Your diet is everything that you eat and drink. What is a definition of a balanced diet?
> A diet which provides an adequate intake of energy and nutrients needed for the maintenance of our body and thus good health.
We require macronutrients > carbohydrates, proteins and fats to provide energy and provide the raw materials for growth and repair.
We also require micronutrients > vitamins and minerals for the healthy functioning of cells and cellular reactions. The key components that must be provided by a balanced diet are shown in the tables below:
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The body is able to synthesize much of what it needs from the food eaten, but there are some substances that cannot be made from anything else. These are > essential amino acids, essential fatty acids and some vitamins.. The diet must also include water and fibre- why?.
Malnutrition occurs from the consumption of an unbalanced diet. What is an unbalanced diet? > A diet in which some nutrients are absent or not in the right quantities to ensure good health and to satify need.
Assessing Dietary Needs
People vary in the amounts of particular macro and micronutrients that they need. Needs are influenced by sex, height, weight, age, activity levels, climate, pregnancy and lactation.
Assessing the amounts and types of food consumed by people is difficult. People tend to underestimate the amount of food they consume, and assessing the amount of protein and vitamins within consumed food is difficult. Transferrence of findings from animal studies may not produce relevant meaning.
It is possible to measure energy consumption by experimentally measuring how much oxygen a person uses up. The use of 1 dm3 equates to the use of 21.2 kJ of energy. How much energy is there in a gramme of the following food types?
| Nutrient | Energy (kj g-1) |
| Alcohol | > 29 |
| Fat | > 37 |
| Carbohydrate | > 16 |
| Protein | > 17 |
Introducing Dietary Reference Values
The idea of Recommended Daily Amounts was introduced by the US government in 1943 in order to assist the planning of meals for soldiers in World War 2. The RDA of a micronutrient is the amount that will satisfy or exceed the needs of 97.5% of the population. In 1991 however, COMA (Committee on Medical Aspects of Food Policy) introduced the concept of the Dietary Reference Value (DRV). The DRV was introduced to show that there was no single reccommended diet for everyone- two people of the same age might have very different metabolisms and consequently very different requirements for the same food component.
Where data was available, graphs similar to the one on the left were made. They have a typical shape- a normal distribution. The graph allow three different DRVs to be calculated:
| Abbreviation | ||
| LRNI | > Lower Reference Nutrient Intake | > For nutrients only The amount sufficient for those with low needs. Most people need more than this |
| EAR | > Estimated Average Requirement | > For energy and nutrients The estimate of the average requirement of a population. 50% of people will need mre than this, 50% need less |
| RNI | > Reference Nutrient Intake | > For nutrients only Enough or more than enough to meet the needs of almost all the population, including those with high needs |
No RNI or LRNI is produced for energy as individual requirements vary so much. What kinds of factors cause this variation?
Go here to see the EARs for energy according to age and sex.
Safe Intakes
For some nutrients there was insufficient data to construct normal distribution graphs as shown above. For such nutrients Safe Intakes were specified. These are DRVs set well below the level known to cause toxic effects.
Tolerable Upper Intake Level (TUIL)
These are new definitions based upon the highest level of daily nutrient intake that is likely to pose no risks of adverse health effects to almost all individuals in the general population. It is not a recommended level of intake nor a level that is desirable to attain.
Uses of DRVs
DRVs refer to groups of people, not individuals. They do however provide a guide to the adequacy of a diet.
They are useful in analysing information from dietary surveys, eg the analysis of diets of specific groups such as young children or prisoners. They are particularly useful to caterers and dieticians devising meals for institutions such as old peoples homes or schools.
They cannot be used for people suffering disease which influences the absorption of nutrients from the digestive tract.
Food Labels
Food labels are require by law, and must be presented ina standard format.
If a food is declared a source of a micronutrient, it must contain > at least 17% of the Recommended Daily Allowance
If a food is declared a rich source of a micronutrient, it must contain > at least 50% of the Recommended Daily Allowance