We evolved to love sugar.
Our ancestors needed it. High-energy foods were rare. Every berry mattered. That ancient drive to pack calories into our fat reserves? It saved them.
Today, that same instinct drags us to the vending machine at 2 am for chocolate we didn’t plan on eating.
We know the score. Excess sugar wrecks teeth. It fuels diabetes. It builds fat. It fogs the mind. We tell ourselves it’s fine though, because diet is hard and willpower is finite. But what if we switch? If we go clean tomorrow. Do the lights come back on. Fully?
A new systematic review suggests a sobering answer: no.
The rodent data is messy
Simone Rehn at the University of Technology in Australia and her team dug into the data. They didn’t look at people, at first. Rodents don’t lie about what they ate in the cafeteria.
They analyzed 27 preclinical studies. Rats and mice. Some fed high-fat, high-sugar binges (HFHS). Some fed standard chow.
Here’s the setup: feed the rats junk. Let the damage cook. Then switch half of them to a healthy diet.
“Improving diet quality does benefit memory. But those improvements were incomplete.”
After weeks on the good food, the switched rats performed better in memory tests than their junk-food-eating cousins. So dieting helps. True enough.
But here’s the catch. Their memory didn’t return to normal. They didn’t catch up to the rats who never ate the junk. The gap remained. A scar tissue of sorts, cognitive-wise.
Fat fades. Sugar stays.
It gets stranger when you look closer at what made them sick.
The team looked beyond memory, too. Activity levels. Motivation. Signs of anxiety or depression. Most of that stuff? No consistent change from switching diets. The brain damage wasn’t total chaos. It was specific. Mostly memory.
And the culprit varied.
When rodents stopped eating high-fat diets, their memories bounced back significantly. The brain recovered.
High sugar? Different story.
Diets high in added sugar—even if they were mixed with fat—showed little to no recovery.
Sugar seems to hold the damage in place. Fat washes away. Sugar sticks.
Mike Kendig, senior author and also at UTS, notes this is hard to prove in humans. Humans are chaotic. When you fix your diet, you also usually start jogging. You sleep better. You feel less depressed. You clean your kitchen. All that noise drowns out the specific sound of the brain healing—or failing to heal—from the sugar alone. Rodents provide silence. And the silence tells us something unpleasant about the sweetness of excess.
The hippocampus takes the hit
The epicenter appears to be the hippocampus. This brain region handles spatial memory. Learning. It also regulates appetite, which feels almost ironic here.
Previous studies link HFHS diets in humans to shrinkage in the hippocampus. Smaller volume. Poorer function.
Rehn’s team’s work backs that up. The diet reversal improved spatial memory—which the hippocampus drives—underscoring how sensitive that structure is. It reacts to what you put in your mouth. Quickly. And poorly, if that input is syrup and fried fat.
So should you mourn your past lattes with three pumps of caramel? Probably not. Despair is a bad coping mechanism.
The point is precision. We operate under the belief that health is elastic. Stretch it thin today, snap back tomorrow. Clean eating is always there if we just decide to try.
The data suggests it’s not quite that forgiving. Especially regarding sugar.
Protecting the brain might mean prevention. Not repair. Because some damage doesn’t vanish. It just gets quieter. Or does it.
