In a study by Alexis Stranahan, leptin-receptor-defective diabetic mice had fewer dendritic synapses in the hippocampus than normal mice under all tested conditions.
"she simply counted—not simply, it actually takes a lot of work, but counted synapses and found that, two things: one, the diabetic mice, regardless of whether they were intermittent fasting or had running wheels in their cages, had smaller number of synapses than did the normal mice." (said at 0:44:05)
In a study specifically investigating hippocampal neuron morphology in leptin-receptor-deficient diabetic (db/db) mice subjected to voluntary wheel running and caloric restriction, Alexis Stranahan and colleagues found the opposite of the speaker's claim: running wheel activity, dietary restriction, and their combination significantly increased hippocampal dendritic spine density on dentate granule neurons, rather than db/db mice failing to increase spine/synapse numbers under these conditions. While untreated diabetic mice exhibit baseline reductions in synaptic plasticity, spine density, and neurogenesis compared to control animals, exercise and dietary restriction actively attenuated and enhanced dendritic spine density in these mice.
- contradicts: Voluntary exercise and caloric restriction enhance hippocampal dendritic spine density and… (Hippocampus 2009)
"Running wheel activity, caloric restriction, or the combination of the two treatments increased levels of BDNF in the hippocampus of db/db mice. Enhancement of hippocampal BDNF was accompanied by increases in dendritic spine density on the secondary and tertiary dendrites of dentate granule neurons. These studies suggest that diabetes exerts detrimental effects on hippocampal structure, and that this state can be attenuated by increasing energy expenditure and decreasing energy intake." (abstract, results, passage verified)
pubmedfull study (doi)