Children's biology makes them much more vulnerable to sugar and salt in food. And a new study has confirmed that processed toddler foods often have high levels of added sugar and sodium.

Researchers at the U.S. Centers for Disease Control found that in foods targeted at children aged one to three, three-quarters of dinners have high sodium content, a third of the dinners contain added sugar, and a majority of toddler snacks contain added sugar.

An earlier study in Canada reached similar findings.

So we decided to look into why such high levels occur. The answer is more interesting than some people may expect. 

Born for sugar

We seem to be born with a taste for sugar. Before we can speak, we communicate our desire for sweet by smiling or relaxing our face when, say, a sweet solution is placed in our mouth. A sweet taste can also reduce pain, acting like an opioid. There's even evidence that we have the ability to detect sweet before birth.

A pair of protein molecules, T1R3 and T1R2, joined together in taste buds detects sweetness, and it's already working well at birth. Although sugar is abundant today, humans evolved in an environment where it was a rare commodity, so the T1R2+3 receptor tells us the sweet food is likely a valuable energy source.

Julie Mennella

Julie Mennella, a pysychobiologist at the Monell Chemical Senses Center in Philadelphia, says 'the child's biology really makes them vulnerable for the foods that the food industry is making that put in a lot of added sugar and salt.' (Peter Olson/Monell Center)

A few months after birth, babies develop the ability to detect salt in foods.  Salty taste signals minerals are in the food, and children's preference for salt is heightened during periods of rapid growth, says Julie Mennella, a psychobiologist at the Monell Chemical Senses Center in Philadelphia who has been studying children's tastes for three decades. She is arguably the leading researcher in that area.

Not only are toddlers predisposed to like the tastes of sugar and salt, studies show children like them way more than adults, about twice as much for sugar.

That means "the child's biology really makes them vulnerable for the foods that the food industry is making, that put in a lot of added sugar and salt," Mennella says. 

When food processors add sugar and salt

When food processors add sugars and salt to toddlers' food, they do several things.

First, both sugar and salt play a role in the manufacturing process independent of taste. Second, they do add a taste note that's preferred. They also mask bad taste.

Mennella explains that young children have a predisposition against bitter taste, which includes many vegetables, because bitter signals poison.

As well, added sugar and salt teach children how sweet or salty a food should be.

"So if you only feed the child sweetened yogurt, they are going to prefer sweetened yogurt," she says.

By becoming familiar with sweet and salty foods, toddlers develop a long-lasting preference for them. Not only does the added sugar and salt mean the child will like it more, and may consume too much, it also means they will continue to like sweet and salty foods when they are older.

Mennella says overconsumption early in life has health consequences later in life, too. "Many illnesses of modern society are related to poor food choice driven by our taste preferences."

Health problems later

Toddler Foods Study

Obesity expert Dr. David Lau recommends meals and snacks prepared at home for children, like this snack Kathy Burnett made for her daughters Claudia and Sabina, right, Jan. 29, in Chicago. (M. Spencer Green/Associated Press)

Dr. David Lau, an obesity expert and endocrinologist at the University of Calgary, also says what toddlers eat "may track into adulthood, eventually leading to health issues over the long term."

Too much sugar and salt early on may lead to increased risk of obesity, Type 2 diabetes, high blood pressure and cholesterol problems early in life. "Already we're seeing more preschool children who are overweight and obese in Canada, so the trend certainly is already there," Lau says.

Lau served on the World Health Organization's International Obesity Task Force.

"My recommendation would be to have the parents prepare foods for the children,' Lau told the CBC's Vik Adhopia.

'Biology is not our destiny'

Mennella adds, "Biology is not our destiny, we can learn to like different types of foods and that's where experience plays in."

Asked if that strong desire toddlers have for sweet and salty can be reduced, she says she's unaware of any research on the issue. 

She does note the trend to add non-nutritive sweeteners to toddler foods, which will reduce caloric intake, but she explains that it won't lessen the desire for sweet. And for salt, she says there isn't a good substitute.

She does note a couple of intriguing things about salt preference. The children of mothers who experienced morning sickness during pregnancy, which leads to dehydration, are more likely to have higher salt intakes in adulthood. Scientists have found the same pattern for people who had a lower birth weight.

Sugar

Children and adults who have a drive for sugar or salt likely have a drive for both. (iStock)

Mennella says scientists also don't know the biology or the mechanisms that lead children to have a much higher bliss point for sugar. Bliss point is the food industry's term for the amount of added sugar, salt or other food  that creates maximum enjoyment. 

But that higher bliss point has been observed across cultures and, in humans, other primates and rodents, scientists find that adolescence is when the bliss point drops to adult levels.

Another finding is that children and adults who have a drive for either sugar or salt likely also have a drive for the other, challenging the old notion that there are sweet people and salty people.

So Mennella wants to see more research on the brain regions that underlie reward. Noting that salt is often called the primordial narcotic, she says "Many drugs of abuse are co-opting the brain pathways that were designed for these tastes, not the other way around."