provide information on:  Indirect measures of the kinds of nutritional problems most likely to be encountered in a population Multi-factorial aetiology of conditions in developed countries  Current burden of disease statistics available from the AIHW Disability adjusted life years (DALYs) are the years of life lost due to premature mortality & disability & measure the number of healthy years of life lost as a consequence of death or newly diagnosed disease or injury in the population.
    28. 28.  Weight & height are used in population studies as they:  provide an overall measure of nutritional status  are non-invasive  are quick to carry out  use minimal (& cheap) equipment  Provide information on:  the growth of children  the prevalence of obesity or underweight