Just a few decades ago, our genes and what they say about us was largely a mystery. Now, with a quick swab of your mouth scientists can reveal everything from your family history to the diseases that you are susceptible to.

This is all thanks to the human genome project, the biggest collaborative project aimed at better understanding the biology of our species. In the 90s, scientists from the US, UK, Japan, France, Germany, Canada and China worked together to work out the base pairs in our DNA.

Now the technology which this pioneered is becoming more readily available commercially, meaning firms are able to trace a person’s maternal and paternal lineages and pinpoint which regions of the world their ancestors were from.

Meanwhile nutrigenomics services like DNAFit analyse a person’s DNA and their genetic variations to give them a personalised workout and diet plan.

Ideal diet and vitamin and micronutrient intake; a person's carbohydrate and fat sensitivity; lactose and gluten intolerance risk; ability to recover after exercise; salt, alcohol, and caffeine sensitivity as well how prone a person is to of soft tissue injury are all measured.

Olympic athlete Greg Rutherford swears that DNAFit helped him to hone his exercise regime, but it's not cheap: tests cost between £99 to £249.

The kit sent to DNAFit customers (DNAFit)

So I gave it a go. The test involves swabbing the inside of your mouth with a specially-designed cotton bud for around for a couple of minutes, before sealing it in a protective tube and posting it off to the DNAFit lab based in the Norwich. A week or so later I found an email in my inbox containing my results.

As a glutton, I skipped straight to the food report to check my ideal diet. The Mediterranean diet, rather than the “low carb” or “low fat” is apparently the one I should stick to. While I’m sensitive to caffeine and salt, I am more responsive to the positive effect of alcohol on cholesterol. I’m lactose intolerant, more prone to risk of damaging my DNA with smoked and chargrilled meat, but don’t need to up my intake of cruciferous vegetables like cabbages and kale. As for exercise, I err towards being better at endurance activities like road cycling than power-based sports, such as sprinting.

Olympic champion Greg Rutherford with his DNAFit infographic (DNAFit)

To piece together profiles, DNAFit test 45 gene variants in the human body. But, considering there are 10 million variants in the human body, how accurate and useful are the results? I’ve been drinking milk without any issues for over two decades. And most of us could do with cutting down on caffeine and salt. My lacklustre performance at sprinting was also never much of a mystery.

Extreme Diets: The Eating Habits of the The A-list Show all 16 1 /16 Extreme Diets: The Eating Habits of the The A-list Extreme Diets: The Eating Habits of the The A-list The Grapefruit Diet This golden oldie has been around since the 1930s and was a favourite among classic Hollywood stars, like Marilyn Monroe. It involves eating half a grapefruit before every meal and is based on the idea that grapefruits contain a fat-burning enzyme that boosts the metabolism. Rex Extreme Diets: The Eating Habits of the The A-list The Air Diet Based on the French concept of breatharianism, the idea that air alone can keep our bodies active, the air diet involves sitting in front of food, placing a piece onto a fork, holding it up to your mouth… But not eating it. Instead, you are to subsist on water and salt soup only. Madonna is apparently a fan of pretend eating. Extreme Diets: The Eating Habits of the The A-list The ‘Liquids Only’ Master Cleanse Diet She did look good in Dream Girls, didn’t she? But the lengths Beyoncé went to to achieve her svelte frame were a tad extreme. Instead of solid foods, she survived on liquids – famously a mixture of lemon juice, maple syrup, cayenne pepper and water – for 14 days. Apparently, this helps to detoxify the body (a process it actually does every day, naturally and unaided by weird diets) and stimulates tissue growth. The dieter is also encouraged to drink laxative tea twice a day. Glamorously. Reuters Extreme Diets: The Eating Habits of the The A-list The Ice Diet Renee Zellweger apparently fills up on ice to stop her piling on the pounds from non-water based foods. Which is, of course, totally ridiculous. Getty Extreme Diets: The Eating Habits of the The A-list The Watercress Soup Diet Liz Hurley once revealed that she regularly subsists on a six-cup-a-day diet of watercress soup when she wants to lose weight for a role. The low-calorie leafy green is also a diuretic, helping to combat water retention. It’s also a completely mental thing to do. Getty Extreme Diets: The Eating Habits of the The A-list Placenta Pill Diet When January Jones gave birth to her son Xander, she had her placenta dried and crushed and stuffed into pills, that she then took as a supplement to lose weight. No idea if it worked or not, but it successfully made us feel queasy reading about it. Getty Extreme Diets: The Eating Habits of the The A-list The Victoria’s Secret Angel Diet If you’re crazy – and, you know, called Adriana Lima or something – then this diet, usually undertaken nine days before a runway show, is for you. It involves omitting all solid foods entirely and subsisting only on protein shakes, supplements and vitamins. You also have to work out twice a day, consult a nutritionist, and, 12 hours before a show, stop drinking liquids entirely to drain the excess fluids from your body and dehydrate as much as possible. Getty Extreme Diets: The Eating Habits of the The A-list The Five Hands Diet Victoria Beckham apparently adopted the Five Hands Diet technique after she gave birth to baby Harper. That means eating only five handfuls of high energy and protein foods a day. So, nuts then. Getty Extreme Diets: The Eating Habits of the The A-list The Baby Food Diet Yep. No real food. Just baby food. And 14 jars of the pap a day at that. Jennifer Aniston loves it. Allegedly. As (also allegedly) does Reese Witherspoon. BANG Extreme Diets: The Eating Habits of the The A-list The Drunk Diet This was invented by Lady Gaga, who once eschewed her evening meals for a swig of whiskey – but adhered to a strict exercise plan, even when hung over. Getty Extreme Diets: The Eating Habits of the The A-list The Apple Cider Vinegar Diet Drinking apple cider before every meal seems like a terrible idea. But Megan Fox does it as a metabolism booster, which helps to rid the body of excess water weight and burn calories faster. Apparently. Getty Extreme Diets: The Eating Habits of the The A-list The Hard Boiled Eggs Diet Nicole Kidman was asked to shed as much weight as possible for her role in Cold Mountain, so she went on the Hard Boiled Eggs diet: That’s an egg for breakfast, and two or three for dinner. And that’s it. Extreme Diets: The Eating Habits of the The A-list The Seven-Day Colour Diet This diet, apparently beloved by Christina Aguilera, at least has some nutritional merit. In order to get the correct balance of nutrients, eating a wide variety of fruits and vegetables across the colour spectrum is a wise idea. But the Seven-Day Colour Diet says you should only eat one colour of food per day of the week. Monday = white food. Tuesday = red food. Wednesday = green food and so forth. Bonkers. Getty Extreme Diets: The Eating Habits of the The A-list The Cabbage Soup Diet Does what it says on the tin. You can apparently consume unlimited supplies of cabbage soup (lucky you), as well as some low calorie fruit and vegetables. Sarah Michelle Gellar is apparently an advocate. Getty Images Extreme Diets: The Eating Habits of the The A-list The Grapefruit Oil Diet Not to be confused with The Grapefruit Diet, this involves sniffing grapefruit oil in the vain hope that the aroma alone might trigger liver enzymes into calorie-burning, detoxifying gear. Jennifer Lopez is rumoured to partake in this lunacy. Getty Extreme Diets: The Eating Habits of the The A-list The Macrobiotic Diet Gwyneth Paltrow’s love of all things Macrobiotic is well documented. It involves a strict, mostly vegetarian plan with grains as the staple food, avoiding highly processed or refined foods and most animal products. She also has a 21-day GOOP cleanse, that involves eating just one meal a day and chewing each mouthful at least 13 times. Getty

Commenting on whether honing in on 45 variants is enough to gain a deep understanding of what we should eat, Dr Tim Spector, Professor of Genetic Epidemiology, said: “sadly not.”

“Although diet choices are often partly genetic, these gene variants are often associated with risk of allergy or disease," he says. "They explain only a small fraction of the differences between people. There are a few exceptions like for lactose intolerance, coffee drinking or alcohol or coeliac disease but basing diet recommendations on genetic tests not usually helpful."

Instead, he points towards the gut microbiome - which varies widely between individuals - as the best way to personalise a diet.

“Genetically testing your microbes is more valuable than testing your own genes at the present,” he suggests.

The views of Marcela Fiuza a British Dietetic Association spokesperson and dietitian, chime with Professor Spector’s scepticism.

“I think the area of nutrigenetics is one of the most exciting areas in nutrition research,” he says. “By combining genetic information with anthropometrics, biochemical and dietary assessments, we will be able to provide personalised advice and customised diet plans. However, there is still a way to go before we get there. There will be a point where we will know more but for now these tests are only weakly informative.”

“I have not used genetic testing with my clients up to this date,” she adds. “I have had clients coming to me after having done genetic tests in other clinics asking for clarification and advice on their results.”

Dr Turi King, Reader in Genetics and Archaeology at the University Leicester elaborates that there many be difference between populations, and that environmental factors including diet, exercise and smoking can play a larger part that our genes, for instance relating to conditions such as coronary heart disease.

“There’s a lot of interactions going on and it’s often not as simple and straightforward as we might hope.

“But there is no doubt, particularly with the research that is going on, that we will be finding out more and more about what parts of our DNA are involved with diet, exercise and disease in the future.”