WHAT ENABLES YOU to solve novel problems is a faculty called fluid intelligence. It’s your on-the-spot reasoning ability, in contrast to crystallized intelligence, which is more dependent on learning. Unfortunately, fluid intelligence begins to decline even before middle age, while crystallized intelligence gathers steam over time.

Fluid intelligence, researchers find, depends on the healthy function of the frontal and parietal cortices, and studies show that it can be optimally preserved by consumption of specific omega-3 fats. These are not the well-known omega-3 fatty acids found in fish, EPA and DHA; all are derived from land-based food. Omega-3 fats from fish are still important. But so are other omega-3 fats.

Nutritional neuroscientist Marta Zamroziewicz, along with neuroscientist Aron Barbey, at the University of Illinois, studied the frontoparietal network of the brain in the healthy elderly, aged 65 to 75- They also looked at the nutritional intake of those subjects. But unlike most researchers, they measured an array of polyunsaturated fats in the blood, because nutrients don’t act in isolation. By measuring blood levels of the fatty acids, the researchers bypassed the limitations of most nutritional research-flawed recall of food intake and variability of nutrient absorption.

As a result, they got a clear picture of which nutrient patterns best preserve the structure of the frontoparietal gray matter. They turned out tobe alpha-linolenic acid, stearidonic acid, and eicosatrienoic acid. Subjects with high blood levels of the three omega-3s tended to have a larger left frontoparietal cortex. Further, the size of the frontoparietal cortex predicted performance on tests of fluid intelligence.

Nuts, seeds, and oils are the primary sources of the three omega fatty acids. Alpha-linolenic acid is found in nuts, especially walnuts, and in seeds and their oils, especially rapeseed oil. Stearidonic acid is also found in seed oils. Eicosatrienoic acid is most abundant in flaxseed oil and also found in yellow mustard. Intake of these nutrients, studies show, may prevent or slow cognitive decline.

In a related set of studies, Zamroziewicz and Barbey found that the brain structure most revealing of memory function in the aging process is the fornix, and its integrity hinges on a abundance of both omega-3 fats and omega-6 fats. The fornix is an area of white matter situated between the hypothalamus and the hippocampus. The state of its microstructure, including the myelination of component nerve fibers, is a more sensitive indicator of memory decline than gray-matter studies of its next-door neighbor, the hippocampus.

The researchers measured blood levels of more than a dozen polyunsaturated fatty acids and their relationship to both white-matter integrity of the fornix and performance on tasks of memory in 94 healthy elderly subjects. A mixture of omega-3 and omega-6 fatty acids is most robustly linked to both. The nutrients directly enhance memory processes and indirectly affect them by maintaining the microstructure of the fornix.

As susceptible as memory is age-related decline, the fornix is responsive to nutritional interventions. The Western diet oversupplies omega-6 fats relative to omega-3s, making a healthier balance of the fatty acids essential. Such a balance, say researchers, allows for optimal regulation of the two roles of the fatty acids-incorporation into cell membranes and conversion to inflammatory mediators.