Kidney patients, please take note! “Healthy oil” is a hot topic in the news. Are you choosing the right cooking oil?

Author: Chen Zhou, Department of Nephrology, Shanghai Changhai Hospital

Reviewer: Mei Xiaobin, Chief Physician, Nephrology Department, Shanghai Changhai Hospital

Oil is an essential part of our daily diet. It not only provides fat and calories to meet our energy needs, but also increases the aroma and taste of food, making us happier when eating. However, did you know that different oils have different characteristics and functions, and have different effects on our bodies, especially for patients with renal insufficiency, they need to pay more attention to choosing the right oil.

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So, how should kidney patients choose cooking oil? Let’s first understand how much oil we should consume every day and what is the difference between animal oil and vegetable oil.

How much oil should we consume every day?

The 2022 edition of the Dietary Guidelines for Chinese Residents recommends "less salt and less oil", with adults consuming no more than 5 grams of salt per day. So, how much oil should we consume every day?

The Chinese Nutrition Society recommends consuming 25 to 30 grams of cooking oil per day, which is equivalent to about two and a half to three spoonfuls of an ordinary white porcelain spoon. You can also use a scaled oil pot to control the amount of oil used for cooking. This amount is suitable for most people, including kidney patients. However, if you are overweight, obese, or have abnormal blood lipids, it is recommended to reduce it to about 20 grams per day.

1. Why should we use less oil?

Because too much oil will increase our calorie intake, leading to weight gain and obesity; at the same time, too much oil will also increase our blood lipid levels, which may lead to arteriosclerosis and cardiovascular disease. For us kidney patients, weight control and blood lipid control are very important measures to protect the kidneys.

2. How can we use less oil?

Here are a few tips for you:

(1) Choose low-fat or fat-free foods, such as milk, yogurt, soy milk, etc.

(2) Choose light or low-fat cooking methods, such as boiling, steaming, and making soup.

(3) Choose foods that are high in fiber or rich in water, such as fruits, vegetables, and whole grains.

(4) Choose a variety of vegetable oils to use together, such as olive oil, rapeseed oil, peanut oil, etc.

(5) Choose an appropriate amount of nuts or seeds, such as walnuts, peanuts, flax seeds, etc.

Following these tips can help us better control fat intake and protect kidney health.

Is animal oil better or vegetable oil better?

When choosing cooking oil, we need to distinguish between animal oil and vegetable oil. Animal oil refers to oil made from animal fat or butter, such as lard, butter, mutton fat, chicken fat, butter, etc. Vegetable oil is extracted from plant seeds or fruits, such as olive oil, rapeseed oil, peanut oil, corn oil, linseed oil, etc.

From a nutritional point of view, the main difference between animal oil and vegetable oil lies in the types and proportions of fatty acids they contain. Fatty acids are the basic units that make up fat. According to their chemical structures, they can be divided into saturated fatty acids and unsaturated fatty acids. Saturated fatty acids refer to fatty acids without double bonds, which are usually solid at room temperature, such as lard and butter. Unsaturated fatty acids have one or more double bonds and are usually liquid at room temperature, such as olive oil and rapeseed oil.

So, what effects do saturated fatty acids and unsaturated fatty acids have on our bodies? Generally speaking, saturated fatty acids are considered "bad fats" because they increase low-density lipoprotein (LDL) cholesterol in the blood, commonly known as "bad cholesterol", thereby increasing the risk of arteriosclerosis and cardiovascular disease. On the contrary, unsaturated fatty acids are considered "good fats" because they increase high-density lipoprotein (HDL) cholesterol in the blood, commonly known as "good cholesterol", thereby reducing the risk of arteriosclerosis and cardiovascular disease.

However, not all unsaturated fatty acids are the same. Based on the location and number of double bonds, unsaturated fatty acids can be divided into monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA). MUFA refers to unsaturated fatty acids with only one double bond. They can lower total cholesterol and LDL cholesterol while maintaining or increasing HDL cholesterol, which is beneficial to cardiovascular health. Oils rich in MUFA include olive oil, rapeseed oil, tea oil, etc.

PUFA refers to unsaturated fatty acids with 2 or more double bonds, which can be further divided into ω-3 fatty acids and ω-6 fatty acids. Both ω-3 fatty acids and ω-6 fatty acids are essential fatty acids for the human body, which means that the human body cannot synthesize them by itself and must be ingested from food. They play many important roles in the human body: ω-3 fatty acids can reduce triglycerides (TG) in the blood, reduce thrombosis, inhibit inflammatory response, protect the nervous system and vision, etc.; ω-6 fatty acids can regulate blood pressure, promote skin health, enhance immunity, etc.

Oils rich in omega-3 fatty acids include flaxseed oil, sesame oil, walnut oil, etc., while oils rich in omega-6 fatty acids include corn oil, peanut oil, soybean oil, etc.

So, which PUFA should we choose? The key lies in the ratio of ω-3 fatty acids to ω-6 fatty acids. Generally speaking, the human body needs a ratio of ω-3 fatty acids to ω-6 fatty acids between 1:1 and 1:4. Due to changes in the dietary structure of modern people, we tend to consume too much ω-6 fatty acids and lack ω-3 fatty acids. This will lead to an increase in inflammatory factors in the body and cause various chronic diseases. Therefore, we should appropriately increase the intake of ω-3 fatty acids and reduce the intake of ω-6 fatty acids.

In summary, compared with animal oils, vegetable oils are healthier because they contain more unsaturated fatty acids, which can reduce the risk of cardiovascular disease. Among vegetable oils, we should choose oils rich in MUFA or omega-3 fatty acids, such as olive oil, rapeseed oil, flaxseed oil, etc.

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What are the characteristics of various vegetable oils?

In addition to understanding the difference between animal oil and vegetable oil, we also need to understand the characteristics and uses of various vegetable oils. Because different vegetable oils have different nutrients, tastes, colors, stability, smoke points and other characteristics, these characteristics will affect the effectiveness and safety of using them in cooking. Next, let's take a look at the characteristics of several common vegetable oils.

1. Olive oil: Olive oil comes from olives and is rich in MUFA, which helps reduce the risk of heart disease. One tablespoon of olive oil usually contains less than 1 mg of sodium, less than 1 mg of potassium and no phosphorus, which is suitable for us kidney patients. However, olive oil is not resistant to high temperatures (smoke point 190°C) and is not suitable for frying. It is often used as a vegetable salad dressing to add flavor to cold dishes. Olive oil has a light fruity aroma that can enhance the overall flavor of food.

2. Rapeseed oil: Rapeseed oil is made from rapeseed and is rich in omega-3 fatty acids and omega-6 fatty acids, which are good for the brain and heart. In addition, it does not contain phosphorus and potassium, and has a low saturated fat content, making it more suitable for kidney patients. Rapeseed oil has a high smoke point of about 205°C, making it suitable for cooking and baking. The downside is that it doesn't taste very friendly.

3. Peanut oil: Peanut oil is made from peanuts and is rich in omega-6 fatty acids. Peanut oil has a strong flavor and a very high smoke point (225°C), making it very suitable for frying and stir-frying.

4. Flaxseed oil: Flaxseed oil is made from flax seeds and is rich in ω-3 fatty acids and ω-6 fatty acids. However, flaxseed oil is not resistant to high temperatures (smoke point 107°C), so it is generally not used for cooking. It is mostly used to make vegetable salads or add a little flavor to steamed vegetables. Note that flaxseed oil can easily go bad and should be stored in the refrigerator.

5. Corn oil: Corn oil comes from corn germ, is cheap, has a high smoke point (232°C), and is suitable for frying. Many fast food chains use corn oil to fry French fries. Corn oil contains a lot of saturated fat and ω-6 fatty acids, which contain both "good fatty acids" and "bad fatty acids."

6. Coconut oil: Coconut oil comes from mature coconut kernels or coconut meat. It contains a lot of saturated fat (90%), which increases the risk of heart disease and is not recommended for consumption. Coconut oil is often used to make desserts or spices.

7. Cottonseed oil: Cottonseed oil is made from cotton seeds and contains a lot of saturated fat, which increases the risk of heart disease and is not recommended for consumption. Cottonseed oil is often used to make salad dressings and mayonnaise. When buying food, you should carefully check the nutrition facts and raw material ingredients to avoid consuming this oil.

Choosing cooking oil is a problem we face every day, but not everyone can do it well. For kidney patients, choosing cooking oil is a science. You need to choose the right cooking oil according to your specific situation and reasonably control the intake of oil to protect the health of the kidneys and cardiovascular system.