Fats' comeback: why butter, lard, and eggs are not the enemy

Editor's note: This article was previously published and has been updated according to scientific and informative criteria. The text is for informational purposes only and does not replace the advice of your doctor.

IN BRIEF

• Dietary fats have useful biological roles (vitamin absorption, satiety) but their health effects depend on the type, dose, and dietary context.
• Artificial industrial fats (trans fats) are associated with established cardiovascular risks and should be avoided. [2]
• Replacing some saturated fats with polyunsaturated fats can reduce some cardiovascular events; replacing them with refined carbohydrates is less effective. [5][6]
• The association between dietary cholesterol (e.g., from eggs) and cardiovascular risks depends on the context, individual metabolic conditions, and the quantity consumed; observational studies show variable results. [7]

Abstract: what does science say?

The topic is the role of fats in the diet: butter, lard, and eggs are part of food traditions but have long been labeled as health enemies. Modern scientific literature shows greater complexity than historical simplifications: some fats (industrial trans fats) are clearly harmful, while others (natural fats present in traditional foods) have effects that depend on the quantity, production method, and what is used to replace them. Evidence from observational studies and clinical interventions suggests that the quality of the dietary pattern and nutritional substitutions (for example, polyunsaturated instead of saturated) matter more than the quantity of fat alone. However, the evidence has methodological limitations: observational data do not prove causality, and clinical studies are heterogeneous in duration and design. In practice, the current message is moderation and attention to the quality of fat and the overall dietary context.

Eating Fats: A Balanced Picture

Dietary fats play important biological functions: they are a dense energy source, promote satiety, and aid in the absorption of fat-soluble vitamins and bioactive compounds. However, observational literature and experimental interventions indicate that not all fats are equivalent regarding their potential health effects. Randomized clinical studies that compared fat reduction strategies show variable results; a consistent line of evidence indicates that replacing saturated fats with polyunsaturated fats can reduce some coronary events, while replacing them with refined carbohydrates is not advantageous. [5][6]

Types of Fats: Quality and Risk

Trans Fats: Why Avoid Them

Industrially produced trans fats (partially hydrogenated) are associated with adverse effects on the lipid profile (they increase LDL, reduce HDL) and an increased risk of coronary heart disease. This evidence has led to regulatory restrictions and public policies to limit their use in foods. For public health, the removal of trans fats from food supply chains is considered an effective and proven intervention. [2]

Saturated Fats: Between Context and Substitutions

The evidence on the associations between saturated fat intake and cardiovascular risk is complex and sometimes conflicting. Observational meta-analyses have found not always consistent results, while reviews of clinical studies indicate that replacing saturated fats with polyunsaturated fats can reduce the risk of coronary events. The quality of the substitution (polyunsaturated vs. refined carbohydrates) is a determining factor for the outcome. [3][5]

Dietary Cholesterol and Eggs

Modern observational studies show variable associations between egg consumption (or dietary cholesterol) and the risk of cardiovascular events and mortality. Some analyses of large cohorts report a modest increase in risk with high consumption; others find no significant associations. Differences may depend on how eggs are consumed (with many processed foods vs. in balanced dietary patterns), the metabolic characteristics of the population, and the control of confounding factors. [7]

Factors Influencing the Effect of Fats

Health depends on the overall dietary pattern: it's not enough to say "more fat" or "less fat." The source (natural vs. industrial), processing (hydrogenation, refining), dose, and caloric substitution matter. Furthermore, ultra-processed foods, rich in industrial fats and sugars, show associations with a higher cardiovascular risk regardless of fat content alone. [8] Individual metabolic profiles (e.g., diabetes, obesity, hyperlipidemia) also modify the relationship between the consumption of certain fats and clinical risk.

What This Means in Practice

In light of the evidence, a prudent approach based on food quality is preferable to the demonization or adoration of entire groups of nutrients. Prioritizing unprocessed sources, limiting products with trans fats and industrial preparations, and considering the type of fat when modifying the diet are choices supported by evidence. Balanced dietary patterns rich in vegetables, legumes, whole grains, lean or traditional protein sources, and sources of unsaturated fats — such as some versions of the Mediterranean diet — are among the most studied and favorable for cardiovascular prevention. [1] For weight and risk factor control, behavioral interventions that improve overall diet quality seem more effective than an exclusive focus on fat percentage. [9]

Useful Practical Points

• Prioritize unprocessed fats: extra virgin olive oil, nuts, fish, and, where present, traditional non-industrial animal products.
• Avoid industrial trans fats found in many baked goods and industrial snacks. [2]
• When reducing the consumption of a fat, choose unsaturated sources (polyunsaturated/monounsaturated) as a substitute, not refined carbohydrates. [5][6]
• Consume eggs in moderation within the context of a diet rich in plant-based foods; individual recommendations may vary in the presence of metabolic conditions. [7]
• Limit ultra-processed foods: high consumption is associated with a higher cardiovascular risk. [8]

Limitations of Evidence

It is important to distinguish between observational data and evidence of causality: prospective studies can show associations, but they do not directly prove that a food causes an event. Randomized clinical trials provide greater causal strength, but often have limitations (duration, adherence, size) and do not always replicate real-life conditions. Furthermore, measuring diet is difficult: assessment errors, changes over time, and confounding factors can influence results. For these reasons, modern guidelines prioritize evaluations based on dietary patterns and food quality rather than a simple percentage of fat.

Editorial Conclusion

The discussion on dietary fats requires balance: some "fats" have a solid risk profile (industrial trans fats), while other traditional fat-rich foods are not automatically harmful, and their effect depends on the dietary context and quality. The most reliable food choices for public health are based on overall dietary patterns, reduction of ultra-processed foods, and attention to the type of nutritional substitutions. In the absence of specific clinical conditions, moderation and preference for unprocessed foods remain sensible recommendations.

EDITORIAL NOTE

Article updated for informational purposes according to criteria of rigor and clarity. It does not replace individual medical advice.

SCIENTIFIC RESEARCH

1. Prevención con Dieta Mediterránea (PREDIMED) trial. https://doi.org/10.1056/NEJMoa1200303. [Randomized study on Mediterranean diet and cardiovascular prevention]
2. Trans fatty acids and cardiovascular disease. NEJM review. https://doi.org/10.1056/NEJMra054035. [Review on harmful effects of trans fats]
3. Meta-analysis on saturated fats and cardiovascular disease. https://doi.org/10.3945/ajcn.2009.27725. [Prospective analysis on SFA and CVD risk]
4. Systematic review and meta-analysis of dietary fatty acids and coronary risk. https://doi.org/10.7326/M13-1788. [Review on fatty acids and coronary risk]
5. Cochrane review: Reduced or modified dietary fat for preventing cardiovascular disease. https://doi.org/10.1002/14651858.CD011737.pub3. [Systematic review on fat reduction/modification]
6. Effects on Coronary Heart Disease of Increasing Polyunsaturated Fat in Place of Saturated Fat: systematic review and meta-analysis of RCTs. https://doi.org/10.1371/journal.pmed.1000252. [RCTs and SFA→PUFA replacement]
7. Higher intake of dietary cholesterol or eggs and risk of cardiovascular disease and mortality (pooled analysis). https://doi.org/10.1136/bmj.l1214. [Analysis on dietary cholesterol and eggs]
8. Ultra-processed food intake and risk of cardiovascular disease: NutriNet-Santé cohort. https://doi.org/10.1136/bmj.l1451. [Association between ultra-processed foods and CVD]
9. Effect of Low-Fat vs Low-Carbohydrate Diet on 12-Month Weight Loss (DIETFITS randomized clinical trial). https://doi.org/10.1001/jama.2018.0245. [Practical comparison of dietary patterns for weight loss]