With a combined age of 1,075 years and 68 days the 13 Donnelly siblings of County Armagh can proudly lay claim to being the world’s oldest family.Indeed their ability to defy the passing years has seen them inducted into the Guinness book of world records.But what can now be revealed is the secret behind their longevity – traditional porridge oats.Having grown up on a farm their diet has always been made up of locally sourced ingredients; free range pigs and chickens for bacon and eggs and vegetables grown in their own backyard.However, the Donnelly clan are convinced that what has really guaranteed their long life is their habit of eating porridge, not just for breakfast everyday, but for supper too.”The key is that you need to get your oats at night,” said Leo Donnelly, who at 72 is the youngest of the siblings. “We’ve always followed Daddy’s habit of that nice warm bite before sleep.”Porridge at around 10pm, then porridge again for breakfast at 7am. Cooked oats, milk, perhaps a spot of jam on top.”He added: “It has always stood us well, porridge before sleep and after sleep. People thought it was unusual, but now the living proof is there for all to see.” A bowl of porridge an hour before exercise also ensures blood sugar levels remain steady through a workout, while providing enough energy to keep you going. The Donnelly secret to longevity: a bowl of porridge with a spoonful of jamCredit:Egle Duleckyte / EyeEm For all the grinding hardship of rural life in Ulster during the period, Ellen Donnelly lived until 94. Not that there weren’t some narrow scrapes.”A cow was having calves and it got agitated,” said Leo. “The animal went at Mummy with the horns, caught her, and flung her through the air over its shoulder. Mummy’s poor hip was dislodged and it was frightening, but she just carried on. She was 40 at the time.” But for the Donnellys tucking into a bowl of porridge is just part of their fundamentally wholesome diet and lifestyle, which also sees them steer clear of alcohol.”The farm oats in our porridge were always local and of the finest quality,” said Leo. “Our diet has never been from processed of polluted foods.”We worked with nature, everything eaten was either grown or reared by us. Mummy would say go outside and wring a chicken’s neck, that would be for dinner. The vegetables we ate we had grown, the fruit we ate we picked, the eggs laid were from our chickens, the bacon came from our pigs, the bread we made by hand. Farm oats did not arrive from foreign lands.”The result, says Leo, is there for all to see.”There was never a fat Donnelly raised,” he maintains.The Donnelly siblings’ parents Peter and Ellen established their family farm in County Armagh, Northern Ireland, in 1921, and had 16 children in total (with no TV there wasn’t much else to do, says Leo).Three of the children died, but the surviving siblings range in age from 72 to 93 years.Mrs Donnelly’s only exception to her teetotal rule was to consume a bottle of Buckfast fortified tonic wine after each birth, “to build her up again”. The family’s reliance on oats and their apparently beneficial effect on their health and long years have prompted researchers to launch a study of the Donnellys’ diet. Members of the Donnelly family with their Guinness world record certificateCredit:Alleycats TV for BBC One A family photograph of the Donnelly clan, outside their County Armagh homeCredit:Family collection The recipe for long life, according to the Donnelly familyBreakfast at 7am.Porridge served with homemade seasonal jam.Lunch at 1pm.Cooked seasonal vegetables from the farm (including broad beans, cabbage, cauliflower, peas, potatoes), occasional eggs, homemade bread and cups of tea. Those that weren’t sold for commercial use were eaten by the family, supplying them with a ready source of epicatechin polyphenol, which has been shown to improve arterial health.It was a passing thought from one of the clan that led the results of all this good health being officially recognised by Guinness World Records.“At my sister Maureen’s 90th birthday my late brother Austin wondered aloud if we might be the world’s oldest family,” said Leo. “We sought an answer, but sadly he died just before we could get it officially verified. Wonderful Austin would be proud.”George Holley-Moore, research manager at the International Longevity Centre (ILC) , said: “The Donnelly family’s story is of great interest to us. It is an example of the longevity revolution that has taken place in the UK. We know that a healthy lifestyle, with a good diet and frequent exercise, reduces the risks of a number of health conditions and can enable a healthy older age, and the Donnelly family are prime examples of this.” The benefits of porridge oatsPorridge has been shown to lower blood pressure, combat diabetes, reduce cholesterol and protect the body against heart disease.A study in the US found people who ate a diet rich in wholegrains, such as oats, were about 15% less likely to die from heart disease, compared with people who opted instead for white and refined options.Oats are naturally high in Vitamin B-12, a crucial component in regulating the body’s melatonin levels and sleeping patterns.The grain is also naturally loaded with beta-glucan, a magic genie that lowers “bad” LDL cholesterol and reducing heart disease.Porridge was labelled a superfood when it was discovered that avenanthramides, antioxidants that are only found in oats, minimise plaque build-up in artery walls and reduce the hardening of arteries. Leo says that what would now be referred to as an organic diet accounts for much of the family’s remarkable health and endurance.“We had our own grain and thrasher and rolled everything ourselves. The animals ate the grain we thrashed as well so it was a totally natural cycle of food,” he said.“We would also slaughter four pigs a year and that would do us for bacon and treats, the meat was kept in huge tea chests. You didn’t have pesticides infecting everything in those days. They keep having to use stronger ones now and it is just big evil companies making money. People were healthier eating real food.”The quality of the apples grown on the Donnelly’s 100-acre farm was recognised by the UK’s finest producers, with the fruit being used by cider makers, as well as by Mr Kipling for their pies. Rolled porridge oatsCredit:Snap Decision Dinner at 6pm.Meat would have been served in the evening, but generally just at the weekends for a treat. It was served with potatoes and other seasonal vegetables. Chicken and bacon from their own animals, occasionally beef as well.Otherwise, freshly-gathered eggs, soup, seasonal vegetables from the farm, homemade bread and seasonal fruits (including raspberries, blackberries, strawberries) made up the evening meal.Supper at 10pmPorridge with the option of apple jam on top.Snacks throughout the day were limited to apples from the trees as they worked, homemade bread and many cups of tea. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.