So, Are Dietary Saturated Fats Good, Bad, or Neutral?

Healthy Aging

The Science Behind Those Saturated Fat Headlines

While saturated fats have been gaining a lot of attention in the news these days, the science around them hasn’t actually changed that much over the past decade. So, when asked the question, “Are dietary saturated fats good, bad, or neutral?”, the answer remains, “Yes.” Without hype or fanfare, let’s review the latest science supporting how saturated fats – based on the food source and the type of saturated fat – can influence our health in different ways. Let’s dive in.

Not all saturated fats are created equally.

First, it’s good to know that there are two distinct types of saturated fats: even-chain and odd-chain saturated fatty acids. As their names suggest:

Even-chain saturated fats have an even number of carbons – including C16:0.

• As reviewed by Korbecki et al., C16:0 and its metabolites activate pro-inflammatory pathways, including NF-kB, TNFɑ, and IL-6.
• Sergi et al. show how C16:0 also induces mitochondrial dysfunction.
• C16:0 is routinely used in preclinical models to induce inflammation, insulin resistance, and fatty liver disease, as demonstrated by Saraswathi et al.
• In prospective cohort studies following large populations over many years, such as with Forouhi et al. and Li et al., higher levels of even-chain saturated fatty acids, including C16:0, have repeatedly been associated with a higher risk of developing type 2 diabetes and cardiovascular disease.

Odd-chain saturated fats have an odd number of carbons – including C15:0.

• C15:0 directly inhibits pro-inflammatory pathways, including JAK-STAT and NF-kB, as shown by To et al. and Aabis et al.
• Venn-Watson et al. and Duan et al. showed that C15:0 supports mitochondrial function.
• C15:0 has also been shown in preclinical models to protect healthy immune responses as well as metabolic, liver, gut, and cardiovascular health (Venn-Watson et al., Aabis et al., Singh et al.).
• In the same prospective cohort studies that showed links between C16:0 and poorer metabolic and heart health, higher levels of C15:0 were associated with better long-term metabolic and cardiovascular health (Forouhi et al. and Li et al.).
• Further, randomized clinical trials have shown that people who supplemented with pure C15:0 and had raised C15:0 levels were associated with protected liver, red blood cell, cardiovascular biomarker, and gut microbiome health.

Different saturated fatty acids are present at different amounts within food.

Importantly, even-chain saturated fats are present at much higher levels than odd-chain fats in high-fat foods. For example, Williams showed that red meat has 200 to 800 mg of C16:0 per 100 g of meat compared to 6 to 10 mg of C15:0 per 100 g of meat.

The opposing effects of even vs. odd-chain saturated fatty acids were used by Teng et al. to explain why studies sometimes show that foods with saturated fats are bad, while others show they are good. And why the net effects are sometimes neutral – the bad fats may be canceling out the good ones.

In Bishop et al.’s paper, they cover how C15:0 has both insulin-sensitizing and immune calming effects in preclinical models, while C17:0 had just immune calming effects. In contrast, models fed dairy fat had increased inflammation and impaired liver function. Further, they showed that C16:0 was proinflammatory and impaired glucose response. In this study, they concluded that dairy fat had a net negative effect because of the relatively higher amounts of C16:0.

In the recent Argavani et al. cross-over clinical trial, they showed that people who ate more daily servings of dairy fat had higher C15:0, which was associated with improved vascular function… but also had higher C16:0, which was associated with higher blood pressure. Their conclusion? Different saturated fatty acids in dairy fat have different effects.

This is why it’s important to see if studies not only look at overall dietary saturated fats, but potential different effects of different saturated fatty acids (like, C15:0 vs. C16:0).

The types of high-fat foods also matter.

Interestingly, Jenkins et al. showed that rodents fed overall high-fat diets have lower C15:0 levels. One hypothesis is that C15:0, present in foods at low levels, is unable to compete for absorption compared to other fats, which are present at much higher levels.

In contrast, as demonstrated by Arghavani et al., C15:0 levels are reliably increased based on how much dairy fat we eat.  And different sources of dairy fat can have different C15:0 levels. For example, Van Gastelen et al. showed that dairy fat from grass-fed cows had 26% more C15:0 compared to dairy fat from corn-fed animals. Further, cheese (including cheese from grass-fed sheep, like pecorino, as described by Serrapica et al.) can have some of the highest levels of C15:0.

Yuan et al. and Jeong et al. showed in their prospective cohort studies that higher amounts of dietary cheese (more than other dairy products) were associated with higher C15:0 during pregnancy and better cognitive development in children as well as better long-term cognitive health in adults, respectively.

So, when you see studies looking at the effects of dietary saturated fats on health, check to see if they differentiate between different dietary sources of those fats. 

These are just a few reasons, among many others, why the science on saturated fats are so mixed.