Refined Diets Without Fiber May Trigger Early Memory Changes in Ageing Brain: Study - Video

Just three days of poor eating may be enough to disrupt memory in the ageing brain. New research suggests that it's not just fat or sugar that poses a problem-but a lack of fiber. In a recent animal study from The Ohio State University, scientists found that refined, low-fiber diets rapidly impaired emotional memory in older rats, even before obesity developed. The findings were published in Brain, Behavior, and Immunity.

As people age, the brain becomes more vulnerable to inflammation and metabolic stress. Highly processed diets have previously been linked to memory decline, but researchers wanted to pinpoint which dietary components were most harmful. To investigate, the team fed young and aged male rats either standard chow or one of five refined experimental diets for three days. These diets varied in fat and sugar content—ranging from low-fat/low-sugar to high-fat combinations—but all shared one feature: they lacked fiber.

Behavioral testing revealed a striking pattern. Older rats consuming any of the refined diets showed impaired long-term emotional memory linked to the amygdala, the brain region responsible for processing fear and risk-related learning. In contrast, hippocampal memory—associated with spatial and episodic recall—was disrupted only in aged rats on a high-fat, low-sugar diet. This pointed researchers toward a common denominator beyond fat or sugar.

Gut and blood analyses provided a clue. All fiber-deficient diets led to significantly lower levels of butyrate, a molecule produced when gut microbes break down dietary fiber. Butyrate is known to have anti-inflammatory properties and can cross the blood-brain barrier. Reduced butyrate levels may therefore promote unchecked brain inflammation, particularly in vulnerable ageing regions like the amygdala.

At the cellular level, the team observed impaired mitochondrial function in microglia from aged brains. Unlike cells from young animals, these mitochondria showed reduced respiration and limited ability to respond to energy demands—signs of compromised resilience.

Importantly, these cognitive effects occurred rapidly and were not primarily driven by weight gain. The researchers now plan to explore whether fiber or butyrate supplementation can reverse diet-related memory deficits, highlighting the potential brain benefits of a fiber-rich diet in older adults.

REFERENCE: Butler, M. J., et al. (2025). The aged amygdala’s unique sensitivity to refined diets, independent of fat or sugar content: A brain region and cell type-specific analysis. Brain, Behavior, and Immunity. DOI: 10.1016/j.bbi.2025.106220. https://www.sciencedirect.com/science/article/abs/pii/S0889159125004623?via=ihub