The Soybean Oil Scandal: How It May Be Fueling the Obesity Epidemic

Is Your Cooking Oil Programming Your Brain for Disease?

Three Studies That Show How Soybean Oil Is the Silent Saboteur in Our Battle Against Obesity

Groundbreaking Study at UC Riverside Reveals Soybean Oil’s Surprising Impact on Health — Study #1

A study conducted at the University of California, Riverside, unveiled startling insights into how soybean oil, a staple in the American diet, might be silently contributing to both metabolic and neurological health issues. The research, published on January 8, 2020, in the journal Endocrinology, was led by first author Poonamjot Deol, with senior authors Dr. Margarita Curras-Collazo and Dr. Frances Sladek.^¹

The Research Journey

In an attempt to uncover the dietary effects on brain function, researchers fed groups of male C57BL/6N mice isocaloric high-fat diets for up to 24 weeks. Three primary dietary fat sources were tested: conventional soybean oil, rich in linoleic acid (an omega-6 fatty acid); Plenish, a genetically modified version of soybean oil with low linoleic acid content (produced by DuPont Pioneer); and coconut oil, known for its high saturated fat content. A small amount of soybean oil was added to the coconut oil diet to provide essential fatty acids. A low-fat vivarium chow served as the control diet.

Using advanced techniques like RNA sequencing for gene expression analysis and immunohistochemistry for oxytocin measurement, the team delved into the effects of these diets on the hypothalamus, a pivotal brain region for metabolic regulation.

Key Revelations

Metabolic Disruption: Mice on soybean oil diets exhibited significant metabolic disruption compared to those fed coconut oil. The soybean oil diets correlated with glucose intolerance, pointing to a direct link between dietary soybean oil and diabetic-state markers. This suggests that the nature of fat in our diet can profoundly influence our metabolic health.

Genetic Alterations: The study found that over 100 genes in the mice’s hypothalamus were dysregulated when fed soybean oil. The coconut oil diet, by contrast, had negligible effects on hypothalamic gene expression compared to the control. Importantly, the gene responsible for oxytocin production (Oxt) was notably affected — it was the only gene dysregulated by both soybean oil diets that was simultaneously associated with neurological, metabolic, and inflammatory disease categories. While hypothalamic oxytocin immunoreactivity decreased, plasma levels paradoxically rose, suggesting a disturbance in the oxytocin system.

Neurological Concerns: Given oxytocin’s role in social bonding, stress, and even metabolism, the study posits that altered levels might contribute to conditions like autism, depression, anxiety, and neurodegenerative diseases like Alzheimer’s, hinting at soybean oil’s broader impact on neurological health. The researchers believe this discovery could have ramifications not just for energy metabolism, but also for proper brain function.

Health Implications

This research casts a shadow over soybean oil’s widespread use in food preparation and processed foods, urging a reconsideration of dietary oil choices. As Poonamjot Deol put it: “If there’s one message I want people to take away, it’s this: reduce consumption of soybean oil.”^⁴

The team notes that the findings apply specifically to soybean oil — not to other soy products or to other vegetable oils. Dr. Sladek cautioned: “Do not throw out your tofu, soymilk, edamame, or soy sauce. Many soy products only contain small amounts of the oil, and large amounts of healthful compounds such as essential fatty acids and proteins.”^⁴

The Road Ahead

While the study provides compelling data, further human research is needed to confirm these findings. The specific compounds in soybean oil affecting health remain unidentified, with linoleic acid and stigmasterol being excluded as primary factors. The study used only male mice; because oxytocin is so important for maternal health and mother-child bonding, similar studies need to be performed using female mice. Identifying the responsible compounds is an important area for future research — “this could help design healthier dietary oils in the future,” said Deol.^⁴

New Research Highlights Soybean Oil’s Detrimental Health Effects — Study #2

In a significant study published in the journal PLOS ONE, researchers led by Poonamjot Deol shed light on how different types of dietary fats can impact metabolic health differently, with soybean oil coming under scrutiny for its potential to promote obesity and diabetes-related issues.^²

The Study

Objective: The aim was to explore how diets high in various fats affect metabolism, with a particular focus on liver health.

Methodology: The researchers designed a series of four isocaloric diets, all at 40% of calories from fat (4.87 kcal/gm), and fed them to male C57BL/6 mice from weaning. The diet groups were: a high-fat diet primarily from coconut oil (HFD); a high soybean oil diet (SO-HFD, with 19 kcal% from soybean oil and 21 kcal% from coconut oil); a high fructose diet with coconut oil (F-HFD, with 25.9 kcal% from added fructose); and a combined high soybean oil and high fructose diet (F-SO-HFD). A standard vivarium chow served as the low-fat control. Researchers conducted regular weight measurements, glucose tolerance tests, insulin resistance evaluations, liver function tests, genome-wide gene expression profiling, and metabolomics analysis of liver tissue.

Key Discoveries

Obesity and Diabetes: The group consuming soybean oil not only gained more weight but also showed higher incidences of diabetes markers like glucose intolerance and insulin resistance. This was in sharp contrast to the mice on coconut oil, despite both diets being equally high in total fat content. Soybean oil also produced more obesity than fructose — a finding Deol called “a major surprise” given the widespread focus on sugar as the primary driver of the obesity epidemic.^⁵

Liver Health: The soybean oil-fed mice developed severe fatty liver with hepatocyte ballooning and very large lipid droplets, signs consistent with non-alcoholic fatty liver disease (NAFLD). They also showed shorter colonic crypt length. The study included the first genome-wide expression profiling and metabolomics analysis of livers from mice fed a soybean oil-enriched diet.

Drug Metabolism: Soybean oil significantly affected the expression of many cytochrome P450 (Cyp) genes involved in metabolizing drugs and environmental toxicants, suggesting that a soybean oil-enriched diet could affect one’s response to drugs and environmental toxicants, if humans show the same response as mice.

Implications for Nutrition

Dietary Choices: The findings suggest that when considering dietary fats, the source matters. Soybean oil, commonly used in cooking and processed foods, might not be as benign as previously thought, particularly in terms of promoting obesity and metabolic syndrome.

Focus on Liver Health: The study points to the liver as a critical organ affected by dietary fats, suggesting that our eating habits could have significant implications for liver function, which in turn affects overall health.

Considerations and Future Directions

Animal Model: While the study provides valuable insights, it’s based on mouse models, which have metabolic differences from humans. Further research is needed to confirm these effects in human subjects.

Short vs. Long-Term Effects: The study’s duration might not reflect the long-term health consequences of soybean oil consumption in humans. Chronic effects over years or decades could differ from what was observed.

Seed Oils Show Promise in Combating Obesity Through Gut Health — Study #3

A study published in the European Journal of Nutrition by Waleed A.S. Aldamarany and colleagues at Southwest University (Chongqing, China) and Al-Azhar University (Egypt) has turned the spotlight on certain seed oils, revealing their potential as dietary allies against obesity by positively influencing gut microbiota.^³

Study Overview

Methodology: Mice were divided into six groups: a normal diet group; a high-fat diet group; an orlistat-treated positive control group (receiving 20 mg/kg body weight of the anti-obesity drug orlistat); and three oil supplementation groups in which mice on a high-fat diet received 2 g/kg body weight of perilla seed oil, sunflower oil, or tea seed oil. Researchers tracked changes in body weight, fat accumulation, blood glucose, lipopolysaccharides, insulin resistance, serum lipid levels, oxidative stress, liver histology, and the composition of gut microbiota using advanced sequencing techniques.

Key Discoveries

Microbiota Influence: Different seed oils had distinct impacts on the gut microbiome. The introduction of these oils led to an increase in bacterial species associated with healthier metabolic profiles, restoring a more balanced gut microbial environment disrupted by the high-fat diet.

Perilla Oil’s Potential: Perilla oil stood out with its ability to significantly reduce obesity markers. It appeared to foster a gut environment that supports metabolic health, suggesting a beneficial role in weight management.

Metabolic Improvements: All three seed oil supplements significantly reduced body weight, organ weight, blood glucose, LPS levels, and insulin resistance. Serum lipid profiles improved across the board, with reductions in total cholesterol, triglycerides, and LDL cholesterol, and increases in HDL cholesterol. The treatments also alleviated oxidative stress, hepatic steatosis, and reduced liver lipid accumulation.

Selective Effects of Seed Oils: Unlike soybean oil, which previous research has linked to obesity, this study indicates that perilla, sunflower, and tea seed oils might offer protective or even therapeutic effects against obesity, thanks to their unique fatty acid compositions.

Implications for Diet

Strategic Dietary Inclusion: The findings advocate for a more nuanced approach to dietary fat intake, where certain oils could be strategically included to support gut health and potentially mitigate obesity.

Personalized Nutrition: This research underscores the importance of personalized dietary strategies, where understanding an individual’s gut microbiome could guide the selection of dietary fats for optimal health outcomes.

Considerations and Future Research

Human Relevance: While the results are promising, the study’s direct applicability to human health is limited by the differences between mouse and human gut microbiomes. Human studies are essential to validate these findings in a real-world context.

Complexity of Human Diets: Human dietary patterns are far more varied than those studied in controlled lab conditions, which means further research must consider this complexity.

Contrasting the Insights from All Three Pivotal Studies on Dietary Oils

Figure 1: Three Biological Pathways Examined Across Studies

Specific Health Focus

Neurological and Metabolic Interplay: The UC Riverside 2020 study ventured beyond traditional metabolic outcomes. They delved into how soybean oil might influence neurological health by examining changes in hypothalamic gene expression and the oxytocinergic system in mice. This study suggests that the consumption of soybean oil could have repercussions not just for body weight and metabolism but also for social behavior, stress responses, and potentially even neurodegenerative diseases. The study’s focus on brain chemistry provides a novel angle, suggesting that what we eat might directly influence our mental and neurological health.

Liver Health and Metabolic Syndrome: The 2015 research published in PLOS ONE focused squarely on the metabolic consequences of dietary fats, with a particular emphasis on liver health. Their findings underscored the liver’s role as a central organ in the metabolic disturbances caused by certain dietary fats, showing how soybean oil can lead to severe liver issues, alongside obesity and diabetes. This research highlights the liver not just as a metabolic regulator but as a potential site for dietary-induced damage.

Gut Microbiota and Obesity: The European Journal of Nutrition study took a different approach by investigating how perilla, sunflower, and tea seed oils might mitigate obesity through their effects on gut microbiota. This study stands out by exploring the indirect pathways through which dietary fats can influence health, namely via the gut. It suggests that by fostering a healthier microbial environment, certain seed oils could help manage body weight and metabolic health.

Figure 2: Three Body Systems Targeted by the Studies

Dietary Interventions

Soybean vs. Coconut Oil: Both the UC Riverside studies directly pit soybean oil against coconut oil. This comparison was crucial in demonstrating that not all high-fat diets lead to the same health outcomes. Soybean oil, rich in polyunsaturated fats, was consistently shown to have detrimental metabolic effects compared to the more saturated coconut oil, highlighting the importance of fatty acid composition in dietary health.

Exploring Alternatives: The Aldamarany et al. study diverged by focusing on oils less commonly highlighted in the obesity discussion. By showing that oils like perilla could potentially reduce obesity markers, it opens up a conversation about diversifying the sources of dietary fats beyond the usual suspects, suggesting there might be beneficial fats we’ve overlooked in our culinary practices.

Figure 3: Oils Compared in Each Study

Mechanisms of Action

Brain Alterations: The UC Riverside 2020 research linked soybean oil with changes in the expression of genes critical for hypothalamic function, particularly those involved in oxytocin regulation. This points to a direct neural pathway through which diet might influence behavior and metabolism.

Liver Pathology: The 2015 study detailed how soybean oil exacerbates liver conditions, providing a mechanistic link between diet, liver function, and metabolic diseases. It suggests that dietary fats can directly contribute to non-alcoholic fatty liver disease (NAFLD), insulin resistance, and diabetes.

Gut Microbiota: The Aldamarany et al. study introduced the concept of dietary fats modulating gut bacteria to affect health outcomes. This indirect mechanism shows how diet can influence metabolic health by altering the body’s microbial environment, which in turn affects nutrient absorption, energy balance, and even immune function.

Future Research Directions

Human Trials: Each study calls for human research to confirm mouse model findings, acknowledging the limitations of animal studies in predicting human health outcomes.

Gender Specificity: The UC Riverside studies’ focus on male mice underlines the need to understand how dietary fats might affect females differently, highlighting gender as a critical variable in nutritional research.

Identification of Specific Compounds: A key area for future exploration is pinpointing which components of soybean oil are responsible for its adverse effects, potentially leading to the development of healthier oil variants.

Diet-Microbiome Interaction: The Aldamarany et al. study’s implications suggest a burgeoning field of research into personalized nutrition, where diets might be tailored not just to individual metabolism but also to one’s gut microbiome profile.

Conclusions

These studies collectively challenge the notion of a one-size-fits-all approach to dietary fats. While soybean oil emerges as a concern for both metabolic and neurological health, other oils like perilla might offer protective health benefits through different biological pathways. This underscores the complexity of nutrition science, where the source of fats, their interaction with our body’s systems, and even our unique microbiomes play pivotal roles in determining health outcomes. As we move forward, a more nuanced understanding of dietary fats will likely lead to dietary recommendations that are not only about reducing fat intake but optimizing the type of fats for individual health needs.

Endnotes

1. Deol, P., Kozlova, E., Valdez, M., Ho, C., Yang, E.-W., Richardson, H., Gonzalez, G., Truong, E., Reid, J., Valdez, J., Deans, J.R., Martinez-Lomeli, J., Evans, J.R., Jiang, T., Sladek, F.M., & Curras-Collazo, M.C. (2020). Dysregulation of Hypothalamic Gene Expression and the Oxytocinergic System by Soybean Oil Diets in Male Mice. Endocrinology, 161(2), bqz044. https://doi.org/10.1210/endocr/bqz044. PMID: 31912136.

2. Deol, P., Evans, J.R., Dhahbi, J., Chellappa, K., Han, D.S., Spindler, S., & Sladek, F.M. (2015). Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse: Potential Role for the Liver. PLOS ONE, 10(7), e0132672. https://doi.org/10.1371/journal.pone.0132672. PMID: 26200659.

3. Aldamarany, W.A.S., Taocui, H., Liling, D., Mei, H., Yi, Z., & Zhong, G. (2023). Perilla, sunflower, and tea seed oils as potential dietary supplements with anti-obesity effects by modulating the gut microbiota composition in mice fed a high-fat diet. European Journal of Nutrition, 62(6), 2509–2525. https://doi.org/10.1007/s00394-023-03155-3. PMID: 37160801.

4. University of California, Riverside. (2020, January 17). America’s most widely consumed oil causes genetic changes in the brain. UCR News. https://news.ucr.edu/articles/2020/01/17/americas-most-widely-consumed-oil-causes-genetic-changes-brain

5. University of California, Riverside. (2015, July 22). Soybean oil causes more obesity than coconut oil and fructose. ScienceDaily. https://www.sciencedaily.com/releases/2015/07/150722144640.htm

6. University of California. (2015). Soybean oil may be more fattening than fructose or coconut oil. https://www.universityofcalifornia.edu/news/soybean-oil-may-be-more-fattening-fructose-or-coconut-oil

7. Inacio, P. (2020, January 30). Soybean Oil Linked to Obesity, Induces Genetic Changes in Brain Region Controlling Metabolism, Mouse Study Shows. Genetic Obesity News. https://geneticobesitynews.com/2020/01/30/soybean-oil-induces-genetic-changes-brain-region-controlling-metabolism-linked-obesity-mouse-study/

8. Springer Nature. European Journal of Nutrition, Volume 62, Issue 6 (2023). https://link.springer.com/journal/394/volumes-and-issues/62-6