By triathlon coach Joel Enoch

Although we all know that excess fat isn’t great for optimal health, is it actually better for open water swimmers to have a higher percentage of body fat? Could a few extra pounds plump up your chances of success?

Fat plays several vital roles in the body, providing the energy for day-to-day life, transporting vitamins, and protecting vital organs. In addition – most importantly for open water swimmers in cold water – fat provides insulation, helps buoyancy and can provide fuel for long-distance endurance endeavours.

Fat works for whales, but what about people?

When comedian David Walliams swam the English Channel in 2006 for Sport Relief, he lost around 8kg while training and then spent the final month struggling to put some of the fat back on.

Certainly for cold-water swims, this fat is beneficial. “Although temperatures in the Channel rarely dip below 15-16°C, this is still cold enough that all but the strongest swimmers with low body-fat percentages will struggle to maintain performance,” says Walliams’ trainer for the swim, Olympian and sports science professor, Greg Whyte.

Whyte’s data shows that a two-hour immersion in 15°C water could result in loss of useful consciousness in some swimmers, and significantly increase the risk of drowning.

Research has shown that for those who take part in non-wetsuit, long-duration, open water events, increasing body-fat percentage improves insulation, and thus the ability to stay in the water for longer.

Medical researcher and ultra-endurance athlete Dr Beat Knechtle tested this by observing the performance of two swimmers with different body fat percentages in the 4°C waters of Lake Zurich.

Both swimmers were of a similar ability, and the training and the preparation of each swimmer was standardised to eliminate variables, but the swimmer with the higher body-fat percentage managed to last nearly 20 minutes longer in the water. Knechtle concluded: “More fat is probably helpful when swimming in cold water.”

The question of enjoyment is also relevant. Leaner people won’t just suffer an accelerated physiological effect on core temperature, but they will also feel the cold earlier.

So, even though the distance being swum is achievable and the cold may not be enough to result in a DNF (Did Not Finish), the cold may leave an athlete feeling like they can’t, or don’t want to, continue. After all, most people want to enjoy their time in the water, and probably don’t find the sensation of simultaneously having their head in a clamp while their feet are sawn off at the ankle that much fun at all.

So, for cold-water swims at least, fat sounds fab. But, before ordering that extra portion of pie and chips, bear in mind that the need for increasing levels of body fat is virtually eradicated by the wearing of a wetsuit, in all but the most extreme of conditions.

Also, there seem to be other factors than body fat that improve a swimmer’s ability to withstand the cold. Data analysis of elite open water swimmers in the US found that there was little difference between the body-fat percentage of open water and pool-based swimmers.

Furthermore, many of the record-breaking Channel swimmers also have a lean build, leaving Whyte to suggest, “It seems that elite swimmers can sustain body temperature through higher workloads.”

In other words, by becoming fit enough to maintain a high work rate throughout a long-distance swim, a swimmer may be able to fend off the effects of the cold water more successfully than a weaker swimmer with a similar build. This obviously highlights the need to include high-intensity training in a programme, even when preparing for longer swimming events.

So, although in some cases body fat may be a useful tool, the effects of swimming in cold water are a little more complex than the message: ‘fatter is better’.

Also, body fat seems to have no positive effect at all on long-distance swims in warmer water. To prove this, Dr Beat Knechtle looked at participants of the 26.4km Lake Zurich Marathon Swim – the longest open water swimming contest in Europe, which takes place during summer when water temperatures are consistently around 20 degrees. Under these conditions, Knechtle says the research suggested “body fat seems of no help for a fast race time”.

Does fat slow you down?

In most sports, athletes dispense with the spare tyre because it slows them down, and it seems that there’s no exception when it comes to swimming.

While very little research has been carried out on average or recreational swimmers, one regularly quoted study, published in the Journal of Strength and Conditioning Research in 1994, took 10 competitive swimmers and simulated the increase of body fat by placing latex pads underneath tri-suits.

The results showed that speed decreases as body fat increases. This is largely due to an increase in the separation and backflow of water molecules (known as eddy currents) as a result of the expanded body profile (‘form drag’). 

However, while these results are interesting, it has been acknowledged that they must be viewed with caution, since the latex may differ from body fat in consistency, thereby changing drag characteristics. “Also,” say the authors, “the subjects were not extremely lean and it is not known whether increases in buoyancy due to a greater percentage of fat tissue might aid a leaner population.” 

The findings are also possibly of limited significance to beginner or mid-level swimmers, especially in wetsuit-legal swims. This is because – as well as form drag – the major elements affecting swim speed are frontal surface resistance and friction drag.

All three of these are vastly improved by wearing a wetsuit, irrespective of body fat. It is likely, then, that by wrapping yourself in neoprene you will reduce the negative effect on streamlining caused by increased levels of body fat. So, while body fat is broadly speaking a good thing for cold water swims, if you’re an elite athlete or swimming in warmer water, it’s bad.

However, wrapping yourself in neoprene may compensate for some of the loss in speed resulting from the spare tyre. 

Does fat make women swim faster?

What about the difference between the sexes? Women naturally store slightly more body fat than men, and fat is less dense than muscle, so “there is an intriguing debate about whether women are better suited to long-distance swimming than men,” as Professor Whyte explains. “Not only because they typically carry more fat but that it is also distributed in a way that gives them a better centre of buoyancy, enabling more efficient swimming.” 

Although elite female swimmers do not match the performances of elite men in the water, they are more closely matched than in almost any other sport.

In a study analysing the gender gap in 82 events over five sports (swimming, track and fi eld, weightlifting, cycling and speed skating) published last year, the smallest gender gap was the 6.36 percent found in 1500m freestyle swimming.

Incidentally, data analysis from Steven Munatones at Open Water Source suggests that, outside of the elite field, women compete even more closely with men and in some cases their average performance is better. However, the benefits of womens’ fat distribution do not seem to include improved protection against the cold.

Study results suggest that a woman’s core body temperature drops more than a man’s over a 10km swimming event, despite their increased levels of stored fat. 

Much-needed fuel?

Fat is the main source of fuel for general functions in the human body, and it continues in this role during exercise up to around 70 percent of maximum effort. So, for long-distance and slower-paced swims, body fat performs an important function. However, burning fat for fuel during exercise is conditioned by training. Simply having the fat in place does not mean you have access to it during a swim; even slim swimmers have sufficient fat to use as a fuel source. 

It is also important to recognise, firstly, in order to utilise fat effectively as a fuel source during exercise, you need carbohydrates. People who are swimming to lose weight should therefore avoid low-carbohydrate diets as this will result in a loss of performance and less than optimal use of fat.

Secondly, we can only store about 1.5hrs worth of carbohydrate that can be used to fuel high-intensity exercise. For people taking part in events longer than this, the use of carbohydrate gels or drinks during the swim is vital to performance and keeping warm enough to finish the swim. 

Clearly there are trade-offs to be made between warmth and speed. Where you want to be on the continuum will be determined by what type of swimming you want to do. If you are attempting a long distance or cold-water swim, then seek expert advice.

For the casual swimmer, Whyte suggests: “Just do the training and don’t get hung up about your body composition.” He does point out, however, that for some larger swimmers in wetsuit-compulsory events, over-heating could be a problem.

So, if you are carrying a few extra pounds, don’t buy the thickest wetsuit on offer.