Saturated Fats: Dietary Angels or Demons?

In order to reduce cardiovascular events, dietary guidelines recommend restricting saturated fatty acids—without taking into account differences among them—to <10% of the daily caloric intake.

grasas saturadas

It should be noted that there are many different saturated fatty acids, each with its own biological effect. Moreover, said biological effect could be modified by the food matrix and the carbohydrate content. Saturated fatty acids such as dairy, dark chocolate, and unprocessed meat are not associated with increased risk of cardiovascular disease or diabetes.

There is no robust evidence that supports this arbitrary 10% limit to help reduce events or mortality. Furthermore, available evidence even shows a slight benefit.

Saturated fatty acids are a heterogeneous group of fats characterized by their simple link between carbon atoms which can be classified by chain length.

Short-chain saturated fatty acids are present mostly in dairy, while medium- and long-chain can be found in red meat, dairy, and plant oils.

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It should be noted that most sources of saturated fatty acids contain them in different proportions and in combination with other nutrients that may significantly influence their biological and physiological impact.

When talking about food, it is useful to distinguish between fats and fatty acids. Saturated fats can be defined as foods that are primarily solid lipids at room temperature. Examples include butter, fats contained in hard cheese, animal fats—like tallow and lard—, and plant oils—such as cocoa butter, coconut oil, and palm oil.

Recent studies have shown that replacing the caloric intake of fats with carbohydrates did not reduce cardiovascular risk and, in fact, it may increase global mortality.

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Systematic reviews have indicated that there is no significant association between cardiac events and mortality, and some even showed a reduction in stroke.

A large and diverse study, PURE (Prospective Urban Rural Epidemiological), was recently published. It tries to determine whether fatty acids are angels or demons.

With over 135,000 patients from 18 countries on 5 continents (80% of patients were from developing countries), the study showed that increasing the consumption of all fats saturated, monounsaturated, and polyunsaturated—reduced the mortality risk and had a neutral effect on cardiovascular events.

On the other hand, a diet high in carbohydrates was associated with higher mortality rates, but not more cardiovascular events.

The diet with the lowest mortality risk was high in fibers (10 to 30 g/day), proteins (14% to 30% of all caloric intake), and monounsaturated fats (10% to 25% of all caloric intake). This diet also included a moderate intake of polyunsaturated fats (5% to <7%) and starch (20% to 30%).

Diets high in starch and sugars were linked to the highest risk of death and cardiovascular events.

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It now seems that trying to reduce carbohydrates (specially refined ones, like sugars) is more effective than reducing fat intake.

Two observations test the hypothesis that restricting fats will reduce low-density lipoprotein (LDL) and, in turn, events.

Large LDL particles, compared with smaller ones, are more cholesterol-enriched and less strongly associated with events. Smaller LDL particles have a stronger link to cardiovascular events and are unaffected by diet.

A Mediterranean diet lowers cardiovascular risk without a major impact on LDL level. Furthermore, despite an LDL increase, the sodium-glucose cotransporter 2 inhibitor reduces events.

Despite many decades of nutrition research, the scientific community has not yet reached a consensus on “the one diet” (for example, the Mediterranean diet) that achieves optimal metabolic health for all. The highly heterogeneous outcomes of dietary intervention studies suggest that some individuals have better outcomes from specific diets than others.

The overall effect of fats and oils does not only depend on saturated and unsaturated fatty acids contents. Unhealthy compounds introduced by processing also play a major role.

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The concept of manufacture process contaminants generated through the high-temperature treatment of oils in the presence of trace metals has become one of the main unhealthy suspects. The metabolic effect of “virgin” oils is completely different from that of those which underwent several manufacture processes.

  • Yogurts and cheese: Dairy consumption is the main source of saturated fatty acids in most diets. Current guidelines recommend low fat or fat-free dairy products to limit saturated fatty acids intake. However, there is plenty of evidence showing that cheese and yogurt lower cardiovascular risks.

Cheeses and yogurts consist of complex food matrixes and major components include saturated fatty acids, proteins (casein), sodium, phospholipids, probiotics, and bacteria, which in turn produce bioactive peptides, short-chain fatty acids and vitamins. Saturated fatty acids cannot explain the cardiovascular effect of diary because of said complex component matrix.

  • Dark chocolate: Pure chocolate has saturated fatty acids and other nutrients that may be more important than fats. These additional components in chocolate may have antioxidative, antihypertensive, anti-inflammatory, antiatherogenic, and antithrombotic properties. These effects reduce cardiovascular events and the incidence of type 2 diabetes.
  • Meat: Processed meat consumption is associated with an increase in cardiovascular risk; however, non-processed meats have no effect on risk. As such, saturated fatty acids from meat are unlikely sources of said risk.

Multiple randomized cohort trials suggest that there is low to very low certainty that restricting red meat consumption may have a significant effect on cardiovascular events. Only one analysis found a small but significant association of processed meat, unprocessed red meat, and poultry consumption with cardiovascular events.

However, the concept of food matrix should be brought up again. Red meat is more than saturated fatty acids: it is the main source of protein, bioavailable iron, minerals, and vitamins. 

Recommendations included in current guidelines are based on studies carried out 20 to 30 years ago and deviate from current evidence.

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Original Title: Saturated Fats and Health: A Reassessment and Proposal for Food-Based Recommendations.

Reference: Arne Astrup et al. J Am Coll Cardiol. 2020 Aug 18;76(7):844-857. doi: 10.1016/j.jacc.2020.05.077.

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