While following the ketogenic diet, you will get 70 to 85% of your daily calories from fat. This means that you will be eating a lot of fat. All fat is not created equal — in fact, there are dozens of different fatty acids, all with distinct physiological effects — so it’s essential that you carefully assess the types you plan to include so as to create a diet that is tasty, highly conducive to ketosis, heart-healthy, and environmentally sustainable.
One of the most important types of fat to include in a ketogenic diet is medium-chain fatty acids. You can also get a large portion of your fat from monounsaturated long-chain fatty acids, found in foods like olive oil, nuts, and avocados.
Omega-3 fatty acids are essential for brain health and reducing inflammation and need to be included in small quantities. In general, you will need to avoid consuming excessive amounts of saturated and omega-6 fatty acids and avoid trans fatty acids completely. Below, we’ll explain more about each type of fat and what types of foods provide it.
Medium-Chain Triglycerides (MCTs)
An important type of fat to include in ketogenic diets is MCT. MCT stands for medium-chain triglyceride, a type of fat that has eight to twelve carbon atoms in its fatty acid tail. In contrast, long-chain fatty acids, which make up the vast majority of fat in our diet, have fourteen to twenty-two carbon atoms in the tail.
These types of fats are processed very differently by the body. Long-chain fatty acids are absorbed from the small intestine into the lymphatic system. Along with cholesterol, they get packaged into small spheres known as chylomicrons and circulate throughout the body.
As a result, there are many opportunities for these circulating long-chain fatty acids to be taken in by adipose cells and stored as fat tissue instead of being burned as fuel. Researchers have also found that chylomicrons may play a role in the development of atherosclerotic plaque. Medium-chain and short-chain fatty acids, however, go through a different pathway.
After being absorbed in the small intestine, they travel directly to the liver via the hepatic portal vein. They can be absorbed into mitochondria, the energy producing units of the cell, without the presence of carnitine, a signaling molecule required for the absorption of long-chain fatty acids. There, they are preferentially metabolized for energy, usually resulting in high levels of acetyl CoA and the formation of ketone bodies.
If you eat a particularly large amount of medium and short chain fatty acids in a meal, they will boost ketosis, even if the meal also contained a moderate amount of carbohydrate. In fact, without medium-chain fatty acids, it’s difficult to restrict carbohydrates enough to consistently remain in ketosis. Ensuring that you include medium-chain fatty acids in your diet is key if you are following the modified ketogenic diet. Coconut oil is the best whole food source of medium-chain fatty acids, containing about 63% (along with 30% long-chain saturated fatty acids and 7% unsaturated fatty acids). However, about three-quarters of these are the 12-carbon fatty acid lauric acid.
Lauric acid is categorized as a medium-chain fatty acid because it does not require carnitine to be shuttled into the mitochondria and burned as energy, as do long-chain fatty acids. Our bodies don’t process it like other mediumchain fatty acids, though, because only about 70% of lauric acid goes directly to the liver for fast energy release.
The rest is circulated through the body like longchain saturated fats. Thus, it’s not quite as conducive to ketosis as 6-, 8-, and 10carbon fatty acids are, but is nonetheless more ketogenic than other fats. Butter, ghee, and other high-fat dairy products also provide a small quantity of MCTs, about 6% of total fat.
This is usually not a major source of MCTs in the ketogenic diet, since these foods should be consumed in moderation due to their high long-chain saturated fatty acid content. The best supplemental source of highly ketogenic 8and 10-carbon mediumchain fatty acids is MCT oil, which is refined from regular coconut oil. With 8and 10-carbon medium-chain fatty acids contents between 80 and 100%, it is the best way to deliver a major ketogenic fat boost to your diet. See the section on Supplements to Support Ketogenesis for more information on MCT oil and where to buy it.
Long-chain Monounsaturated Fats
Long-chain monounsaturated fats are a heart-healthy energy source and for many people, a major component of the ketogenic diet. While they are not as ketogenic as medium-chain fatty acids, they are a good choice for supplying your additional energy needs. The best sources of monounsaturated fats are high-oleic sunflower, safflower, and canola oil; extra-virgin olive oil; almonds, hazelnuts, macadamia nuts and their oils; and avocados and their oil. Monounsaturated fats make up at least 64% of the fat in these foods, and saturated fats less than 15%.
Among these fat sources, olive and avocado are some of the best due to their very low omega-6 content (more on omega-3 and 6 fatty acids below). Try to consume most of your monounsaturated fats from olive and avocado, with moderate amounts of other nuts and oils.
Omega-3 and Omega-6 fatty acids
Polyunsaturated long-chain fatty acids do not make up a major source of energy in most diets, but certain types are essential in small quantities. You’ve probably heard about omega-3s, the class of fats found in fish, shellfish, and flaxseed, and in smaller amounts in nuts and beans. They are essential for many cellular functions, and they reduce inflammation and the risk for a range of chronic diseases.
Only one type of omega-3, alpha-linolenic acid (ALA), is technically essential because the other omega-3s can be synthesized from it. However, conversion rates are low so it’s good to get all three omega-3 fatty acids by eating fish in addition to the flax, hemp, nuts, and other plant foods in which ALA is found.
You only need about 0.5–1.0g of omega-3 fatty acids per day. Omega-6 fatty acids are another type of long-chain polyunsaturated fatty acid. As with omega-3s, just one type, linoleic acid, is essential in small quantities because the human body can use it to synthesize the other necessary omega-6 fatty acids.
These fats have important roles in metabolism, bone structure, and reproductive function. Linoleic acid is supplied by vegetable oils such as soy, corn, canola, safflower, sesame, and sunflower, as well as chicken, beef, pork, and eggs.
Some types of omega-6 fatty acids promote inflammation in the body, raising the risk of cancer, heart disease, and diabetes. Research suggests that linoleic and gamma-linolenic acid, found primarily in plant sources, are not as inflammatory, while arachidonic acid, found primarily in red meat, poultry, eggs, and milk, has a stronger inflammatory effect. The current recommendation is to consume about
2–4g of omega-6 fatty acids per day. Over the past few decades, omega-6 consumption has increased greatly in the Western diet, a fact which many scientists believe is partly to blame for higher rates of chronic disease.
The underlying issue may be less to do with omega-6 content itself than with the ratio of anti-inflammatory omega-3s to inflammatory omega-6s. The current western diet has an omega-3:omega-6 ratio of between 1:14 to 1:25, but diets with extremely strong scientific support, such as the Mediterranean diet, have a ratio of about 1:1, and many doctors recommend a ratio of no more than 1:4. Hunter-gatherer diets also likely ranged from 1:4 to 4:1. Luckily, it’s not too hard to restore a healthy omega-3:omega-6 ratio on the ketogenic diet.
Here are some simple tips to help achieve it:
- Eat 2–3 servings of fatty cold water fish each week, especially mackerel, salmon, cod, herring, whitefish, and sardines. Take fish oil supplements if you don’t eat much fish.
- Include 1–2 servings of ground flaxseeds or flax oil in smoothies.
- Leafy greens and cruciferous vegetables (spinach, kale, watercress, Brussels sprouts, etc.) contain small amounts of omega-3s — these are a key part of ketogenic diets anyway, so make sure you eat plenty!
- Limit how much you cook with sunflower, corn, cottonseed, peanut, and soy oils. While they are low in saturated fat, they are very high in omega-6s and very low in Omega-3s.
- If you eat meat and poultry, do not buy conventionally raised, which have lower 3:6 ratios. Look for grass-fed or pastured. Grass-fed lard and butter have good 3:6 ratios as well, but should be limited due to high saturated fat content.
- Use mostly olive oil and coconut oil for cooking, which are relatively low in omega-6 fatty acids.
Saturated fatty acids Not all saturated fatty acids are ‘bad.’ In fact, all of the medium-chain fatty acids in coconut and MCT oil are saturated, but they don’t have the same kind of negative health effects that other saturated fats do. When we’re talking about saturated fat, we’re really concerned about long-chain saturated fats from red meat and high-fat dairy.
These are the kinds of fat linked with heart disease, atherosclerosis, and high cholesterol. More research is needed on exactly how much saturated fat is safe to include in a ketogenic diet, but a safe target is no more than 20% of total caloric intake.
Aim to have at least half of this be medium-chain fatty acids, which are saturated but don’t carry the same heart disease risk. Just 1½ tablespoons of MCT oil provide 20g. This recommendation is based on weight-loss studies of the ketogenic diet, in which participants ate high-fat diets containing up to 20% of calories from saturated fat without adverse effects to HDL, LDL, or blood triglyceride levels.
This means that for a 1,800 calorie diet, no more than 40 grams of saturated fat should be consumed, with at least 20g as MCTs. If you have a family history of heart or artery disease, you should seek further advice from your doctor.
Meat and dairy fats can still be a part of the ketogenic diet, but should be eaten in smaller quantities than other fat sources. Chicken fat is one of the best choices, with 30% saturated fatty acids. Lard from duck, geese, beef, and pork is quite high in saturated fats, with 40–50% saturated fatty acids. These fats should be used in moderation. Butter and ghee are even higher in saturated fat, with about 60% of total fats being saturated. Similarly, the percentage of saturated fat in high-fat dairy products like cheese, sour cream, and heavy cream is very high.
These foods are rich and delicious additions to the ketogenic diet, but they should be consumed in moderation. Trans fatty acids The largest source of trans fatty acids in the American diet is hydrogenated and partially hydrogenated vegetable oils, found in many types of processed foods.
Very small amounts occur naturally in some meat and dairy products, but in most cases this is not a significant source. Hydrogenated oils are popular in the food industry because they can improve the texture of processed foods and increase shelf life. However, they are strongly linked with heart disease, higher LDL cholesterol, and weight gain. They should be totally avoided. This is usually not too
difficult since the ketogenic diet excludes most processed foods, but check the labels of products like margarine and shortening, which are likely to contain them.