Evidence-based nutrition?

Evidence-based nutrition means that the nutrition advice and recommendations are based on evidence which has been assessed in an unbiased or impartial manner.

Studies, designed to investigate the relationship between a specific nutrient or food component and a disease or health condition, provide nutritionists with the necessary evidence to develop food-related recommendations.

Evidence from epidemiological, experimental and intervention studies is assessed in terms of:

• The strength and quality of the evidence.
• Consistency in the evidence.
• Demonstration of a plausible mechanism to explain the link between the nutritional factor and health outcome.
• Relevance of the findings for the population to whom the advice will be communicated.

In epidemiological studies, large groups of people are classified according to the type and amount of food that they usually eat. For example, they may be classified according to the amount of wholegrain cereal-based foods or pulses that they consume. After a number of years, the number of people in each group suffering from a particular disease or health condition is measured. Scientists can use this information to work out which factors can help to increase or decrease the risk of getting a disease or health condition.

Experimental studies are conducted in the laboratory to find out how the nutrient or food component functions and therefore how it provides the observed health benefit or damage. Being able to explain how a food contributes to the health outcome adds credibility to the hypothesis.

Intervention studies, particularly long term randomised controlled trials, are considered the best evidence for determining how well a nutrient or food component prevents the development of a disease or health condition. In these studies, groups of people are randomly chosen to receive either a treatment or no treatment and then followed over a period of time to see what effect the treatment has on the disease or health condition compared to the group receiving no treatment. Randomised means that an impartial method was used to allocate the participants in the study to either the treatment or placebo group. Controlled means that the participants in the study and the nutritionists running the study don't know which participants are receiving the treatment or the placebo.

Studying the relationship between diet and health is not easy. It requires subjects in a study to remember all the foods that they have eaten and to report this information accurately and truthfully. Nutrient composition data of foods consumed must be available and accurate, which is not always the case. It takes many years for the effect of diet to manifest itself and so studies need to be conducted over long periods of time. Finally, large numbers of people are required in the study to detect an effect from the diet.

For this reason, evidence to support nutrition recommendations is sometimes incomplete or inconsistent.