This post was written by Michael Goran, PhD, and Emily Venutra, PhD, MPH, authors of the new book Sugarproof.
Too much sugar can have broad effects on kids’ bodies and, as they discuss in their new book Sugarproof, kids can be more vulnerable to the harmful effects of too much sugar. Growing kids can have delicate digestive systems. Upset stomachs, aching tummies, and other maladies are hallmarks of childhood, and too much sugar may be a silent contributor to this problem.
If your child is having frequent, unexplained tummy problems, one possibility is that they are reacting to excessive amounts of fructose and an inability to absorb it properly from the gut. Fructose is a part of regular white table sugar and also found in concentrated amounts in high fructose corn syrup, fruit juices, other fruit-based sugars like fruit juice concentrates, and agave syrup. In order to transfer glucose or fructose from the gut into the bloodstream, the body needs special transport receptors in the gut, which recognize them and help move them into the bloodstream. Glucose is so critical to providing vital energy throughout the body that there are more than a dozen different transporters for glucose alone.
Fructose, on the other hand, can only be absorbed through the GLUT-5 transporter. GLUT-5 isn’t even present in newborns because they aren’t expected to be consuming fructose; it is not a natural component of breast milk. As children grow up and become exposed to more fructose, the gut gradually develops and turns on GLUT-5 receptors. However, when the gut is bombarded by high amounts of fructose, children, and sometimes-even adults, might not have enough GLUT-5 to fully absorb it all. If there aren’t enough fructose transporters, then fructose gets stuck in the gut where it gets eaten by gut-residing bacteria. The fructose essentially ferments in the gut, and this process produces hydrogen gas or other compounds that can cause bloating and cramps. Known clinically as fructose malabsorption or dietary fructose intolerance, it could be a factor in what’s causing your child’s chronic digestive issues.
A clinical test for fructose malabsorption involves taking a large dose of fructose and then monitoring hydrogen gas in the breath for several hours. However, there is an easier way to diagnose the problem at home. If your child is subject to frequent bouts of gas and bloating, simply try reducing sugars, especially high fructose offenders, and see if there is any improvement in symptoms. In a study with 222 kids aged 2-18 years who had unexplained abdominal issues, it turned out that 55% had fructose malabsorption after a breath test. The kids who tested positive were advised to go on a low fructose diet, and after that, symptoms improved in 77% of these patients.
Excess sugar consumption can also damage the gut by causing increased intestinal permeability, or leaky gut. Excess fructose consumption has been linked to leaky gut, and leaky gut has been shown to be a factor contributing to type 2 diabetes and cardiovascular disease. Recent studies show that this effect of fructose is dose dependent, and low or moderate amounts of fructose like what you would get from fruit consumption would not cause these effects.
Another way that sugar can cause digestive issues is through the way it affects the growth of various bacteria in the digestive tract, or the gut microbiota. For example, in a rodent study, a scientist at USC, Dr Scott Kanoski, gave rats free access to their normal food and water as well as a second bottle that was either plain drinking water or one that had 11% solutions of sugar in different rations of fructose to glucose, to mimic sugary beverages. The ratio of fructose to glucose had no significant impact on the gut microbiome. However, sugar in general had major effects, altering the ratio of harmful to beneficial bacteria.
Studies of the effects of sugar on gut bacteria in infants and children are lacking. One recent study in teenagers showed that dietary fructose intake was the only dietary component that was associated with any effects on the gut microbiome. Teenagers with higher consumption of fructose in the diet had lower abundance of the beneficial microbes Eubacterium and Streptococcus.
If your child is experiencing frequent digestive issues, too much sugar and especially fructose, may be a contributing factor. Try a low fructose diet and see if the symptoms resolve. One common meal that can be high in sugar and fructose is breakfast, especially if it includes juice; so one good place to start is eliminating juice. In Sugarproof, there are lots of ideas for reducing sugar at breakfast, including several recipes, like this savory breakfast idea for Korean-inspired Savory Breakfast Pancakes.