Dr. Kumar’s Take:
This study from the 1960s looked at over 1 million Indian railway workers and found something surprising: heart disease was seven times more common in South India than in North India—even though North Indians ate up to 19 times more fat, mostly saturated animal fats like ghee. South Indians, by contrast, ate less fat overall and more polyunsaturated seed oils like groundnut oil. The study also found that smoking was much higher in the North. These findings challenge the idea that saturated fat causes heart disease.
Key Takeaways:
✔ Heart disease was 7x more common in South India than North India.
✔ South Indians ate much less fat and more seed oils than North Indians.
✔ Smoking was more common in North India, but heart disease was lower.
Actionable tip:
Replace seed oils with olive oil, avocado oil, or grass fed butter or ghee. These fats are mush less oxidizable then polyunstaturated fats.
Brief Summary:
This 5-year study (1958–1962) included 1.15 million Indian railway employees aged 18–55. It examined deaths from heart disease across eight railway zones in India. Heart disease rates were much higher in South India, despite these populations eating less saturated fat, more polyunsaturated oils, and smoking less than North Indians.
Study Design:
- Retrospective analysis of 679 male deaths from ischemic heart disease across Indian railway zones.
- Population: 1.15 million workers aged 18–55, with uniform employment structures across regions.
- Data collected from railway hospital records, ECGs, death certificates, and dietary surveys.
- Dietary patterns assessed through interviews, roadside eateries, and national dietary data.
Results:
- Southern zone: 135 deaths per 100,000 workers.
- Northern zone: 20 deaths per 100,000 workers.
- Fat intake: Up to 19x higher in North India (mostly animal fat from ghee and milk).
- Sugar intake: Also 9x higher in North India.
- Smoking: 8x higher in North (Punjab) than South (Madras), yet heart disease was lower in the North.
How Fat and Diet May Play a Role
The South Indian diet was low in fat, especially animal fat, and used more polyunsaturated seed oils like groundnut (peanut) oil. The North Indian diet used more ghee and dairy fat, which are high in saturated fat. Yet, the North had much lower rates of heart disease.
This study suggests that polyunsaturated fat may play a causal role in cardiovascular disease, likely due to its highly oxidizable nature.
Related Studies and Research
Soybean Oil and the Omega Balance Shift – Reviews how the rise of soybean oil disrupted ancestral omega-6 to omega-3 ratios.
The Rise of Linoleic Acid in U.S. Adipose Tissue – Tracks the dramatic increase of linoleic acid stored in body fat across decades.
Omega-6 Linoleic Acid and Heart Disease Risk – Explores how excessive linoleic acid may promote cardiovascular disease.
Linoleic Acid and Obesity: A Review – Evaluates links between omega-6 intake and rising obesity trends.
Health Risks of Linoleic Acid – Summarizes emerging concerns about excess LA consumption and metabolic disease.
Saturated and Trans Fats: Risk Comparison Study – Compares effects of different fat types, including omega-6 and saturated fat, on heart disease risk.
Mediterranean vs. Low-Fat Diets for Heart Health – Discusses traditional fat sources vs industrial seed oils in cardiometabolic outcomes.
Frequently Asked Questions
Why was heart disease higher in the South if they ate less fat?
The study suggests that the type of fat (seed oil vs. saturated fat) may influence heart disease risk more than total fat amount.
Does this mean saturated fat is healthy?
Saturated fat has been a vital part of the human diet since the dawn of our species. It’s demonization has only occurred in the last 75 years.
How reliable is this study?
While it’s an observational study from the 1960s, it included over 1 million people and had consistent results across different zones and occupations. Later studies have echoed some of its findings.
What about smoking?
Surprisingly, the North had higher smoking rates but lower heart disease. Despite this finding, there is no evidence that smoking is anything but deleterious. If you currently smoke, your number one priority should be to quit, as this will make the largest impact on your health.
Conclusion
This landmark study from Indian railway workers essentially refuted the diet heart hypothesis stating that saturated fat causes heart diesease. South Indians, who consumed less fat and more seed oils, had more heart disease, not less. This flips the common narrative and urges us to re-examine long-held beliefs about diet and heart health.