Massa Mohamed Ali, HBSc Candidate, University of Toronto
Perhaps you've heard of insulin resistance as it relates to diabetes and heart disease. But if you don’t have either, why does it matter?
Every time we eat any form of a carbohydrate, our body responds by secreting the hormone insulin from the pancreas to regulate our blood sugar. This happens after the food passes through our intestines, gets broken down, and ends up in the bloodstream in the form of glucose molecules. Insulin allows glucose into the cells for energy. It is the key that signals a cascade of events for glucose to enter the cell. If we aren't careful with our diet and lifestyle choices, cells may become resistant to insulin, which makes them unable to use glucose. With nowhere to go, glucose stays in the blood and disrupts our body's homeostasis. Over time, these reactions in the body may trigger chronic disorders (especially in those already at a higher risk genetically) that could have been prevented through simple blood sugar balancing habits.
Symptoms of dysregulated glucose levels arise long before the onset of disorders. These start with glucose spikes. A 2018 Stanford study showed that 80% of the non-diabetics tested experienced high spikes from common foods like cereal and milk. In the span of an hour, a glucose spike can increase the glucose concentration in the body by more than 30 mg/gL, and can then decrease just as quickly. In the short term, these spikes disrupt our hunger cues and lead to cravings, fatigue, migraines, mood swings, poor sleep, hormone imbalances and reduced cognitive function. In the long-term, chronic conditions such as insulin resistance, Alzheimer's disease, fatty liver disease, cancer, arthritis, depression, infertility, poly-cystic ovarian syndrome (PCOS), type 2 diabetes, and heart disease may develop. Moreover, some researchers are calling Alzheimer's 'type 3 diabetes' because of the effects of insulin resistance on the aging brain.
Alzheimer's: Type 3 Diabetes
Insulin receptors are present in organs all over the body, including the brain. The brain uses glucose as its main energy source. With insulin resistance, neurons are not able to receive sufficient amounts of glucose to carry out basic tasks, including learning and memory. A 2017 study published in Neuron found a gene responsible for disrupting how the brain processes insulin. This gene is present in about 20% of the general population and over 50% of Alzheimer's cases. In mice, a high-fat diet accelerated the activation of this gene, therefore further impairing insulin function in the brain and suggesting that lowering saturated fat intake may be preventative. While genetics remains one of the contributors to developing Alzheimer's disease, scientists agree that it is a unique combination of genetic, environmental, and lifestyle factors that cause the associated changes in the brain. These changes include a loss of neurons and their connections because of amyloid plaque formation and tau protein tangles. Through influencing the phosphorylation and formation of plaques and tangles, insulin resistance contributes to neurodegeneration. Insulin resistance has also been associated with depression, Parkinson's disease, and cognitive decline.
More on Cognitive Decline
A 2019 study published in Frontiers in Neuroscience shows that insulin promotes synaptic plasticity in the hippocampus by modulating long-term potentiation (LTP) and long-term depression (LTD). These mechanisms allow for better learning and memory. With higher blood sugar and lower insulin sensitivity, the brain is unable to use these mechanisms, which may lead to a faster rate of cognitive decline. In a 10-year longitudinal study, researchers found that those with higher blood sugar had worse cognitive performance and thinking over time. Therefore, chronically consuming high amounts of carbohydrates and unbalanced meals changes the brain’s chemistry.
These changes begin years before the first disease symptoms appear and could start after years of glucose spikes, fatigue after meals, and sugar crashes. Additionally, brain insulin signaling helps regulate whole body metabolism. A recent Nature study has shown that brain insulin sensitivity is associated with one's body fat distribution. The more sensitive the brain is to insulin, the healthier one's body weight and visceral fat is. Not only is regulating insulin healthy for your brain, but it is also automatically healthy for the rest of your body.
Listening to Your Body
You've probably experienced the familiar craving for dessert after a meal, or the common afternoon slump. Both feelings could be indications of an unbalanced meal and a sugar crash. You might resort to drinking more coffee, chewing gum, or aiming for better will power, which are all quick fixes that act as band-aids and don’t address the root issue. This is also common with the prescription of birth control pills for the management of PCOS, which is often triggered by insulin resistance. Learning what our bodies are telling us early on is essential, particularly with regard to our eating behaviors. Regardless of our genetics, the decisions we make about food are one risk factor we can control for maintaining our brain and body health. We are not defined by our genes, but by our lifestyle choices.
Interestingly, research has shown that the same food can result in different responses in each person. In her book titled Glucose Revolution, biochemist Jessie Inchauspé writes,
"These differences are due to many factors: the amount of baseline insulin we have, our muscle mass, different gut microbes, being more or less hydrated, being more or less rested, being more or less stressed, whether or not we have just worked out (or we work out after eating)—the list goes on. Some studies even found that if you think you’re about to eat something sugary, that can cause the food to cause a bigger spike for you than someone else."
She also mentions that a meal that normally does not cause a large glucose spike may in fact cause one in an individual who has not had enough sleep or is stressed.
WHAT YOU CAN DO
So how do you regulate your blood sugar as you go about your day? And what helps you avoid big glucose spikes and crashes? While you can use a glucose monitor to know your exact blood sugar response to certain foods and events throughout your day, you don't have to. Fortunately, there are a number of simple lifestyle changes we can establish for a better, healthier, and more energetic state. Jessie lists them in her book as the following:
- Eat a savoury breakfast, not a sweet one.
- Eat a balanced meal in the right order: lots of veggies first, then proteins and fats, then starches, and sugars last.
- Never have sugar on an empty stomach.
- Use your muscles after meals. This could include washing dishes, cleaning up, or going for a 10-minute walk.
- Drink a tablespoon of apple cider vinegar diluted in a glass of water before eating to lower your glucose spike by up to 30%.
Over time, these habits along with proper sleep, hydration, physical activity, and stress management, can vastly reduce one's risk of chronic diseases, including cognitive decline and Alzheimer's disease. Below are the links available for further reading on this growing area of research.
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