Many companies such as DNAFit and NurtiFit are offering a diet plan tailored specifically to your DNA and it sounds very appealing.

You swab the inside of your mouth with a cotton bud, post your sample to a laboratory, and two weeks later you have a report detailing your optimal diet; the best and worst foods for your body; how sensitive you are to gluten, milk, eggs, and alcohol; and even how to exercise to maximise your body’s potential. Apparently by following this plan you will loose 33% more weight than doing it on your own.

What’s the evidence?

The problem is- there isn’t really any! There are posters and  information sheets which make hazy reference to ‘studies that were done’, but a quick scan didn’t produce the papers referenced.

One website states “We use hundreds of studies to bring you the genetic information in the DNAFit report. Take a look below at some of our reference papers to give you an insight into the world of exercise and nutrigenomics.”

Most of the companies offering DNA diet plans are using one particular study to back up their claims…

THIS STUDY WAS NEVER PUBLISHED.

The method used (in this unpublished study) is also questionable- it was based on results from a previously published study on the effectiveness of different diets for weight loss. In this original study, obese women were put on four different diets over a year: very low carbohydrate, low carbohydrate/high protein, low fat and very low fat.

Two years after the results were published, the DNA diet researchers collected DNA samples from the women in this previous study. They compared weight loss for women who were on a diet that was ‘consistent with their genotype’ to those individuals on diets ‘not suitable for their genetic pattern’. Individuals were categorised into three genotypes – which is an unrepresentative number!

Individuals on a diet identified as ‘appropriate to their genotype’ by the Weight Management Genetic Test, lost an average of over 2.5 times more weight than individuals on diets that were ‘not appropriate to their genotype’.

An oral presentation at a conference appears to be as far as the investigators got to publishing the results – for such ground-breaking gene based therapy it seems a little odd that this was not further researched.

The research is retrospective, and mysteriously, 44 people who sent back DNA are missing from the analysis. Unsurprisingly, the company who stands to profit from the findings appear to have produced the results!

We asked Registered Dietitian Bridgette Wilson her opinion on this study. She said: “If this was a breakthrough it would be important to conduct a prospective clinical trial – do the genetic testing first, then assign people to a diet (blinded so they don’t know if it is the correct one for their DNA) and then see if the results stack up. My guess would be that this was done – but as the company didn’t find what they wanted (i.e. genetic testing does not predict how effective a weight loss diet will be) they never published it – the pitfall of commercially funded and controlled research.

The company DNAFit claims they are one step ahead the other companies offering a similar service, as they investigate 45 gene variations (called SNPs) and only include those that have been studied in specific gene-diet interaction studies, and the results have to be repeated several times.”

While they may have found some gene associations with certain diets, this is based on a limited assay of a few genes previously associated with diet and weight loss. Therefore, there is not enough evidence to suggest someone should change their diet on this evidence alone.

There is some evidence that a few SNPs investigated by DNAfit might indicate dietary needs, such as increased need for folic acid and vitamins B6 and B12 in certain individuals. However, the other recommendations given by these plans such as ‘eat more green vegetables’ and ‘reduce your saturated fat’ are little more than modified dietary guidelines.

The verdict

Nutrigenomics is a very exciting area of nutrition research that has huge potential in healthcare; allowing us to potentially tailor treatment to the individual. However, the evidence is not strong enough to warrant tailored diets based on genetic testing. Ordering a diet plan from a commercial online nutri-genetics service is NOT worth the hefty price tag – up to £250 for the full DNAFit package!