Review links early life diet to intelligence and IQ in adolescence

A review of 73 studies has linked nutritional influences to teenage cognitive outcomes, finding that unhealthy diets in early life, especially infancy, could have lasting consequences for intelligence in adolescence. 

Adolescence is a key period of neuroplasticity, when the brain’s ability to adapt, create, and reorganize pathways related to learning, injury, or new experiences is marked by functional and structural changes driven by endocrine and hormonal shifts during puberty.

“What stands out most clearly is that the foundations of cognitive health appear to be laid very early. A poorer diet in the first years of life was linked to lower intelligence years later, in adolescence, even after accounting for many other influences,” says lead author of the study Hayley Young, professor at Swansea University’s School of Psychology, UK.

“The picture during adolescence itself is more mixed: some interventions show promise, but the evidence is far from settled. That is exactly why we need better-designed studies, so we can establish whether adolescence is a genuine second window of opportunity to support the developing brain through nutrition, rather than assuming it is.”

Increasing IQ levels

The review has been published in Advances in Nutrition and included 73 studies, 48 of which were controlled trials and 25 were prospective studies. It investigated how diets and eating patterns impact people aged eight to 19.

Two of the studies found that eating fish frequently at age 15 was associated with higher IQ levels and academic grades at 18.The researchers looked at how brain development progressed over time by examining longitudinal studies and links between diets early in life and their later cognitive and academic performance.

Two of the studies found that eating fish frequently at age 15 was associated with higher IQ levels and academic grades at 18. Another study found that following a Mediterranean diet was positively associated with higher grades when consumed for six to 12 months.

School breakfast programs were shown in two studies to have a positive effect on academic performance and arithmetic scores. Researchers observed improvements when students ate breakfast for at least three months, but there were no changes observed for reading or writing.

Other studies looking at general diet quality linked a larger brain volume by age 10 to consuming whole grains, soft fats, and dairy. Another study examining the Western diet was negatively associated with information processing speed and spatial memory at age 17. Higher intakes of fried potatoes, red meat, and potato chips, and a lower intake of leafy greens and fruit, were linked to poorer performance.

Eating fast food daily at age 10–11 was linked to poorer math, literacy, and science grades by age 13–14, even when adjusting for other foods consumed.

The authors summarize that processed and fast foods for adolescents were consistently linked to poorer academic and cognitive outcomes.

Looking at nutrients

The researchers accounted for a wide range of nutrients and dietary components, such as iron, choline, iodine, vitamin D, polyphenols, fatty acids, grains, and multinutrient interventions.

The review notes that eliminating nutritional deficiencies in zinc, iron, and iodine could improve global average IQ scores.The review notes that eliminating nutritional deficiencies in zinc, iron, and iodine could improve global average IQ scores by 10 points.

The most researched deficiency was iron, included in 12 trials. Supplementation was shown to be dependent on baseline levels, as those with iron deficiency or anemia showed improved hemoglobin levels, verbal memory, and both non-verbal and full-scale IQ. However, for adolescents who had sufficient levels of iron at baseline, no improvements were observed.

Four studies investigated iodine supplementation’s cognitive outcomes. All participants were either mildly deficient in iodine but still had a functioning thyroid or moderate to severely deficient with hypothyroidism. In the latter group, three studies showed improvements in non-verbal IQ after supplementation, and one study found no improvements.

The researchers note that many of the studies used show different findings, which may appear inconsistent. However, they stress that concluding that this shows evidence of diet having little influence should be cautioned.

They say nutrition impacts depend on multiple factors, such as population characteristics, duration of intervention, timing of dietary exposure, and the cognitive abilities being measured.

Diet and brain health

Prior studies have also shown that following a diet high in fat and sugar from an early age can change how the brain regulates eating. It found that even if starting a healthy diet later in life or losing weight, the regulation of eating remains the same. The findings suggest that frequent consumption of energy-dense, nutrient-poor foods high in sugar and fat shapes children’s food preferences and eating patterns in adulthood.

Another study found that older people who follow a healthy diet have a slower development of chronic diseases, including cardiovascular disease and dementia. The diets investigated were those prioritizing consuming vegetables, fruit, whole grains, nuts, legumes, and unsaturated fats, while reducing the intake of sweets, red and processed meat, and butter or margarine.

Healthy diets have also shown benefits for teenagers’ mental health, resulting in fewer depressive symptoms.