Summary
This long-term study followed 458 men with coronary heart disease for up to seven years to understand what truly influences survival after a heart attack. Most of the men had already changed their lifestyles before joining the study—they had lost weight, cut back on smoking, and improved their diets on their own. Researchers then randomly assigned them to one of two diets:
- One diet was higher in polyunsaturated fats (PUFA) and lower in saturated fats.
- The other diet was higher in saturated fats (SFA) and lower in polyunsaturated fats.
After five years, 81% of all participants were still alive, and survival was even better—86%—for men who were entering the study after their first heart attack. Interestingly, survival was slightly better in the group eating more saturated fat, though the difference was not statistically significant.
When the researchers looked closely at all the data, they found that dietary fat intake simply didn’t predict survival. Instead, what mattered most were the usual clinical indicators of how badly the heart had been damaged. One lifestyle factor did stand out: regular physical activity strongly improved survival, even when all other factors were kept constant.
Body weight and smoking didn’t reach statistical significance in the formal analysis, but the researchers suspected they still played important roles—likely contributing to the good outcomes in both groups because many participants had already lost weight and cut smoking before the trial began.
The big takeaway:
Because these men had already made several important lifestyle changes after their heart attacks—losing weight, smoking less, exercising more—it became very difficult to isolate the specific effect of dietary fats. Their overall health improvements overshadowed any potential influence of swapping saturated and polyunsaturated fats.
The authors concluded that men recovering from a heart attack are not the best population for testing the “lipid hypothesis”. After such an event, people naturally change many behaviors at once, and these changes—especially increased physical activity—may have a far greater impact on survival than altering dietary fat ratios.
PMID: 727035
DOI: 10.1007/978-1-4684-0967-3_18
Abstract
Background: Dietary modification to reduce saturated fatty acids and increase polyunsaturated fatty acids has often been recommended for secondary prevention following myocardial infarction. However, the independent impact of such dietary changes on long-term survival remains uncertain when multiple lifestyle adjustments are made after a coronary event.
Methods: A total of 458 men with documented coronary heart disease were enrolled and followed for 2–7 years. Prior to entry, most participants had already initiated lifestyle changes, including weight loss, reduced smoking, and dietary alterations. Participants were randomly assigned to one of two diets:
Higher-PUFA diet: 9.8% of calories from saturated fat and 15.1% from polyunsaturated fat;
Higher-SFA diet: 13.5% of calories from saturated fat and 8.9% from polyunsaturated fat.
Survival outcomes were analyzed using multivariate models incorporating clinical severity, lifestyle factors, and dietary composition.
Results: Overall 5-year survival was 81%, and 86% among men entering after a first myocardial infarction. Survival was slightly higher in the group consuming more saturated fat and fewer polyunsaturated fats, but none of the dietary fat variables were significantly related to survival when controlling for confounders. Instead, prognosis correlated strongly with clinical indicators of myocardial and coronary disease severity. Recreational physical activity demonstrated a robust positive association with survival. While body weight and cigarette smoking did not emerge as statistically significant predictors, the authors note that relative leanness and lower cigarette consumption likely contributed beneficially across both groups.
Conclusions: In men recovering from myocardial infarction, multiple concurrent lifestyle changes—such as weight loss, reduced smoking, and increased physical activity—appear to exert greater influence on survival than alterations in dietary lipid composition alone. The study concludes that post-infarction patients, having already modified several lifestyle variables, are not an ideal population for testing the lipid hypothesis, as the effects of dietary fats are overshadowed by stronger influences from other behavioral and clinical factors.
Woodhill JM, Palmer AJ, Leelarthaepin B, McGilchrist C, Blacket RB. Low fat, low cholesterol diet in secondary prevention of coronary heart disease. Adv Exp Med Biol. 1978;109:317-30. doi: 10.1007/978-1-4684-0967-3_18. PMID: 727035.