The Effects of Food on Daily Thinking Ability

The scientific literature suggests that having a healthy diet can reduce cognitive decline with aging and also reduce the incidence of dementia. However, what effect does having a healthy diet directly influence intelligence when you are a young or middle-aged adult? Is the quality of your mental function significantly influenced by what you ate for lunch today?

You should view the effects of your diet today in terms of both its short- and long-term effects on your brain Foods containing pharmacological stimulants, such as coffee, tea, or dark chocolate can boost mental processing speed and improve performance on numerous cognitive tasks. Unfortunately, the benefits are temporary. Other foods, such as vitamins and the balance of fats, proteins, and carbohydrates have more long-lasting effects on brain function that may take months or years to be fully expressed [click here for more on this topic]. For example, the Mediterranean diet, which is rich in fruits, vegetables, and fish, and is often considered the gold standard of good healthy diets, has been associated with reduced dementia incidence in later life. What about today? If your lunch contains lots of fruit and fish, will you be more intelligent this afternoon at work?

Some recent studies have attempted to answer this question.

Middle-aged adults in one large study consumed a typical Mediterranean diet for six months. The study did not find any evidence of an association between consuming the Mediterranean diet and any evidence of improved cognitive function, such as working memory, visual memory, or problem-solving. No changes were reported in the subjects’ brain function as determined by standard neuroimaging. In addition, a study of neural activation in task-related brain areas did not show any effects due to the diet.

In another study, 1250 healthy middle-aged adults adhered to the Mediterranean diet for 18 months. Cognition was measured using the Trail Making Test, the Verbal Fluency Test, and the Logical Memory Test. The study monitored the subjects’ metabolite profile (250 different measures) to confirm diet compliance (always a weakness when studying the effects of a long-term diet). After adjusting for known risk factors, the Mediterranean diet did not improve cognitive performance.

What about specific dietary nutrients?

One study investigated the effect of adding different types of dairy products. The study considered the cognitive effects of consuming one hundred grams per day of fermented, non-fermented, full-fat, low fat, or sugary dairy foods on 1300 healthy middle-aged adults for six years. The study measured subjective cognitive decline, memory, verbal fluency, and executive and motor functions. This diet was compared to consuming one hundred grams per day of meat, fish, eggs, fruits, and vegetables, but no dairy. Overall, the study reported no effect of adding dairy to the diet or substituting meat, vegetables, or fruit for dairy on cognitive function.

If what you eat each day has no direct, measurable immediate effect on brain function, what does it do?

Independent of one’s diet, having a higher BMI is consistently associated with poor performance on working memory tasks. Eating a poor diet every day may not immediately impair your thinking, however, will eating a poor diet for many years that leads to obesity will impair daily cognitive abilities?

Yes. The culprit is obesity, that is, body fat. Recent epidemiological and clinical studies indicate that obesity is a risk factor for cognitive decline and impaired memory in adults. Increased adiposity has a demonstrated direct negative effect on brain health via mechanisms triggered by central inflammation and insulin resistance, with the most pronounced decrements observed for cognitive domains that are prefrontal- and hippocampal-dependent. Many laboratories around the world, including my own, have documented the mechanisms that underlie how excessive body fat impairs brain function.

Overall, a healthy diet has minimal effects on daily intelligence measures in healthy young and middle-aged adults. However, a poor diet over a lifetime, leading to obesity, will significantly impair overall cognitive function and accelerate brain aging. The beneficial or harmful consequences of daily dietary choices develop slowly over years and decades. Bottom line: if you are changing your diet to become healthier, be very patient.