Does being overweight mean being fat?

Popular saying: The main way to measure a person’s fatness or thinness is to look at his weight, and those who are heavy are fat.

Fake rumors

Verification points:

People with heavy weight are not necessarily fat. The main way to judge whether a person is fat or thin is to look at the fat content.

In this era where almost everyone is shouting "I want to lose weight", do you know what is considered fat? If you are overweight, are you fat? If you are of normal weight, are you not fat? From a health perspective, in what situations do you need to lose weight? Today, let's answer these questions.

The mainstream method has drawbacks. The most familiar method for judging fatness and thinness is the BMI method. BMI is the abbreviation of Body Mass Index, which literally means height-weight index, and is defined as weight (kilograms) divided by height (meters) squared. For example, Passerby A: weighs 70kg and is 1.7m tall, then his BMI = 70/1.7/1.7 = 24.2. For the same person, if the height remains unchanged, the larger the BMI, the heavier he is, and the more likely he is to be obese. The BMI value can be used to divide fatness and thinness. Table 1 lists the standards applicable to Chinese and Europeans and Americans respectively [1, 2].

Table 1. BMI range classification

As can be seen from Table 1, for Chinese people, when BMI reaches 24, it is considered overweight; more importantly, when it reaches 28 or above, it is considered obese. Correspondingly, the BMI critical points for overweight and obesity in Europeans and Americans are 25 and 30 respectively. Anyone who is overweight or obese is considered fat, which is not good for health. Using BMI to distinguish between fat and thin has played a huge role in public health; however, there are many limitations in judging fat and thin by BMI. In practical applications, there are many "pitfalls" that can cause a lot of jokes.

James is a fat man?

Image credit: Gary A. Vasquez, USA TODAY Sports

This year's NBA Finals Most Valuable Player LeBron James is 2.03 meters tall, weighs 113 kg, and has a BMI of 27.4, which is considered overweight. In other words, the BMI assessment system has determined that James is an overweight fat man. Look at the picture below, James in a swimsuit, can you associate him with the word "fat"?

James has a lot of muscle, but the BMI system misjudged him as an overweight person. In fact, the BMI system not only misjudged James' physical condition, but also misjudged many more people's physical condition.

The picture below is a half-naked muscle photo of American football star Gronkowski. He has a good figure! But if we judge fatness and thinness by BMI, he is worse than James, because his BMI has reached 30.6, which is already in the obese range. It is unfair to wear this fat hat!

The BMI method of judging fatness and thinness counts the two top athletes mentioned above as fat, who have well-developed muscles, little fat, and are not fat at all. What's wrong with that?

What is the problem with BMI? Does BMI only make mistakes in judging fatness and thinness in top athletes? How about ordinary people? BMI can also make mistakes in judging fatness and thinness in ordinary people. The problem is that BMI only recognizes weight and does not distinguish between fat and muscle. Although the BMI and weight are the same, if there is more fat, it will look fatter.

Fat content is the percentage of total body fat to body weight. For example, if a person weighs 70kg and has 14kg of fat in his body, his fat content is 20%.

Does being overweight mean being fat? In order to find out whether it is excessive weight or excess fat that is detrimental to health, doctors at Mount Sinai School of Medicine in New York, USA, conducted a study[3]. They found a group of men of similar age and height and divided them into three groups: one group with an overweight BMI and obesity (high fat content), one group with an overweight BMI but thinness (low fat content), and another group with a normal BMI and thinness (low fat content), as shown in Table 2.

Table 2. Basic data of subjects

Next, the doctors conducted physical examinations on all the subjects and assessed their risk of cardiovascular disease. The results are shown in Table 3. The health indicators of those with overweight but thin people and those with normal BMI and thin people are almost the same, and the risk of cardiovascular disease is relatively low. In other words, having more muscle than the average person does not pose a health hazard. As long as the fat content is kept low, an overweight BMI itself does not harm health. However, the physical examination results of subjects with overweight BMI and obesity (high fat content) are not so optimistic. Many health indicators are overweight or substandard, which increases the risk of cardiovascular disease. These results can be understood as follows: Cardiovascular disease is mainly related to fat content. It is not the excessive weight itself or the increased muscle that is harmful to health, but too much fat (excessive fat content).

Table 3. Physical examination results and cardiovascular disease risk assessment

BMI can be used to judge fatness or thinness, but it may be wrong for people who are overweight and have a lot of muscles. But what about people who are light in weight?

If you are light, does that mean you are not fat? If you are light and have a normal BMI, does that mean you are not fat? It is not certain, and the error rate may even scare you.

The researchers also gave all the subjects a physical examination and found that the risk of cardiovascular disease for people with a thin BMI but obese fat content was comparable to that of people with an obese BMI and obese fat content, and 2 to 4 times higher than that of people with a thin BMI and normal fat content. This is called BMI saying that you are thin, but it is not necessarily true! Because people with normal BMI may also have low muscle content, and the normal weight is filled by high fat content, which in turn endangers health. Being light and having a normal BMI does not mean being thin. You also need to pay attention to the fat content and be wary of becoming a "hidden fat person."

For the sake of health, let's lose fat! At this point, we know that from a health perspective, it is not BMI or weight that determines whether you are fat or thin, but fat content. When pursuing healthy weight loss efforts, the most important physiological indicator to pay attention to is fat content, not weight or BMI. Let's take a look at the golden standard for judging fatness and thinness.

Table 4. The golden standard for judging fatness and thinness - fat content scale

There are natural gender differences in the ratio of fat to muscle between men and women. Under the same fat-skin condition, the fat content of men is generally lower than that of women. The scale for judging fatness and thinness based on fat content is shown in Table 4. From a health perspective, for men, the fat content is best controlled within the range of 5%-20%; for women, it is best controlled within the range of 13%-25%.

Now you know who needs to lose weight, right? For the sake of health, men with a body fat content greater than 20% or women with a body fat content greater than 25% should lose weight. People who have higher requirements for their body shape can consider pursuing a lower body fat content, but it is recommended that the body fat content should not be less than 5% for men and 13% for women. Because too low a body fat content can easily cause endocrine disorders and malnutrition, which is not good for health.

How do you measure your body fat? This is a highly technical question, and I will write another article to explain it. Here is a small spoiler: swimming pool, bioimpedance, and vernier caliper.

How much weight should be lost? How much weight should be lost to be considered successful? It depends on the fat content. Remember the passerby mentioned above? Now I will give a quantitative calculation using the passerby as an example. You can follow the example and calculate your ideal weight.

Passerby A, weighs 70kg and has a fat content of 20%; the goal of losing weight is to reduce the fat content to 15%, and the existing muscles must be retained.

Then the ideal body weight = 70*(1-20%)/(1-15%)=65.9 kg, which means that Passerby A needs to lose 4.1 kg of fat.