Dietary DNA tests: how they work, and what they’re useful for

09 Feb 2022
by Helen Phadnis

In this article, registered Dietitian, Helen Phadnis, discusses DNA testing.

The use of dietary DNA testing has become more popular and accessible over the past few years, but is it just a new fad, or does it work to improve our health? 

In this article I will explain the reasons why dietary DNA testing is useful, how it can be incorporated into standard dietetic advice, and who can benefit. 

Let’s dive in!

Why look at our DNA? 

Have you ever noticed that a diet that might have worked for a friend did not work for you? Our DNA determines how we look, not only on the outside, but on the inside too. DNA codes for proteins that alter the way each of us digest, absorb, metabolise and excrete food and nutrients. 

The problem with nutrition guidelines

The science behind government nutrition messages, and diet advice that doctors and dietitians work according to, contains outliers - people who respond in a way that isn’t ‘normal’. The majority of people will benefit from these recommendations, but at best some won’t benefit, or at worst it could make their health worse. 

Take caffeine for example. Differences in our CYP1A2 genotype determine whether we are fast or slow caffeine metabolisers. This is because the CYP1A2 gene codes for the enzyme in our livers that breaks down caffeine. 

Fast caffeine metabolisers have a reduced risk of heart attacks when drinking 1-3 cups of coffee daily, for them coffee is ‘heart healthy’. Slow caffeine metabolisers however have a doubled risk of heart attacks when drinking two cups of coffee daily, which increases to a quadrupled risk at 4 cups daily (1 - see references below). This means they should limit their caffeine intake to control blood pressure. 

Avoid trial and error

We have known for a long time that we all react in a different way to diets. Trial and error has been important in the process of making diet change to see if it works for you.

But diet is so multifaceted it is hard to know what has and hasn’t worked. DNA testing can eliminate some of this trial and error, and unpick the key diet factors to improved health for you. 

Motivation and understanding

Once we understand what diet is best for us it is still hard to make those diet changes.

When compared to dietitian intervention only, dietitian plus DNA testing improves understanding, motivation and compliance to healthy eating (2, 3)

What can dietary DNA testing help with?

Heart health

Blood pressure control

DNA testing can reveal if caffeine and therefore tea and coffee intake will contribute to raised blood pressure (slow caffeine metabolisers), or help to lower it (fast caffeine metabolisers). 

Similarly some of us (the majority) benefit from a low salt diet to lower blood pressure. However for other genotypes there will be no benefit, and others still will see increased blood pressure on a low salt diet (4, 5)

Cholesterol control

The French paradox of regular wine consumption alongside low levels of heart disease suggests that regular modest alcohol consumption could be healthy for some of us.

Differences in our ADH1C gene mean that some of us metabolise alcohol more slowly, which leads to higher ‘healthy’ HDL cholesterol levels (6). For slow alcohol metabolisers 2-4 units of alcohol daily (1 glass of wine) reduces risk of heart disease. Fast metabolisers to do experience this benefit. 

Gut health

Coeliac disease and wheat intolerance diagnosis

Coeliac disease is an autoimmune disease involving the development of an allergy to the protein in wheat, barley and rye: gluten. Only some of us have the genetics to be at risk of developing coeliac disease, and this genotype is also associated with wheat intolerance. 

To get an accurate diagnosis of coeliac disease it is necessary to eat gluten in two meals daily for 6 weeks. For those who experience gut intolerance to gluten this may be unacceptable. Testing the HLA genotype is a recognised step in diagnosing these situations within NICE guidelines (7)

Lactose intolerance diagnosis 

Primary lactose intolerance occurs when our bodies are unable to digest the sugar (lactose) within milk. This happens as some people are unable to produce the enzyme lactase dehydrogenase past the age of 5. This can then cause symptoms of bloating and diarrhoea. 

We can assess if a person is able to produce the lactase enzyme as an adult by testing the LCT genotype. This can cut out trial and error when understanding the cause of bloating and diarrhoea (8)

Weight loss

Gaining genetic insights into how your body responds to nutrients helps with greater and better sustained weight loss, when compared to group weight loss programmes that do not incorporate DNA testing (9)

A more in-depth article on DNA testing for weight loss can be found here.  

Micronutrient requirements

Vitamin and mineral requirements also vary from person to person. For example the Department of Health in the UK recommends daily supplementation of vitamin D 10mcg, to maintain healthy blood levels through the winter, and therefore healthy immunity and bones. 

Several genes contribute to vitamin D metabolism. When assessed together those with certain genetics will not be able to obtain adequate vitamin D status on 10mcg daily, and should take 20mcg per day or more (up to 100mcg/d) (10).

Where can you get a dietary DNA test? 

Dietary DNA tests are widely available on the internet, direct to consumer. It is important not to get a test without the support of a healthcare professional to help you interpret the results, and apply to your diet. 

Dietitians are nutrition experts, who are legally bound to provide science-based advice. There are a small but growing number of dietitians that have undergone further post-graduate training within nutritional genomics. These DNA trained dietitians will be able to arrange your dietary DNA testing, and help you use these insights as a piece of a puzzle to benefit your specific health goals. 

Dietary DNA testing is not available on the NHS at present. You can search the BDA freelance dietitians directory to find a dietitian who specialises in this area. 

Final Thoughts

Dietary DNA testing can provide us with genetic insights into how our bodies digest, absorb, metabolise and excrete food and nutrients differently to other people. 

This information can be used to improve our heart health, gut health, and the success of weight loss attempts. 

To find out more about how you might benefit from a dietetic consultation incorporating dietary DNA testing get in touch with registered dietitian Helen.


1. Coffee, CYP1A2 genotype and risk of myocardial infarction

2. Disclosure of Genetic Information and Change in Dietary Intake: A Randomized Controlled Trial

3. Effect of personalized nutrition on health-related behaviour change: evidence from the Food4Me European randomized controlled trial

4. Renin-angiotensin system genetic polymorphisms and salt sensitivity in essential hypertension 

5. Blood pressure and interactions between the angiotensin polymorphism AGT M235T and sodium intake: a cross-sectional population study

6. Causal Role of Alcohol Consumption in an Improved Lipid Profile: The Atherosclerosis Risk in Communities (ARIC) Study

7. How should I assess a person with suspected coeliac disease?

8. Molecular genetics of adult-type hypolactasia

9. Enhanced long-term dietary change and adherence in a nutrigenomics-guided lifestyle intervention compared to a population-based (GLB/DPP) lifestyle intervention for weight management: results from the NOW randomised controlled trial

10. Genetic Variation in CYP2R1 and GC Genes Associated With Vitamin D Deficiency Status