On St Patrick’s Day 2014, two bombs exploded in the world of nutrition.

The first explosion, which shattered orthodox teaching and left the credibility of the nutritional industry in tatters, was the announcement by researchers at Cambridge University that there is no evidential basis whatsoever for believing that eating saturated fat – the sort found in butter, milk and meat – causes heart disease.

The second explosion, which further reduced the credibility of health professionals, the processed food industry and Government health departments, was the report that the researchers at Cambridge did find a link between trans fats and heart disease.

We can summarise the findings succinctly: bad is good, and good is bad.

Careless with credibility
Now, to allow one explosion to damage your credibility is surely bad, but to allow a second one to take place at the same time is surely careless indeed.

This dissembling of nutritional orthodoxies, which have been spouted for the past 50 years, is unprecedented.

That the nutritionists were indeed confused by the findings, published in the journal, Annals of Internal Medicine , is probably best exemplified by what Dr Frank Hu, a professor of nutrition and epidemiology at Harvard, told the New York Times.

Admitting that “the single macronutrient approach is outdated”, Hu went on to say: “I think future dietary guidelines will put more emphasis on real food . . .”

Fancy that: dietary guidelines from industry professionals and university nutritionists that emphasise the fact that people should eat “real food”.

So let’s get started right away and bring a treasured old slogan back into action: “An apple a day keeps the nutritionist away.”

One might have thought that Dr James Reilly and his cohort at the HSE would have leapt into action and acknowledged the report from Dr Rajiv Chowdury and his team at Cambridge University.

But when I perused the HSE's Your Guide to Healthy Eating Using the Food Pyramid , I was taken aback to read that, "To have a low level of saturated fat, which is very important for your heart, you need to limit butter to once a week."

HSE advice
And what should you be having instead, on the advice of the HSE:

“Spreads and oils provide essential fats . . . choose low-fat and reduced fat spreads.”

And then on page 21 of the Guide to Healthy Eating , it states: "Saturated, hydrogenated [hardened] and trans fats are the 'bad' fats because they raise the amount of harmful cholesterol in your blood and increase your risk of heart disease."

If you are thoroughly confused by now – why are saturated fats which have no connection to heart disease lumped in with hydrogenated fats and trans fats which do cause heart disease? – you might very well be asking yourself a simple question: who on earth can you trust when it comes to advice on healthy eating for yourself and your family?

And the answer is simple enough: your granny.

Your granny wouldn’t eat dairy spreads, but she spread good butter on the slice of bread she baked herself. She poured full-fat milk on her porridge, and put a good knob of butter on her champ as she brought it to the table.

She enjoyed the fat of the meat every bit as much as the lean, and loved Imokilly cheddar cheese on a slice of soda bread. She ate fish on Friday, and fasted during Lent.

To buy meat she visited a butcher’s shop, and the fish came from the fishmonger. Her vegetables were grown locally and she loved going out to pick blackberries and seaweeds. When it was your birthday she made you her special cake, a Victoria sponge.

Your granny knew what was good in food, and she knew what was bad in food.

What's good and bad
And some health professionals still know what is good and bad in food. Dr Robert Lustig, who made the viral video Sugar: The Bitter Truth about the dangers of sugar, has published a new cookbook, The Fat Chance Cookbook .

Lustig makes a simple point about modern food: “There’s one thing that doesn’t work for any country: processed food. And any country that adopts processed food, which is now everywhere, is getting sick.

“This is why I want to be known as the anti-processed food guy, not the anti-sugar guy.”

A health professional who stands up and says: bad is bad, and good is good. Maybe there’s still hope.

John McKenna is author of The 100 Best Restaurants in Ireland, guides.ie