A recent study provides evidence that while a diet high in fat and sugar is associated with memory impairment, habitual caffeine consumption is unlikely to offer protection against these negative effects. These findings, which come from two related experiments, help clarify the complex interplay between diet, stimulants, and cognitive health in humans. The findings were published in Physiology & Behavior.

Researchers have become increasingly interested in the connection between nutrition and brain function. A growing body of scientific work, primarily from animal studies, has shown that diets rich in fat and sugar can impair memory, particularly functions related to the hippocampus, a brain region vital for learning and recall.

Human studies have started to align with these findings, linking high-fat, high-sugar consumption with poorer performance on memory tasks and with more self-reported memory failures. Given these associations, scientists are searching for potential protective factors that might lessen the cognitive impact of a poor diet.

Caffeine is one of the most widely consumed psychoactive substances in the world, and its effects on cognition have been studied extensively. While caffeine is known to improve alertness and reaction time, its impact on memory has been less clear. Some research in animal models has suggested that caffeine could have neuroprotective properties, potentially guarding against the memory deficits induced by a high-fat, high-sugar diet. These animal studies hinted that caffeine might work by reducing inflammation or through other brain-protective mechanisms. However, this potential protective effect had not been thoroughly investigated in human populations, a gap this new research aimed to address.

To explore this relationship, the researchers conducted two experiments. In the first experiment, they recruited 1,000 healthy volunteers between the ages of 18 and 45. Participants completed a series of online questionnaires designed to assess their dietary habits, memory, and caffeine intake. Their consumption of fat and sugar was measured using the Dietary Fat and free Sugar questionnaire, which asks about the frequency of eating various foods over the past year.

To gauge memory, participants filled out the Everyday Memory Questionnaire, a self-report measure where they rated how often they experience common memory lapses, such as forgetting names or misplacing items. Finally, they reported their daily caffeine consumption from various sources like coffee, tea, and soda.

The results from this first experiment confirmed a link between diet and self-perceived memory. Individuals who reported eating a diet higher in fat and sugar also reported experiencing more frequent everyday memory failures. The researchers then analyzed whether caffeine consumption altered this relationship. The analysis suggested a potential, though not statistically strong, moderating effect.

When the researchers specifically isolated the fat component of the diet, they found that caffeine consumption did appear to weaken the association between high fat intake and self-reported memory problems. At low levels of caffeine intake, a high-fat diet was strongly linked to memory complaints, but this link was not present for those with high caffeine intake. This provided preliminary evidence that caffeine might offer some benefit.

The second experiment was designed to build upon the initial findings with a more robust assessment of memory. This study involved 699 healthy volunteers, again aged 18 to 45, who completed the same questionnaires on diet, memory failures, and caffeine use. The key addition in this experiment was an objective measure of memory called the Verbal Paired Associates task. In this task, participants were shown pairs of words and were later asked to recall the second word of a pair when shown the first. This test provides a direct measure of episodic memory, which is the ability to recall specific events and experiences.

The findings from the second experiment once again showed a clear association between diet and memory. A higher intake of fat and sugar was linked to more self-reported memory failures, replicating the results of the first experiment. The diet was also associated with poorer performance on the objective Verbal Paired Associates task, providing stronger evidence that a high-fat, high-sugar diet is connected to actual memory impairment, not just the perception of it.

When the researchers examined the role of caffeine in this second experiment, the results were different from the first. This time, caffeine consumption did not moderate the relationship between a high-fat, high-sugar diet and either of the memory measures. In other words, individuals who consumed high amounts of caffeine were just as likely to show diet-related memory deficits as those who consumed little or no caffeine.

This lack of a protective effect was consistent for both self-reported memory failures and performance on the objective word-pair task. The findings from this more comprehensive experiment did not support the initial suggestion that caffeine could shield memory from the effects of a poor diet.

The researchers acknowledge certain limitations in their study. The data on diet and caffeine consumption were based on self-reports, which can be subject to recall errors. The participants were also relatively young and generally healthy, and the effects of diet on memory might be more pronounced in older populations or those with pre-existing health conditions. Since the study was conducted online, it was not possible to control for participants’ caffeine intake right before they completed the memory tasks, which could have influenced performance.

For future research, the scientists suggest using more objective methods to track dietary intake. They also recommend studying different populations, such as older adults or individuals with obesity, where the links between diet, caffeine, and memory may be clearer. Including a wider array of cognitive tests could also help determine if caffeine has protective effects on other brain functions beyond episodic memory, such as attention or executive function. Despite the lack of a protective effect found here, the study adds to our understanding of how lifestyle factors interact to influence cognitive health.

The study, “Does habitual caffeine consumption moderate the association between a high fat and sugar diet and self-reported and episodic memory impairment in humans?,” was authored by Tatum Sevenoaks and Martin Yeomans.