Humans are consuming more fructose than ever before and that’s becoming problematic – not just for our (remarkably expanding) waistlines, but more importantly for our brains.
For most of human history, honey and fruits provided the main source of fructose. Both were scarce: honey collectors faced colonies of bees, while many of our favorite fruits did not exist in their current sugary forms.
However, many people cannot properly digest this now common sugar – and the problem is that consumption has increased.
Historically, we have consumed less than 5 g of fructose per day, but current consumption levels are between 50-80 g per day in developed countries.
More alarmingly, over the past few decades, numerous human studies and animal experiments have suggested an association between fructose malabsorption and symptoms of anxiety and depression.
A new study – in Brain, Behavior and Immunity – precisely explored the effects of fructose malabsorption in both humans and mice and provided a possible explanation for the link between sugar and emotional states.
As detailed by , on the human side, the study followed a group of 55 healthy male volunteers, aged between 18 and 35 years, with a BMI below 25 and without gastrointestinal, psychiatric or neurological conditions.
Participants ingested 35 grams of fructose and underwent a breath test. The concentrations of hydrogen and methane in exhaled air revealed that 60% had fructose malabsorption. Participants then kept a seven-day food diary at home, documenting all food sources consumed during that week.
They also completed two questionnaires to assess possible mood disorders. THE State-Trait Anxiety Inventory (STAI) evaluated anxiety traits such as nervousness and apprehension, while the Hospital Anxiety and Depression Scale (HADS) measured pathological anxiety and depression.
The researchers then collected stool samples from the participants to perform an analysis of the microbiota (intestinal microbes), as well as blood samples to analyze proteins and other compounds linked to inflammation in the body.
In parallel, this work included a model in rats – normal and which were genetically modified to present fructose malabsorption.
Both human participants and mice showed physical and biological signs associated with increased symptoms of anxiety. In both cases, it was noted that the Anxiety was associated with an unbalanced gut bacterial ecosystem and the presence of inflammation.
Notably, human participants with malabsorption showed “significant differences” in the relative abundance of five types of gut bacteria: agathobacter, bifidobacterium, prevotella, enterococcus e zhenpiania.
They also showed a “slight but significant increase in state anxiety”, as measured by the STAI questionnaire, without reaching pathological levels.
Interestingly, researchers found that the abundance of certain microbes was positively associated with different sources of fructose, such as dairy products, beverages or added sugars from sweets.
Other microbial populations were negatively correlated with fructose sources, such as those from fruits and vegetables. These microbes may also be associated with anxiety-like symptoms, perhaps through the production of metabolites that induce inflammation.
New pathways to alleviate anxiety-like symptoms
“Clinical and preclinical data from this study show that Fructose malabsorption is associated with changes in the intestinal microbiotaelevated markers of systemic inflammation and an increase in anxiety-like behaviors”, conclude the researchers, cited by Refractor.
