Dr. Michael Ruscio, DC is a clinician, Naturopathic Practitioner, clinical researcher, author, and adjunct professor at the University of Bridgeport. His work has been published in peer-reviewed medical journals and he speaks at conferences around the globe.
Do You Need a DNA Test to Determine the Best Diet for You?
Some at-home genetic tests claim to help people choose diets based on their DNA.
However, genetic testing for food sensitivity is expensive and isn’t actually very useful.
Several studies show your health will benefit just as much from a standard healthy eating regime rather than a more specific one based on your DNA results.
Many food sensitivities and intolerances are highly complex and may be related to gut issues rather than genetic factors.
Even if you do have a genetic predisposition to a disease or obesity, making healthy diet and lifestyle changes will offer excellent protection.
The best way to determine food sensitivities is by following an elimination diet and then listening to your body as you reintroduce foods one by one.
Individualized nutrition and medicine sounds very appealing. After all, no two of us are alike, and it feels reassuring and safe to be given a specific list of types of foods you “should” or “shouldn’t” eat based on the results of your personal genetics.
In recent years, many practitioners have gotten on board with genetic testing, and I’ll admit I was somewhat carried along with this functional health trend, too. However, I always look to the research to inform and guide my opinions; it’s the right thing to do so we’re all working with the most accurate and up-to-date information possible. While gene testing can help identify a few key conditions, its usefulness in navigating more common issues like obesity, brain fog, bloating, constipation, and eczema simply isn’t supported by the latest evidence.
More to the point, I’ve seen how an excessive amount of lab and genetic tests can cost patients a lot of money, cause distress, and ultimately make no difference to the way their condition needs to be managed or the results they get. In fact, at-home food sensitivity tests, which we’ll look at in this article, can cause actual harm if you unnecessarily cut out food groups and nutrients for prolonged periods that you don’t need to. And there’s little to no evidence proving their accuracy—many food reactivity tests are questionable .
Let’s discover why generalized dietary advice can often be more helpful than a specific set of “rules” based on your genes.
What is Genetic Testing for Food Sensitivity?
You may have heard of nutrigenomics, which is the name given to the study of how your genes (or your DNA) influence your response to specific foods or nutrients.
Genetic testing for food sensitivity is a specific branch of nutrigenomics that claims to identify how your body and digestive system deal with particular foods and nutrients, giving you a picture of the foods and supplements you might have a harder time tolerating and need to avoid.
Companies that offer diet genetic testing usually only need a saliva sample or a cheek swab, so the sample collection is an easy, pain-free process. However, it can be very expensive, costing anywhere from $130 to over $600 depending on the complexity of the test.
Interpreting the results of genetic testing, including genetic diet tests, is the complex part. It is also the aspect that often fails you as a patient because:
One-off genetic testing may not be accurate or reproducible—for example, it can frequently flag false positives for certain gene variations [2, 3].
The analysis is often an oversimplified, general interpretation with no account of a patient’s personal health or nutritional status, factors that are just as crucial, if not more so than genes .
It’s very telling that genetic specialists, who tend to understand gene test results better than anyone else, are typically much more skeptical about the clinical value and utility of these tests than other healthcare practitioners .
What Research Shows About Genetic Tests
There are a few cases where genetic testing ordered by a health professional can be useful in diagnosing medical conditions. For example, gene tests (usually blood tests) can be pivotal in helping confirm inherited diseases or predict known gene-linked diseases such as Huntington’s disease, cystic fibrosis, and colon and breast cancers [7, 8, 9, 10].
Bonafide medical genetic testing will always be recognized by a CLIA-certified lab or stricter state standards to ensure analytical validity (CLIA stands for Clinical Laboratory Improvement Amendments) .
Conversely, direct-to-consumer genetic tests that promote the idea of gene-based solutions to more general health and wellness issues or to predict what sort of diet you should eat are not so tightly regulated and are likely less precise.
Additionally, many food sensitivities and intolerances are related to physical problems in the gut, such as leaky gut [12, 13, 14, 15] or with the gut microbiome, such as in SIBO [16, 17]. Genetic testing isn’t capable of predicting these problems.
But don’t just take my word for it. Like most people, I assumed that genetic testing offered a beneficial technological advancement in healthcare. But what really changed my mind about genetic testing for food sensitivity and other general health applications was the many studies that show little to no benefit.
Let’s look through some of those studies so you can make up your own mind about how to proceed.
Genetic Testing Doesn’t Help Weight Loss
In a 10-week randomized controlled trial (the “Preventomics” study) , 100 overweight adults aged 18–65 years were allocated either a personalized diet based on their genes or a standard healthy diet. The study looked at changes in fat mass, body weight, and waist circumference, as well as other metabolic markers like blood lipids, blood glucose, and inflammation.
If gene testing was helpful, you might have expected the gene-specific dieters to shed more pounds, but in fact, both groups lost almost identical amounts of body fat and weight. Moreover, both diets resulted in significant improvements in insulin resistance and blood lipid profile, but there were no significant differences between groups.
Genes Don’t Predict the Best Diet
In another seminal article, the DIETFITs study , researchers set out to compare the effect of a healthy low-fat versus a healthy low-carb diet on weight loss. But they also wanted to study genetic and physical makeups that could potentially influence how effective each type of diet would be for trial participants.
In particular, they looked at genetic sequences that could mean people do better with a low-fat diet and insulin sensitivity issues that could mean a low-carb diet would be better.
Despite the difference in fat and carb levels, both healthy diets were equally effective at helping reduce their weight (by about 12 pounds on average over the year). But the real kicker: people’s DNA and physical makeup didn’t make any difference to the results either. In other words, it made no significant difference if a person was “matched” to their preferred genetic diet or not.
Genetic Testing Doesn’t Improve Lipid Levels
In this study, participants in the Food4Me clinical trial  were identified as either carrying the APOE4 gene or not. They were then randomized to receive either general diet and lifestyle advice or personalized diet and lifestyle advice based on their APOE4 status.
People with APOE4 variants tend to make more cholesterol and may be at higher cardiovascular risk, so they are traditionally told not to eat saturated fat-containing foods like steak, eggs, coconut oil, and cheese.
You might expect that receiving specific dietary advice based on APOE4 gene status would bring increased benefits. However, this was not the case, and personalizing dietary recommendations based on gene testing did not result in any bigger improvements in either cholesterol levels or body mass index than standard health eating advice.
What comes out repeatedly from these studies is that generic healthy eating advice is often just as good as making more specific dietary changes based on genetic testing for food sensitivity.
My concern as a clinician is that slavishly following the results of your genetic analysis might lead to you eating a restricted range of food (for example, cutting out meat or even some vegetables and fruits) when you don’t need to.While “generic” recommendations sound less precise than “personalized to your genes,” they are often based on a wealth of successful clinical trials and can be adapted to your own preferences.
Environment Trumps Genetics
Overall, factors like lifestyle and environment often have a more powerful influence on health outcomes than small genetic differences .
In other words, though we can’t directly control our basic genetic makeup, we can influence our environment (our dietary and lifestyle choices), which affects how our genes are expressed.
For example, if a genetic test says you have markers that increase the risk of obesity, then you may interpret that as predicting you’ll develop a weight problem. But the effect of your genetics on your weight is likely minimal and pales compared to things you can control, like diet and exercise.
One study that looked at this in more detail found that when people had gene variants, or single nucleotide polymorphisms (SNPs, pronounced “snips”), relating to conditions including obesity and high fasting blood sugar, they still had no more than a 10% likelihood that these gene variants would actually be expressed (i.e., lead to the health problem in question).
The authors concluded that “the data suggest that most disease risk is dominated by the effect of the modern environment, providing further evidence to support the pursuit of lifestyle-based interventions that are likely to be beneficial regardless of genetics.”
What Works Instead of Genetic Testing for Food Sensitivity?
In my experience, it is usually better for patients to avoid the distraction and expense of gene testing for food sensitivities and to tune into their own body and gut symptoms instead.
Many of my patients with gut issues and other symptoms like brain fog and fatigue find success with a diet based loosely on the paleo diet (i.e., ancestrally focused and containing only whole foods as much as possible). This type of diet can be considered the healthiest and lightest touch “elimination” diet because it minimizes additives, ultra-processed ingredients, and the most common allergens like gluten and cow’s milk. But it’s not overly restrictive, so you’re unlikely to run into nutritional deficiencies more prevalent with strict elimination protocols.
Sometimes, moving onto a low FODMAPs diet is needed for those with a greater reactivity to food (particularly to carbohydrates) while others can do perfectly well with a Mediterranean-style diet that includes a broader range of foods from the start.
After you have identified the level of elimination diet that works for you, you can reintroduce potential culprit foods and monitor your reaction with a food and symptom diary.
In a nutshell, trial and error is the key to personalizing your own diet plan, and though this might not be as easy as following a more regimented plan based on genetic testing for food sensitivity, it will usually be more suited to you and your needs in the long run.
Takeaway: Genetic Screening Is Rarely Helpful
Genetic testing that your doctor orders from a qualified lab can tell you whether or not you have an inherited disease, a higher risk of developing a particular disease, or a mutation you could pass along to your children.
But beyond this very specific medical use, gene testing has little usefulness for optimizing overall health and wellness or for identifying the best diet for your needs.
Specifically, food sensitivities and intolerances occur for many different reasons that genetic health testing can’t predict. The best way to determine which foods may be bothering you is by following an elimination diet and listening to your body.
If you have food intolerances and sensitivities that are more complex, you may benefit from reaching out to one of our highly experienced practitioners at the Ruscio Institute for Functional Health, who can guide you through the process of regaining your health.
My book Healthy Gut, Healthy You will also support you through eight powerful steps to lessen symptoms by strengthening your gut.
The Ruscio Institute has developed a range of high-quality formulations to help our patients and audience. If you’re interested in learning more about these products, please click here. Note that there are many other options available, and we encourage you to research which products may be right for you.
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