Nutritional Status

Public health professionals, clinicians and researchers continually review dietary intake at a national population level right down to a single household or individual. This is for a whole host of reasons, with diet-related health issues and nutritional status always high on the agenda.

There is no one measure to determine the nutritional status of an individual. Often referred to as the ‘ABCD’ methods of nutritional assessment the following measurements and analyses may be used singly or interchangeably:

Anthropometric measurements – anthropometry meaning ‘measurement of the human body’ – includes metrics such as height, weight, waist and hip circumference, body composition and lean muscle mass. These measurements can be used as baseline figures for fitness regimes or as diagnostic tools to assess overweight and obesity. Equipment needed to record these measurements ranges from a simple set of weighing scales and a tape measure to more complex apparatus which analyses bioelectrical impedance (BIA).

• BIA devices, hand-held or ‘bathroom’ scales, measure the ability of different tissues in the body to impede or resist a weak, external, electric current. Tissues with a lower water content, e.g. fat, will impede the current more than tissues which have a higher water content, e.g. muscle. Studies have shown that BIA gives more accurate estimates for ‘fat mass’ and ‘free fat mass’ (fat mass = fat, fat free mass = everything else, so bone, muscle, internal organs, water etc.) than conventional anthropometry, particularly where height, weight, gender and age are also included in the calculations¹.

• Body Mass Index (BMI) – weight (kg) / height (m²) – is a measure of weight corrected for height, making it possible to compare the weight of individuals of differing statures and gives a result which falls into one of the following categories:

  • below 18.5 – underweight range
  • between 18.5 and 24.9 – healthy weight range
  • between 25 and 29.9 – overweight range
  • between 30 and 39.9 – obese range   (Source: NHS)
  
  BMI is straightforward to measure and calculate but can have its limitations. For example, excess weight and a subsequent higher BMI may not necessarily be due to excess fat, it could be muscle, notably in athletes and body builders. On the flip side, a healthy BMI score doesn’t always equate to a healthy body when other markers are taken into account, such as cholesterol and blood sugar levels.
  
  Follow this link for the NHS ‘BMI Healthy Weight Calculator’
  
  
• Dual-Energy X-ray Absorptiometry (DEXA Scan) is used to measure bone density and assess the risk of bone-related diseases such as osteoporosis, which can lead to bone fractures. This can then inform appropriate lifestyle changes, such as including more sources of calcium in the diet, increasing weight bearing exercise and considering whether supplements or medication might be required.

Biochemical assessment, e.g. laboratory analysis of blood or urine samples, a small selection of which are outlined below:

• Hb or haemoglobin is an iron-containing protein found in red blood cells. It has a high affinity for oxygen and carries the oxygen we breathe in from our lungs to other tissues in the body where it is used to help ‘burn’ or oxidise the nutrients we have digested. A low red blood cell count will result in low Hb levels and may cause symptoms of anaemia, e.g. tiredness and shortness of breath. Before anyone donates blood in the UK they will have their Hb levels checked to make sure they are high enough. No point donating blood if it leaves the donor with a low Hb and low energy levels due to decreased oxygen delivery to the tissues.

• HbA1c – haemoglobin again, but this time ‘glycated’ haemoglobin, or haemoglobin with glucose attached to it. Red blood cells circulate in the blood stream for up to 12 weeks before being replaced, so HbA1c is a useful way to measure the average plasma/glucose concentration over this period. If the level of HbA1c is raised it may be an indicator of diabetes. Check out this link for more information
  
  
• Serum lipids – the lipids/fats which circulate in the blood plasma, including triacylglycerol and cholesterol, are insoluble in plasma and require a specific transport mechanism known as lipoproteins. LDL or Low-Density Lipoproteins deliver cholesterol to the tissues; HDL or High-Density Lipoproteins remove cholesterol from the tissues and transport it to the liver for excretion; VLDL or Very-Low-Density Lipoproteins mainly deliver triacylglycerol to the tissues. It’s often surprising to learn most cholesterol in the body is actually made in our liver rather than originating from the cholesterol in our diet. We typically consume less than 1g of cholesterol per day, whereas around 8g is found in the plasma and around 140g in the body in total². An NHS guide to the recommended serum lipid levels can be found here

Clinical examination, possibly including a medical history to uncover any signs or symptoms of diet-related disease or ill health.

Dietary assessment, at the request of a dietician, nutritionist or researcher, may involve one of the following:

• 24-hour dietary recall is a retrospective review of a previous day’s dietary intake, usually facilitated by a trained interviewer
• a food frequency questionnaire, often used in larger research studies to inform on diet and health outcomes, offers a pre-defined list of foods and drinks for the respondent to indicate when and how often they consumed the items over a set period. This could be anything from 1 week to a month, or longer
• a food diary, where everything consumed over a period of three or four days, or a week, is weighed and recorded

Food composition databases are available to assist with calculating the energy and nutrient content of the diet. The Food and Agriculture Organisation of the United Nations provide a directory of food composition databases from around the world which is linked here

In terms of calorie requirements, food labels show daily guidelines of 2000 kcal for women and 2500 kcal for men and an Estimated Energy Requirement (EER) can be manually calculated using the following formula (or follow this link for a calculator)

EER = 354 – (6.91 x A) + PA x [(9.36 x W) + (726 x H)]

Where A = age, PA* = physical activity, W = weight, H = height