Recently I did a DNAfit test: this is a genetic test that examines 45 gene variants which reflect the body’s capacity to respond to nutrition and exercise. The idea is to help people optimize their diet and exercise regime to their genetic profile. I feel this is such an important idea, because however much we try to learn about the complex field of nutrition and how nutrition might affect our microbiome and our epigenetics, we come back to the same problem, which is that different diets suit different people! Research has shown that people vary significantly in their blood sugar responses to identical meals! In the future, nutrition advice will need to become more personalised. So I was intrigued by the concept of DNA testing to see an individual's response to nutrition and exercise - DNAfit testing is even being piloted for obese patients by the NHS in Essex.
But what does a DNAfit test looking at diet and fitness genes actually tell you?
The diet section of the report summarises the best of one of three styles of eating for your genes: low carb eating, low fat eating, or Mediterranean style eating (the Mediterranean diet has higher carb intake than the low carb diet, and higher fat intake than the low fat diet). The genes related to carbohydrate sensitivity give you an idea of how likely you are to suffer from the ill effects of carbohydrates: for example, the TCF7L2 gene is linked to type 2 diabetes. Two T alleles increase the risk of developing type 2 diabetes by 2.5 times, but a low carb diet can reduce this risk back to just above normal (1.2 times). Carb sensitive people will respond best to a low carb diet. Those who are sensitive to saturated fat (CC alleles at the APOA2 gene, or AA alleles at the FTO gene) will have a much higher risk of obesity if they eat a diet with over 10% saturated fat. In this case a low fat diet will suit them better.
The next section of the report looks at detoxification ability with regard to diet. Phase 1 detoxification pathways are involved in how we metabolise chemicals (heterocyclic amines and polycyclic aromatic hydrocarbons) found in certain meats cooked at high temperatures. Those who produce a rapid increase in toxic metabolites would be better ensuring that they do not burn meat on the barbeque, or go for crispy bacon – in fact cooking meat in stew or curries and reducing grilled meat would be a good idea. Phase 2 detoxification pathways are involved in how well we process certain medications: a deletion at the gene suggests the enzymes aren’t working well. 50% of people have a deletion at the GSTM1 gene and 20% of people have a deletion at the GSTT1gene. These people with poorer enzyme function would benefit by introducing more cruciferous vegetables into their diet.
Another gene analysed is the famous MTHFR gene: there is much about this gene on the internet and its possible link with a number of conditions. The MTHFR gene is linked to homocysteine and cardiovascular risk, and if you have a CT or TT allele, B vitamin and methylfolate supplementation may be helpful in reducing homocysteine levels.
Another gene looks at how quickly you metabolise caffeine: – fast metabolisers can tolerate more caffeine and it doesn’t necessarily affect their sleep, whilst slow metabolisers should not have more than 200mg per day. In one study, slow metabolisers of caffeine who drank more than 4 cups of coffee per day had an increased heart attack risk. Plus, if you have a poor vitamin D receptor status, you should reduce your caffeine intake to moderate your risk of osteoporosis.
Finally a gene associated with lactose intolerance is examined and tells you if you are one of the 65% of the world’s population who can’t tolerate lactose (more than a glass of milk is likely to cause symptoms).
The fitness profile looks at a number of genes relevant to power and endurance and bearing in mind the relevance of each of these genes for these parameters, it puts the results into an algorithm that summaries in percentage terms how you respond to power and endurance exercise. My result came back as 60% power, 40% endurance, which means that I should bias my time spent exercising accordingly (i.e. 60% of the time on power exercise and 40% on endurance) as this result is indicative of how well I adapt to different forms of exercise. Essentially the thinking is that there is no point putting in lots of effort to something you don’t respond well to. From a motivation perspective, I found the result interesting. I do very little power exercise, despite knowing all the benefits of power exercise in terms of bone mass and weight loss (increased muscle mass burns calories). But the though that I might actually respond well to power exercise and see good results was motivational – plus, combined with the fact that further down the report I have a poor vitamin D receptor status which could increase my risk of osteoporosis.
The next section looks at aerobic training and gives you a score of how you respond: high responders adapt well to aerobic exercise, and are more likely to enjoy it as they get the endorphin buzz and see good results. Low responders are more likely to stick to walking!
The recovery section looks at how well you deal with oxidative stress and inflammation. How does this change what you do? Fast recoverers would be able to do a high intensity training session daily. Medium recoverers would be better suited to 3 hard sessions per week, whilst slow recoverers may be better suited to a maximum of 2 hard training sessions per week. Those at high or very high risk of injury need to be proactive – stretching and warming up, regularly checking their running shoes and they may want to think about alternating exercises – e.g. rather than doing three running sessions a week, doing two running sessions and 1 swimming session per week. Those at intermediate risk might only need to make such changes in the lead-up to a competition, when they are really increasing their training.
But does the test actually make a difference to outcomes?
Last year, an Italian study of 191 obese people found that those using a DNA-matched diet lost 33 per cent more weight and gained more muscle than those who were simply counting calories. New understanding of the genes involved in taste preferences could help not just weight loss but also avoidance of chronic diseases such as hypertension, diabetes and cancer.  Personally I found it useful to be given one of three potential diet styles (low carb, low fat or Mediterranean) and to better understand which type of exercise i might best respond to, although many people may already know from their symptoms how they respond to carbs, lactose or alcohol. Detoxification and MTHFR pathway response or response to certain types of exercise is harder to guess and if knowing these things might motivate you to make changes then perhaps the test is useful.
Overall I can see why a DNA matched programme might motivate people to make positive changes (though genes aren't the whole story either so its more for motivation purposes than for definitive answers) . The differences between individuals' responses to different foods is important - there is certainly no one diet that fits all. Simply calorie counting has its limitations since all calories really aren't the same; in a study looking at monkeys fed identical calories for 6 years, the group that had 17% of their calories from transfats had three times the visceral fat and much worse insulin profiles than the group that had 17% of their calories from natural fats. How our body processes foods matters - and how each of us responds to the same foods is likely to vary. Other limitations of the calorie approach are that calorie recommendations for men and women don't account for age, height weight or exercise, plus many food packets grossly over or underestimate calories and anyway only about 1 in 7 people come close to estimating the calories they need.
Exercise, although excellent for health, has limited benefit on weight: in a meta analysis of seven studies looking at exercise alone or exercise plus diet versus diet alone, exercise had little influence on weight loss or keeping weight off. Thats not to say you shouldn't exercise - from a health perspective its much better to be fat and fit than slim and unfit, and exercise is also critical for mental functioning and prevents a number of diseases.
In the future, a more personalised approach to weight loss and exercise makes sense, because we know that genes play a big role in weight- identical twins are much more similar to each other in terms of body weight and fat than fraternal twins (on average identical twins are less than 1kg apart in weight!) In fact gene related characteristics are thought to account for up to 60% of the differences between people - but just because its gene related, it doesn't mean its completely unchangeable. 50% of the differences between those who have a sweet tooth versus those who don't is due to genes -but the other 50% is due to behaviour. (We only need look at the rapidity of the massive obesity epidemic to know that it really can't be explained by genes alone!).
An interesting concept and if nothing else such a test might help motivate - knowing your weaknesses may help you steer clear of them!