Researchers at Purdue University investigated how diet affects memory in rats. Two diets were compared. One group was fed a standard laboratory rat diet, while the other group was fed a high-energy diet with much more sugar and fat.
Before being placed on different diets, rats were trained to perform certain tasks that required memorization of certain skills. After four weeks on their respective diets, rats were tested again to determine how well they remembered to perform the tasks.
Interestingly, the researchers found that some of the rats on the high-energy gained less weight than other rats on the same diet. They called the rats that gained less weight “diet-resistant” rats.
The researchers found that rats fed the high-energy diet had impaired performance on previously-learned tasks, and that this impaired memory was greatest in the rats that had gained the most body fat. That is, the decrease in memory was associated not only with the diet but also with the amount of body fat.
Additionally, rats fed the high-energy diet had an increase in blood-brain barrier permeability. The blood-brain barrier is responsible for guarding the brain from unwanted molecules and is essential for maintaining brain homeostasis. The authors note that they are cautious of this finding, as similar research has not replicated this outcome. If the function of the blood-brain barrier is indeed affected by diet, it could help explain why memory decreases as a result of being fed a high-energy diet.
With this study, the authors add to a growing body of evidence that suggests obesity and metabolic disease lead to cognitive dysfunction. Recently, data has indicated that chronic high blood sugar can lead to Alzheimer’s disease (Cholerton, 2011). Rat studies show that high-energy diets are associated with a reduction of a critical molecule called brain-dervied neurotrophic factor (BDNF), and this decrease leads to reduced learning and memory (Moletni, 2002; Kanoski, 2007). Lastly, high-energy diets are associated with inflammation in peripheral tissues and the hypothalamus (Thaler, 2010), which may play a critical role in Alzheimer’s development (Davidson, 2012).
Ultimately, diet appears to not only impact how we look and how we feel, but also how our brain functions in the present and in the future.
Find the actual research paper here.
Cholerton B, Baker LD, Craft S. Insulin resistance and pathological brain ageing. Diabet Med 2011;28:1463–75.
Davidson TL, Monnot A, Neal AU, Martin AA, Horton JJ, Zheng W. The effects of a high-energy diet on hippocampal-dependent discrimination performance and blood–brain barrier integrity differ for diet-induced obese and diet-resistant rats. Physiol & Behav 2012; 107: 26-33.
Kanoski SE, Meisel RL, Mullins AJ, Davidson TL. The effects of energy-rich diets on discrimination reversal learning and on BDNF in the hippocampus and prefrontal cortex of the rat. Behav Brain Res 2007;182:57–66.
Molteni R, Barnard RJ, Ying Z, Roberts CK, Gomez-Pinilla F. A high-fat, refined sugar diet reduces hippocampal brain-derived neurotrophic factor, neuronal plasticity, and learning. Neuroscience 2002;112:803–14.
Thaler JP, Schwartz MW. Minireview: inflammation and obesity pathogenesis: the hypothalamus heats up. Endocrinology 2010;151:4109–15.