Carrying a bit of excess lockdown fat? Dr Ed Shattock of DDRC Healthcare sets out the safety concerns for overweight divers.

Obesity describes excess body fat to the extent that it can have a negative impact on that person’s health. Current estimates suggest that one in four adults and one in five children in the UK are obese and this number is unfortunately increasing. Obesity is generally measured using Body Mass Index (BMI) which looks at weight in relation to height and can be broken down into several categories.

Healthy weight is considered 18.5 and 24.9 kg/m2 – you can check your own BMI using the NHS calculator. BMI is not a perfect measurement, for example, it will overestimate body fat in more muscular and taller individuals, but is a useful “rule of thumb” for broad categorisation.

The UK Diving Medical Committee suggests that anyone with a BMI of greater than 30 kg/m2 should normally be excluded from diving. This often causes concern with divers during medicals who may not have been told previously that weight can be a problem for diving. So why is it important for a diver to be a healthy weight?

Obesity and decompression illness (DCI)

Nitrogen is at least five times more soluble in fat tissue than in muscle. Therefore, divers with a greater amount of body fat will be able to store an increased amount of nitrogen, potentially resulting in increased numbers of bubbles forming post-dive.

A study in 2017 looking at bubble grades after diving supported this idea by showing that divers with a higher BMI had more significant bubbles post-dive. However, translating this increased bubbling to an actual increased risk of DCI is not so clear cut and there are several studies with conflicting results. This is likely due to DCI being a relatively rare event, which makes large studies of the factors involved problematic.

We should also remember that dive tables, and the computers that are programmed using them, were created using young, fit divers. The greater the difference between the individual using the tables and the divers the tables were based on, the greater the risk that the table will not represent safe limits for that individual.

Obesity and fitness

Increasing obesity correlates well with decreasing aerobic fitness. Although diving is mostly a low-intensity activity, the ability of a diver to respond to an emergency scenario is extremely important. A diver with poor fitness may struggle to rescue themselves if they get into trouble and will be less able to assist a buddy in a similar situation. Furthermore, divers with good fitness levels have been shown to have lower risk of DCS and also use gas less quickly allowing them to dive for longer.

Obesity also comes with an increased risk of other underlying health issues such as diabetes or heart disease. These diseases come with an increased risk of death while underwater as well as increasing the risk of certain diving-related problems. The main culprit here is Immersion Pulmonary Oedema (IPO) a life-threatening condition linked to high blood pressure, another common finding in obesity. IPO describes

an increased amount of blood returning to the heart when submerged, as a result of compression of peripheral blood vessels by water pressure. This increased blood volume may overwhelm a poorly functioning heart, leading to fluid on the lungs and difficulty breathing. It is often described as feeling like you have run out of air.

Obesity and Covid-19

Another condition of concern with obesity is Covid-19. We know that overweight or obese patients are more likely to suffer from severe Covid symptoms when compared to their healthy weight counterparts, so losing some weight may be more important now than ever. ‘Long Covid’ or persistent symptoms following resolution of Covid-19 infection, is also now being studied and although it seems to affect even those who were asymptomatic, it is likely that those who have had more serious Covid-19 are more likely to suffer from ongoing symptoms. One of the main concerns of this for divers will be persistent shortness of breath and underlying lung changes, which may lead to an increased risk of air trapping.

Obesity and fitness to dive

Overall, obesity increases your risk of other serious underlying health conditions, reduces your fitness level and may increase your risk of DCS. So, maintaining a healthy weight and a good level of fitness is clearly an important part of diving safety. If a diver has any concerns about their weight and how it could impact their diving, they should discuss it with their local diving referee.


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This column article was originally published in SCUBA magazine, Issue #112 March 2021. For more membership benefits, visit

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