Felice Jacka, a leading researcher of nutritional psychiatry, has found links between ultra-processed foods and the health of our brains. She explains that our gut microbiome affects various aspects of health, including metabolism, blood glucose, body weight, gene expression, serotonin levels, stress response, mitochondrial function, and immune system. Jacka’s research has shown that a western junk food diet can impair cognitive functions and shrink the hippocampus, a brain region important for mental health, learning, and memory. The industrialized food system, which produces ultra-processed foods, is the leading cause of illness, early death, and biodiversity loss globally, costing around $20tn per year. Jacka suggests that reducing consumption of ultra-processed foods is crucial, but acknowledges that many people don’t have the option due to their affordability and the lack of healthy choices available. She has also found a connection between ultra-processed foods, poor diet quality in mothers and children, and neurodevelopmental disorders such as ADHD. Jacka acknowledges that the term “ultra-processed food” may have some fuzzy borders and misclassifications, but warns against industry tactics to confuse people and muddy the waters, similar to what the tobacco industry did with smoking and lung cancer.