Does Sugar Cause Alzheimer’s Disease?

Alzheimer’s disease, a devastating neurodegenerative disease feared by so many, is finally being recognized as a disease heavily influenced by our lifestyle. The greater community is only just beginning to talk about the things that cause the pathophysiology of Alzheimer’s disease to progress. While there are many potential contributors to dementia, eating a diet high in sugar is a major contributor to the development of Alzheimer’s disease. For this reason, it is imperative to modify the diet to reduce or eliminate simple sugars in order to prevent and reverse the signs and symptoms of Alzheimer’s.

While excess sugar consumption can contribute to Alzheimer’s disease for anyone, it appears to be even more of a contributor in individuals who carry ApoE4. Specifically, research shows that ApoE4 carriers who consumed snacks with a higher glycemic load were twofold to threefold more likely to develop Alzheimer’s disease. For that reason, ApoE4 carriers should pay particular attention to their intake of sugary foods.

How Does Sugar Intake Contribute to Alzheimer’s Disease?

While research showing the link between sugar intake and Alzheimer’s disease has been around for a long time, new research continues to point to this ever important connection (1). In recent years, the connection has been so great that some have referred to Alzheimer’s disease as Type 3 Diabetes. While development of Alzheimer’s disease is more complex than this description presents (as there are many other contributors to Alzheimer’s) the connection between consumption of a high sugar diet and the development of Alzheimer’s disease is indisputable. There are several mechanisms of action that contribute to this pathophysiology.

High sugar diets create insulin resistance

Insulin resistance is likely the single most important metabolic contributor of Alzheimer’s disease. The standard American or western diet creates an environment of insulin resistance through high consumption of added sugars, simple carbohydrates, processed foods, and high fructose corn syrup. This sugar laden diet combined with a sedentary lifestyle creates the perfect storm for insulin resistance. Simply put, in insulin resistance, the cells stop responding to (or become resistant to) the signals that insulin sends. The signals that insulin sends are imperative for proper human function. Most notably is insulin’s role in metabolism. Insulin signals the cells to allow for the uptake of glucose into the cell to be used for cellular energy. When cells lose their sensitivity to insulin and become resistant to this signal, the cell cannot effectively uptake glucose and then lacks adequate energy. In a sense, the state of insulin resistance starves the cell. The resistance to insulin signaling is also of utmost importance in brain tissue. Insulin is an important supporter of brain cells. Disrupted insulin signaling can result in the development of beta amyloid plaque formation as insulin is a major player in the regulation of beta amyloid formation (2).

Insulin dysfunction generally predates blood sugar dysfunction, so often the first signs of trajectory that leads to insulin resistance is elevated fasting insulin levels. A fasting insulin of higher than 4.5 milli-international units per liter is suboptimal, which can be determined by a simple blood test. Once insulin dysfunction has taken hold, fasting blood glucose levels and hemoglobin A1c levels will begin to rise. While there are different types of tests that can determine insulin resistance, the most simple is the homeostasis model assessment-estimated insulin resistance (HOMA-IR) which is a calculation using relatively routine blood tests: fasting insulin and fasting glucose.

High sugar diets contribute to inflammation and oxidative stress

Perhaps the most common cause of systemic inflammation in Alzheimer's is hyperpermeability in the gut, colloquially referred to as “leaky gut.” Diets high in simple, added sugars contribute to the development of leaky gut and the structural breakdown of the gut lining. This allows molecules including partially digested food particles, toxins, and microbes to pass unintentionally through the wall of the small intestine. The molecules that are now either prematurely or mistakenly in the bloodstream set off inflammatory cascades. Uncontrolled inflammation, which can easily occur in the presence of gut hyperpermeability, is a major driver of cognitive dysfunction.

Inflammation can cause the generation of reactive oxygen species leading to oxidative stress. Oxidative stress is particularly damaging to fat tissue, and since the brain is composed primarily of fat, high levels of oxidative stress can cause significant damage to the brain. Oxidative stress can also increase the expression of pro-inflammatory proteins such as IL-6 and TNF-α , resulting in neuroinflammation.

In the cooking process, a chemical reaction can occur between sugars and fats or proteins that creates glycotoxins known as advanced glycation endproducts (AGEs). This only occurs when cooking animal products. High levels of AGEs in the diet create inflammation and oxidative stress. You can avoid AGEs in the diet by using low, moist heat, shorter cooking times, and incorporating acidic ingredients such as lemon juice, and vinegar. However, the body also creates AGEs when proteins and fats combine with sugars in the bloodstream. Thus it is essential to reduce or eliminate sugars in the diet to prevent endogenous production of inflammatory AGEs (3).

How to Reduce Sugar in the Diet

Avoid processed and packaged foods

Processed foods are packed with added sugars. There are at least 61 different names for sugar on food labels (4). This makes identifying sugar in processed and packaged foods more difficult that one might think. Sugar hides under names like rice syrup, dextrose, high fructose corn syrup, and barley malt. While checking food labels (both the ingredient list and the added sugar listed on the nutrition facts) is one way to look out for added sugars in the diet, a simpler approach is to avoid eating these highly processed foods altogether. As processed foods are generally lacking in nutrients, swapping these out for nutrient dense whole foods is a healthier choice in general.

Eliminate sugary beverages

While many people realize that packaged foods like cookies, cakes, muffins, and snack bars have added sugars, bottled beverages often appear like nutritious options yet can be laden with added sugars. Bottled iced teas, coffees, sports drinks, and fruit flavored beverages can easily contain as much as 10 teaspoons of added sugar. Skip the bottled beverages and instead choose plain brewed ice tea or coffee or water sweetened with fresh fruit if you need a twist of sweet flavor.

Use whole fruit to sweeten foods

Whole fruit is the best possible choice when it comes to sweetening your foods. Whole fruit contains fructose, but because it is packaged with fiber, vitamins, minerals, and phytonutrients, it is metabolized differently than added sugars. Using fruit, you can sweeten your foods while also increasing your intake of disease fighting nutrients. For example, rather than choosing sugar laden fruit flavored yogurts (whether dairy based or plant based), choose the plain variety and add your own berries or other fruit for flavor. For those already battling insulin resistance, it’s best to choose low glycemic fruits, such as blueberries, blackberries, raspberries, and strawberries until you are insulin sensitive.

Skip the artificial sweeteners

For many looking to cut sugar from their diet, opting for an artificial or non-nutritive sweetener seems like a logical alternative. However, these sweeteners can contribute to dysbiosis, an imbalance in the microbial composition of the gut. Dysbiosis itself can contribute to inflammation and other issues, so it’s best to avoid most artificial and non-nutritive sweeteners.

Will I Prevent Alzheimer’s Disease if I Avoid Sugar?

There are many potential contributors to Alzheimer’s disease. For many people, insulin resistance and inflammation are major drivers of their cognitive decline. Thus, eliminating or even reducing sugar in the diet is an extremely helpful step in preventing Alzheimer’s. However, there are many other factors regarding one’s diet, lifestyle, and health history that must also be considered. If you would like more information on preventing Alzheimer’s disease, sign up for the Amos Institute Cognitive Health Program today.

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References:

1. Kandimalla, R., Thirumala, V., & Hemachandra Reddy, P. (2017). Is Alzheimer’s disease a Type 3 Diabetes? A Critical Appraisal. Biochimica et Biophysica Acta, 1863(5):1078-1089. doi:10.1016/j.bbadis.2016.08.018
2. Yamamoto, N., Ishijkuro, R., Tanida, M., Suzuki, K., Ikeda-Matsuo, Y. & Sobue, K. (2018). Insulin-signaling Pathway Regulates the Degradation of Amyloid β-protein via Astrocytes. Neuroscience, 385:227-236. doi:10.1016/j.neuroscience.2018.06.018
3. Lee, H.J., Seo, H.I., Cha, H.Y., Yang, Y.J., Kwon, S.H. & Yang, S.J. (2018). Diabetes and Alzheimer’s Disease: Mechanisms and Nutritional Aspects. Clinical Nutrition Research, 7(4):229-240. doi:10.7762/cnr.2018.7.4.229
4. UCSF (n.d.). Hidden in Plain Sight. https://sugarscience.ucsf.edu/hidden-in-plain-sight/#.YIiUKH1KhQI