Body Mass Index (BMI) is a number calculated from a person's height and weight. BMI does not measure body fat percentage, just how much one weighs vis-à-vis their height. It is considered that when reading our results, please remember: 'A score of 18-24 indicates you're at a healthy weight. A score between 25 and 29 means you are overweight while over 30 signifies obesity.
BMI is calculated as follows:
BMI (body fat) = weight (kg) / [height (m)]2
OR = [weight (kg) / height (cm) / height (cm)] x 10,000
In order to standardize the BMI calculation between countries, the World Health Organization has developed a table for each country with a standardized reference for each height and weight. For women, an increased risk of developing these diseases is associated with a BMI of over 35. In terms of life expectancy and other health issues, people who are considered to have a BMI of 30 or over are at an increased risk for developing chronic diseases such as diabetes, cancer, cardiovascular disease, and premature death.
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BMI does not take into account body composition indicators such as muscle mass or bone density. It also has been suggested that BMI may be more related to body fat percentage than it is to total body fat. Additionally, the BMI does not account for metabolic rate, so it can be misleading when used as a sole indicator of health status. It is therefore a very simplistic measurement that provides only a rough estimate of the amount of fat in the human body.
Also, while individuals with average BMIs generally have lower mortality and improved quality of life, some people are at low BMIs and still have exceptional health outcomes. In fact, in about ten percent of the population, an individual will be underweight (less than the fifth percentile) and still live a long and healthy life.
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Once again we see that correlation does not predict causation. This possibility can be seen in studies where an abnormally low BMI is combined with other measures to determine a "metabolic syndrome". Metabolic syndrome is a condition where an individual has obesity, hypertension, and diabetes. An abnormally low BMI is typically accompanied by high levels of fat-free mass. Individuals with this combination are at a lower risk for diabetes, heart disease, hypertension, and premature death.
Sure, BMI is a convenient and quick method for estimating someone's health status. However, its simplicity can lead to false categorization of people as overweight based on their actual body composition.
How can you tell if you have a normal metabolism?
If you maintain your weight with little effort and can eat what you want without gaining weight, then it's likely that your metabolism is healthy. However, if the thought of eating more makes your stomach feel queasy then it's probably not. In addition, if you are big in diameter but not necessarily around, your metabolism is likely fine. Finally, if you've gained weight after cutting back on calories then it's likely that your metabolism is weak.
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Aside from disagreements over what constitutes healthy metabolism, there are also questions about how accurately BMI measurements represent a person's body mass. The key question is how much muscle is being used when someone calculates their BMI. Linda Bacon at UCLA shows that muscle mass only accounts for 8% of the variation in BMI, meaning that most people overestimate their weight based on their BMIs. Read more about studies like this one which show just how inaccurate our BMI measures are and make you realize that you could be underweight with normal body composition and fat mass, or overweight with normal levels of muscle.
What is metabolism and how does it change?
Metabolism is the process of breaking down food in order to create energy that our bodies use for everything from thinking and moving, to breathing and sleeping. So how does this all work? Our bodies gain calories by eating and digesting food, which we either burn or store for later use. This is why we have an internal calorie counter or metabolism (the calories in and calories out method). The body then uses the energy from these calories to run itself and perform all the functions that it needs to do.
The major organ systems in our bodies use different amounts of energy, depending on their functions. The brain uses a great deal of energy, while skin and muscle tissue require little.
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The Health at Every Size (HAES) movement advocates that dieting is not the best way to achieve optimal health because it causes people to eat more, exercise less, become obsessed with their weight/body image, and can lead to eating disorders. The HAES movement promotes a non-diet approach that focuses on well-being instead of weight loss.
Any weight loss that does occur with HAES is not intentional but rather comes from individuals adopting healthier eating habits and leading more active lifestyles. The HAES movement also discourages the use of weight for diagnosing health problems because it can be misleading, inaccurate, and stigmatizing. Cami Brownhill, a nutritionist with the University Health Network as of 2012, recommends a healthy lifestyle that includes eating a balanced diet, maintaining an active lifestyle, and developing long-term strategies for achieving and maintaining healthy body weight. Confidence in one's body plays an important role in overall well-being, including mental health.
Regardless, there are some benefits associated with having significantly lower BMIs, including reduced risk for certain diseases such as diabetes and heart disease. In addition to these benefits, individuals with a lower BMI have been found to have higher self-esteem and better mental health.