Is saturated fat bad?

With the popularity of the carnivore and ketogenic diet over the past several years, guidelines recommending limiting saturated fat has come under fire. Proponents of these diets will argue that the link between saturated fat and heart disease is weak, and that saturated fat is not harmful. Let’s explore how saturated fat increases risk, why the recommendations are to limit to it, and how to eat to get there

What are saturated fats?

As we’ve talked about before, fats are composed of a chain of carbon atoms bonded to hydrogen atoms. Saturated fatty acids are fully hydrogenated and do not contain a double bond. That is, they are completely “saturated” with hydrogen atoms around their carbon chain. This chemical structure allows them to be packed tightly, which results in a completely solid substance at room temperature.

Saturated fats mostly come from animal products (such as butter, dairy, and meats), but are also found in high amounts in palm oil and coconut oil.

Saturated fatty acids differ on the basis of their carbon chain length, and can be categorized as short chain (4-6 carbons), medium chain (8-12 carbons), long chain (14-20 carbons), and very long chain (22+ carbons). 

Different subtypes can have a different impact on the body (and risk of cardiovascular disease) when consumed.

While the vast majority of our circulating saturated fatty acids are influenced by dietary intake, palmitic acid can be synthesized by the body if carbohydrates are overconsumed (a process called de novo lipogenesis). 

Do saturated fats increase cholesterol and risk of heart disease?

In short - yes, a diet high in saturated fat has been linked to increased risk of heart disease. 

While there is some evidence that saturated fat consumption may impact inflammation, coagulation, and other heart disease risk factors, the biggest impact saturated fat has on our bodies is that it unequivocally increases LDL (bad) cholesterol (and apoB - our most accurate marker of cholesterol particles in the body). As we’re discussed before, elevated levels of apoB (cholesterol containing particles) are the causative agent in the development of heart disease. 

We know this from loads of metabolic ward studies - ie studies in which healthy people volunteer to be admitted to the hospital and have all their food provided to them. Researchers then analyze their blood to determine what happens. A meta-analysis of 84 of these studies demonstrates that for every 1% of total daily energy from saturated fats gets replaced by other macros, you see a reduction in LDL-c by 1.3 mg/dL (carbs), 1.6 mg/dL (MUFAs), and 2.1 mg/dL (PUFAs). Similar reductions in apoB are seen.

What’s the mechanism? LDL cholesterol particles are removed from the body by the liver via the LDL receptor on its surface. Saturated fat is thought to decrease LDL receptor activity, which decreases excretion of LDL particles. As a result, there is an increase in circulating LDL in the body and an increased risk of heart disease. Different subtypes of saturated fat appear to have different strengths in regards to their ability to increase LDL and apoB with lauric, myristic, and palmitic having the largest effect and stearic acid (dark chocolate!) having little to no effect.

How much saturated fat should you consume?

This is where it can get confusing - but once you understand, it becomes super clear. Stick with me!

The effect of saturated fat intake on cardiovascular disease is not linear, it is sigmoidal. A sigmoidal relationship means that at a certain intake of saturated fats, the risk of heart disease shoots up and stays up even if saturated fat intake continues to increase. It also means that at any intake of saturated fats below this level, the risk is relatively unchanged. This implies the existence of a threshold level that must be reached before heart disease risk increases. A large meta-analysis of 15 randomized, controlled trials examining the association between saturated fat and heart disease found this threshold to be 8-10% of calories coming from poor sources of saturated fat. 

The Dietary Guidelines for Americans recommend keeping saturated fat < 10% of total calories. The American Heart Association recommends a lower target of 5-6% for those with heart disease or high cholesterol.

To give you a sense of what this means, let’s take the higher target of 10% and an “average” 2000 calorie diet. This means about 200 calories to come from saturated fat. Since there are 9 calories in 1 gram of fat, for someone consuming a 2000 calorie diet, the absolute max recommended intake of saturated fat is ~22 grams. For the average American, 22 grams could easily be achieved with a glass of milk, a serving of beef or pork, and a baked potato with butter in just one meal! Even the leanest of red meat will still contain at least 4.5 grams of saturated fat per serving, and if you add butter, you’re adding 7 grams of saturated fat per tablespoon. This can add up fast if you’re regularly consuming animal products. 

Is all saturated fat bad?

Here’s where it gets more complex. 

Not all foods with saturated fat are inherently bad for you, and it depends on the overall diet the person follows. The food matrix (ie how the saturated fat is packaged) can also potentially effect the impact on LDL cholesterol and heart disease risk.

For example, fish and olive oil contain a good amount of saturated fat, but they also contain a lot of other nutrients with a hypocholesterolemic effect, yielding an overall net negative or neutral effect on cholesterol, and correspondingly, heart disease. Dark chocolate is also famous for being the “healthy chocolate.” This is because it contains the saturated fat subtype, stearic acid, which as mentioned above, has little to no effect on cholesterol. Research has found that intake of cheese reduced LDL-c compared to butter, despite similar saturated fatty acids contents (however, cheese still increased LDL-c compared to tofu and reduced-fat cheeses!). It’s important to look at the overall nutritional value of a food before throwing it out because it contains saturated fat.

So, are there things you should avoid or limit? Yes! The big offenders, or poor sources of saturated fat, are butter, red meat, coconut oil, whole milk, palm oil, and (probably) too much cheese.

What should you eat instead of saturated fat?

This is key

Refined carbohydrates, like white rice, pasta, cookies, cakes, and bagels, are equally as bad for you. Trials that replaced saturated fat with these items showed no change in incidence of heart disease.

Trans fats, found in fast food and fried food, increases the incidence of heart disease when swapped in for saturated fat. 

On the other hand, replacement foods that decrease risk of heart disease are those that contain “healthy” fats - polyunsaturated and monounsaturated fats. In other words, if you swap out high saturated fat food with monounsaturated or polyunsaturated fat, the available evidence suggests that the risk of heart disease decreases. Research suggests that substituting 5% of saturated fat intake with polyunsaturated fat would be expected to lower LDL by 10.6 mg/dL, which could reduce disease risk by as much as 18% if maintained for an extended period. Polyunsaturated fat may be superior to monounsaturated fat with regard to heart health risk reduction, and it has been linked to greater decreases in atherosclerotic cardiovascular disease events like stroke and heart attack. 

Now, where to find them! Good sources of monounsaturated fat include olive, canola and peanut oils, as well as avocados, peanut butter and nuts. Polyunsaturated fats are found in sunflower and soybean oils, walnuts, flaxseeds, pumpkin seeds, and fatty fish like salmon and herring.

My final thoughts on saturated fat

The totality of evidence supports the conclusion that foods high in saturated fat, particularly butter, coconut oil, and red meats, increase LDL cholesterol (and apoB), which in turn raises risk for heart disease. However, just as with all things nutrition, it’s important to take the entire dietary pattern into account. When possible, swapping foods high in polyunsaturated fats or monounsaturated fats with foods high in saturated fat is probably a good idea. While it’s not always necessary to count grams of saturated fat, some of my patients find it useful to track for a week or so until they get a sense of how much saturated fat is in their typical diet. Others simply focus on limiting or eliminating animal products and processed/packaged foods, while increasing consumption of veggies, whole grains, fruits, legumes, lean protein, nuts, and seeds. With the average American consuming about 11-12% of their total calories in saturated fat, it’s worth taking a peak at your saturated fat intake, particularly for those with high cholesterol, heart disease, a family history of heart disease, or diabetes. As always, the emphasis should be on achieving an overall dietary pattern that is cardioprotective, rather than any one specific nutrient.

Interested in discussing with Dr Harkin an optimal dietary plan to prevent heart disease?