Q: I gave up smoking five years ago, go to the gym six days a week and have dropped two dress sizes – but I’m classed as obese by my GP! Why doesn’t my BMI reflect my true fitness?


BMI is defined by your height and weight, and the categories are as follows: normal, 18.5–24.9; overweight, 25–29.9; and obese, 30 or more. BMI is a useful measure to identify changes in your weight, but it doesn’t take into account your build or body composition, such as how much muscle compared to fat you have. Indeed, it’s possible to have a high BMI due to being very muscular. Many body builders or rugby players might be classified as obese according to their BMI, even though their percentage of body fat is well within the healthy range (or in some cases, below it).

When discussing BMI with your doctor, it’s important to talk about the implications for you as an individual – that is, whether you may still need to lose some weight or if your high BMI is related to muscle rather than fat. Regardless of BMI, giving up smoking and doing plenty of exercise are likely to have significant benefits in terms of reducing your risk of chronic diseases such as heart disease or cancer, so please don’t feel disheartened. You’re clearly well on your way to a healthier lifestyle.