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Sugar, Stress, and Your Brain

You can probably guess that sugar isn’t great for your brain health. But did you know just how not-great it is? Take a look at just one aspect of the problem: how sugar interacts with stress – both physical stress and psychological stress.

Sugar, Physical Stress, and Psychological Stress

First of all, it’s important to distinguish between psychological stress and physical stress

Psychological stress absolutely has physical consequences, but not all physical stress feels psychologically “stressful.” For example, some people find it downright relaxing to go for a nice, long run – it’s not psychologically stressful at all. But to your body, that run is a pretty major physical stress.

Eating sugar alleviates short-term psychological stress, but causes long-term physical stress to your brain. And that long-term stress can cause problems with memory and spatial reasoning down the line.

Sugar Reduces Feelings of Stress

Stress eating: it’s a thing for a reason.

This study gave people either a sugar-sweetened drink or an aspartame-sweetened drink 3 times a day for 2 weeks. Sugar, but not aspartame, reduced baseline levels of the stress hormone cortisol and the cortisol spike in response to stress. So in other words, subjects felt less stressed in general just going about their lives, and when they were put in stressful situations, they stayed on a more even keel and didn’t react as strongly to the stress.

This study put male rats in very stressful circumstances, but also gave the poor stressed rats either a normal rat diet or a high-fat, high-sugar diet (basically rat McDonald’s). The rats on the normal diet showed signs of anxiety and generally being stressed out by their stressful cages (which is what you would expect). But the rats on the high-fat/high-sugar diet were completely chill: even in the stressful cages, they didn’t feel any more anxious. It just didn’t get to them at all.

This study found that a cafeteria diet (again, think rat McDonald’s) could reduce the effects of early-life stress in rats. The researchers stressed the rats by separating them from their mothers as babies. Rats fed a normal diet became anxious and depressed. But rats who ate at rat McDonald’s did a lot better, psychologically speaking. Their steady diet of rat-Big Macs and rat-Coke actually protected them from the psychological damage of their childhood trauma.


Your brain’s suggestion for making all these things feel better: sugar!

This makes sense from an evolutionary perspective. Think about the things that might have caused psychological stress for a person in the Paleolithic. Famine would have been a big one. Predator animals. Diseases. Harsh weather conditions. All of those situations require a lot of physical energy expenditure to survive. In all of those situations, it’s very beneficial to seek out and eat high-calorie foods. So it makes sense that we would develop a drive to eat high-calorie foods under psychological stress, because back in the day, the people who turned to sugar under stress were more likely to survive the bear/famine/hard winter.

So you’re under stress, you eat some sugar, your lizard brain calms down about the prospect of starving to death or being eaten by a bear, and you feel better.

So if you get stressed and you’re having irresistible urges to reach for the ice cream and cookies, have some compassion for yourself. You’re craving these things because they really will relieve your feelings of stress and anxiety, at least for the moment. Sugar is dangerous precisely because it’s such an effective short-term fix.

Non-sugar stress relief isn’t the issue at hand here, but here are some alternate suggestions with proven cortisol-lowering benefits: walks in nature, meditation, yoga, deep/controlled breathing, and if you’re actually hungry instead of just craving sugar, a real nutritious meal.

Of course, there’s a good reason to resist that quick fix: the long-term health problems of self-medicating with sugar.

Sugar and Stress in the Brain: The Long Term

The problem is that in the long term (or even the medium term, really), chronically high sugar intake causes physical stress to your brain. In particular, it messes with the hippocampus. The hippocampus is an area of the brain that controls memory, especially spatial memory.

Remember that study from the caged rats? The high-fat/high-sugar rats also showed something else besides a nearly miraculous ability to stay calm in stressful cages. They had inflammatory changes in the hippocampus, a sign of physical stress. The physical stress problems were building up even while the sugar was making the rats feel psychologically less stressed.

This study gave rats either a high-sugar diet or a high-fat + high-sugar diet. Both groups had memory problems caused by inflammatory stress in their hippocampi. The researchers also ruled out sugar-induced weight gain as a cause of the problem. The plain sugar group didn’t have any significant weight gain, but still had higher levels of inflammatory markers and memory changes. So in plain English, if you make a rat obese by feeding it junk food, the rat will probably start having memory problems, but the memory problems are caused by the junk food, not the obesity.

In this study, 30 days of either table sugar or high-fructose corn syrup reduced spatial learning and memory in adolescent rats. Just like in the previous study, the sugar-fed and corn-syrup-fed rats had higher levels of inflammatory stress markers in their hippocampi. Interestingly, the HFCS (55% fructose, 45% glucose) was worse than the table sugar (50% fructose, 50% glucose).

OK, but you’re not a rat. So what about some studies in humans?

Here’s one. First the researchers found that a high-fat + high-sugar diet was associated with worse performance on measures of hippocampal memory. Next, they picked out two groups of people: one group with a low fat/sugar intake and one with a high fat/sugar intake. They compared the two groups and found that the low fat/sugar group did significantly better on tests of hippocampal memory than the high fat/sugar group.

…But Wait, There’s More!

If you’re thinking something like “hey…isn’t Alzheimer’s disease also related to sugar somehow?” then you’re right on the money.

Alzheimer’s disease is related to sugar – it’s actually been nicknamed “type 3 Diabetes” because it’s so strongly connected to metabolic problems and insulin resistance. And you can read all about that here if you’re interested. But the problems above aren’t the same as Alzheimer’s disease – for one thing, half of these studies were in baby or teenage rats (or humans): sugar-related hippocampal problems show up way before someone would get a diagnosis of Alzheimer’s.

The same dietary cause (sugar) might easily be a factor in developing Alzheimer’s down the line, but this is a much more short-term issue and it applies even to people who never get a diagnosis of Alzheimer’s.

Summing it Up

In the short term, eating sugar might relieve feelings of stress, because it basically scratches a very old evolutionary itch that’s still hanging around in our brains long after it’s become maladaptive. But in the long term, consistently high sugar intake is actually dangerous to the brain, especially to memory and the hippocampus. Unfortunately, sometimes our short-term Band-aids are actually dangerous in the long run.