According to Dr. Perlmutter, author of the book Grain Brain, a high-fat diet should protect neurons from damage. In this new study, researchers show that a high-fat diet damages neurons, particularly those involved in the sense of smell:
Hyperlipidemic Diet Causes Loss of Olfactory Sensory Neurons, Reduces Olfactory Discrimination, and Disrupts Odor-Reversal Learning, Journal of Neuroscience, May 2014
We report marked loss of olfactory sensory neurons and their axonal projections after exposure to a fatty diet.
Mice maintained on fatty diets learn reward-reinforced behaviors more slowly, have deficits in reversal learning demonstrating behavioral inflexibility, and exhibit reduced olfactory discrimination
When obese mice are removed from their high-fat diet to regain normal body weight and fasting glucose, olfactory dysfunctions are retained.
New Research Links Bad Diet To Loss Of Smell, Florida State University Press release, 21 July 2014
The research was conducted over a six-month period where mice were given a high-fat daily diet, while also being taught to associate between a particular odor and a reward (water).
Mice that were fed the high-fat diets were slower to learn the association than the control population. And when researchers introduced a new odor to monitor their adjustment, the mice with the high-fat diets could not rapidly adapt, demonstrating reduced smell capabilities.
“Moreover, when high-fat-reared mice were placed on a diet of control chow during which they returned to normal body weight and blood chemistry, mice still had reduced olfactory capacities,” [lead author] Fadool said. “Mice exposed to high-fat diets only had 50 percent of the neurons that could operate to encode odor signals.”
It was the first time researchers had been able to demonstrate a solid link between a bad diet and a loss of smell.
An unfortunate part of this story is that once the mice returned to a regular low-fat diet and lost weight, they didn’t fully regain their sense of smell.