“What's a healthy weight for me?”
It's a great question and often not an easy one to answer.
Our weight number is often seen as a measure of our health. And it can certainly play a role, but we tend to add extra importance to our weight compared to things like blood pressure, glucose, or cholesterol. Of course, excess weight can be linked to all of those things, but what really matters is the type of weight we carry and where we carry it.
It's no secret that our weight number shows more than just body fat, although when we step on a scale we can easily lose sight of that. Muscle, water, and bone all weigh something too, and our weight number doesn't show us those differences. Body composition, which can be tricky to measure, can give us a better idea of whether our weight - or more specifically body fat - may pose health risks.
But even a body composition measurement can be misleading. For example, Japanese sumo wrestlers weigh between 300-400 pounds with a high proportion of body fat and carry much of that weight in their midsections, the part of the body that typically lends itself to greater health risks. Yet active sumo wrestlers consistently display normal blood pressure, glucose, and cholesterol.
How can this be? The secret is in the type of fat that they carry. Due to high levels of physical activity, the body of a sumo wrestler will predominantly carry subcutaneous (meaning "under the skin") fat rather than visceral fat. Visceral fat is the more dangerous type of fat in the body, accumulating around vital organs and disrupting metabolic function. A high proportion of subcutaneous fat has far fewer health risks than visceral, and helps explain why some individuals can remain fairly metabolically healthy despite a high BMI.
Keep in mind, however, that when a sumo wrestler stops training they often see a dramatic shift in metabolic function as their physical activity decreases, even though their weight may stay exactly the same. As physical activity decreases, subcutaneous fat is gradually converted to dangerous visceral fat. Conditions like diabetes and heart disease soon follow. This demonstrates that their behaviors, not their weight number, had the most significant impact on their health. For those struggling with weight loss, this should come as a relief - generally speaking, you have far greater control over your habits than you do with changing your weight number.
Glenn Gaesser, a professor of exercise science at Arizona State University, has gone so far as to suggest that obesity is not a cause of metabolic disease at all, but is simply another symptom of poor health behaviors. We do know that you don't have to "cure" obesity to improve metabolic function - a weight decrease as small as 5-7% of body weight can have a significant impact, even if the individual remains at an elevated BMI.
Whether or not you should attempt to lose weight depends on more than just the number on the scale. Is excess body fat (and, more specifically, visceral fat) negatively affecting your health? The scale alone may not reveal that, but your bloodwork probably will. If that's the case, know that diet and exercise changes will impact those numbers and the type of body fat you carry, even if you don't lose significant amounts of weight.
This isn’t to say that weight loss can't be helpful for health. Even without metabolic problems, excess weight inevitably affects joint health and is linked to sleep apnea among other things. But weight isn't the whole picture. When it comes to health, one thing never is.