Source: Austin Perlmutter/DALL-E
You’ve almost certainly heard some variant of the idea that sugar is toxic, deadly, or otherwise the worst possible thing for your overall and potentially your brain health. In truth, sugar is key to healthy brain function, but there’s some important nuance that’s worthy of our understanding.
The first thing to understand is the differentiation between blood sugar and dietary sugar. Though they have overlap, they are not the same. Dietary sugar includes molecules like sucrose, fructose, and lactose that occur naturally in foods, as well as added sugars, which are concentrated in things like syrups, cane juice, fruit juice concentrates, and more. Blood sugar is a measurement of blood glucose levels, which can be significantly influenced by dietary sugar and general diet, as well as variables like exercise, sleep quality, stress, hormone levels, and pharmaceuticals.
How does dietary sugar influence brain health?
When we eat a meal rich in rapidly digestible carbohydrates or added sugars, blood sugar levels tend to go up more than if we consumed a fiber-rich vegetable or a piece of meat. This is the concept of the glycemic index, and it’s one way that dietary sugar links to blood sugar. However, for most people, any individual meal (even if it’s loaded with added sugar) is unlikely to have much of an effect on brain health or function. Instead, patterns of diet consumed over longer periods of time that are rich in added sugars may be dangerous to brain health. In particular, added sugars in the form of sugar-sweetened beverages have been linked to stroke, depression, and dementia. Foods with added sugars are also a key component of the ultra-processed “Western diet,” which is linked to higher risk for dementia, and recently has been found to disrupt multiple aspects of brain function in animals.
How does blood sugar influence brain health?
Apart from those on a very restricted low-carb/ketogenic diet or those engaging in fasting, most people’s brains primarily run on glucose. Research indicates that as we age, our brains may have more trouble getting access to this fuel. This is even more pronounced in Alzheimer’s disease, which has been sometimes labeled “type 3 diabetes” for this reason. Conditions associated with poor blood sugar regulation are linked to higher risk for brain conditions. For example, type 2 diabetes may increase risk for dementia by 60%, and even insulin resistance is now linked to worse cognition. Conditions of very high and very low blood sugar are dangerous to our brains, and we’re learning that too much variability between highs and lows may also be an issue.
What are some of the connecting mechanisms?
Both high dietary added sugar and high or variable blood sugar have been linked to worse brain outcomes by way of processes like insulin resistance (which may make it harder for our brains to access glucose) as well as inflammation, which over time has been linked to higher risk for conditions like depression as well as dementia. Mechanistically, high blood sugar levels may lead to the development of advanced glycation endproducts (AGEs) which generate oxidative stress that promotes inflammation.
Excess dietary added sugar also contributes to the development of over-inflated fat cells, which are also believed to promote more inflammation in the body that may damage the brain. One important point to make here is that fructose, which is a dietary sugar found naturally in fruits and a common component of added sugars in foods and beverages, does not raise blood sugar like glucose, but may still have long-term detrimental effects on brain function through inflammation as well.
What should we do about this information?
How do we integrate this information into a better understanding of sugar and the brain? At a basic level, for most people, research suggests that maintaining relatively stable blood sugar is an excellent strategy for protecting brain health. Much can be said about mechanisms, subsets of unique populations (e.g., type 1 diabetics), but for most people, regular exercise, a diet rich in minimally processed foods with lots of fiber, stress mitigation, and good sleep are key. When it comes to dietary sugar, almost everyone benefits from avoiding added sugar in their diet, and from minimizing consumption of foods that rapidly convert into digestible sugar (think white bread, cookies, candies, etc.).
