Patricia Daly knew Domini Kemp before they met. In that two degrees of separation way they had a couple of mutual friends. But it wasn't until 2013 when Kemp came for a consultation that Daly realised the friends who insisted the two would get along like a house on fire were spot on.

Both women are working mothers with two children apiece. Both have had cancer, twice. And both were convinced that food was something they could use to help them get through treatment and onwards. Now they've published The Ketogenic Kitchen, a collaboration cookbook based on what they learned and ate through illness to wellness.

The book comes in the middle of a clean-eating wave that can feel like the attack of a clone army. Beautiful 20-something women report glowing skin and endless energy from wheat-, dairy- and sugar-free diets making dates and coconut oil sound like a recipe for immortality served with a side order of fabulousness.

The buzz about nut butters is a mixed blessing. Do they hope keto (short for ketogenic) is going to become the new paleo? Kemp and Daly both do a grin-grimace at the question. “I actually hope it doesn’t,” Kemp says. Britney Spears and comedian Melissa McCarthy have been reported to be eating by the keto rules: manna from publishing heaven. But Kemp is not delighted by it, not least because of the backlash that inevitably follows the adulation of another trendy diet. “You don’t want it to become a fad. It’s metabolic therapy. It is such a serious thing and has such serious benefits for some people.”

Put very simple keto eating (they hate the word diet) chops the top off the food pyramid and flips it upside down. Instead of carbohydrates you get the bulk of your calorie intake from healthy fats, with adequate protein. Carbs are treated with the caution once reserved for butter.

The irony that the high queen of bagels (Kemp introduced mainstream Ireland to bagels in 1999) is advocating low-carb eating has not been lost on her.

“That’s the mad thing,” she says. “None of us saw carbs as a bad thing. It was all like ‘just keep it low fat. Don’t have butter on it, don’t have mayonnaise’ and it’s hard because now . . . it’s a complete turn around. I definitely do struggle but at the same time we’ve always in Itsa [Bagel] had things other than bagels to eat, like the lentil and veg soup that was there, the salads; all that stuff. Do I go in and eat bagels anymore? Not really. I do sometimes and then you’re like ‘ooh these are really tasty’.” This is met with loud giggles from her co-author.

Daly's teens and early 20s were "carb city" thanks to a serious athletic career. For a decade from the age of 14 she trained as a triathlete, and was a member of the junior Swiss national team alongside Olympian Nicola Spirig. Their coach recommended a vegetarian carb-loaded diet based on the coach's success with Natascha Badmann, the first European woman to win the Ironman Triathalon.

“I stopped eating meat and my dad was pulling out his hair. At the end of a year I had a massive iron deficiency,” Daly says. “It was a prime example of what works for one person doesn’t work for everyone.”

Daly left Switzerland a decade ago to travel with her Irish boyfriend (now husband) Johnny Daly. She had met him on an Irish Cycling Safaris holiday two years earlier. "Yes I fell for the tour guide," she says.

It's still a slightly embarrassing how-we-met story to tell. She moved to Ireland in 2007 and began working in the international banking arm of Bank of Ireland, a job involving lots of travel and 4am starts. In July 2008 a flickering in the corner of her right eye was diagnosed as a detached retina because of a tumour.

Two years later she got the news that the tumour had doubled and was growing aggressively. After frantic research she found German studies that led her to a ketogenic diet, to try to starve the cancer cells of what they needed to grow. Everything she did was alongside, rather than any replacement for, conventional medical treatment. After her recovery she trained as a nutritional therapist and now works with cancer patients, like Kemp who came to her after treatment for breast cancer.

The book is in two parts. The first half by Kemp gives low carb recipes. The second is aimed at someone who wants to go full keto with a practical meal planner to avoid having to prepare something from scratch three times a day. Both sections are full of great family friendly recipes. (The no-drizzle three-minute mayonnaise is worth the cover price alone). It’s a serious book that doesn’t take itself too seriously, perhaps the only one in its genre where you’ll see wheatgrass described as tasting like silage.

How does Daly manage to cook for her children (aged four and six) given her limited diet? "Yesterday I made a stir fry with prawns and lots of vegetables, coconut oil and coconut cream and all the spices. Then I just fished out some broccoli and prawns because the sauce is too spicy for them and they have it with a bit of basmati rice, which I cooked for them but didn't eat. It just adds the good fats for their diet. They love the lamb pizza." It is the most Homer Simpson recipe you'll find in a healthy eating book. The base of the pizza is made from minced lamb.

“That [lamb pizza] is bloody ridiculously good,” Kemp says. “You get creeped out making it because it looks disgusting. It shouldn’t work. From a chef point of view I’m looking at it going ‘nah’. But it is fab.”

The book will be published in America in the autumn. It's the kind of guide Kemp wishes she could have found when she was diagnosed and went home to "Google 'when am I going to die?'"

They have a questionnaire to help people decide if they should lower their carb intake. Low carb and keto eating is not a religion, Daly says firmly. The last thing they want to do is fuel the orthorexia culture of obsession with only eating food considered healthy. A lot of people can handle carbs just fine, like Daly’s husband Johnny and Domini’s sister Peaches.

“There’s no point in bashing vegans or vegetarians or high carb/low-fat people,” Daly says. “Everyone needs to find their cup of tea. I know it’s so frustrating for people; they just want a clear-cut answer. ‘Tell me what to do. Tell me what to eat.’ But it does not exist. It’s a dynamic process like everything in life.” theketogenickitchen.com