BECKYHITCHIN
Of cake and calories
How much energy do we burn while diving , and does it justify the traditional cake binge ? Becky Hitchin carries out a ( mostly ) unbiased review of the existing research
One of my biggest conundrums when diving is knowing exactly how many calories I ’ ve used during a dive - and most importantly , how many cakes I can eat guilt-free afterwards . I thought I would do a not-very-scientific reckoning to help all the readers happily indulge in appropriate amounts of Jaffa cakes , shortbread , chocolate cake , or whatever else is your particular fancy after a dip in cold waters . To start : kitting up . As we all know , as soon as you ’ ve got your drysuit on , basic activity becomes like weightlifting in a sauna . Saunas increase one ’ s calorie consumption to 1.5x that of sitting normally . Without finding an official calorie counter for the gymnastics involved in getting a drysuit on and wriggling into kit , I ’ m going to suggest calories burned during yoga to be a good comparison . I estimate 10 minutes kitting-up . That ’ s 70 calories . About 1.5 Jaffa cakes . Not bad before even getting in the water ! Of course , it often comes with a layer of sweat forming in your drysuit for added discomfort , and later evaporation . American diving researchers once estimated that an average shore-dive in temperate water burns as much as 600 calories per hour . I wanted to see where this figure came from , as it seems a lot for 60 minutes of floating around in the water waving at nudibranchs . So . There ’ s a number of reasons why diving in cold water will use energy . When our bodies are cold or in a cold
22 environment , they continue to work to maintain body temperature at 37 ° C . But in the higher densities of water , it ’ s generally said that heat is drawn off our bodies at least 25 times faster than in air . And unless you ’ re diving in a drysuit with dry gloves and a full-face mask , part of the body is always directly exposed to the water . In fact , the rate of loss of heat is proportional to the temperature difference between the points of contact , and heat loss in cold water can be 1,000 times greater than in air if we are actively swimming along .
It certainly feels like it after a while in very cold water . Maybe photographers really do have the best idea – stay as still as possible for the whole dive .
In the cold , our bodies undergo a process called vasoconstriction – where blood ( and heat ) is retained in the core . Eventually we start to shiver , a process to stay warm but which uses a lot of energy . Also , we breathe . It ’ s rather essential . Unless you ’ ve got the luxury of a rebreather , then the air we inhale is close to ambient temperature , and our lungs have to work to warm it . The deeper you dive , the more water pressure increases and a body needs to exert more effort to move or push through the water . Deeper dives use more calories . Working out the actual amount of heat loss anyone would undergo during a dive is subject to too many factors to think about here . Age , weight , distribution of body tissues , speed of swimming through the water ( again , photographers win out ), whether people are daft enough to go diving without gloves – or , for goodness ’ sake , hoods - on . On the physics side , discussion of heat transfer coefficients , turbulent flow , Reynolds numbers are bandied about . All lovely , but getting us away from the point of this article , which is cake . From a deep dive through the literature , PADI and others seem to agree on a loss of calories during a dive going upwards from 600 calories . I ’ m going to be bold and go for 800 to 1,000 , given the likelihood that a typical PADI dive isn ’ t in 8 ° C water , and for at least an hour . So , let ’ s add this up . 70 calories kitting up , let ’ s say 900 diving , and at least 70 calories de-kitting and warming back up . 1,040 calories . That ’ s 22 Jaffa cakes . With only 10 in a pack , that ’ s a great result . You could opt for eight shortbread cookies . Or two good sized pieces of sticky , gooey chocolate cake .
The conclusions from this extremely unreliable scientific study are important . It seems that actually I don ’ t eat enough Jaffa cakes after a dive . Undertaking this study has given me – and I hope all of you - the reassurance to go forth and clear the cake counters of cafes , pubs and all your local shops . �