Image: ABC. By Cathy Johnson.

Swimming is great for fitness and muscle tone, but if you’re exercising with your waistline in mind, some might tell you to throw in the towel.

That’s because there’s a belief held by many that swimming is a lousy way to achieve weight loss. But is this really the case?

“If you want to lose weight, you’re better off walking around a pool than swimming in it,” according to Sydney exercise physiologist and personal trainer Andrew Cate.

“That’s obviously a bit extreme, but it does make the point. From a fat-loss perspective, swimming has some real negatives compared to other forms of exercise.”

Buoyancy effect.

It’s true that swimming involves some flotation, and this may reduce the work you have to do to move your body along, compared to land-based exercise — especially if you carry a bit of body fat, which increases buoyancy.

On the other hand, you have to work against the ‘drag’ effect of the water on your body and if your stroke is not very efficient, this may increase the energy you use swimming too.

University of Western Australia academic and researcher Kay Cox agrees there are some potential pitfalls in swimming to whittle your waistline, but she’s shown it can definitely be done.

She led a 2010 study of inactive older healthy women who took up a swimming program and compared them to those who took up a walking program.

The study, published in the journal Metabolism – Clinical and Experimental, showed that after a year on the program, the swimmers had lost more weight and more off their waistlines than those on the walking program.

Both groups exercised at the same intensity (as measured on heart rate monitors) and for the same amount of time three times a week. The first six months they were supervised, they then continued for a further six months unsupervised.

The differences weren’t huge — the swimmers lost an average of 1.1 kilograms more weight and around 2 centimetres more off their waists compared to the walkers.

But it’s nonetheless a significant finding – especially given that very few well-designed studies have ever looked into the issue.

“I think swimming is good for anyone who wants to lose weight,” said Associate Professor Cox, who has a long-term history as a Masters swimming coach.

“It takes the load off your joints compared to running or walking, which means you’re less likely to get injuries and so you’ve got a better chance of sticking with it.”

Cool water and appetite.

Professor Cox believes it’s the cool environment in the pool (26 degrees Celsius) that may explain, at least in part, why the swimmers in her study had the edge when it came to weight loss.

Paradoxically, cool water may also explain why many swimmers find fat hard to budge.

It comes down to the impact of this cool environment on two aspects of the body in the post-swim period: the swimmer’s appetite (which affects how much they eat afterwards) and the energy the swimmer expends to restore their normal body temperature.

Exercise that raises your body temperature, which is most land-based exercise, tends to suppress your appetite, but swimming has the opposite effect because the body temperature usually remains relatively low, Professor Cox said.

Most swim centres maintain water temperatures around 26-27 degrees Celsius and many ocean swimmers subject themselves to even chillier water still.

“If you swim, particularly in cold water, the thing you immediately want to do when get out is have something warm to eat or drink to restore your body temperature,” she said.

So it’s easier for swimmers to undo all their hard fat-burning work simply by over-eating after their workout – compared to land-based exercisers.

Professor Cox believes the women in the study got around this by being extra vigilant about their food intake. All participants in the study were specifically asked to eat the same diet as before they started the exercise program (and food diaries suggest they did this).

What’s more, when you get warm from a walk (or other land-based exercise), you can cool yourself in passive ways – like simply stopping moving around.

But warming yourself after a swim is likely to involve expending more energy (which translates to burning more fat).

“I think if [swimmers] do the same amount exercise as they would on land and don’t compensate by eating more afterwards, it could be the same, if not more effective [at bringing about weight loss]. But you have to spend the time and get the intensity up,” Professor Cox said.

Get your swim technique right.

But to be able to swim well enough to lose weight, you might need a little more help and guidance than if you took up walking – at least initially.

“Technique does matter because if you can’t swim well enough to keep going, you won’t burn the kilojoules. You’ll feel exhausted and give it away. But someone who has basic swimming skills, who can swim 10 to 12 metres without stopping, can build it up,” Professor Cox said.

Many swim centres offer stroke improvement lessons or you could try hiring a coach for just a few sessions.

“There are a lot of benefits from swimming, particularly for overweight people, when you put them in an environment where exercise is not going to be painful,” Professor Cox said.

But the best exercise for weight loss is the one you will stick at – so make your choice based on what you enjoy.

“If you’re going to swim three days a week for the rest of your life, compared to walking six days a week, but giving up after two weeks, well, the choice is easy,” Mr Cate said.

Professor Cox added: “Swimming won’t be for everyone, but if you just ask the basic question can you lose weight by swimming, the answer is yes, you can.”

This post originally appeared on ABC News.