I recently interviewed Dr. Cate Shanahan, a board-certified family physician who is a leading authority on nutrition and human metabolism. Her new book, “Dark Calories,” discusses the dangers of seed oils — often referred to as the greenwashed term vegetable oils — insulin resistance, and the importance of proper nutrition for optimal health.
Shanahan describes how early in her career as a family physician, she felt deeply unsatisfied with her ability to help patients with chronic diseases:1
“I felt like the part of my practice that was around the chronic disease management, that part felt so false and so hollow, and I really questioned whether or not I was making any difference or even doing good at all.”
Ultimately, however, these early career frustrations led to important nutritional insights. A personal health crisis in 2002 led her to dive deep into nutritional research, particularly around essential fatty acids and polyunsaturated fats. This research opened her eyes to the dangers of vegetable oils and conflicts with what she had learned in medical school.
The Dangers of Seed Oils
Shanahan explains that seed oils, are one of the most harmful components of the modern diet: “Vegetable oils promote oxidative stress, toxins, all sorts of toxins can promote oxidative stress. And vegetable oils are the most potent source of toxin in the food supply.”
She explains that these oils, along with ultraprocessed foods, refined sugars/flours and refined protein powders, make up about 75% of the average person’s calorie intake in developed countries. This is problematic because these refined ingredients lack nutrition and promote inflammation and oxidative stress in your body. Shanahan also delves into the connection between oxidative stress and mitochondrial function:2
“When you look at nutrition and health through the lens of oxidative stress, it is so powerful because it helps bring everything into clarity. You just have to ask the question, OK, is this thing promoting oxidative stress?”
Oxidative stress damages mitochondria, which are crucial for energy production in cells. This is one reason why focusing on mitochondrial health can address many health issues at their root. So, while oxidative stress damages mitochondria, the focus should be on enhancing mitochondrial function, not just eliminating oxidative stress.
My new book, “Your Guide to Cellular Health: The Unifying Theory of Health for Ultimate Longevity and Joy,” will be out shortly and is loaded with details on how to improve your mitochondrial function.
HOMA-IR: Defining the Threshold of Metabolic Health Versus Metabolic Disease
A key focus of Shanahan’s work is on how insulin resistance affects overall health, including brain function. She explains:3
“Insulin resistance makes us build fat that we can’t burn. And it also, at the same time, deprives our brain cells of energy. And so being insulin resistant is to be in a state of regular, excessive hunger.”
This state of insulin resistance can lead to mood issues, difficulty concentrating and general cognitive decline. “My whole life, I felt like I had something wrong with me because I would have this difficulty having conversations after work because I would be so mentally drained,” Shanahan explains.4
She introduced me to the homeostasis model assessment of insulin resistance (HOMA-IR) test, discovered in 1985, which is the gold standard for measuring insulin resistance. If you use HOMA-IR data, up to 99% of the U.S. population may have some degree of insulin resistance. Using this test is a simple way to assess your metabolic health.
You can figure out your HOMA-IR using two simple tests — your fasting blood glucose, which you can do at home, and then a fasting insulin level, which is an inexpensive test. Multiply those two numbers, and if you’re in the U.S., you divide by 405, and if you’re in Europe you have different units than the US and need to divide by 22.
If the result is below one, you’re not insulin resistant. The lucky less than 1% of the population does not have insulin resistance. Shanahan shares how she determined this threshold for defining metabolic health:5
“That cutoff value of 1.0 or less being normal, you know, ideal, really was not easy to sort out, because there is currently no consensus. So, when you look at some research, they give you different numbers, a lot might be 3.6 or 2.7 or 2.4. And they’re all over the place. I chose 1.0 based on some older data and based on healthy cut offs of glucose and insulin levels.
The reason I wanted to use the older data is so important to talk about. And that is because over time as our diets have been getting worse … we’re eating about three or four times the volume of vegetable oil that we were back in the 80s … So, our population basically is getting less healthy. And that means we aren’t studying normal people anymore. We haven’t defined health recently, and we define health based on the bell curve.
So, if somebody’s within the 95%, with average numbers, we define that as normal … that’s how, for example, a fasting insulin level is defined as by some labs 25 versus healthy people seem to have fasting insulin levels of five or less. So, it’s five times … that’s how far off our averages are.
We’ve deviated so far at the population level from normal metabolic health that we can’t even define it. And with modern data, we have to go back in the past.
And so back in the past, researchers did, you know, some the same kinds of population studies and they looked at longitudinally, the people who had the HOMA-IR score of 1.0, they followed them for a few years, and they stayed healthy, they didn’t develop metabolic diseases like Type 2 diabetes.”
The Importance of Proper Carbohydrate Intake
While Shanahan long embraced low-carbohydrate diets, she’s shifted her position, as have I, and now recognizes the importance of proper carbohydrate intake for brain health and overall health. While reducing refined carbohydrates may be helpful, your body and brain require a minimum number of healthy carbohydrates for optimal function. For most adults this is around 250 grams per day.
While many people initially feel better on low-carb diets, this is because their endotoxin load decreases. The low-carb community’s focus on carbohydrate restriction without adequately addressing the role of vegetable oils in metabolic dysfunction will ultimately make health worse, however.
Shanahan expresses frustration with the low-carb community’s resistance to her research on the dangers of seed oils, noting that low-carb diets often appear to work not just because of carbohydrate restriction but because they often inadvertently reduce intake of harmful seed oils.
The mitochondrial damage caused by oxidative stress ultimately affects your gut as well, leading to its deterioration. This results in a disruption of the gut microflora, causing a shift toward more pathogenic bacteria. The presence of these harmful bacteria is significantly worsened when consuming most carbohydrates, which introduces a confusing and conflicting factor into the equation.
Dextrose, a simple sugar, is one short-term solution to address carbohydrate needs in people with damaged guts that prevents them from eating more complex carbs that will activate the release of endotoxin. Slowly sipping a dextrose solution of up to a pound in a half gallon of water throughout the entire day helps to maintain stable blood sugar levels and provides your brain with necessary glucose without causing an endotoxin reaction. Drinking it quickly can cause serious metabolic complications and should be avoided. This is also a temporary solution that helps heal the gut so one can progress to longer chain starch molecules.
Shanahan suggests using whole foods that digest and break down slowly, such as complex carbohydrates found in foods like rice. To ensure the foods you’re eating are truly slow digesting, she recommends using a glucometer. This approach can help you tailor your diet to your unique metabolic responses:6
“If you’re not sure, you can always do a little biohacking trick and get a continuous glucometer and see how these foods are actually affecting your blood sugar, and it’s a lot of fun to do. And you can validate the idea that just a little bit that these slow-digesting carbohydrates truly are slow digesting, for you. Because everyone is a little different.”
Shanahan also points out the role of health agencies like the American Heart Association (AHA) in perpetuating the myth that seed oils are beneficial. Calling AHA a “corrupt organization” that has perpetrated “the biggest scandal … on the American population in history,”7 she argues that the AHA’s promotion of vegetable oils as heart-healthy has led to widespread health issues:8
“If you think about all the pain and suffering that’s been caused by promoting vegetable oils as healthy, and taking people away from the foods that they love, the traditional foods that supported health throughout history, that’s billions of deaths on their hand, and untold amounts of suffering.”
Rethinking Carbohydrates and Metabolic Health
My interview with Shanahan offers a fresh perspective on the role of carbohydrates in human health, challenging common beliefs in the low-carb community. Healthy carbohydrates are essential for optimal brain function and overall health. The real culprit behind many metabolic issues is not carbohydrates themselves, but rather the prevalence of processed foods and vegetable oils in the modern diet.
Addressing insulin resistance and oxidative stress, as well as the underlying mitochondrial dysfunction, are key factors in protecting your metabolic health. Shanahan’s personal experience with insulin resistance and its impact on cognitive function provides a compelling argument for the need to improve metabolic health.
Perhaps most importantly, our conversation underscores the need for a more holistic approach to nutrition and health. By focusing on eliminating harmful processed foods and vegetable oils, while thoughtfully incorporating whole-food carbohydrates, many people can improve their metabolic health and overall well-being. This offers hope for those struggling with low-carb diets or insulin resistance, as it’s possible to enjoy a wider range of foods while still achieving optimal health.
By focusing on the quality of your food choices and moving away from heavily processed ingredients, you can take significant steps toward better health and cognitive function. As Shanahan concludes:12
“When I improved by diet, I improved my metabolism, I improved my personality. Objectively, you could ask my husband. I improved my immune system function. I improved every aspect of my health. And it just came from getting these … main bad, big bad ingredients out of my diet.”
By understanding the hidden dangers in our modern food supply and making informed choices, you can work toward similar improvements in your own health and well-being. It’s a call to action for individuals to take control of their health through informed dietary choices and a return to more traditional, nutrient-dense foods.
