Study Links Fructose Malabsorption to Higher Anxiety, Not Fruit Itself

A new study published in Brain, Behavior, and Immunity suggests that the issue is not fruit itself, but how the body handles fructose, the simple sugar found naturally in fruits and vegetables and also in soft drinks, industrial juices and processed foods. Researchers say average human intake has risen from under 5 grams a day for most of history to as much as 50 to 80 grams daily in developed countries.

The team from the French National Research Institute for Agriculture, Food and Environment studied the question in two parts, first with 55 healthy young men and then in mice. The men recorded everything they ate for a week, averaging about 30 grams of fructose a day, and nearly 40 percent exceeded recommendations for added sugar. Breath tests showed that about 60 percent had fructose malabsorption, even when their intake was no higher than that of men who absorbed it well.

Those with malabsorption scored higher on a questionnaire measuring baseline anxiety. The difference did not suggest a clinical psychiatric disorder, but it did point to greater stress. They also had higher levels of inflammatory proteins and bacterial toxins in blood, along with differences in gut bacteria.

In mice fed 5 percent fructose for four weeks, animals with impaired fructose absorption showed more fear- and depression-related behavior, major changes in gut bacteria, and inflammation in microglia, the brain’s immune cells. The researchers stress that the human study was observational and included only men, so it does not prove fructose causes anxiety or show whether women would respond the same way. They say clinical studies are still needed to see whether reducing fructose helps people with malabsorption. The findings do not mean people should avoid fruit, since whole fruit comes with fiber, vitamins, minerals and antioxidants, unlike sugary drinks, strained juices and processed foods.