It’s not cool to talk about your tummy troubles when you’re a pop star. But when you’re a pop star in your 60s, what’s the point of pretending things work like they used to in your Eighties heyday?

You have to be truthful about the realities of life, insists a disarmingly honest Limahl – the spiky-haired frontman of 1980s chart-toppers Kajagoogoo, who’s promoting his new Christmas single, One Wish for Christmas.

“As you get older, your joints, your eyesight, hips and knees wear out, and I think the tummy and the bowel etc, which are constantly working, are just another thing that goes,” says Limahl, who has irritable bowel syndrome (IBS) and lactose intolerance. “And I’m 63 next – you can’t ignore that. People mainly remember me from 40 years ago when I was 23, so I feel a responsibility not to look too old and decrepit. It takes effort! I haven’t embraced my grey – it looks great on George Clooney, but I don’t want it on me!”

The singer’s weathered well and really doesn’t look hugely different from the Eighties idol he once was (although the hair is more floppy than spiky now, and no longer two-tone black and white, but definitely not grey or thinning). But his life isn’t only about singing and image –  health is of course vitally important too, and he’s had trouble with his digestive system for years. However, he says he got the root of the problem earlier this year.

“I think the IBS has been brewing over a few years, and it came to a head this year,” he reveals. “It seemed like everything I ate caused bloating, which feels very uncomfortable and looks awful. If I was performing that day, I’d got to the point where I didn’t want to eat because I was scared of going on stage and bursting out of my clothes and looking like I’d put on five stone. I look pregnant if I eat the wrong things, it’s awful.

“With IBS, there are different symptoms for different people. Some people get diarrhoea, but with me it’s the opposite, I can get constipated, but that exacerbates the problem. And of course it’s not very cool to talk about constipation as a pop star! But I have to face the realities of life, like everyone else. There’s mental and physical pain involved.”

Limahl was eventually diagnosed with IBS after having blood tests, an endoscopy and a CT scan, and admits: “When it started, oh God I was worried! I thought the worst.”

He went to see a qualified nutritionist, who told him his problem was with FODMAP foods – an acronym for fermentable oligosaccharides, disaccharides, monosaccharides, and polyols – simple sugars that are sometimes poorly absorbed and rapidly fermented by the gut.

“Researchers have found people with IBS don’t tolerate certain sugars in foods,” explains Limahl. “They don’t get digested, and once they hit the colon all the bad bacteria go, ‘Woo-hoo, it’s party time!’ and create gas by consuming the undigested sugars. I think I’ve explained that right!”

With the guidance of his nutritionist, Limahl went on an elimination diet for three months to find out exactly which foods caused his problems. His diet is now more  restricted – but probably not in the way most people would expect a gentle-on-the-tummy diet to be.

“There are so many foods that affect me,” he says. “I have an app that I use to check foods, and I’ve become an expert food label reader. The two biggest surprises for me were honey, because it’s high in fructose, and dried fruit. It’s weird – I can have an orange, but I can’t have orange juice, because that’s concentrated with fructose. I can’t eat garlic, and I can have red peppers, but not yellow or green.” He can also eat green beans – but only 15 of them.

“There’s a lot of things ending in ‘ol’ that are often in manufactured cakes and biscuits that I can’t have. I’ve just got to find the stuff I can eat. You’ve got to dig around and make it work for you and then it’s ok. I thank my lucky stars – at least I can eat some stuff. I suddenly got my life back!”

He explains that certain FODMAPS are ok for certain people, and stresses: “It’s very individual. IBS is such a massive, broad-spectrum umbrella. It really restricts my diet, but I’d rather be in control than just be stressed about it all the time. If you decide to have a blow-out for a special occasion, you know you’re going to suffer for two days, but that’s ok, you have that choice.”

At around the same time as his IBS was becoming more of a problem, Limahl also discovered he was lactose intolerant. However, he says he now carries a supplement with an enzyme in it to help him tolerate lactose. “It’s about taking back a bit of control. I also carry a supplement to help me tolerate oligosaccharide foods like beans, peas, lentils, and even oats.”

That clever little supplement means he can have porridge for his breakfast every day. “I can have banana in it, but only a third of a firm banana, otherwise it’s problems for me,” he says.

As well as being affected physically when he eats the wrong foods, Limahl, who lives with his partner Steve in Hertfordshire, admits the IBS affects his mental health too. “You feel mentally ill when you eat something that doesn’t agree with you. I look down, my stomach is bloated, I feel uncomfortable. It takes your mind off concentrating on whatever you’re doing, and it lasts for hours – it’s quite awful. I reckon there’s millions of people around the world suffering with these types of symptoms.

“My nutritionist says that in the near future, she thinks low FODMAP foods will be as common in restaurants as vegan food is today. It’s a new science that people are finding out about, and I’m glad I can talk about it and hopefully spread the word.”

Limahl’s new single One Wish For Christmas is available now.