For the longest time, the people who spent their careers studyingnutrition could only guess at the extent to which people were attracted to sugar. That all changed in the late 1960s, when some lab rats in upstate New York got hold of Froot Loops, the super-sweet cereal made by Kellogg's. The rats were fed the breakfast cereal by a graduate student named Anthony Sclafani who, at first, was just being nice to the animals in his care. But when Sclafani noticed how fast they gobbled it up, he decided to concoct a test to measure their zeal.

Rats hate open spaces; even in cages, they tend to stick to the shadowy corners and sides. So Sclafani put a little of the cereal in the brightly lit, open centre of their cages – normally an area to be avoided – to see what would happen. Sure enough, the rats overcame their instinctual fears and ran out in the open to gorge.

Their predilection for sweets became scientifically significant a few years later when Sclafani – who had become an assistant professor of psychology at Brooklyn College – was trying to fatten some rats for a study. Their standard Purina Dog Chow wasn't doing the trick – even when he added lots of fats to the mix. The rats wouldn't eat enough to gain significant weight. So Sclafani, remembering the Froot Loops experiment, sent a graduate student out to a supermarket to buy some biscuits and sweets and other sugar-laden products. And the rats went bananas, they couldn't resist. They were particularly fond of sweetened condensed milk and chocolate bars. They ate so much over the course of a few weeks that they grew obese.

The details of Sclafani's experiment went into a 1976 paper that is revered by researchers as one of the first experimental proofs of food cravings.

Since its publication, a whole body of research has been undertaken to link sugar to compulsive overeating. In Florida, researchers have conditioned rats to expect an electrical shock when they eat cheesecake, and still they lunge for it. Scientists at Princeton University found that rats taken off a sugary diet will exhibit signs of withdrawal, such as chattering teeth. Still, these studies involve only rodents, which in the world of science are known to have a limited ability to predict human physiology and behaviour. What about people and Froot Loops?

For some answers to this question, and for most of the foundational science on how and why we are so attracted to sugar, the food industry has turned to a place called the Monell Chemical Senses Center in Philadelphia. It is located a few blocks west of the Amtrak station, in a bland five-storey brick building easily overlooked in the architectural wasteland of the district known as University City. Scientists at Monell are among the world's foremost authorities on taste.

In 2001, they identified the protein molecule, T1R3, that sits in the taste bud and detects sugar. More recently they have been tracking the sugar sensors that are spread through the digestive system, and they now suspect that these sensors are playing a variety of key roles in our metabolism.

The stickiest subject at Monell, however, is not sugar. It's money. Taxpayers fund about half of the centre's $17.5 million annual budget through federal grants, but much of the rest of its operation comes from the food industry, including the big manufacturers, as well as several tobacco companies.

A large golden plaque in the lobby pays homage to PepsiCo, Coca-Cola, Kraft, Nestlé and Philip Morris, among others. It's an odd arrangement, for sure; one that evokes past efforts by the tobacco industry to buy "research" that put cigarettes in a favourable light. At Monell, the industry funding buys companies privileged access to the centre and its labs. They get an exclusive first look at the centre's research, often as early as three years before the information goes public, and are also able to engage some of Monell's scientists to conduct special studies for their particular needs. But Monell prides itself on the integrity and independence of its scientists. Some of their work, in fact, is funded with monies from the lawsuits that states brought against the tobacco manufacturers.

"At Monell, scientists choose their research projects based solely on their own curiosity and interests, and are deeply committed to the pursuit of fundamental knowledge," the centre said in response to my questions about its financial structure.

Indeed – as I would discover – although Monell receives industry funding, some of its scientists sound like consumer activists when they speak about the power their benefactors wield, especially when it comes tochildren.

Back in the 1970s, researchers at Monell discovered that children and African Americans were particularly keen on foods that were salty and sweet. They gave liquid solutions, of varying sweetness and saltiness, to a group of 140 adults and then to a group of 618 children aged between nine and 15, and the children were found to like the highest level of sweetness and saltiness – even more than the adults. Twice as many children as adults chose the sweetest and saltiest solutions.

The Monell scientist who undertook this groundbreaking study, however, raised another issue that reflected his anxiety about the food industry. Children didn't just like sugar more than adults, this scientist, Lawrence Greene, pointed out in a paper published in 1975.

Data showed that they were actually consuming more of the stuff, and Greene suggested there might be a chicken-and-egg issue at play: some of this craving for sugar may not be innate in children, but rather the result of the massive amounts of sugar being added to processed foods.

Scientists call this a learned behaviour, and Greene was one of the first to suggest that the increasingly sweet American diet could be driving the desire for more sugar, which, he wrote, "may or may not correspond to optimum nutritional practices".

In other words, the sweeter the industry made its food, the sweeter children liked their food to be.

I wanted to explore this idea a bit more deeply, so I spent some time withJulie Mennella, a biopsychologist who first came to Monell in 1988. Mennella has got closer than any other scientist to one of the most compelling – and, to the food industry, financially important – aspects of the relationship children have to sugar.

In her most recent project, she tested 356 children, aged between five and 10, who were brought to Monell to determine their "bliss point" for sugar. The bliss point is the precise amount of sweetness – no more, no less – that makes food and drink most enjoyable.

Food technicians typically refer to the bliss point privately when they are perfecting the formulas for their products, from fizzy drinks to flavoured crisps but, oddly enough, the industry has also sought to use the bliss point to defend itself from criticism, that it is jamming the supermarkets with foods that create unhealthy cravings.

In 1991, this view of the bliss point as a natural phenomenon took centre stage at a gathering of one of the more unusual industry associations. Based in London, the group was called the Associates for Research into the Science of Enjoyment, or Arise, and its sponsors included food and tobacco companies.

Arise saw its mission as mounting a "resistance to the 'Calvinistic' attacks on people who are obtaining pleasure without harming others". An Australian psychologist named Robert McBride captivated the audience with a presentation he called "The Bliss Point: Implication for Product Choice". Food manufacturers need not fear the implication of pleasure in the word "bliss", he began. "Nutrition is not foremost on people's mind when they choose their food," he said. "It's the taste, the flavour, the sensory satisfaction." And when it comes to these attributes, none is more powerful – or more conducive to being framed by the bliss point – than the taste of sugar, he said.

"Humans like sweetness, but how much sweetness? For all ingredients in food and drink, there is an optimum concentration at which the sensory pleasure is maximal. This optimum level is called the bliss point. The bliss point is a powerful phenomenon and dictates what we eat and drink more than we realise."

Julie Mennella agreed to show me how the bliss point is calculated. I returned to the centre on a warm day in November, and she took me into a small tasting room, where we met our guinea pig: an adorable six-year-old girl named Tatyana Gray. Tatyana had brightly coloured beads in her hair and a pink T-shirt that read "5-Cent Bubble Gum" across the front. The expression on her face was one of cool professionalism: this was a job she could handle.

"What's your favourite cereal in the whole world?" Mennella asked Tatyana, just for fun.

"My favourite cereal is… Cinnamon Crunch," Tatyana replied.

She sat at a small table, with little stuffed versions of Big Bird and Oscar the Grouch perched next to her. As a lab assistant started to assemble the food to be tested, Mennella explained that the protocol for this experiment had been derived from 20 years of trials, and was designed to elicit a scientifically measurable response.

"We are dealing with foods that are very well liked, and so we're going to ask the child which one they like better. The one they like better, they are going to give to Big Bird because they know that he likes things that taste good.

"We're looking at a wide range of children, as young as three, and we don't want language to play a role here. The child doesn't have to say anything. They either point to the one they like, or, in this case, they give it to Big Bird. It's meant to minimise the impact of language."

Why not just ask the children straight out if they like it, I asked.

"It just doesn't work, especially for the young ones," she said. "You can give them everything and they will say yes or no. Though, in this context, it tends to be yes. Children are smart. They'll tell you what they think you want to hear."

We tested this notion by asking Tatyana which she preferred: broccoli or the Philadelphia-made snack called the Tastykake.

"Broccoli," she said, ready for a pat on the head for her response.

For our bliss point test, Mennella's assistant had whipped up a dozen vanilla puddings, each created at a different level of sweetness. She started by putting two of the variations into small plastic cups and setting them in front of Tatyana.

Tatyana tasted the one on the left, swallowed, and took a sip of water. Then she tasted the one on the right. She didn't speak, but she didn't have to. Her face lit up as her tongue pressed into the roof of her mouth, pushing the pudding into the thousands of receptors waiting for sweetness.

Being an old hand at the test, she ignored the stuffed animals and simply pointed to the cup she preferred.

In the testing that Mennella conducted to calculate Tatyana's bliss point for sugar, the six-year-old worked her way through two dozen puddings, each prepared to a different level of sweetness. The puddings were presented to her in pairs, from which she would choose the one she liked more.

Each of her choices dictated what pudding pair would come next, and slowly Tatyana moved toward the level of sweetness that she preferred most of all.

When Mennella got the results, it was plain to see that there was no way Tatyana would ever have fed Big Bird a twig of broccoli over a Krimpet, a Kreamie, or anything else from the Tastykake line.

Tatyana's bliss point for the pudding was 24% sugar, twice the level of sweetness that most adults can handle in pudding. As far as children go, she was on the lower side; some go as high as 36%.

"What we find is that the foods that are targeted to children, the cereals and the beverages, they are way up," Mennella said. "Tatyana's favourite cereal is Cinnamon Crunch, and what we will do is we will measure the level of sweetness that the child prefers in the laboratory with a sucrose solution, and it matches the sugar content of the most preferred cereal. There are individual differences, but, as a group, in every culture that has been studied around the world, children prefer more intense sweetness than adults."

Beyond the basic biology, there are three other aspects of sugar that seem to make it attractive to children, Mennella said. One, the sweet taste is their signal for foods that are rich in energy, and since children are growing so fast, their bodies crave foods that provide quick fuel.

Two, as humans, we did not evolve in an environment that had lots of intensely sweet foods, which probably heightens the excitement we feel when we eat sugar. And finally – sugar makes children feel good.

"It's an analgesic," Mennella said. "It will reduce crying in a newborn baby. A young child can keep their hand in a cold water bath longer if a sweet taste is in their mouth."

These are huge, powerful concepts – concepts that are crucial to understanding why so much of the grocery store food is sweet, and why we feel so drawn to sugar.

We need energy, and Cinnamon Crunch delivers it quickly. We've been intimate with sweet taste since we were born, and yet our ancestors had nothing as thrilling as Coke. Sugar will even make us feel better, and who doesn't want that?

Mennella has become convinced that our bliss point for sugar – and all foods, for that matter – is shaped by our earliest experiences. But as babies grow into youngsters, the opportunity for food companies to influence our taste grows as well. For Mennella, this is troubling. It's not that food companies are teaching children to like sweetness; rather, that they are teaching children what foods should taste like. And increasingly, this curriculum has been all about sugar.

"What basic research and taste in children is shedding light on – and why the foods that they are making for children are so high in sugar and salt – is that they are manipulating or exploiting the biology of the child," she said. "I think that anyone who makes a product for a child has to take responsibility because what they are doing is teaching the child the level of sweetness or saltiness the food should be.

"They are not just providing a source of calories for a child," she added. "They are impacting the health of that child." 

http://www.guardian.co.uk/science/2013/mar/16/sugar-and-food-industry-michael-moss#