Food Diaries, Labels and What Our Report Covers

By David Hall, founder of IntoleranceLab · Updated September 2026

This page explains what our reference report covers, how to keep a useful food diary, how to read an ingredients label, and when to speak to your GP. It is practical, general information. It is not medical advice.

What our report is

Intolerance Lab provides a proprietary, non-diagnostic reference service. You post us 9–10 hairs, a few centimetres long, and we email you a structured reference report. Gold is £49 and covers 700+ reference entries — 350 foods and drinks, and 350 everyday non-food items. Platinum adds reference material on preservatives and E-numbers, plus an 85-item informational vitamin and mineral guide; that guide is reference material only and does not report your levels.

There is no kit to wait for. Your instructions arrive by email, you post your sample using standard UK postage to our laboratory at the Jarrow business centre, and your report is emailed within 3 working days of your sample arriving. A 90-day no-quibble satisfaction promise applies from the moment your report is delivered, and it concerns your experience of the service.

The service is for anyone aged 6 and over. It is not offered during pregnancy or while breastfeeding — please speak to your GP instead.

Not sure which foods to look at first? An at-home hair screen can help you narrow the list down before you start changing what you eat. See what the screen covers →

Keeping a food diary

A food diary is the practical tool most people find useful, and it costs nothing. The NHS approach is to write down what you eat and drink, when you ate it, and how you felt afterwards, over a period of several weeks.

A few things that make a diary more useful:

• Write it down as you go rather than at the end of the day.
• Record drinks, sauces, dressings and snacks, not just meals — these are the easiest things to forget.
• Note the brand and the portion, because recipes differ between manufacturers.
• Keep it going for long enough to see a pattern rather than a single bad day.
• Take it with you when you see your GP or a registered dietitian. It is far more useful to them than a description from memory.

Reading an ingredients label

In the UK, the 14 regulated allergens must be emphasised in the ingredients list of prepacked food — usually in bold — when they are used as ingredients. They are: celery, cereals containing gluten, crustaceans, eggs, fish, lupin, milk, molluscs, mustard, tree nuts, peanuts, sesame, soya, and sulphur dioxide or sulphites.

Two things worth knowing:

• A “may contain” statement is voluntary. It is a manufacturer’s note about possible cross-contamination, not a legal requirement, so its absence does not prove anything either way.
• Ingredients hide in unexpected places. Celery turns up in stock cubes and soups, milk in some crisps, and sulphites in dried fruit and wine.

Reintroducing foods, one at a time

If you have cut something out and want to bring it back, do it slowly and one item at a time. Conservative diary guidance is to leave at least three full symptom-free days before trying a different item, and to wait longer if you are not back to your normal baseline.

Please get help from a registered dietitian before restricting anything for a child, before cutting out a major food group such as dairy or wheat, or if your diet is already narrow. Cutting out food groups without support can leave gaps in your nutrition. If you are replacing dairy, look for plant drinks fortified with calcium and iodine, check the carton rather than assuming, and note that rice drinks are not suitable as a milk replacement for children under four and a half.

When to speak to your GP

If you are thinking about cutting gluten out of your diet, speak to your GP first. Reducing gluten before testing for coeliac disease can make that diagnosis harder, so keep eating gluten until you have had that conversation.

A food allergy is not the same thing as a food intolerance, and an allergy can be serious. If you have ever had a sudden or severe reaction to a food — swelling, difficulty breathing, or feeling faint — that is a matter for your GP, and you should call 999 for a suspected severe allergic reaction.

Sheep’s and goat’s milk are not suitable substitutes for someone with a cow’s-milk allergy, because they contain similar proteins. All three contain lactose.

What this service does not do

This proprietary reference service is non-diagnostic. It does not measure bodily reactions or diagnose intolerance, sensitivity, allergy, nutrient status or any medical condition. Speak to your GP about persistent symptoms; call 999 for a suspected severe allergic reaction.

See what is included and order online