Healthy fats on a keto or low-carb diet

Fat is one of the three macronutrients (“macros”) found in food. On a keto or low-carb diet, fat is your primary energy source, so choosing healthy types and eating the right amount is important. Here’s a guide to everything you need to know about fat on a carb-restricted diet.

Woman thinking of butter

What is fat, and what roles does it play in the body?

Dietary fat is found in both animals and plants. Although its main function is to provide your body with energy, it plays a number of other important roles, including:

  • Helping you absorb the fat-soluble vitamins A, D, E, and K
  • Regulating inflammation and immunity
  • Maintaining the health of your cells, including skin and hair cells
  • Adding richness to food, helping you feel full and satisfied

 

The fat in food is in triglyceride form. Each triglyceride contains a glycerol molecule attached to 3 fatty acid chains that are made up of carbon and hydrogen atoms.

Fat_triglyceride_shorthand_formula

Example of an unsaturated fat triglyceride. Left part: glycerol; right part, from top to bottom: palmitic acid, oleic acid, alpha-linolenic acid.

The fatty acids are classified by the number of bonds they contain between the carbons in their chains, as well as the length of their chains.

Saturated vs. unsaturated fatty acids

  • Saturated fats don’t have any double bonds between the carbons in their chains. They are “saturated” with hydrogen and remain solid at room temperature. Healthy sources of saturated fats include butter, cream and ghee. You can read more about what fats to eat .
  • Saturated fat

    Saturated fatty acid myristic acid

  • Monounsaturated fats have one double bond between carbons in their chains. Healthy sources of monounsaturated fats include olive oil, avocados and nuts. You can read more about what fats to eat .
  • Oleic-acid-skeletal

    Monounsaturated fat oleic acid

  • Polyunsaturated fats have more than one double bond between carbons in their chains. Healthy sources of polyunsaturated fats include fatty fish, grass-fed meat and pastured eggs. You can read more about what fats to eat .
  • Linoleic_acid

    Polyunsaturated fat linoleic acid

There are two families of polyunsaturated fatty acids (PUFA’s): omega-3 and omega-6 fatty acids. These are named for the position of the first double bond in their carbon chains.

Fatty acid chain length

  • Short-chain fatty acids have 5 or fewer carbons. Short-chain fatty acids are present in small amounts in butter and cream.
  • Medium-chain fatty acids (also known as medium-chain triglycerides or MCTs) have 6-12 carbons. Examples of foods that contain medium-chain fatty acids include coconut oil, MCT oil and butter.
  • Long-chain fatty acids have 13 or more carbons. Most of the fats in food are made up of long-chain fatty acids. Examples of foods that contain long-chain fatty acids include meat, poultry, fish, dairy, nuts, seeds, avocado and olives.

How are fats absorbed in the body?

Once fatty foods have been digested, their triglycerides are broken down into individual fatty acids and glycerol.

Both saturated and unsaturated long-chain fatty acids are absorbed into the bloodstream, packaged with cholesterol and proteins, and transported throughout your system to be used or stored as body fat.

Short-chain and medium-chain fatty acids are absorbed differently. Instead of being transported throughout your bloodstream, they are taken up directly to the liver, where they can be converted to ketones and used as a quick energy source. Additionally, they are less likely to be stored as fat compared with long-chain fatty acids.1


What is cholesterol?

Cholesterol is a waxy substance that is found only in animal foods. Unlike fatty acids, it doesn’t provide energy. However, your body needs it in order to produce steroid hormones, vitamin D, and bile acids that help digest fat. All of your cells make cholesterol; in fact, most of the cholesterol in your blood comes from your body rather than the food you eat. Dietary cholesterol does not raise blood cholesterol levels much, if at all, nor does it increase heart disease risk.2


What types of fat should I eat?

We recommend eating fats that occur naturally in food and have been minimally processed.

Although for several decades the American Heart Association and other health organizations have advised people to reduce their saturated fat intake, studies have consistently failed to show a link between saturated fat and heart disease.3 Because of this, the role of natural saturated fats in a healthy diet is now being reconsidered. All in all, saturated fats appear to be neutral in their health effects.

Saturated fat is found in a number of healthy foods that can – and should – be enjoyed on a balanced keto or low-carb diet.

Additionally, no food contains 100% saturated, monounsaturated, or polyunsaturated fat. For example, fatty meats contain roughly equal amounts of monounsaturated and saturated fat and a small amount of polyunsaturated fat.

However, in some foods, one type of fat is usually predominant. Therefore, we consider butter a good source of saturated fat and olive oil a good source of monounsaturated fat.

Below are several healthy sources of each type of fat.

Saturated fat sources

Saturated fats

  • Butter and ghee (clarified butter)
  • Cream
  • Coconut oil4
  • Cheese
  • Lard and tallow

Monosaturated fat sources

Monounsaturated fats

  • Olives and olive oil
  • Avocados and avocado oil
  • Macadamias and macadamia oil
  • Almonds, Brazil nuts, hazelnuts, pecans
  • Lard and tallow

Polyunsaturated fat sources

Polyunsaturated fats

Omega-3
  • Fatty fish (salmon, mackerel, herring, sardines, anchovies)
  • Grass-fed animals
  • Dairy from grass-fed animals
  • Eggs from pastured chickens
  • Algae
  • Chia seeds
  • Flaxseeds
  • Hemp seeds
  • Walnuts
Omega-6
  • Found in almost every food, including meat, nuts and seeds.
  • Vegetable and seed oils (especially safflower oil, sunflower oil, soybean oil, cotton seed oil and corn oil) – as well as processed foods that contain them – are loaded with omega-6 fatty acids. In fact, these are typically the major source of omega-6 PUFAs in modern Western diets. We recommend avoiding these vegetable and seed oils.5

Aim for a healthy omega-6:omega-3 PUFA ratio

The omega-6 PUFA linoleic acid and the omega-3 PUFA alpha-linolenic acid are considered essential fatty acids because your body can’t make them on its own, so they must be consumed in food. Alpha-linolenic acid is found mainly in seeds.

However, the most important omega-3 fats are EPA and DHA, that are found in fatty fish and grass-fed meat. These long-chain fats have evidence-based health benefits, including a reduction in heart disease risk factors.6 Although alpha-linolenic acid can be converted to EPA and DHA in your body, the conversion isn’t very efficient.

Achieving a balance of omega-3 and omega-6 fatty acids is also important. Omega-3 fats may help to decrease inflammation, whereas high intake of omega-6 fats may increase it, especially if your omega-3 intake is low.

It’s believed that our evolutionary diet contained roughly equal amounts of omega-3 and omega-6 fats. However, due to heavy reliance on processed foods, most Western diets today contain more than 15 times as much omega-6 as omega-3. Some researchers suggest this may be a major contributor to heart disease, diabetes, and other chronic disease.7

Having fatty fish at least twice a week, choosing meat and dairy products from grass-fed animals, and eating whole foods can help your omega-6:omega-3 ratio.

The healthiest fats to cook with

Saturated fats such as butter, ghee, coconut oil and lard are the best options for frying and deep frying since they are resistant to heat and don’t oxidize when reaching high temperatures, as more unstable fats such as vegetable and seed oils do.

Monounsaturated fats like olive oil and avocado oil are not as heat-resistant so they are better used cold as a dressing or in a oil based condiment such as mayonnaise or pesto.

Poly-unsaturated fats – like safflower or corn oil – should never be used at high temperatures because of their sensitivity to oxidation, that can transform them into potentially unhealthy substances.

More

For more about good and bad fats & sauces on a low-carb diet, have a look at our full visual guide:



What types of fat should I avoid?

We recommend avoiding processed vegetable and seed oils, such as safflower, sunflower, canola, corn and soybean oils. Especially for cooking which makes them even more harmful for the body. In addition, ideally stay away from mayonnaise, margarines and spreads that contain these oils.

Unlike fats found naturally in foods, vegetable and seed oils are highly refined products that don’t provide any nutritional value. They’re extremely high in polyunsaturated omega-6 fats, which most of us already get more of than we need.

Additionally, these fats are prone to rancidity when exposed to light or air, and they may become further damaged and create toxic byproducts when heated.8


How much fat should I eat?

On a low-carb or keto diet, most people don’t need to count calories or fat grams. While keeping the carbs low, and the protein within a fairly wide moderate range, most people can eat as much fat as they require to feel satisfied after a meal. This often allows the body weight to stay in or approach the normal range.

If you still need to or want to calculate grams, follow these general guidelines: The amount of food you should eat on a keto or low-carb diet depends on a number of things, including your protein and carb intake, your current weight, and your weight goals. Are you trying to lose weight, maintain, or gain weight?

Figure out your protein and carb needs first, and then fill in your remaining energy needs with fat.

Overall, keto diets are proportionally higher in fat than low-carb diets. A keto diet typically provides about 70-80% of calories as fat, compared to about 50-65% for a more liberal low-carb diet.

You may have heard that on a keto diet, the more fat you eat, the more fat you will lose. This is simply not true. If you eat more fat that you need to stay satisfied, you will slow down or stop weight loss, even if you eat very few carbs.

This also applies to the medium-chain fats found in coconut oil and MCT oil, which are normally burned rather than stored. Your body won’t burn its own fat if it has excess dietary fat coming in, regardless of the type.

Importantly, although adding less fat at meals can help you burn more of your own body fat, don’t make the mistake of trying to follow a diet that is low in both carbs and fat, despite being hungry. Starving yourself isn’t healthy or sustainable. Eat enough fat to feel full and satisfied after a meal, yet not stuffed.

Once you’re at your goal weight, adding a bit more fat at meals while continuing to eat the same amount of carbs and protein may help you maintain your weight long term. This usually happens automatically, if you follow your hunger signals.

/ Franziska Spritzler, RD

 

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