This Christmas many Irish hosts may have to turn to Google in search of recipe inspiration. Their lunch guests' dietary restrictions, which have now become the norm, could have them seeking out ideas for gluten-free mince pies, dairy-free eggnog and Paleo-friendly turkey stuffing.
Declaring yourself as food intolerant and electing to eliminate something from your diet - whether that's for weight loss or health reasons, or both - is very on-trend. A slew of celebrities have helped popularise this, including Gwyneth Paltrow who says that going gluten and dairy-free changed her family's life. Supermodel Miranda Kerr avoids wheat while tennis star, Novak Djokovic claims that following a gluten-free diet pushed him to the top of his sports career.
It's clear that many of us believe that certain things we are eating are harming our bodies and a lot of the time, it's self-diagnosed. What's more difficult to ascertain is the degree to which this is true.
In certain cases, it obviously is. 'I'm allergic to this' or 'I'm intolerant to that' are phrases commonly interchanged but they are not the same. A food allergy, which is a reaction in our immune system to a perceived threat, cannot be cured although it can be managed and it can also be potentially life-threatening. Common ones in Ireland include cow's milk, shellfish and fish, peanuts, tree nuts, wheat and egg. Food intolerance meanwhile doesn't involve the immune system, and generally has gut symptoms such as bloating and wind. It can make your life miserable and it might cause symptoms but it won't kill you. Dairy and grains with gluten are common culprits as well as reactions to chemicals in the diet, such as sulphites and additives. While the incidence of severe food allergies is relatively small, it's difficult to give a precise figure as to how many people in this country have food intolerance.
"In terms of food allergies in children, with small children about age two, you're looking at 5pc who will have food allergies, and in adults it's 1-2pc. It drops a little because children with food allergies usually grow out of milk and egg allergies," says Ruth Charles, paediatric dietitian with the Irish Nutrition & Dietetic Institute and secretary of the Irish Food Allergy Network. "But in terms of food sensitivities and food intolerance, we really only have estimates for adults and it's anything between 10 and 45pc of the population."
Despite the recent increase of interest in gluten-free diets, this is not reflected in a dramatic rise in the number of people who need to avoid gluten for medical reasons. Coeliac disease is the condition which causes some adults and children to react to the protein gluten, which is found in wheat barley and rye, damaging the lining of the small intestine and reducing a coeliac's ability to absorb nutrients. It presents itself in 1pc of the Irish population and while there is greater awareness of the condition than in previous decades, the path to diagnosis can still be a long one.
For coeliacs, going gluten free is a necessity and not a lifestyle choice because even one grain of gluten can cause harm. Cross contamination, for example using a knife on normal loaf and then using it to cut a gluten-free loaf, must be avoided.
Defining a food allergy or a condition like coeliac disease is clear enough, defining food intolerances isn't, and thus the wide-ranging estimate of the 10-45pc of people who have them.
"It's hard to know because the definition is so loose, so what you might call an intolerance and what I might call an intolerance could be completely different," says Ruth Charles. "There's no level playing field to start off with. There are undoubtedly people who have true food intolerances but unfortunately they get mixed up in the whole bigger picture, where you have anything from famous people going on some kind of elimination diet because it's trendy.
"If we had a proper definition, if it was tighter in terms of saying 'Definitely this is a food intolerance and it's not', it would be a lot easier to know if the rates are going up."
Even if you feel sure that a food isn't agreeing you, it may not be the cause of what's upsetting you. Bread and wheat products are often singled out as foods that cause people discomfort after eating them but it doesn't categorically mean that you're intolerant to them - there might be something else at play. "It could be something like stress-related irritable bowel but because you as a person might say 'Everytime I eat a particular food I feel bloated or I'm not well' it can be perceived as a food intolerance but it mightn't always be the case," says Ruth.
And just because you feel better - or think you feel better - when you stop eating bread, this doesn't necessarily mean good news, health wise. The wisdom of deciding to cut a food or a food group of your diet challenged by many healthcare professionals if it's not medically essential. In a recent review of scientific papers, researchers at the University of Warwick found that there was little science to back up a wheat-free diet and that the majority of the population would benefit from eating wholegrains.
"There are no significant health benefits to cutting it out," says Dr Rob Lillywhite, senior research fellow at University of Warwick. "For coeliacs, certainly, but for 98pc of the population, there's no reason why you shouldn't eat wheat and it's that segment of the population who are being addressed within the research.
"Also the huge expansion of the 'free from' market, we think is just a self-fulfilling prophecy in that people are putting more 'free from' products onto shelves and people are buying them, maybe under the misguided opinion that they're going to offer something more than a regular product."
Dr Lillywhite believes that it is the long-term effects on health that are the greatest concern. "If people cut out fibre on a long-term basis, we don't know the effects that it's going to have but we suspect that it's going to be detrimental. A lack of fibre and synergy from wholegrain products will not protect you against certain cancers, colon problems and Type 2 diabetes that wholegrain foods have been shown to protect against".
There are similar worries about removing dairy from our diets, thus cutting out a major source of calcium, which is essential for bone health - one in two Irish women and one in five Irish men will have an osteoporosis-related fracture in their lifetime - and it needs to be replaced with some other source.
Something like the hugely popular Paleo diet, where you eat only things available during the Stone Age, including meat and plants but excluding wheat, dairy and all processed foods, is not particularly useful, according to Dr. Lillywhite. "We've looked at wholegrain consumption over a long period of time and there's a huge body of evidence that suggests wholegrain consumption is good for you and that message has been adopted by public message bodies world wide," he says.
"To suddenly say you should stop doing this is to go against all the dietary advice that we have ever generated. That itself is a very dangerous step. We don't know what all these fad crash diets are doing for modern health."
According to dietitian Ruth Charles, the diagnosis for either allergy or food-intolerance is a diet of exclusion. "Contrary to what you might be led to believe by looking at all the tests that are available, the only absolute test for any kind of food allergy or intolerance is that you eat the food and you get the symptoms.
"You take away the food, the symptoms disappear. You put the food back and again the symptoms come back again. That is the only gold standard and silver bullet method of diagnosing it," she says.
"You're telling your symptoms and your history to someone who is used to dealing with allergies and intolerances and they are able to pick through that and find out if this is a food allergy-related issue or it's not."
For severe allergies, like peanut, this is done in the controlled environment of a hospital and there is a specific blood test for coeliac disease, followed by a biopsy of the small intestine. While food-intolerance blood tests, which measure antibodies associated with particular foods, are widely available online, the Irish Food Allergy Network's stance, as well as that of the Irish Association of Allergy and Immunology's is that there is neither a rational, scientific basis or proven role for tests such as these, or other alternative tests for food allergies and intolerance, including hair analysis.
"In a healthcare situation, where you are diagnosed with a food allergy or intolerance, you will always be taught how to cope with that but with a lot of the alternative testing, you get tested and told to avoid 12 foods and off you go, goodbye," says Ruth Charles.
"That's very limiting for an individual apart from the fact that it's not always necessary. Telling someone to restrict or cut out food is a very life-limiting condition because you're left with very little food to eat, it costs a lot more to do it and it's really not what most healthcare services would be about. Most healthcare would be about putting as much food back into somebody's diet as safely as possible.
"I'm not against alternative testing but whenever you go for a test for anything you need to be asking the person doing the test: 'What is it going to tell me?'; 'What does this test actually do?'; 'How do you know it does that?' and 'If you're telling me I'm allergic to 12 foods, how am I going to find out when I'm not going to be allergic to them?'"
Dieting has always been a lucrative industry and going 'free from' has now gone beyond fad, translating into big business, especially when it comes to gluten-free. Market research company Mintel says that the US gluten-free market was worth $10.5bn last year although Euromonitor puts it at a more conservative estimate of $486.5m. In the UK the Food Standards Agency says the gluten-free market is worth £238 million and in Ireland we're also following suit. Earlier this month, and in response to the growing demand for gluten-free products, Glanbia opened an oats-only mill in Portlaoise, the first of its kind in Ireland, which will process oats for certified gluten-free products. In October, Ballynogluten, Ireland's first gluten-free pop-up market, took place in Cork, while dairy-free ice cream brand Nobó scooped up the Start-Up of the Year Award at the Lovin' Dublin food and restaurant awards last week.
The wider availability of these kinds of foods is great news for anyone who is food intolerant. Aged eight, Cian McCarthy, now a 16-year-old student, was suffering from bloating, sinus, nausea and lethargy. Through checking ingredients of the foods he was eating and referencing his food journal in which he recorded each meal and snack, his parents were able to identify the culprits as being wheat and dairy within four weeks.
His health markedly improved when he eliminated both from his diet and now when he accidentally consumes any wheat or dairy the effects are immediate. "My skin goes bad, I feel sick, I get cloudy in my head and my sinuses go mad. I just feel upset," he says. He maintains that his food intolerances have made him make healthier food choices overall and to experiment with other less wheat-based cuisines, such as Chinese and Mexican, which are more rice orientated. While it is a restrictive way of eating, he finds the range of dairy and wheat-free options in supermarket and health food stores to be good.
But making the distinction between those who are choosing to avoid food out of choice, as opposed to having to avoid them, can cause some confusion, particularly when eating out.
An example is if someone who is choosing to avoid gluten and does so for the majority of a meal but then has cake because there isn't a gluten-free dessert-choice. "When a coeliac then goes into a restaurant, they're asked 'How serious a coeliac are you?' but with coeliac disease you're either coeliac or you're not," says Emma Clarke Conway of the Coeliac Society of Ireland.
"There might be different degrees of sensitivity in how someone reacts to gluten but you can still be damaging the line of your intestine when you consume any gluten at all. That's the fundamental difference for people to really think about. Certainly there are people who go on a gluten-free diet because they have found that genuinely it makes them feel better and there is much research to be undertaken to discover why that is.
"And there are definitely people who are doing it because they've heard that you lose weight which, trust me, you don't."
While the directives for someone who is acutely affected by food allergies and intolerances are clear-cut, it would seem that there are still many shades of grey for people who aren't.
If someone feels that their health has improved because they have decided to give up bread or cheese, do they need to be concerned about future health problems? We really don't know as of yet but in the meantime there is always the standard but not very sexy advice of eating a healthy, balanced and varied diet.