Donal O’Neill’s father, Kevin, had hardly put on any weight since the 1960s when he won two All-Ireland football medals with Down.

He was always fit and never drank alcohol but in January 2010 he had a heart attack. Though he pulled through, Donal, who founded the Gaelic Players’ Association in 1999, was perplexed.

“I got angry,” he says. “I come from a marketing background. I’ve worked with the big food companies. I know what they do. The more I found out how far removed we are from what works in maintaining health, the more annoyed I got.

“I started to think it was a little bit strange for a man who had been so fit and healthy – he had sailed through these stress tests for checking heart issues.

“That was my starting point and then I thought, ‘Am I next?’ When they moved to look at my father’s brother, my uncle Seán O’Neill, who was the more famous footballer, they discovered he had type 2 diabetes; again – not a man who had abused himself in any way. The research fascinated me.”

His craving led to a documentary entitled Cereal Killers, which has just been released by Yekra, the same American company that distributed Oliver Stone's movie, Looking for Fidel. It investigates cardiovascular disease, which kills 10,000 people in Ireland a year, the equivalent of the capacity of Hill 16 in Croke Park, remarks O'Neill.

Despite not having any film-making experience, O'Neill produced Cereal Killers with sports physiologist Prof Tim Noakes. O'Neill is also the focus of the film, as he undertakes a 28-day, high-fat diet monitored by Noakes and his colleagues in Cape Town, South Africa, where O'Neill lives.

O’Neill wanted to find out what would happen with an exercise and food regime that involved cutting carbohydrates and sugar. So he gorged on foods high in fat such as meat and bacon, Greek yoghurt, and eggs “the single best food to improve your cholesterol profile”. We’ve been fed misleading information about the elements of a healthy diet, he believes.

“Fat is good. What we’re told is clearly dictated by corporate and political interests. Sugar – and high-fructose corn syrup, the sugar replacement in a lot of soft drinks – is probably the single, most damaging component of the food chain.

The International Diabetes Federation, for example, which aims to combat diabetes, is a commercial partner of Novo Nordisk, the world's biggest producer of insulin, and the food-processing giant, Nestle.

“There is an interesting study of wholemeal brown bread, which is held up as being healthy. They found that three out of five people will get a more aggressive blood/sugar elevation response to brown bread than they will to plain sugar.

“One of the most devious products out there is Kellogg’s Special K. It has 23 grams of sugar per 100 grams. A bar of Lindt 90 per cent dark chocolate has 7 grams of sugar so you’d need to eat nearly half a kilo of 90 per cent dark chocolate to get the same amount of sugar you’d get in a big bowl of Special K.”

One of the most interesting passages of Cereal Killers is the fork in the road taken by the food industry in the 1970s. Competing factions tussled over the cause of heart disease. One side argued dietary saturated fat was the culprit, the other side, sugar. The anti-fat brigade prevailed. Its nutritional guidelines, based on incomplete research by US scientist Ancel Keys, informed the creation of The Food Pyramid in 1977, which is still promoted by the US government today and is sustained by powerful lobbies, despite huge increases in heart disease, obesity and diabetes.

A key finding for O’Neill was that his cholesterol rose from 6.5 to 7.2; he had what Noakes calls “the good kind” of cholesterol – large-particle cholesterol, which helps to reduce inflammation in the body. O’Neill laments that medical tests don’t allow for the difference between small and large particle cholesterol levels.

“It’s probably the single best marker of your cardiovascular risk, and we don’t measure it. That doesn’t make any sense to me. They’re only looking at the tip of the iceberg.”

Cereal Killers is released by Yekra. See also cerealkillersmovie.com.