Where epidemiology fits in evidence

Plant-based nutrition has rarely been more contested. Seed oils are vilified, butter is celebrated, protein is treated as a pure quantity question, and nutrition epidemiology is routinely dismissed by people who have never read one of its papers. In this episode, I sit down with Dr Andrea Glenn, an Assistant Professor at NYU and Visiting Scientist at the Harvard T.H. Chan School of Public Health, to look at what the strongest evidence actually shows.

We cover the recent plant-versus-animal protein data from the Nurses' Health Studies and Health Professionals Follow-up Study, the Portfolio Diet, the new CHEAP trial, the JAMA Internal Medicine butter and plant oil paper, and the new 2026 AHA dietary guidance.

What we cover:

• The plant-to-animal protein ratio and its association with cardiovascular and coronary heart disease risk
• The Portfolio Diet, what it contains, and how its LDL-lowering effects compare to a low-dose statin
• Butter, beef tallow, tropical oils, and what the latest mortality data show
• Why "low-carb" is not one diet, and why food sources matter as much as the macronutrient breakdown
• A grounded defence of nutrition epidemiology and the role of food frequency questionnaires
• Practical takeaways for how to eat in line with the new AHA guidance

This is the conversation I wanted to have for anyone tired of nutrition by hashtag. If it lands, a quick rating or review on Apple Podcasts or Spotify makes a real difference.

To follow more of Dr Andrea Glenn's work, find her on Instagram at instagram.com/andrea.glenn.rd, on X at x.com/andreaglennrd, and on LinkedIn at linkedin.com/in/andrea-glennrd.

• Intro (00:00)
• Plant vs Animal Protein Ratio and Heart Disease (01:17)
• Does Total Protein Amount Also Affect CVD Risk? (05:33)
• Why Nutrition Epidemiology Critics Often Get It Wrong (11:00)
• Where Epidemiology Fits in the Evidence Hierarchy (17:28)
• Sensitivity Analyses: How Scientists Test Their Results (22:16)
• What It's Like Doing Science at Harvard (28:55)
• The Portfolio Diet: Origins and the Science Behind It (32:21)
• The CHEAP Trial: Testing Portfolio Diet Long-Term (41:03)
• Portfolio Diet in Cohort Studies: What the Data Shows (50:24)
• Unsaturated Fats: Are They Inherently Heart-Protective? (56:16)
• Phytosterol Supplements: LDL Benefits vs Safety Questions (01:00:06)
• Butter vs Plant Oils: What Mortality Data Actually Shows (01:06:57)
• Plant vs Animal MUFAs and Type 2 Diabetes Risk (01:12:11)
• Low-Carb Diet Quality and Diabetes Risk: New Data (01:15:37)
• 2026 AHA Dietary Guidelines: Key Differences Explained (01:20:23)
• Portfolio Diet's Potential to Reduce Disease Burden (01:26:35)

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Simon Hill, MSc, BSc (Hons)

• Creator of theproof.com
• Host of The Proof with Simon Hill
• Author of The Proof is in the Plants

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