What is a Healthy Weight?
What does it mean to you when you say that someone is healthy? Have you thought about it? I think many of us use the term without thinking too much about it. While there are probably semantic nuances in the true definition, I think we would all agree that something that increases the length of your life while decreasing your risk of disease is healthy. I think that the most important reason for all of us to strive for a healthy weight is to live as long and as healthy a life as possible. A ‘healthy’ weight will do just that. While it is nice to look good in a bathing suit, we at the Weight Loss Counter Revolution are primarily concerned with your health.
The medical and scientific community have all agreed on a healthy weight based on the body mass index (aka the BMI). Simply, the BMI accounts for the contribution of your height to your weight. The medical community around the globe all agree that a BMI of 22-23 is ideal, a someone with a BMI over 25 is overweight and someone with a BMI over 30 is obese. But where did they come up with these numbers? Did a group of scientists pick them out of a hat? Did they use a survey? Was it based on a collection of opinion? Of course not. In the Weight Loss Counter Revolution book, all the details are given to explain how the medical community came up with these numbers. For the purpose of brevity, I will give you one of the biggest studies on the topic. One of these was published in The Lancet (Lancet 2009; 373: 1083–96) and combined data from over 57 separate studies to create a collection of over 900,000 individuals. They were trying to see the relationship between BMI and the risk of dying. Their results are shown in the graph below.
The bottom line on the graph is the BMI ranging from 15 to 50. The line on the left is the number of deaths per year per 1000 patients. What you see displayed is what they call a ‘J’ shaped curve. As your BMI goes down (i.e. you get too skinny) and as your BMI goes up (i.e. you get too fat) the number of deaths increases. What you’ll notice is the the bottom of the ‘J’ falles somewhere around 23. This means that your chance of dying is lowest with a BMI of 23.
That’s why the ideal body weight is at a BMI of 23. It’s not because you look good at that weight (although you might). This is the point where the evidence is clear that the contribution of your weight to your risk of dying is the lowest. It’s not a guess. It’s not opinion.
You’ll also notice that the risk of dying starts to increase somewhat at a BMI of 25. As the number approaches 30, it is clear that the risk of dying is increased and continues to increase from that point on. That is the reason why someone with a BMI of 25 is considered overweight and someone with a BMI of 30 is considered obese. It’s all because of your risk of dying and has nothing to do with guesswork or opinion. It is a known fact. Similar graphs have been found showing your risk of devloping diabetes, heart disease, stroke, etc also increase with the same inflection points.
There is one group of people for whom the BMI does not really apply and that is athletes or people who are heavy weightlifters. Many people try to claim that the BMI is not accurate based on the fact that muscle weighs more than fat. While this is true, for the overwhelming majority of people this caveat does not apply. The funny thing to me is that athletes and heavy weightlifters don’t usually ask me this question. They know they are in good shape and are not concerned with their BMI. The people who ask this question are the overweight and obese people who looking for an excuse to say that their weight is not really that bad – that the BMI calculations are cruelly biased agaisnt them. If you are accusing the BMI of being innacurate that only means that it probably applies to you MORE. And for those of you “big boned” people out there – this is a myth. Differences in bone size or density in no way contribute to risk based on BMI.
The reality is that the BMI numbers are based on studies including MILLIONS of individuals from around the world. These individuals had a broad range of activity level, bone density, genetic make ups. The size of the sample is enough to prevent most potential biases. The numbers are real, consistent, and not subject to legitimate dispute.
The bottom line is that a healthy weight clearly corresponds to a BMI between 20 and 25. Between 25 and 30 you probably have an increased chance of dying and should probably make changes in your lifestyle. If your BMI is 30, you clearly have an increased risk of dying and are at an unhealthy weight.