DR XAND VAN TULLEKEN On Diets That Are Worth The Agony

Like millions of other Britons, you may well have just embarked on a diet in an effort to shape up and slim down in 2018. You may already be losing a few pounds and gaining compliments from friends. But it is a fact that the majority of diets end in failure. So which ones do work?

And which ones simply aren’t worth the misery? And more importantly, why? I set out to answer these questions in my new five-part Channel 4 series How To Lose Weight Well. As we are told constantly, we are in the grip of a health crisis. About 62 per cent of British adults are classified as overweight and one in four is obese - the medical term for excess weight known to raise the risk of heart disease, stroke, cancer and a host of other diseases. Weight is also a subject close to home for me.

Just a few years ago, I ballooned to 19st while my identical twin brother Chris stayed at my previous weight of 12½ stone. At 6ft, this gave me a body mass index score of more than 35, meaning I was obese. As a doctor with a degree in public health, it was not just soul-destroying, but also highly embarrassing.

I made a dedicated study of the world’s most popular diets and took all the good bits - and discarded the waffle and gimmicks - to formulate my Definitive Diet. This is based on the principle that healthy eating must be built seamlessly into your life without any great feeling of sacrifice or social isolation.

After all, we all have the odd party or wedding to go to. Not only that, but if you really love food, as I do, a strict diet can be utterly miserable and simply not sustainable. This, I discovered, lies at the crux of whether any diet succeeds or fails.

Many plans work in the short term if the draconian rules stop your diet saboteurs - whether they are cheese, wine or chocolate - in their tracks. But long-term, our willpower cracks. I made a dedicated study of the world’s most popular diets and took all the good bits - and discarded the waffle and gimmicks.

My new series hammers home this point even further. We asked 30 male and female volunteers to test a different diet plan, having screened them to make sure it was medically safe for them to participate. From five-day to two-week very-low-calorie crash diets, to celebrity-endorsed juice diets, high-carb regimes and even one that involves eating up to four eggs a day, we left no fad unexplored.

I'm surprised that I'm 104! Interestingly, all of the plans worked and everyone lost weight, some more successfully than others. One woman who weighed 11st at the start lost an incredible 1st 4lb in just two weeks. But it is sticking to diets that is the real problem. Some are bland or monotonous, or the food is difficult to source and needs a lot of preparation, which is offputting. Others are simply extreme, requiring incredible willpower to stick to as little as 600 calories a day, as advocated by the Copenhagen Diet that volunteer Sheena followed for 13 days.

So which one worked best? BEST ONE-WEEK DIET: Slimfast, a combination of six shakes and bars a day. BEST TWO-WEEK DIET: CSIRO Low Carb Diet - low-GI, high-protein foods and wholegrains, and two indulgence foods a week. BEST FOUR-WEEK DIET: The Karl Lagerfeld Diet - protein-rich, reduced-carb, maximum of 1,250 calories a day.

BEST SIX-WEEK DIET: Ayurvedic diet, based around your body type and whether your system is fast or sluggish, plus meditation to stop cravings. BEST FOUR-MONTH DIET: The Banting Diet - increased fats and decreased carbs. Elimination of most grains, processed foods and sugars: 1,900 calories per day for men, 1,400 for women.

Yes, she lost a stone, but she was dizzy and constipated and vowed never to do it again. To some degree, there was a common theme. Pretty much all of the diets involved cutting down on (if not cutting out completely) refined sugar and carbohydrates - cakes, biscuits and fizzy drinks - and eating as much freshly prepared food and vegetables as possible. It’s not just about what you put in your mouth, though.

Many of the diet plans stipulated doing at least 30 minutes of physical activity five days a week. Our biggest weight loser, Jake, who shed an impressive 4st 4lb in four months, soon found himself in the gym five days a week - and feeling a thousand times better for it. He was also a great example of making a diet plan work long-term by making it a lifestyle choice. At the end of the four months, he vowed to keep up his low-carb regime five days a week, giving him room to indulge a little at the weekend.

One pair who did brilliantly were IT support worker Si Fong, 40, and his husband Simon Herbertson, a 42-year-old university administrator from Manchester. They described themselves as cliches: fat, middle-aged men with no hair. Ideally, they wanted to drop a couple of stone each. At the beginning, Si weighed 18st 9lb and his weakness was cheese, while Simon weighed 15st 12lb and loved red wine and chocolate.

BEST ONE-WEEK DIET: Slimfast, a combination of six shakes and bars a day. The Dude diet is not your typical regime and consisted of ‘real’ food such as beef, curry and tacos with unlimited tea and coffee, and alcohol in moderation. No white carbs were allowed but Si could indulge during one cheat day a week. The one rule was food had to be cooked fresh and portion sizes had to be reduced.

A typical recipe was baked meatballs (rather than fried) to cut down on the fat content, made with lean beef, and riced cauliflower instead of breadcrumbs. Si loved it because it felt like real food. Not only is alcohol full of sugar and so-called empty calories, it also slows down how we process food - meaning we’re more likely to store it as fat.