.jpg) Dietary Reference Values (DRVs)
Meaningful estimates of nutritional requirements must take account of the distribution of requirements within a population or group. To achieve this, the COMA panel used four Dietary Reference Values (DRVs) (Figure 1). DRVs are estimates of the requirements for groups of people and are not recommendations or goals for individuals.
Estimated Average Requirement (EAR): This is an estimate of the average requirement for energy or a nutrient - approximately 50% of a group of people will require less, and 50% will require more. For a group of people receiving adequate amounts, the range of intakes will vary around the EAR.
Reference Nutrient Intake (RNI): The RNI is the amount of a nutrient that is enough to ensure that the needs of nearly all the group (97.5%) are being met. By definition, many within the group will need less.
Lower Reference Nutrient Intake (LRNI): The amount of a nutrient that is enough for only the small number of people who have low requirements (2.5%).The majority need more.
Safe intake: This is used where there is insufficient evidence to set an EAR, RNI or LRNI. The safe intake is the amount judged to be a level or range of intake at which there is no risk of deficiency and is below the level where there is a risk of undesirable effects. There is no evidence that intakes above this level have any benefits - and in some instances they could have toxic effects.
The COMA panel set EARs for energy, an EAR for dietary fibre for adults, and desirable (adult) population average intakes for fat and carbohydrate. EARs and RNIs were set for protein, whilst LRNIs, EARs and RNIs were set for 9 vitamins and 11 minerals. Safe intakes were set for a further four vitamins (pantothenic acid, biotin, vitamin E and vitamin K) and four minerals (manganese, molybdenum, chromium and fluroride).
How should DRVs be used?
For practical purposes, the RNI should be used when assessing the dietary intake of a group. The nearer the average intake of the group is to the RNI, the less likely it is that any individual will have an inadequate intake. The nearer the average to the LRNI, the greater the probability that some individuals are not achieving adequate intakes. For example, if 20% of a group is typically consuming less than the LRNI, it is likely that most have an inadequate intake. When planning a diet for a group the aim should be to provide the RNI.
Energy requirements
The EARs for energy are based on the present lifestyles and activity levels of the UK population. Although an increase in energy expenditure might have desirable health benefits for many people, the COMA panel did not believe this should be used as an argument for raising the DRVs for energy intake. (If people increase their energy intake without increasing energy expenditure they will become overweight).
Energy requirements are related to age, gender, body size and level of activity. Energy requirements tend to increase up to the age of 15-18 years. On average, boys have slightly higher requirements than girls and this persists throughout adulthood. After the age of about 18 years energy requirements tend to be lower, but this depends on the individual’s level of activity. By the age of 50 years, energy requirements are lower still which is partly due to a reduction in the basal metabolic rate (BMR) and to a reduced level of activity.
The EARs for various groups are shown in Table 2 (see attached pdf). The EARs for adults are based on the current lifestyle in the UK which is fairly sedentary. The EARs were calculated by multiplying BMR by a factor – the Physical Activity Level or PAL – which reflects current levels of physical activity.
Energy EAR = BMR x Physical Activity Level (PAL).
A factor, or multiple of BMR, of 1.4 reflects the lifestyle of most adults in the UK. This factor is suitable for people who do little physical activity at work or in leisure time. If people are more active, larger factors (PALs) are used. For example a PAL of 1.9 would be appropriate for very active adults.
Special note
The EAR for women who become pregnant increases by 0.8 MJ/day (200 kcal/day) but only in the final three months. Although energy is needed for the growth of the fetus and to enable fat to be deposited in the mother’s body, pregnant women can compensate for these extra demands by becoming less active and using energy more efficiently.
Breastfeeding mothers have increased requirements for energy but this will depend on the amount of milk produced, the fat stores that have accumulated during pregnancy and the duration of breastfeeding.
Does the UK diet provide too much energy?
Many people in the UK manage to match their energy intake to their energy expenditure. But people who take in more energy than they require become overweight and if this continues will become obese. In 2001, 46% of men and 34% of women in England were overweight, and 17% and 21% respectively were obese. People who are obese have a shorter life expectancy and are at a greater risk of developing diseases such as coronary heart disease and type 2 diabetes.
How do nutrient needs vary?
Nutritional requirements alter during a lifetime and the COMA panel reviewed the evidence on which the current estimates of nutritional requirements are based. The report set RNIs for each of the groups described above for the following nutrients:
• Protein
• Vitamins - thiamin, riboflavin, niacin, vitamin B6, vitamin B12, folate, vitamin C, vitamin A and vitamin D.
• Minerals - calcium, phosphorus, magnesium, sodium, potassium, chloride, iron, zinc, copper, selenium and iodine.
The major changes in the estimated nutritional requirements at different life-stages are highlighted in the following paragraphs.
Infants
The first 4-6 months of life is a period of rapid growth and development. Breast milk (or infant formula) contains all the nutrients required during this period. Mothers should be encouraged to breastfeed and not to give solid foods to infants before the age of 4 months. Recent Department of Health advice recommends exclusive breastfeeding until 6 months of age. During the early months of life, babies can draw upon iron stores they have accumulated before birth but these stores are rapidly depleted and it is important that the diet given during weaning contains enough iron to meet the baby’s needs for growth and development. Requirements for protein, thiamin, niacin, vitamin B6, vitamin B12, magnesium, zinc, sodium and chloride also increase between 6 and 12 months.
Children 1-3 years
Energy requirements increase because children are active and growing rapidly. Protein requirements do not increase much. There is an increased need for all the vitamins, except vitamin D (some of which will now be synthesised in the skin, following sunlight exposure). Slightly lower amounts of calcium, phosphorus and iron are needed. There is an increased requirement for all the other minerals except for zinc.
In the second year of life, children continue to need energy-dense diets. They should be given whole milk, not skimmed or semi skimmed, and care needs to be taken over the amount of fibre (non-starch polysaccharide or NSP) eaten. If the diet is too bulky due to too many high fibre foods, there is a danger the child will be unable to eat enough food to satisfy its energy needs. After the age of 2 years, semi-skimmed milk may be given provided adequate energy intake is assured, although skimmed milk should not be introduced before 5 years of age.
4-6 years
Energy requirements continue to increase and there is a greater need for protein, all the vitamins (except C and D) and all the minerals (except iron). The RNI figure for vitamin C remains the same as for younger children. No value is given for vitamin D since the action of sunlight on the child’s skin will now be the major source of this vitamin.
7-10 years
There is a marked increase in requirements for energy and protein. There is no change in the requirement for thiamin, vitamin C or vitamin A but the requirements for the other vitamins and minerals are increased.
11-14 years
Energy requirements continue to increase and protein requirements increase by approximately 50%. By the age of 11, the vitamin and mineral requirements for boys and girls start to differ.
Boys: There is an increased requirement for all the vitamins and minerals.
Girls: There is no change in the requirement for thiamin, niacin, vitamin B6, but there is an increased requirement for all the minerals. Girls have a much higher iron requirement than boys (once menstruation starts).
15-18 years
Boys: Energy and protein requirements continue to increase as do the requirements of a number of vitamins i.e. thiamin, riboflavin, niacin, vitamins B6, B12, C and A; and magnesium, potassium, zinc, copper, selenium and iodine. Calcium requirements remain high as skeletal development is rapid.
Girls: Requirements for energy, protein, thiamin, niacin, vitamins B6, B12 and C, phosphorus, magnesium, potassium, copper, selenium and iodine all increase. Boys and girls have the same requirement for vitamin B12, folate, vitamin C, magnesium, sodium, potassium, chloride and copper. Girls have a higher requirement than boys for iron (due to menstrual losses) but a lower requirement for zinc and calcium.
Adults
19-50 years
In comparison to adolescents, energy requirements are lower for both men and women, as are requirements for calcium and phosphorus. There is also a reduced requirement in women for magnesium, and in men for iron. The requirements for protein and most of the vitamins and minerals remain virtually unchanged in comparison to adolescents (except for selenium in men which increases slightly).
Pregnancy
During pregnancy, there are increased requirements for some, but not all, nutrients. Women intending to become pregnant and for the first 12 weeks of pregnancy are advised to take supplements of folic acid to help reduce the risk of their child having a neural tube defect. In addition, all women of child bearing age are advised to choose a diet that supplies adequate amounts of folate (Department of Health, 1992.) Additional energy and thiamin are required only during the last three months of pregnancy. Mineral requirements do not increase.
Lactation
During lactation, there is an increased requirement for energy, protein, all the vitamins (except B6), calcium, phosphorus, magnesium, zinc, copper and selenium.
50+ years
Energy requirements decrease gradually after the age of 50 in women and age 60 in men as people typically become less active. Protein requirements decrease for men but continue to increase slightly in women. The requirements for vitamins and minerals remain virtually unchanged for both men and women. There is one exception - after the menopause, women’s requirement for iron is reduced to the same level as that for men. After the age of 65 the RNI for vitamin D is 10 µg/day. The reduction in energy needs, coupled with unchanged requirements for vitamins and minerals, means that the nutrient density of the diet becomes even more important. Nutrient density means the quantity of vitamins and minerals in relation to the amount of energy supplied by the foods and drinks consumed.
UK Recommendations
Fat, protein, carbohydrate and alcohol provide energy. There is evidence to suggest that the energy mix of the diet can influence the risk of developing various diseases, such as coronary heart disease (e.g. too much fat) and certain cancers (e.g. too much alcohol). The COMA panel reviewed the evidence and concluded that it would be useful to set DRVs for total fat (fatty acids and glycerol), fatty acid subclasses, sugars and starches (see Table 3 in the attached pdf). Guidelines also exist for alcohol intake.
The Committee also suggested that the average intake of fibre or NSP should be 18g/day (individual range 12-24g/day) for adults but recommended that children’s intakes of NSP should be less than this. Alcohol should provide no more than 5% of energy in the diet, but as some people do not drink, DRVs were calculated for diets containing alcohol (total energy) and not containing alcohol (food energy).
Surveys such as the National Diet and Nutrition Survey series compare current intakes of nutrients with the various DRV values to assess where problems exist and to assist in forming government policy.
© British Nutrition Foundation 2004
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