A four-day Western-style dietary intervention causes reductions in hippocampal-dependent learning and memory and interoceptive sensitivity
Attuquayefio T, Stevenson RJ, Oaten MJ, Francis HM. (2017) PLoS One PLoS One 12(2):e0172645.
Web URL: Read this and related articles via Pubmed here. Free full text of this article is available online.
Abstract:
In animals, a Western style diet-high in saturated fat and added sugar-causes impairments in hippocampal-dependent learning and memory (HDLM) and perception of internal bodily state (interoception).In humans, while there is correlational support for a link between Western-style diet, HDLM, and interoception, there is as yet no causal data. Here, healthy individuals were randomly assigned to consume either a breakfast high in saturated fat and added sugar (Experimental condition) or a healthier breakfast (Control condition), over four consecutive days.
Tests of HDLM, interoception and biological measures were administered before and after breakfast on the days one and four, and participants completed food diaries before and during the study.
At the end of the study, the Experimental condition showed significant reductions in HDLM and reduced interoceptive sensitivity to hunger and fullness, relative to the Control condition.
The Experimental condition also showed a markedly different blood glucose and triglyceride responses to their breakfast, relative to Controls, with larger changes in blood glucose across breakfast being associated with greater reductions in HDLM.
The Experimental condition compensated for their energy-dense breakfast by reducing carbohydrate intake, while saturated fat intake remained consistently higher than Controls.
This is the first experimental study in humans to demonstrate that a Western-style diet impacts HDLM following a relatively short exposure-just as in animals.
The link between diet-induced HDLM changes and blood glucose suggests one pathway by which diet impacts HDLM in humans.
FAB RESEARCH COMMENT:
This human study confirms what numerous animal studies have already shown, and observational studies in humans have strongly indicated - namely, that:- memory and learning are impaired by a 'western-type' processed-food diet, high in both sugar and saturated fats
It is also striking that significant negative effects on memory and learning were evident within just 4 days - even though the dietary intervention involved changes to just one main meal each day (breakfast).
These cognitive impairments were also found to relate to the greater blood sugar swings seen in those given the high-fat, high sugar breakfast. Other findings include:
- Those receiving the 'western-style' breakfast also continued to consume more saturated fats than the control group for the rest of the day (although they did reduce their susbsequent carbohydrate intake).
- They also showed reduced 'interoception', i.e. less ability to sense changes in internal body states - a capacity which is important for appetite regulation, among many other functions.
The tasks used to assess memory and learning were chosen for their sensitivity to functioning of the hippocampus (a tiny, seahorse-shaped structure found deep on each side of the brain). This brain area is absolutely essential for making new memories, i.e. the transfer of information from immediate to longer-term storage.
Hippocampal dysfunction is implicated in a wide range of developmental and psychiatric conditions in which behaviour and learning are impaired - including ADHD, depression and dementia. The hippocampus is also one of the few brain regions in which new brain cells can be generated in adulthood.
Animal studies have repeatedly shown that western-type diets impair performance on memory and learning tasks that depend on the healthy functioning of the hippocampus.
This study shows that the same is true in humans.
Practical Implications
For anyone interested in improving their brain health, this demonstration that even 4 days of eating a typical western-type breakfast, high in sugar and saturated fats, can impair memory and learning should provide an incentive to make positive dietary changes.
To change any established behaviour is never easy - but many people's motivation could surely be boosted by knowing that
- simply eating a healthier breakfast for just 4 days could lead to measurable improvements in memory and learning
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