Nutrition and public health

Malnutrition includes undernutrition, deficiencies or excesses of vitamins and minerals, and overweight, obesity and diet-related disease. These problems can occur within the same population. A single national average can therefore leave important differences out of view. WHO's explanation of malnutrition.

Be specific about the outcome you are discussing. A measure of food intake, a nutrient biomarker and a measure of growth or body size describe different things. Name the indicator before drawing conclusions from a percentage or trend.

For each estimate, find the population, year, measurement method and source. Ask whether the figure comes from a survey, an administrative system or a model. Look for the age range, geographical coverage and uncertainty around the estimate.

WHO's Nutrition Landscape Information System interpretation guide explains country-profile indicators and their meaning. It is a useful companion when a dataset uses an unfamiliar definition. Use the definition associated with the estimate you are reading, rather than assuming that similarly named indicators are identical.

A practical note-taking format is:

• Population: who was included, and who was not?
• Measure: what was measured and how was the indicator defined?
• Time: when were the data collected, rather than when was the web page updated?
• Comparison: are methods, age groups and coverage comparable?
• Uncertainty: how precise is the estimate, and what information is missing?

Begin with a question that can guide a decision. For example: “Which groups are least well represented in this survey?” is more useful than assuming that a country average describes everyone equally. “What changed between the two survey methods?” is a necessary question before treating a difference as a real trend.

Then separate three tasks: describing the problem, explaining its possible causes and evaluating an intervention. Each task needs suitable evidence. A survey may describe a pattern well without establishing why it occurred or showing that a particular programme will change it.

The WHO nutrition portal provides routes to guidance, publications and nutrition work across the life course. Follow the original publication when you need methods, recommendations or the basis for a policy discussion.

Choose two estimates that appear to describe the same nutrition problem. Put the population, collection year, definition and method side by side. Mark what is comparable and what is not yet clear. Write one sentence describing the evidence and a second identifying the question it cannot answer.

This exercise keeps uncertainty visible without making the discussion vague. It also helps separate a useful finding from an unsupported generalisation about an entire country or community.

Continue with reading nutrition research or nutrition evidence and policy.