Markers of nutritional status, nutrition and food

Health and Social Behaviour: Markers of nutritional status, nutrition and food

Individual markers of nutritional status

Anthropometry

  • Anthropometry is the means by which body composition can be assessed in living people. The results reflect both health and nutritional status, and can be used to predict health and survival.
  • The most common techniques employed when measuring body composition anthropometrically are: body weight, BMI, mid-arm muscle circumference, and skin fold thickness.

Body weight measures the total weight of an individual, including muscle, fat, water and bone. Changes in body weight are an important indicator of nutritional status; being underweight or overweight adversely influences mortality and
morbidity.

Body Mass Index (BMI)

BMI is measured using weight (in kilograms) divided by height (in metres, squared). It reflects body fat stores and is an important way of classifying subjects into weight categories, which correlate with risks. BMI is used to classify adults into
a number of weight categories.

NOTE:  BMI does not take into account muscle mass. It is also not appropriate for children – their weight should be monitored using growth charts.

http://www.dh.gov.uk/en/Publichealth

Growth Charts

Anthropometric indices are the main criteria for assessing adequacy of growth and optimal nutritional status in infancy and childhood.  In infants and children under 5 years old, assessment of growth is the single most important measurement
of nutritional status. Presence of undernutrition in children is assessed using weight for age, height for age and weight for height.

Height for age shows linear growth, and can be used to measure for long term growth faltering or stunting. Weight for Height shows proper body proportions and harmony of growth. It is sensitive to acute growth disturbances and detects wasting.
 Weight for age is used to diagnose underweight children. To be classified with wasting, underweight or stunting, the child must be 2 SD (or more) below the standards compared to internationally accepted reference standards (e.g. NCHS/WHO
(National Centre for Health Statistics / World Health Organisation) of international reference populations.

Skin fold thickness

Skin fold thickness measures the relationship between subcutaneous fat and total body fat, measured by pinching a fold of skin with subcutaneous fat between a pair of skin fold callipers, used to estimate adiposity.

Waist circumference

Waist circumference is an accurate measure of central obesity and is a valuable tool in predicting obesity risk. A waist circumference of >94cm in men and >80cm in women, indicates an increased risk of diseases such as coronary heart disease
(CHD). This measurement is widely used in the classification of obesity.  Waist to hip ratio can also be used to look at predicting heart disease and mortality risk, but has little advantage over waist circumference.

http://nationalobesityforum.org.uk

Biochemical and Haematological considerations

Physiological chemistry values can be altered by profound nutritional depletion. However, biochemical and haematological measurements have only limited value in the assessment of nutritional status. They can often change on a daily basis and are
also frequently compensated for by homeostatic mechanisms. Disease also affects these parameters so may give an inaccurate view of nutritional status. Vitamins, minerals and trace elements in blood can be measured but they will only usually show
depleted levels if there is a severe nutrient deficiency e.g. iron, zinc.

Individual markers of nutrition and food

There are 2 approaches of measuring dietary assessment – prospective and retrospective.

Prospective methods involve collecting or recording current data.

Advantages:

  • They are direct methods of measuring current diet.
  • Can be carried out for varying lengths of time according to the level of accuracy needed.

Disadvantages:

  • They are labour intensive and require good literacy and numeracy levels.
  • Data may be inaccurate due to inaccurate recording (over- or under-estimation of intake).
  • Data may not reflect the actual diet as the subject may alter it for ease of recording or because they felt their diet was being scrutinised.

Retrospective methods involve recalling either recent or past data.

Advantages:

  • Less labour intensive.
  • Quick to administer compared to prospective methods.
  • Less expensive (less assessor time and equipment needed).
  • Increased chance of obtaining a more representative sample of consumers due to lower respondent burden (there is less effort needed by the subjects to complete the assessments).
  • Can be used to assess diet in the past (historical food consumption of an individual) which is useful when studying links between diet and chronic diseases such as cancer or heart disease.

Disadvantages:

  • Data may be inaccurate due to poor memory (over- or under-estimation of intake). Errors of memory can mean that some foods are omitted from the diet recall – this particularly important with elderly subjects and children under the age of
    about 12 years.
  • Subjects need good skills relating to the perception of food portion size – they need to accurately remember how much they ate and translate this into an accurate description of portion size.
  • If an observer is present, it may cause subjects to overemphasise what they perceive to be the ‘good’ parts of their diet, and minimise the ‘bad’ aspects.
  • Daily variation is less readily assessed using retrospective methods, and subjects who have irregular eating habits will find it difficult to describe a ‘normal’ day.

Prospective Methods:

Food Frequency and Amount Questionnaires (FAQs)

Pre-printed lists of foods, which subjects are asked to fill in, indicating the typical frequency of consumption of foods and average amount (in household measures – e.g. cup, bowl, spoonful). These are often self-administered (no need for
trainer questioner)

The main advantage is that it is good for large epidemiological studies across a wide geographical area. The main disadvantages are that the questionnaire takes a long time to develop and the list usually contains food groups (rather than
individual foods) so subjects must know how to classify foods.

Food diary

There are 2 kinds of food diary – the weighed inventory and the household measures technique.

Weighed inventory is one of the most widely used techniques. Subjects keep a record of all food and drink consumed, all weighed prior to consumption.

The main advantage is the accuracy of the measurement of portion sizes. The main disadvantage is that there could be under-reporting.

Household measures technique is similar to weighed inventory, except that subjects record their portion sizes in household measures (e.g. cup, bowl, spoonful, etc) instead of weighing foods. Aids such as food models or photos can be used to
improve estimates of portion sizes.

The main advantage is that it simplifies the recording process for subjects. The disadvantage is that using household measures may cause a loss of precision, which can cause an individual to be misclassified according to intake.

Duplicate Diet Method

The subject has to weigh and record food consumed, but also weigh and set aside exactly the same portions again. These portions are collected and chemically analysed.

The main advantage of this method is that it is independent of errors associated with food composition tables. The main disadvantages are that it is very expensive and subjects may fail to set aside exactly the same duplicates.

Food Checklists

This method involves subjects being given lists of foods commonly consumed by the population under study. The subject then ticks the foods which they have consumed each day, and record the approximate amounts in household measures. There is space
at the bottom to add foods which are not on the list.

The advantage of this method is that it reduces the amount of recording required, due to the data being displayed in lists. This also reduces the amount of time spent processing the data. The main disadvantage of this method is that subjects may
fail to record foods not listed.

Retrospective Methods:

24 hour recall

A trained interviewer asks subjects to recall and describe every item of food and drink consumed over exactly 24 hours. It involves a systematic repetition of open-ended questions, asking subjects to describe amounts in household measures.

The main advantages are that it is a quick process to administer (10-15 minutes) and has good compliance.  The main disadvantage is that a single 24 hour recall can’t be used to classify a subject according to their intakes – it’s
better suited to estimating average intake of groups of people.

Diet History

A diet history is used to assess usual diet over the recent past.  It begins with a 24 hour recall followed by a 2 hour interview to elaborate on this.  A trained interviewer will ask subjects to describe the variety of foods that they
are likely to eat at each meal, the frequency of their consumption and the typical amounts. They are also asked about the difference between weekdays and weekends, and any seasonal variations.

The advantage of this method is that a large quantity of information can be gained from one interview, and special attention can be paid to specific food groups rich in certain nutrients.

The disadvantage is that it is quite dependent on the skill of the interviewer and effort needs to be taken to ensure that subjects are not over-reporting ‘healthy’ foods or under-reporting ‘unhealthy’ foods.

Local and national food intake data

Indirect measurements of food intake

These measures of food intake are derived from sources providing data on the amount of food available for consumption (food supply data), the volume of food traded at the wholesale or retail level (food disappearance data) or on the amount of food
purchased at a household level (household budget or expenditure data). They are not directly based upon data of food intake.

Food Supply Data is usually produced at the national level. It is based on compilations of data from the multiple sources – primary sources being records of agricultural food production and food exports and imports.  They are usually
referred to as ‘Food Balance Sheets’ or ‘Apparent Consumption Data’, and they represent the food available for consumption in a country – usually expressed per caput in grams or kilograms per year.  The Food and Agriculture
Organization (FAO) has compiled data for most countries in the world – available on line http://www.fao.org/.

The accuracy of food balance sheets depends on the reliability of the basic statistics used (population, supply, utilization and food composition data), which can vary a great deal between countries.  The FAO build in some consistency checks
into their food balance sheets but the data still needs to be evaluated in the context of the purpose for which you wish to use them.

Household Food Surveys

These generally focus on household income and expenditure – usually called ‘household expenditure’ or ‘household budget’ surveys.  Their primary focus is usually collecting information on the amount of money spent on food over a
given period.  Sometimes quantities of food purchased may be collected – but often aren’t processed. This data would be useful to translate the data into nutrient patterns.  This provides useful information for nutritionists on food
expenditure patterns of different types of households.

Household budget surveys (HBS) are conducted at regular intervals in many European countries, data can be accessed at http://europa.eu.int/estatref

Advantages – The surveys are conducted at regular intervals (1-5 years) and on representative samples of households.  Information collected can be classified by socio-demographic characteristics, geographical location and season.

Disadvantages – The type of information collected differs from country to country, most do not include expenditure on food consumed outside of the house (e.g. restaurants) or data on domestic wastage (how much is thrown away or given to pets).
 Nutrient content can not be assessed as food is reported at food group level, not individual foods.  It is also difficult to compare data between countries due to different food codes.

The large amount of nutrition-related data collected can potentially be used for assessing nutritional patterns of different population groups, identifying groups at high risk of nutrition-related conditions, monitoring trends in food patterns
over time, and for developing nutrition policy.

In the UK, the Office of National Statistics conducts the Family Expenditure Survey (FES) – see this link for more information:

http://www.statistics.gov.uk/StatBase 

Food Mapping Exercises

Food mapping has been defined as the process of finding out where people can buy and eat food, and identify the food needs of local people.  It is a type of needs assessment, aiming to identify the geographical areas or communities that have
the greatest needs in terms of food access.

Food mapping is one of the first activities that should take place when planning to set up a food project, and even more so when planning to deliver a programme of different activities to increase access to healthy foods.

The process can be used to get a clearer picture of what types of food initiative or policy changes are needed to address why people may not be eating a healthy balanced diet.

“Food deserts” (see below) in an area can also be identified.

Food mapping can be expensive and time consuming but is very adaptable to the population that is being surveyed – for example in one community you may wish to map access to fresh and healthy foods, in another you may wish to map access to ethnic
foods for a specific population within that community.  Many aspects of food access are looked at including price, quality, opening times, accessibility, transport links, etc. http://www.foodvision.gov.uk

Food deserts are ‘areas of relative exclusion where people experience physical and economic barriers to accessing healthy food’ [definition: Low Income Project Team 1996].  The term food desert is used to describe an urban
environment lacking in certain facilities.  The Independent published on 11 June 1997 described food deserts as “those areas of inner cities where cheap nutritious food is virtually unobtainable. Car-less residents, unable to reach out-of-town
supermarkets, depend on the corner shop where prices are high, products are processed, and fresh fruit and vegetables are poor or non-existent”.

Food deserts are common in inner city areas, especially estates, where there may not be any shops selling healthy, affordable food OR people living there may not have access to shops that are selling it through disability, lack of transport or
fear to leave their homes. http://www.fooddeserts.org

Food Markers - food composition tables

Food composition tables show the nutrient content of a large number of foods, as calculated in isolation in a laboratory. The first food composition tables were published by McCance and Widdowson. There are others available, including INFOODS –
the Food and Agriculture Organization of the United Nations – which are regional-use food composition tables. With advances in technology, there are now a large number of computerised nutritional databases – which allow the user to input foods
and weights, and will produce a detailed calculation of the nutrient content of those foods. Many data bases will also compare these values to DRVs and RDAs for particular genders and age groups. http://www.fao.org 

Population markers of nutritional status

National Diet and Nutrition Surveys (NDNSs)

These are the main national food surveys in the UK.  They are part of a programme of national surveys, which aim to gather comprehensive cross-sectional information on the dietary habits and nutritional status of the British population. 
There are 3 different surveys:

The surveys use a national sample of the population. The series covers foods consumed/nutrient intakes derived from analysis of dietary records, and nutritional status derived from analysis of blood and urine samples, physical measurements and
physical activity records.

The results of the surveys are used to develop nutrition policy and to contribute to the evidence base for Government advice on healthy eating.

Disease levels can also be an indicator of nutritional problems within a population. Some diseases could indicate a poor diet in terms of over nutrition – for example obesity, coronary heart disease, stroke. Other diseases and statistics could
indicate problems with undernutrition – for example Iron Deficiency Anaemia (IDA), Low Birth Weight (caused by Intrauterine Growth Retardation). However, it must be remembered that diseases are often multi-factorial in cause, so other factors need
to be taken into account, such as smoking, exercise, socioeconomic grouping, food access, etc.

National Healthy Eating Goals

See section of Dietary Reference Values

Government campaigns and documents

5 A Day

The Government recommends an intake of at least 5 different portions of fruit and vegetables (in total – not 5 of each) for each person per day. http://www.5aday.nhs.uk/. This recommendation comes from a
number of studies which concluded that 400g (around 5 portions) of fruit and vegetables each day helps to reduce the risk of some cancers, heart disease and many other chronic diseases. http://www.dh.gov.uk/en/Publichealth.
This is a large campaign and includes initiatives such as the school fruit and vegetable scheme http://www.dh.gov.uk/en/Publichealth/Healthimprovement

Food labelling

A lot of new work has been done on food labelling. The FSA has worked on a new ‘traffic light’ labelling system, which supermarkets such as Waitrose and Sainsburys are using. Follow this link for more information on food labelling: http://www.eatwell.gov.uk

Healthy Weight, Healthy Lives – A Cross Government Strategy for England (2008)

This was published in January 2008 and is the first step in a sustained programme to support people to maintain a healthy weight. Healthy Weight, Healthy Lives address issues highlighted in the Foresight report http://www.foresight.gov.uk/Obesity.
Britain has the ambition to become the first major nation to reduce the rising tide of obesity and overweight in the population by ensuring that everyone is able to reach and maintain a healthy weight. The first focus of this strategy is children –
Britain is aiming to reduce the overweight and obesity levels for children to the 2000 levels, by 2020. This target is 13% by 2020. The National Child monitoring Programme reported the 2006/7 average national childhood overweight and obesity
statistics to be 22.9% for reception year, and 31.6% for year 6. In follow up to this, there will be annual progress reports, looking at latest evidence and trends, and making recommendations for the future. For more information on Healthy Weight
Healthy Lives http://www.dh.gov.uk/en/Publicationsandstatistics

References

© Rebecca Nunn 2008