When you hear the word “insulin” what comes to mind first? If your first thought was diabetes, you are not alone. Insulin is most often associated with diabetes, but it plays a key role in many aspects of our health. Did you know that insulin is associated with brain health and cognition? Or that managing insulin levels can aid in weight management?
In this episode, Dr. Lovejoy discusses insulin resistance, blood glucose control, and weight management. She shares several strategies to prevent and reverse insulin resistance through lifestyle habits to empower others to live healthier longer.
- Introduction to glucose, insulin, and insulin resistance: (1:25–5:10)
- Glucose spikes and the use of continuous glucose monitors: (5:11–10:35)
- Prevalence of diabetes and prediabetes: (9:50–18:07)
- Insulin's impact on brain health and cognition: (18:08–21:00)
- Insulin studies in model organisms: (21:01–24:30)
- Dietary fat and insulin resistance: (24:30–29:40)
- Glycemic index and glycemic load: (29:41–34:00)
- The ketogenic diet and insulin resistance: (34:00–42:00)
- Postmenopausal women and insulin resistance: (42:00–48:40)
- The future of GLP-1 agonists: (48:40–57:10)
- AMA: Insulin resistance: (57:11–1:17:30)
- Top tip for optimal fasting insulin levels (1:17:31–end)
About Dr. Jennifer Lovejoy
Dr. Jennifer Lovejoy has spent her career focused on personalized nutrition and lifestyle behavior change. Dr. Lovejoy earned her PhD in Biological Psychology from Emory University and completed a postdoctoral fellowship in Endocrinology and Metabolism at Emory University School of Medicine. During her academic career, she was a professor of Diabetes at the Pennington Biomedical Research Center of LSU and served as Dean of the School of Nutrition and Exercise Science at Bastyr University. She’s a Past-President of the Obesity Society and has published over 90 peer-reviewed research papers. More recently, Dr. Lovejoy was Chief Translational Science Officer at Arivale, a scientific wellness startup integrating multi-omic data with behavioral coaching, and Head of Science at Seven.me, a digital health startup developing a behavioral AI platform. She currently runs Integral Science, LLC, a consulting company.
The role of glucose and insulin in the body
Glucose: Blood glucose (sugar) serves as the primary energy source for our brain and body. Healthy blood glucose levels are therefore essential for maintaining overall health and longevity.
Insulin: Insulin is a key hormone that regulates blood glucose (sugar) levels. This rise in blood sugar following a meal triggers the pancreas to release insulin, and in turn lowers blood sugar levels by moving glucose into cells to be used for energy or to the liver, fat tissue, and muscles to be stored and used as energy for later. Because insulin and blood sugar levels impact so many processes throughout the body, insulin resistance is a contributing factor to multiple chronic diseases that impact healthspan.
Dr. Lovejoy introduces insulin as a hormone tied to healthspan. “We tend to only think about insulin in terms of blood sugar regulation, and that's certainly a major function of insulin. But, it's also involved in bone growth, impacts the vascular system, and has effects on the brain,” she explains. Many organs in the body are impacted by insulin levels.
How blood glucose spikes develop into insulin resistance
What is a glucose spike? A glucose spike describes the increase in blood sugar that happens after consuming a meal. After a meal, the pancreas releases insulin to regulate the increase in blood sugar (glucose) levels caused by the food. These glucose spikes normally return to baseline within an hour of eating.
What are healthy and unhealthy glucose spikes? The difference between healthy and unhealthy glucose spikes refers to how high blood sugar levels rise after a meal. Prediabetes and type 2 diabetes is characterized by a postmeal peak of blood glucose that is higher than normal and takes longer to return to baseline. Over time, unhealthy blood glucose spikes can develop into insulin resistance, where the body's cells become less responsive to the effects of insulin.
What is insulin resistance? Insulin resistance occurs when the insulin produced by the pancreas becomes less effective at transporting glucose out of the bloodstream and into cells. In individuals with insulin resistance, it takes more time and insulin after a meal to lower blood sugar levels. Prolonged insulin resistance can lead to the development of prediabetes and type 2 diabetes
Rates of diabetes
The prevalence of diabetes has increased significantly over the past 50 years. To better understand the magnitude of this disease, Dr. Lovejoy shares current US statistics on:
- Prediabetes: One in three Americans has prediabetes. 
- Diabetes (type 1 and type 2): Around 11%, or 1 in 10 Americans, has diabetes.
- One in five Americans has diabetes and doesn't know they have it. 
Diabetes rates differ significantly by age group and ethnicity: 
- Adults over 65: 29%
- Native American and Alaska natives: 14.5%
- Non-Hispanic Blacks: 12%
- Hispanics: 11.8%
- Asian Americans: 9.5%
- Non-Hispanic whites: 7.4%
So why have rates increased so dramatically? “The increased prevalence of overweight and obesity precedes the increase in type 2 diabetes very clearly and very directly. We know mechanistically that obesity tends to cause insulin resistance, so it makes sense that obesity is the primary driver of increased diabetes rates,” she explains.
So the question becomes, what is the primary driver of the obesity epidemic in the US? She argues it's not solely genetics, because our genetics have not changed in the last 50 or 100 years. “It is something about our environment and our behavior.”
How to test blood sugar markers
So how can we identify glucose dysregulation and the development of prediabetes? Prediabetes is often asymptomatic, making it challenging to detect without a blood test. Comprehensive bloodwork, like InsideTracker’s Ultimate Plan, analyzes three key biomarkers related to glucose regulation: glucose, insulin, and hemoglobin A1c (HbA1c). Depending on your specific levels, InsideTracker then delivers a personalized Action Plan, including recommended ways to improve biomarker levels and achieve optimal health.
Continuous glucose monitors
Continuous glucose monitors (CGMs) are devices that directly measure and capture data on blood glucose levels continuously. CGMs provide users with real-time visibility into how glucose levels fluctuate throughout the day, providing insight on the impact of various factors such as food, exercise, and medication on blood sugar levels.
While CGMs can provide valuable insights into how food affects short-term blood glucose levels, it is important to recognize that they do not provide a comprehensive understanding of how food impacts overall health. For instance, CGMs do not reflect the effects of food on the vascular system. This is particularly significant considering that the primary risk and cause of mortality in individuals with diabetes is often related to heart disease, not directly to blood sugar levels. While a high fat diet may not cause spikes on a CGM, it could still lead to vascular constriction, stiffness, and atherosclerosis, posing risks to heart health.
Insulin and cognitive function
The blood-brain barrier is a protective barrier that separates the blood vessels in the brain from the rest of the body, helping regulate the substances that can enter or exit the brain. Insulin can cross the blood-brain barrier and therefore has direct effects on brain health and cognition.
Insulin resistance and higher levels of insulin are a risk factor for worsened cognition, Alzheimer's disease, and dementia. Studies show that the frequency of mild cognitive impairment and dementia is higher in those with type 2 diabetes compared to a nondiabetic population.Even among healthy populations, a greater degree of insulin resistance is associated with impairments in cognition, or what some people might call foggy thinking. “There is definitely a relationship between chronic high insulin and worsening cognition,” says Dr. Lovejoy.
However, it is worth noting the acute increase in insulin, such as after you eat a meal, actually improves cognition. When you're feeling hungry and find it challenging to concentrate on a difficult mental task, getting a snack can make a noticeable difference in concentration.
Dietary patterns and glucose regulation
Dietary patterns—which refer to overall eating habits and food choices—influence glucose regulation. Dr. Lovejoy discusses how different dietary patterns impact insulin levels, highlighting the negative effects of high-fat diets.
High-fat diets promote insulin resistance
A common misunderstanding in nutrition is that only carbohydrates convert to glucose, making them solely responsible for insulin resistance and diabetes. Dr. Lovejoy debunks this myth by pointing out numerous studies across various populations demonstrate consuming high-fat diets, particularly those high in saturated fats, can lead to insulin resistance independent of weight gain.
The misconception arises because dietary carbohydrates generally cause a higher acute spike in glucose levels compared to dietary fat. However, high-fat diets contribute to insulin resistance by affecting the overall glucose levels over a 24-hour period, including during sleep, exercise, and other activities. Consequently, there has been an undue focus on solely reducing the initial glucose spike to prevent insulin resistance, while overlooking the impact of glucose levels throughout the entire day.
Saturated fat contributes to insulin resistance by negatively impacting the liver, adipose cells, and muscle tissue. These organs, which play a role in insulin and glucose regulation, become less efficient when exposed to excessive saturated fat, gradually leading to impaired insulin response and insulin resistance.
Postmenopausal women and insulin resistance
Lifestyle factors play an important role in insulin resistance and glucose tolerance. Dr. Lovejoy shares advice for postmenopausal women who are experiencing weight gain or insulin resistance:
- Diet: Choose fiber-rich foods, including whole grains, leafy greens, fruits, beans, and complex carbohydrates.
- Exercise: In addition to engaging in regular moderate-to-vigorous activity, consider going for a walk after eating a meal.
- Sleep: Prioritize sufficient and quality sleep.
- Stress mangement: Implement stress mangement strategies.
- Weight loss: Excess weight is the single most important predictor of prediabetes and insulin resistance. A 5% weight loss—if appropriate—can bring glucose levels back into the normal range.
- Limit alcohol consumption: The Dietary Guidelines for Americans (DGAs) recommend moderate alcohol consumption, which means limiting intake to two drinks or less per day for men and one drink or less per day for women. Consider opting for mocktails over alcohol-containing drinks. 
GLP-1 agonists and diabetes care
The current landscape of obesity and diabetes treatment is experiencing a period of innovation, primarily driven by the emergence of GLP-1 agonists and other novel drugs. Experts predict that the standard practices for managing diabetes and obesity will undergo significant transformation, with GLP-1 therapy becoming the cornerstone in diabetes management.
Brain chemistry and GLP-1
Dr. Lovejoy discusses the research on GLP-1 agonists, weight loss, and addiction. She says GLP-1 agonists are currently being investigated as potential anti-addiction drugs, showing promise in lab rats addicted to substances like methamphetamine, cocaine, and alcohol. These medications target the brain's reward system, specifically the dopamine-reward system, implicated in addictive behaviors and compulsive tendencies, thereby exerting their effects on addictive and compulsive behaviors. The problem is that researchers don't quite know what side effects people will experience when they eventually stop taking the medication. Further research is needed to understand how individuals will respond in the absence of the medication before GLP-1 agonists become the standard treatment approach.
AMA: Insulin resistance
This episode of Longevity by Design included an Ask Me Anything (AMA). Here are the audience’s most commonly asked questions about insulin resistance:
HOMA-IR is an equation to assess insulin resistance based on fasting glucose and fasting insulin levels. It is primarily a research tool and not intended for clinical diagnosis. While blood tests for cholesterol and other blood biomarkers provide clear normal ranges, HOMA-IR lacks a defined normal range. HOMA-IR relies on population data rather than established diagnostic thresholds, making it less precise compared to conventional blood tests. Alternatively, looking solely at fasting insulin can also serve as a reliable indicator of insulin resistance.
Is intermittent fasting beneficial for managing insulin resistance?
The majority of intermittent fasting studies have focused on weight loss, making it challenging to isolate the specific effects of intermittent fasting on insulin resistance independent of weight loss. While various forms of intermittent fasting exist, Dr. Lovejoy says prolonged overnight fasting—fasting for 12 to 14 hours—can manage glucose and insulin levels. While short-term outcomes are promising, the long-term effects of intermittent fasting on insulin resistance require further research.
For individuals with prediabetes, experimenting with a 12 to 14 hour overnight fast is generally safe and reasonable to assess its impact on blood sugar levels. Consult with your physician before attempting any form of fasting.
Should individuals with prediabetes or diabetes eliminate carbohydrates?
Prediabetes: When managing prediabetes, it's not about eliminating carbohydrates, rather choosing the right carbohydrates to support blood sugar. Increased consumption of complex carbohydrates such as whole foods, fruits, vegetables, and whole grains can be beneficial. It is recommended to avoid refined carbohydrates like sugar, white bread, and white pasta. By shifting your diet towards high-fiber, complex carbohydrates, you can effectively manage pre-diabetes and improve your overall health.
Diabetes: The American Diabetes Association (ADA) provides nutritional recommendations on carbohydrate intake. Consult with a diabetes educator or a registered dietitian to determine the appropriate carbohydrate intake for your specific needs.
Can type 2 diabetes be reversed with lifestyle alone?
Scientists hold differing perspectives on this topic, depending on how "reversing type 2 diabetes" is defined. Some experts assert that once you have diabetes, it remains with you, even if your blood sugar levels return to normal. Dr. Lovejoy argues she doesn’t agree with this perspective, stating that lifestyle and dietary changes can reduce blood sugar levels to a normal range and maintain them, even in previously diagnosed type 2 diabetes. “In my view, this achievement constitutes a reversal,” she says.
It’s important to maintain healthy lifestyle and nutrition habits even after blood sugar levels become optimal to prevent recurrence of type 2 diabetes.
Top tip for maintaining healthy insulin levels
Dr. Lovejoy’s top tip for improving fasting insulin is to prioritize fiber in your diet. She says this often overlooked dietary nutrient can help manage and improve insulin levels.
Studies have shown only about 5% of Americans currently meet the recommended 30 grams of fiber per day.  To gain valuable insights into your fiber intake, she suggests tracking the grams of fiber you consume for a few weeks. This simple practice can provide an objective measure of your current fiber consumption.