Is there something in your cupboard that could extend your life? Photo from Getty Images.
If I offered you a superfood that would make you live longer, would you be interested?
Naturally it reduces the chances of debilitating heart attacks and strokes as well as life-long diseases such as type-2 diabetes.
And it helps keep your weight, blood pressure and cholesterol levels down.
I should mention it's cheap and widely available in the supermarket.
What is it?
Fiber - it's not the sexiest thing in the world but a major study has been investigating how much fiber we really need to be eating and found there are huge health benefits.
"The evidence is now overwhelming and this is a game-changer that people have to start doing something about it," one of the researchers, Prof John Cummings, tells BBC News.
It's well known for stopping constipation - but its health benefits are much broader than that.
How much fiber do we need?
The researchers, at the University of Otago, in New Zealand, and the University of Dundee say people should be eating a minimum of 25g of fiber per day.
But they call this an "adequate" amount for improving health and say there are benefits for pushing past 30g (1oz).
Is that all?
Well, a banana on its own weighs about 120g but that's not pure fiber. Strip out everything else including all the natural sugars and water, and you're left with only about 3g of fiber.
Most people around the world are eating less than 20g of fiber a day.
And in the UK, fewer than one in 10 adults eats 30g of fiber daily.
On average, women consume about 17g, and men 21g, a day.
Fiber is present in fruit, vegetables, wholegrain bread, pasta and lentils. Photo from Getty Images.
What other foods have more fiber in them?
You find it in fruit and vegetables, some breakfast cereals, breads and pasta that use whole-grains, pulses such as beans, lentils and chickpeas, as well as nuts and seeds.
What does 30g look like?
Elaine Rush, a professor of nutrition at Auckland University of Technology, has put together this example for getting into the 25-30g camp:
- half a cup of rolled oats - 9g fiber | two Weetabix - 3g fiber | a thick slice of brown bread - 2g fiber | a cup of cooked lentils - 4g fiber | a potato cooked with the skin on - 2g fiber | half a cup of chard (or silverbeet in New Zealand) - 1g fiber | a carrot - 3g fiber | an apple with the skin on - 4g fiber
But she says: "It is not easy to increase fiber in the diet."
Prof Cummings agrees. "It's a big change for people," he says. "It's quite a challenge."
Are there any quick and easy tips?
The UK's National Health Service has a page full of them.
They include:
- cooking potatoes with the skin on | swapping white bread, pasta and rice for wholemeal versions | choosing high-fiber breakfast cereals such as porridge oats | chucking some chickpeas, beans or lentils in a curry or over a salad | having nuts or fresh fruit for snacks or dessert | consuming at least five portions of fruit or vegetables each day
What will the benefit be?
Well, after analysing 185 studies and 58 clinical trials, the results are in and have been published in the Lancet medical journal.
It suggests if you shifted 1,000 people from a low fiber diet (less than 15g) to a high-fiber one (25-29g), then it would prevent 13 deaths and six cases of heart disease.
That's during the course of these studies, which tended to follow people for one to two decades.
It also showed lower levels of type-2 diabetes and bowel cancer as well as lower weight, blood pressure and cholesterol levels.
And the more fiber people ate, the better.
What is fiber doing in the body?
There used to be a view that fiber didn't do much at all - that the human body could not digest it and it just sailed through.
But fiber makes us feel full and affects the way fat is absorbed in the small intestine - and things really become interesting in the large intestines, when your gut bacteria get to have their dinner.
The large intestines are home to billions of bacteria - and fiber is their food.
It's a bit like a brewery down there, admittedly one you wouldn't want a pint from, where bacteria are fermenting fiber to make a whole load of chemicals.
This includes short-chain fatty acids, which are absorbed and have effects throughout the body.
"We have this organ set up to digest fiber, which a lot of people just don't use very much," says Prof Cummings.
Why is this relevant now?
The fact fiber and whole-grains and fruit and vegetables are healthy should not come as a surprise.
But there is concern people are turning their back on fiber, with the popularity of low-carb diets.
Prof Nita Forouhi, from the University of Cambridge, says: "We need to take serious note of this study.
"Its findings do imply that, though increasingly popular in the community at large, any dietary regimes that recommend very low-carbohydrate diets should consider the opportunity cost of missing out on fiber from whole-grains.
"This research confirms that fiber and whole-grain intakes are clearly important for longer term health."
The study has been done to help the World Health Organization come up with official guidelines for how much fiber people should be eating to boost health and they are expected next year.
Analysis from BBC Reality Check
One of the suggested ways of boosting the amount of fiber in your diet is to switch from white bread to brown or wholemeal.
This is what has been happening to sales of those products, based on a succession of government surveys of household spending since 1974.
From the mid-seventies to the mid-eighties, white bread fell while brown and wholemeal rose.
Since then, white bread sales have continued to fall, but brown and wholemeal bread sales have been falling for most of that period, although at a slower rate.
So it looks as if while overall demand for bread has been falling, a higher proportion of bread sold has been higher fiber.
Whole wheat pasta has made less of an impact on sales than higher fiber breads, with a survey for the British Journal of Nutrition finding that pasta accounted for less than 1 percent of the occasions on which people were consuming whole grains.