Is Genetic Testing for Fitness and Nutrition Worth It?

DNA technology has progressed massively in the last two decades. We can now map the human genome, and identify a whole range of genetic predispositions. As a personal trainer, I get asked by my London clients if it’s worth them getting their DNA analysed, to see what it says about their response to certain types of exercise and certain foods, and to see if they’re at higher risk of a range of diseases.

Knowledge is power, but only if that knowledge is correctly interpreted. The problem with the genetic testing services which have appeared on the market is that they over-state the significance of genetic results, and leap to false conclusions about what those results mean. This can result in the client making the wrong choices in their exercise regime, or making choices they could have made without the need for genetic testing. The same can apply to nutritional choices, but to a lesser extent.

The obesity epidemic is still growing, and geneticists have discovered that some people are more genetically predisposed to weight gain. This has led to many false conclusions relating to an individual’s ability to control their weight (“it’s not my fault, it’s my genes”) and this over-emphasis on the significance of genetic predisposition has opened up a whole new and potentially very lucrative market of genetic testing.

These are some of the main players in the genetic testing market:


For £125.00 this company will analyse your DNA and highlight inherited risk factors, foods that disagree with you (such as lactose intolerance or gluten intolerance), and any adverse response to certain medications.

23andMe founder Anne Wojcicki is the wife of Google co-founder Sergey Brin. She earned a biology degree at university and went on to work for a biotech hedge fund on Wall Street before founding the company in 2007.

The process for the client is simple. You spit into a test tube containing a liquid solution that preserves your DNA, post it off to a 23andMe  lab in the United States, and back come your results and recommendations.

The results may show you have a genetic predisposition for blood clots, with a recommendation that you should be careful about sitting still throughout long haul flights. Or the results may show a mutated gene which increases your risk of Parkinson’s disease, with a recommendation to drink more coffee, take more exercise, and eat healthily. Increasingly common is the result that you have gluten intolerance, with the recommendation that you eliminate gluten from your diet. All these are worthwhile things to know, and worth acting accordingly.

However, your genetic profile is not the whole story when it comes to your risk of getting certain diseases. Some experts say that genetics is about 20% of the story, whereas your lifestyle choices and your environment account for the other 80%, overriding the effect of any genetic predisposition.

The danger of getting a “good” genetic result eg – you are a very low risk for heart disease or cancer, is that you will take that as licence to eat more unhealthily, drink more alcohol, and take less exercise, in the belief that your genes will protect you from the major diseases. However, lifestyle choices are by far the biggest influence on your risk of getting heart disease or cancer. Genetic test results can lull you into a false sense of security.

23ndMe doesn’t test for exercise-related genetic dispositions, but there are companies that do.


This genetic testing company tests for both nutrition-related predispositions, and exercise-related too, using data from your 23andMe results.

The “Fitness Premium” service launched relatively recently in 2013 claims to tell you your power and endurance potential, your aerobic (VO2 Max) potential, your post exercise recover speed, a profile of your injury risk, and a comparison of your DNA profile verses an Olympic athlete.

The “Diet Premium” service will tell you your optimum diet, your sensitivity to carbs and saturated fat, your lactose tolerance and glucose tolerance. In addition you get a healthy shopping list, and a 12 week eating plan with recipes.

“Diet Pro” give you all the above, and more: your genetic ability to detox, your anti-oxidant requirements, your vitamin and mineral intake, and your caffeine sensitivity are also revealed.

The DNAFit website has a database of personal trainers in London (or any town/city in the UK) who are able to give advice based on your results.

However, the interpretation of the results is dubious. For instance, if your genetic results show that you have a higher endurance capability, the advice is that you don’t need as much recovery time between sets of exercise in the gym. But this doesn’t take into account what weights you’re lifting, how effectively you’re performing each exercise, or what your goals are. You could already be resting for just the right number of minutes for the intensity of your workout. Your genetic predisposition is just one small part of the story.

If your endurance/power results come back as 95% power, the recommendation is to focus mainly on power training rather than cardio. The message these companies put forward is to just focus on your genetic strengths, implying that you’re wasting your time doing types of exercise for which you’re not genetically predisposed. “The end of workouts that don’t work” is the strap-line of one of the testing companies.

However, this is false logic. First, it implies that genetic predisposition is the only relevant variable, when in fact it only accounts for around 20% of your potential. Secondly it implies that you’re already reached your genetic potential in your area of weak genetic predisposition, which in most cases is nonsense. Thirdly, it implies that there’s no point focusing on an area of genetic weakness, where in fact the very opposite is true if you want to optimise your health and fitness.

So the client who relies on the advice to focus just on power training because she is genetically weak in endurance, will neglect cardio training and her cardiovascular fitness will decline still further, increasing her risk of heart disease. I’m not saying she should do only cardio training, but to strike a balance between different types of exercise. So much for DNA fitness testing and the advice that goes with it.

The fact is that you can train up your weaknesses, even if you’re not genetically predisposed to certain exercise, and the benefits of certain types of exercise are far wider than the genetic testing companies imply. For instance, even if your capacity to increase your VO2 Max is restricted by poor genes, there are many other health benefits associated with optimum levels of cardiovascular exercise: stronger heart, stronger lungs, healthier circulatory system, increased capillarization (the number of capillaries reaching all the cells of your body), lower blood pressure, and increased insulin sensitivity which lowers your risk of diabetes.

And other factors can increase your aerobic capacity that have more to do with environment and less to do with genetics, such as pollution levels in your area, or how high above sea-level you live. Think about the marathon runners who live at high altitude, thus producing more red blood cells, who have much higher endurance as a result. Your genes have far less influence on your outcomes than these genetic testing companies want you to believe.

Some of the advice the genetic testing companies provide is advice you could get from any decent personal trainer without the need for genetic testing.

For example you may have a client who is doing nothing but cardiovascular exercise, one hour three times a week, and she’s not losing weight. She takes a genetic test which finds that she is more predisposed to power-type exercise than endurance-type exercise. She is advised to do more power training, ie- resistance training with weights to build more muscle mass, and (surprise surprise) she starts losing the excess body fat.

This is good advice, but to include resistance training would be good advice to anyone regardless of their genetic results. Regardless of your genes, doing only cardio training is not the most effective way to lose weight. It’s universally applicable that resistance exercise is more effective for fat loss than cardio exercise. Regardless of your genes, everyone benefits from resistance exercise which builds muscle mass and increases strength, increases your resting metabolic weight, and helps you burn more body fat. The genetic testing companies want you to believe that your genes are the dominant and defining factor. They’re not.

There are many underweight skinny guys who are obviously not genetically predisposed to gaining muscle. You don’t need a genetic test to discover the blinding obvious. But as millions of previously skinny guys can testify, you can overcome your genetic weaknesses by optimising your nutrition and workouts to build muscle, admittedly not as easily as someone who is genetically gifted to build muscle, but it’s possible. But the genetic testing companies say no, just do workouts according to your genetic predisposition and ignore all other aspects of fitness and wellbeing. Their advice is built on leaping to false conclusions,  pseudo-scientific interpretations, and false logic. Yet people are relying on this advice in ever-increasing numbers.

It’s true that not everyone responds to exercise in the same way, but it is completely false to conclude that if you’re not a genetically gifted responder  then its a waste of time doing that type of exercise.

Most people who are at a genetic disadvantage to gain muscle for example, are still way short of achieving their genetic potential for muscle growth. The genetic testing companies give them an excuse not to try harder, with the false message that they’re wasting their time trying to make further progress, whereas in fact it is perfectly possible for “hard-gainers” (people not genetically predisposed to muscle growth) to make substantial gains in muscle-mass with the right nutrition and workouts and recovery, particularly with the guidance of a personal trainer.

Another genetic testing company competing for your pounds/dollars is XRgenomics, and the test is called XRPredict. It is based on research conducted at Loughborough University, which found that 27 genes determine how well you respond to cardiovascular exercise.

Responders are catagorised into ‘low responders’ who struggle to improve their aerobic fitness (20% of the population), ‘low to moderate’ (35% of us), ‘moderate to high’ (25% of us) and ‘high responders’ (the top 20% of us).

The study was led by Professor Jamie Timmons of Loughborough Uni’s School of Sport, Exercise and Health Sciences, an expert in the relationship between genes and fitness. The research was published on the website National Center for Biotechnology Information in 2010, entitled ‘Using Molecular Classification to Predict Gains in Maximal Aerobic Capacity Following Endurance Exercise Training in Humans’.

As a result of the findings, XRGenomics was established to offer genetic testing and fitness advice. Another genetic test promising to tell you whether you’re likely to benefit from cardiovascular exercise.

However, Professor Jess Buxton, a research geneticist with the British Society of Genetic Medicine said in one media interview that it is “hard to make predictions based on a few genes.”

My advice

As a personal trainer in London with clients wanting to know how best to lose excess weight, get fitter, increase their energy levels and sleep better, gain more muscle, and reduce their risk of illness and disease, I would say that lifestyle choices have a massively greater impact than genetics.

Yes, genetic tests are useful if they identify lactose intolerance of gluten intolerance. But as for the companies that identify your fitness genes and the recommendations that are based on them, I would say that either the advice is universally applicable regardless of your genes, or the advice in other cases is highly misleading.

Dominic Londesborough is a personal trainer in London and author of the blog.