Calling Attention To Her Book

A Comprehensive Summary of Dark Calories: How Vegetable Oils Destroy

by Catherine Shanahan, MD

Catherine Shanahan, MD, has long been recognized as a leading voice in the fight against chronic diseases that plague modern society. Her earlier works, including Deep Nutrition and The Fatburn Fix, established her as a passionate advocate for ancestral eating principles and a staunch opponent of the widespread use of industrially processed seed and vegetable oils. In her book Dark Calories: How Vegetable Oils Destroy, Dr. Shanahan presents a rigorous and disturbing exploration of how these oils undermine our metabolism, harm our cells, and contribute to a host of chronic ailments. This 1,000-word summary aims to distill her arguments, key research findings, and proposed solutions, offering an in-depth look at why she believes these “dark calories” are so destructive—and what we can do about it.


1. Introduction to “Dark Calories”

Dr. Shanahan opens her book by coining the term “dark calories” to describe the hidden, insidious nature of industrial seed and vegetable oils. These oils—primarily soybean, corn, canola, cottonseed, safflower, sunflower, and a few others—became ubiquitous in the mid-20th century as a cheap alternative to more traditional fats such as butter, lard, and tallow. The irony, she notes, is that they are often marketed as “healthy” due to their polyunsaturated fat content, while their actual impact on human health is questionable at best—and devastating at worst.

She points out that these oils do not appear in ancestral diets in anything close to the concentrations seen in modern cuisine. From the perspective of evolutionary biology, she argues, our metabolism has not adapted to handle the highly reactive polyunsaturated fatty acids (PUFAs) that dominate these products. This mismatch between modern dietary practices and our ancient physiology, Dr. Shanahan proposes, is a major contributor to the current epidemic of chronic diseases such as obesity, diabetes, heart disease, and even certain cancers.


2. Historical Context: From Ancestral Fats to Modern Oils

A significant portion of Dark Calories is dedicated to exploring the history that led to the rise of vegetable oils. Dr. Shanahan describes how early industrial processes found a profitable use for cottonseed waste by turning it into cooking oil and later into partially hydrogenated fats like margarine. Over time, these manufacturers promoted their products as healthier and more “modern” than traditional animal fats, capitalizing on emerging scientific theories (later shown to be flawed) linking saturated fat to heart disease.

According to Dr. Shanahan, the shift was so dramatic that vegetable oils became nearly impossible to avoid by the 1970s and 1980s. They were incorporated into salad dressings, baked goods, snacks, and packaged foods of all kinds. The result, she contends, is that most people in industrialized nations now consume far more polyunsaturated fats than their ancestors ever did. This rise in consumption coincided with a corresponding rise in obesity, type 2 diabetes, and cardiovascular disease. While correlation does not necessarily prove causation, Dr. Shanahan outlines research suggesting that vegetable oils play a central role in these epidemics.


3. The Biochemistry of Seed and Vegetable Oils

Central to Dr. Shanahan’s argument is a clear, detailed exposition of how vegetable oils wreak havoc at the cellular level. The first point she emphasizes is oxidation. Polyunsaturated fatty acids are chemically unstable, especially when heated, which leads to the creation of harmful oxidation products such as aldehydes and lipid peroxides. These reactive compounds can cause DNA damage, disrupt cell membranes, and even impair mitochondrial function. Mitochondria, the powerhouses of our cells, need a stable environment and reliable fuel sources to generate energy, but an onslaught of oxidized lipids interferes with these vital processes.

Furthermore, Dr. Shanahan explains how consuming excessive amounts of linoleic acid—the predominant polyunsaturated fatty acid in vegetable oils—alters the fatty acid composition of our cell membranes. This can lead to chronic inflammation and heightened susceptibility to oxidative stress. According to her, cells loaded with excess linoleic acid are primed to release inflammatory signals when stressed, perpetuating a vicious cycle of metabolic disruption and systemic inflammation.


4. Chronic Disease Connections

Perhaps the most alarming sections of Dark Calories are those that draw connections between vegetable oil consumption and chronic illnesses. Dr. Shanahan systematically goes through the evidence linking excessive PUFA intake, especially linoleic acid, to insulin resistance and metabolic dysfunction. She cites studies that show how high-PUFA diets can worsen glucose control, leading over time to the development of type 2 diabetes.

She also dedicates chapters to the ways vegetable oils may compromise cardiovascular health. Contrary to the once-accepted notion that lowering saturated fat automatically improves heart health, Dr. Shanahan highlights research indicating that replacing saturated fats with polyunsaturated fats may not reduce the incidence of heart disease and may, in some cases, increase other risks. Of particular concern are small, dense LDL particles that form when cells and lipoproteins are repeatedly exposed to damaging oxidative stress—a condition strongly correlated with high vegetable oil intake.

Cancer is another area Dr. Shanahan explores, although she is careful to note that the relationship between diet and cancer is complex and multifactorial. However, she lays out a compelling case that the pro-inflammatory and oxidative nature of heated vegetable oils creates a cellular environment more conducive to cancer initiation and progression. By damaging DNA and weakening immune surveillance, these oils add fuel to the fire of carcinogenesis.


5. The Hidden Epidemic and Sociocultural Factors

One of Dr. Shanahan’s key insights is that the damage caused by vegetable oils is often hidden from public view. Because they are used in restaurants, processed foods, and even so-called “health foods,” consumers may have no idea how much of these oils they are ingesting on a daily basis. Food labels rarely specify the quality or sourcing of these oils, nor do they list the quantities of linoleic acid or other potentially problematic compounds.

Moreover, Dr. Shanahan discusses how socioeconomic factors play into the widespread use of these oils. They are cheap and readily available, which appeals to both food manufacturers and financially constrained consumers. This economic reality disproportionately affects lower-income communities, where highly processed foods laden with vegetable oils may be the most readily accessible or affordable option.


6. Detoxifying from Vegetable Oils

Building on her argument that vegetable oils pose a grave threat to metabolic health, Dr. Shanahan offers practical strategies for “detoxifying” from these “dark calories.” She encourages a return to traditional fats, such as butter, ghee, tallow, coconut oil, and olive oil, noting how these sources have been dietary mainstays for centuries in many cultures around the world. These fats, she argues, are more stable, less prone to oxidation, and contain vitamins or other beneficial compounds that support robust health.

Dr. Shanahan also discusses the concept of “fat adaptation” and how shifting away from a high-PUFA diet can help the body improve its metabolic flexibility. This shift may entail reducing carbohydrate intake, focusing on whole foods, and ensuring adequate protein while eschewing processed snacks, baked goods, and fast foods that are almost always cooked or made with vegetable oils.


7. Evidence and Counterarguments

Throughout Dark Calories, Dr. Shanahan anticipates objections from those who defend vegetable oils as “heart-healthy.” She points out that many of the studies extolling the virtues of vegetable oils rely on observational data or on replacing heavily processed foods high in trans fats with vegetable oils. In such comparisons, almost anything might seem healthier than the worst possible alternative. She argues that more rigorous, long-term studies on the direct impacts of PUFA-heavy diets—especially those high in linoleic acid—are necessary to truly understand their health implications.

Additionally, Dr. Shanahan acknowledges that not all polyunsaturated fats are equally damaging and that some forms, particularly omega-3 fatty acids from fish or certain plant sources, are essential. Yet she emphasizes that the ratio between omega-6 and omega-3 fatty acids is critical and that the modern reliance on vegetable oils has sent omega-6 consumption skyrocketing relative to omega-3s, thereby fueling chronic inflammation.


8. Conclusion: Reclaiming Our Metabolic Health

In the final chapters of Dark Calories, Dr. Shanahan delivers a clarion call to fundamentally reassess the role of vegetable oils in our food system. She underscores that reversing decades of misinformation about dietary fats will not be easy, and large-scale changes in agriculture and food manufacturing could take time. However, she argues that individuals can begin protecting themselves immediately by eliminating or drastically reducing processed seed and vegetable oils at home, reading food labels carefully, and advocating for better cooking practices at restaurants and schools.

For Dr. Shanahan, the war on chronic disease begins in the kitchen. She urges readers to embrace the traditional fats cherished by our ancestors and to recognize that the “dark calories” lurking in seemingly innocent cooking oils are at the root of many modern metabolic ills. By lighting a path forward that emphasizes informed consumer choices, clearer labeling, and a return to time-tested nutritional wisdom, Dr. Shanahan believes we can restore the vitality that has been eroded by decades of dietary misinformation and industrial convenience.