ZOE Science & Nutrition – Recap: The Truth About Seed Oils | Prof. Sarah Berry

Date: September 9, 2025
Host: Jonathan Wolf
Guest: Prof. Sarah Berry

Brief Overview

This episode of ZOE Recap distills the key takeaways from a larger discussion on seed oils with Prof. Sarah Berry, a leading expert in nutritional science. Seed oils (like sunflower, soybean, and canola/rapeseed oil) are often maligned online, described as toxic or detrimental to health. Prof. Berry cuts through the hype, addressing common misconceptions, explaining the science behind seed oil production and their health effects, and translating the current research into accessible advice. The conversation is evidence-driven, debunking myths and clarifying what’s genuinely known (and unknown) about seed oils.

Key Discussion Points & Insights

1. What Are Seed Oils? ([00:01]–[02:26])

• Definition: Oils extracted from seeds—such as sunflower, safflower, corn, soybean, and canola/rapeseed.
• Prevalence: Seed oils are a primary source of dietary fat after palm oil.
  • "The largest contributor of fat in our diet comes from palm oil. ...Nearly all of the rest ...come from these seed oils." (Prof. Berry, [01:34])
• Global Differences: Soybean oil is most common in the U.S.; rapeseed/canola dominates in the UK.

2. How Are Seed Oils Made? ([02:26]–[06:35])

• Extraction Methods:
  • Cold-Pressed: Simple physical squeezing; less efficient, retains more phytonutrients.
  • Refined: Extraction with heat and solvents (e.g., hexane) for maximum yield. The oil is then bleached and deodorized to stabilize it.
    • "[Refining] is to remove many minor components that you might find in the oil. ...These terms that you might hear that are used as processing techniques are things like bleaching and deodorization. Now, they do sound quite scary...but...the end oil is therefore very stable. There are no harmful chemicals left in that end stage oil." (Prof. Berry, [04:16])
• Nutrient Loss:
  • Refinement may remove some beneficial phytonutrients, especially vitamin E and polyphenols, but this loss is relatively minor.
    • "The only potential downside...is that ...you might remove some ...favorable elements ...these phytonutrients are typically quite well preserved, but you might get some losses." (Prof. Berry, [05:11])
• Is There a Health Difference?
  • Cold-pressed oils are not significantly healthier than refined oils for most people.
    • "I actually believe...based on current evidence...that these refined oils actually are very similar to the cold pressed oils. And the loss that you get is quite minor." (Prof. Berry, [05:59])

3. Why Are Seed Oils Seen as Unhealthy? ([07:29]–[09:09])

• Public Perception: Social media and popular media often depict seed oils as harmful, using alarming language and infographics.
  • "These alarms like, 'seed oils are toxic; seed oils are going to kill you.' It's absolute nonsense." (Prof. Berry, [08:03])
• Correlation ≠ Causation: Many critics cite rising seed oil intake alongside increases in obesity and chronic diseases, but this ignores confounding factors.
  • "It's not the seed oils themselves that are causing this, it's the ingredients that all of the other ingredients in these foods ... lack of physical activity, our increase in stress, ... all of these other issues." (Prof. Berry, [09:11])

4. What Does the Science Actually Show? ([10:09]–[14:59])

• Epidemiological Evidence:
  • Large-scale studies adjusting for confounders do not show harm from seed oils.
  • Omega 6 (the main polyunsaturated fatty acid in seed oils) is linked to:
    • Reduced LDL ("bad") cholesterol
    • Reduced cardiovascular disease risk
    • Lower all-cause mortality
    • "Consistently, there is a favorable effect from increasing omega 6 ... with a reduction in coronary heart disease." (Prof. Berry, [10:38])
    • "An increase in omega 6 intake ... is actually associated with favorable effects on all cause mortality ... and reductions in cardiovascular disease." (Prof. Berry, [11:21])
• The Sydney Heart Study:
  • This 1960s study is often cited to show harm, but its findings are confounded by the then-prevalent use of trans fats in margarine.
    • "A large proportion of the seed oil that they ate was in margarine spreads, which back in the 1960s was in the form of trans fatty acids ... heavily confounded..." (Prof. Berry, [12:43])
• Current Consensus:
  • "All the recent studies, the epidemiological research shows that as you increase your polyunsaturated fat intake, you reduce your risk of ill health..." (Prof. Berry, [13:37])
  • "Up to some of the data shows up to about 30% ... reduction in cardiovascular disease." (Prof. Berry, [14:14])
• Individual Variation:
  • Some populations, due to genetic variants, may need to moderate omega 6 intake, but for most, higher intake is beneficial.
    • "I do need to caveat ... there are a very small proportion of the population that have a particular genetic variant ... but overall the majority of people will ... benefit from increasing their polyunsaturated fatty acid intake." (Prof. Berry, [14:46])

Notable Quotes & Memorable Moments

• On the hype:
  "Honestly, it drives me insane when I see this."
  • Prof. Berry’s frustration with misinformation ([07:44])
• On the industrial process:
  "It's not as scary as it sounds...there are no harmful chemicals left in that end stage oil." ([04:52])
• On the science:
  "Just because in the same timeframe that seed oils are increasing, these other diseases are increasing, doesn't mean one causes the other." ([09:11])
• On changing science:
  "As I always tell my students, there might be more evidence to say otherwise. But based on current evidence, I don't think there's any harm from the processing techniques that are used to create processed seed oils." ([06:49])

Timestamps for Important Segments

| Segment | Timestamp | |-----------------------------------------|-------------| | What are seed oils? | 00:01–02:26 | | Extraction & Processing | 02:26–06:35 | | Health impact of refined vs cold-pressed| 05:59–06:49 | | Debunking seed oil myths | 07:29–09:09 | | Epidemiology and actual health effects | 10:09–14:59 | | Sydney Heart Study and trans fats | 12:43–13:37 | | Key scientific consensus | 13:37–14:59 |

Conclusion

Professor Sarah Berry argues convincingly, with current best evidence, that fears over seed oils are largely unfounded for most people. Modern refining processes do not leave harmful chemicals, and the end product is nutritionally similar to cold-pressed oils. Most large studies indicate that higher seed oil intake—primarily due to their omega 6 content—correlates with lower LDL cholesterol, reduced cardiovascular risk, and longer lifespan. Individual genetic exceptions exist, but the social-media-fueled panic is not evidence-based. Instead, focus should be on overall dietary patterns, not scapegoating seed oils.