What is the evidence for and against limiting dietary fat, particularly saturated fats, to reduce the risk of atherosclerosis?

Evidence on Limiting Dietary Fat and Saturated Fats for Atherosclerosis Reduction

Current evidence does not support the recommendation to further restrict dietary saturated fat intake to reduce atherosclerosis risk, as multiple recent meta-analyses and large clinical trials show no significant association between saturated fat consumption and cardiovascular disease outcomes. 1

Current Understanding of Saturated Fats and Cardiovascular Disease

Evidence Against Limiting Saturated Fats

• The largest contemporary clinical trial, the Women's Health Initiative (WHI) with nearly 49,000 women, demonstrated that risk for heart attack and stroke was unaffected after 8 years on a low-fat diet where saturated fat provided 9.5% of total daily energy 1
• The PREDIMED trial showed that despite an increase in total fat intake by 4.5% of total energy (including slightly higher saturated fat consumption), major cardiovascular events and death were significantly reduced compared with the control low-fat diet group 1
• Six recent systematic reviews and meta-analyses of randomized trials showed that replacing saturated fat with polyunsaturated fat has no significant effect on coronary outcomes or total mortality 1
• A study of 195,658 participants from the UK Biobank followed for 10.6 years found no evidence that saturated fat intake was associated with incident cardiovascular disease 1

Mechanisms and Biomarkers

• While saturated fats can raise LDL cholesterol, this primarily reflects increases in large LDL particle subspecies, which have much weaker associations with CVD risk than smaller LDL particles 1
• Smaller LDL particles, which are more strongly associated with atherosclerosis risk, are not reduced by saturated fat restriction in most individuals 1
• Decreasing saturated fat intake also lowers HDL cholesterol levels, which may counteract potential benefits 1
• The traditional focus on LDL cholesterol as the primary biomarker may be insufficient, as diet-induced LDL cholesterol reduction doesn't necessarily translate to cardiovascular benefit without considering other metabolic effects 1

Dietary Patterns vs. Single Nutrients

Food-Based Approach

• Evidence supports focusing on dietary patterns rather than isolated nutrients 1
• Plant-based foods (whole grains, fruits, vegetables, legumes, and nuts) are consistently linked with reduced atherosclerosis risk 1
• Replacing animal/tropical fats with olive oil and other unsaturated-fat-rich oils shows cardiovascular benefits 1
• The diet associated with lowest mortality risk in the UK Biobank study comprised high fiber (10-30g/day), protein (14-30%), and monounsaturated fat (10-25%) with moderate polyunsaturated fat (5-<7%) and starch (20-<30%) 1

Carbohydrate Considerations

• Replacing saturated fats with refined carbohydrates and sugars may actually increase cardiovascular risk 1
• Higher consumption of starchy carbohydrates and sugar is associated with higher risk of CVD and mortality 1
• Restricting carbohydrate intake, particularly refined carbohydrates, may be more relevant for decreasing mortality risk in individuals with insulin resistance and type 2 diabetes 1

Practical Dietary Recommendations

• Focus on overall dietary patterns rather than isolated nutrient restriction
• Emphasize consumption of plant-based foods including whole grains, fruits, vegetables, legumes, and nuts
• Consider using olive oil and other unsaturated-fat-rich oils instead of animal/tropical fats
• Limit refined carbohydrates and added sugars, which may pose greater cardiovascular risk than saturated fats
• Recognize that different food sources of saturated fat contain different fatty acid profiles with varying effects on cardiovascular health 1

Common Pitfalls to Avoid

• Focusing exclusively on saturated fat reduction without considering what replaces it in the diet
• Replacing saturated fats with refined carbohydrates, which may worsen metabolic profiles
• Treating all saturated fats as equivalent, when they represent diverse compounds with different metabolic effects
• Relying solely on LDL cholesterol as a surrogate marker without considering particle size and other metabolic effects
• Ignoring the overall dietary pattern and food matrix in which fats are consumed

In conclusion, the most recent and comprehensive evidence suggests that further restriction of dietary saturated fat is unlikely to reduce atherosclerosis risk. Instead, focusing on overall dietary patterns that emphasize plant foods, unsaturated fats, and limit refined carbohydrates appears to be more beneficial for cardiovascular health.