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Dispatches from the Food & Nutrition Conference & Expo (FNCE) 2012

DNA diets: 'They're just not ready for prime time', warn experts

3 commentsBy Elaine WATSON in Philadelphia , 08-Oct-2012
Last updated on 08-Oct-2012 at 15:24 GMT2012-10-08T15:24:42Z

Dr Gail Kauwell specializes in research exploring the association between nutrient-gene interactions and health maintenance/chronic disease risk.
Dr Gail Kauwell specializes in research exploring the association between nutrient-gene interactions and health maintenance/chronic disease risk.

Commercial interest in the role genes play in our risk of developing chronic diseases - and whether we can modify that risk through diet - has never been higher. But firms offering personalised nutritional advice on the back of mail-order DNA tests are way ahead of the science, experts have warned.

Given that generic admonitions to eat well and exercise more do not seem to inspire many of us, there is something very seductive about a personalized nutritional plan based on your own DNA, delegates at the Food & Nutrition Conference & Expo (FNCE) were told yesterday.

Simply send us your DNA, say the genetic testing firms, we’ll screen for SNPs (single nucleotide polymorphisms or genetic variations between people) that we know are associated with increased risk of disease X, Y and Z, and we’ll tell how you can reduce the risk by changing your diet.

For example, people with a particular variant (ApoE4) of a gene (ApoE) associated with fat metabolism are believed to have a heightened risk of developing Alzheimer’s and heart disease, while those with particular SNPs of the eNOS gene (which codes for a protein controlling the elasticity of blood vessels) are believed to have a higher risk of cardiovascular disease.

Mail-order ‘spit kits’ risk damaging credibility of nutrigenomics research

We are 99.6% identical to the person sitting next to us, but that 0.4% could make a worold of difference when it comes to our risk of developing chronic diseases

However, firms trying to cash in via DNA-based nutrition plans risk damaging the credibility of the emerging fields of nutrigenetics and nutrigenomics by going beyond the science, warned Dr Gail Kauwell, a professor in the food science and human nutrition department at the University of Florida at Gainesville.

The problem, she said, is that we are only just starting to learn which SNPs or combinations of SNPs may be disrupting key physiological functions at a molecular level and increasing our disease risk, and we know even less about the extent to which we can modify this risk though specific dietary interventions.

"It's not the same as single gene disorders like cystic fibrosis. SNPS don't predict unequivocally that you will get a disease."

Meanwhile, send your DNA via mail-order ‘spit kits’ to four different DNA-based diet firms and the chances are you will get four different results, she added, noting that there is no oversight of these lab, which undermined confidence in the validity of the tests.

”Data like this really suggests it’s really not ready for prime time. It’s also likely that the information consumers may receive will be incomplete and will change as new information becomes available.

“Also, SNPs that are predictive of disease risk in some populations may not be predictive of risk in others.”

As for the argument that compliance improves if nutritional advice is personalized, the evidence is mixed, she said, observing that people told they have a high risk of developing diabetes, for example, have not routinely been more motivated to change their diet and lifestyle as a result.

Chanock: We must not let the genie out of this bottle too quickly

Dr Chanock: Not enough is known about the interplay between diet and other environmental factors and genes to provide clear recommendations at a clinical level

Meanwhile, not enough is known about the interplay between genes, diet and other environmental factors to provide clear recommendations at a clinical level, said Stephen Chanock, MD, who joined Dr Kauwell on the podium.

Cancer for example, is arguably 100% genetic and 100% environmental, pointed out Dr Chanock, who is Chief, Laboratory of Translational Genomics, at the National Cancer Institute. And scientists are only just beginning to see how the two might be connected, and to what extent modifying the latter can impact the former, he said.

“We have to be very careful. The science is not fully developed so that you can say you should have 14g of fiber as opposed to 27g because of a genetic test results.

“We must never forget that lifestyle and a life time of environmental exposures including diet co-exists with genetics.

“We know about maybe 75 SNPs associated with prostate cancer risk, but which ones or combinations are most relevant? Meanwhile, the ones we know about may only account for 20% of the risk, so do you want to make clinical decisions or recommendations based on that 20%?

“We must be careful not to let the genie out of the bottle too quickly.”

3 comments (Comments are now closed)

What these two researchers believe is not what the scientific evidence shows

I attended this session at the FNCE meeting in Philadelphia and was amazed to hear both speakers talk about gene-disease association studies (ie genomics only), yet make conclusions about nutrigenomics (ie. gene-diet interactions). It’s like comparing apples to genes. Both speakers reminded us that there are no good genetic markers that can be used clinically to predict disease. That’s old news. The same can be said about studies that just aim to link diet with disease risk. That’s even older news. The promise in this field is with ‘modifier genes’. A growing number of studies published in the top-ranked scientific and medical journals clearly show that certain modifier genes can be reliable and valid predictors of a particular response to certain dietary factors.

In the article, one of the speakers is quoted as saying, “We know about maybe 75 SNPs associated with prostate cancer risk, but which ones or combinations are most relevant?” That’s not even a question that experts in the field of nutrigenomics bother asking. The question is “Which SNPs determine whether a particular component of the diet significantly increases/decreases your risk of a disease?” Discovering such a genetic marker allows an individual to know whether a focus on that particular nutrient will impact their risk.
There is no reason to believe that tests based on sound and robust research in nutrigenomics are not "ready for prime time". It is also the right time for dietitians to assert their role as the most qualified healthcare professionals to provide personalized nutrition advice by embracing the science and application of nutrigenomics, or risk losing recognition as the primary provider of DNA-based dietary advice.

Ahmed El-Sohemy, PhD
Canada Research Chair in Nutrigenomics
University of Toronto

Chair of Science Advisory Board
Nutrigenomix Inc.

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Posted by Ahmed El-Sohemy
12 October 2012 | 18h132012-10-12T18:13:51Z

There is a lot of evidence

While a SNP is not a mutation that causes a disease a SNP can cause quite drastic changes in protein expression or function - as in Lactose persistence vs intolerance, folic acid metabolism, the presence or complete absence of enzymes such as GSTM1.

These changes do not cause disease - however the scope of nutrigenetics is not to cure disease or prevent a specific disease. The scope is actually to improve upon standard guidelines as applied to the individual - and the standard guidelines themselves are to promote healthy eating rather than specific disease prevention. Regarding the quote above about specific amounts of a nutrient such as fibre - the standard guidelines do provide specific amounts of each nutrient - of course they are recognised as estimates based on a population mean and no-one really thinks that each amount is the precisely correct amount for each individual.

There is not genie and no bottle, there is just the continuous application of new knowledge to what we know about nutrition.

One problem I fear that leads to this sort of opinion could be the actual problem of many (but by no means all) poor quality and exploitative commercial tests on the market. This is one of the areas that is being looked at closely by ourwww.food4me.org project

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Posted by Keith Grimaldi
11 October 2012 | 14h102012-10-11T14:10:41Z

Your current diet influences your genes

Inherited gene mutations represent maybe 2% of disease. Most are storage disorders that can be delayed by diet. The rest of disease is influenced by epigenetics, non-structural changes in human genes where proteins are made (gene expression) or not made (gene silencing), what is called epigenetics. For example, B vitamins, especially in the womb and early childhood, can influence gene expression via a process called methylation. In essence, nutrients can genetically re-program individuals. Even nutrients can influence gene mutations. Folic acid is critical for DNA repair, as is IP6. Why these "experts" are dragging their feet over what is known about diet and genetics goes unexplained.

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Posted by Bill Sardi
08 October 2012 | 19h082012-10-08T19:08:33Z

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