People who are grossly overweight are often passed fit to dive but equally often have medical conditions associated with their physique. What medical conditions preclude you from diving?
In the past, people who suffered from asthma were always simply banned from diving, but now medical science is tending to differentiate between different forms of illness that produce asthmatic symptoms. It almost boils down to the colour of the inhaler required to treat the symptoms. Check with your doctor.
It is suggested that women should not dive whilst pregnant but there are many cases of that advice being inadvertently ignored. This is because many women divers were unaware that they were in the early stages of pregnancy when they went diving. The fact is there has never been any research done and no one is prepared to say that it's OK. If you know you are pregnant, it's best to wait until you are not.
Anyone with any form of lung disease or circulatory problem should avoid the activity, and if you suffer chronic back pain or have recently suffered a back injury, you should be circumspect about strapping heavy gear on. A large proportion of the population unknowingly have a patent-foramen-ovale (PFO) or hole in the heart. This is suspected as a factor in some cases of decompression illness. However it is hazardous to test for and does not necessarily preclude you from diving.
If you are using any prescribed medication, check with your doctor for any contraindications that might preclude diving
Few doctors are fully aware of the implications of breathing compressed air underwater and have a tendency to be safe and preclude you from the activity. There are medical referees listed by most of the training agencies and it is best to visit your GP with a list of these contacts to hand or be referred to one for a full diving medical examination.
The body mass index, or BMI, is the measurement of choice for many doctors and researchers studying obesity. BMI uses a mathematical formula that takes into account both a person's height and weight in order to calculate how fat they are. BMI equals a person's weight in kilograms divided by height in meters squared. (BMI=kg/m2). If the figure calculated is greater than 24.9, you are overweight. If it is greater than 30 you are clinically obese. It is not a totally reliable guide. There are those trained athletes who have more than their fair share of muscle tissue and consequently calculate a high figure for BMI.