We define overweight and obesity by weight, and of course one of the outcomes of obesity is increasing bodyweight. But it’s only one of the outcomes. From a medical point of view, it isn’t an important one.
The true impact of overweight and obesity comes not from the amount of weight, but the type of weight (adipose tissue, also known as fat), where it is distributed, and the way it interacts with the body. The last part is the most important. Where adipose tissue (fat) is deposited and the way it interacts with the body varies enormously, largely based on our genes. The amount of fat is far less important than these interactions.
Overweight and obesity can have mechanical effects, just from the volume or weight of fat tissue. These can cause joint or back pain, osteoarthritis, obstructive sleep apnoea and other conditions. There can also be metabolic effects, caused be the way fat tissue interacts with the body through chemical or hormonal means. These cause problems like high blood pressure, cholesterol abnormalities, pre-diabetes, diabetes, liver disease, and many others. Overweight or obesity also increase the likelihood of a whole range of malignancies (cancers) throughout the body.
There are also the mental impacts. Obesity is associated with a range of mental health conditions, but there is also the toll taken by pressure to achieve and maintain unrealistic body weight goals. On top of this comes the effect of stigma, bias and discrimination against people of size, evident across society including in education, employment and even healthcare.
Many years ago, researchers in Edmonton, Canada showed us the impact of obesity was not related to weight, but the diseases caused by it. When they took thousands of people and grouped them according to body mass index (BMI), they showed patients’ outcomes didn’t depend on their weight at all. When they re-grouped the patients according to the presence and severity of obesity-related diseases, they showed very clearly that patient’s outcomes depended on the impact of overweight or obesity (not the amount of weight).
This simple study has changed the way obesity specialists all over the world practice, but its implications are even broader than that. Society’s perception that the heavier a person is, the less healthy they must be, is simply wrong. As doctors (and as decent people) we no longer get to make judgements about the health of an individual just by looking at them. Until we know them, their history, and the impact of obesity on them, we don’t know how healthy they are at all. It’s not our role, or our right, to make assumptions about people or advise them, based only on their weight.
Rather than being judgemental, we should be curious about the impact of obesity on an individual, then provide evidence-based treatments to lessen that impact. Because, after all, it’s about the disease, not the weight.