My friend does a lot of swimming and she believes it’s a great exercise to lose weight, is this true?

Well yes and no!

Like any other exercise swimming will suit some people while others may benefit more from a different exercise. The reason for this is our energy system works a little like the gears in a car. When beginning any movement the cells are in a gear, which does NOT favour fat burning. The muscle cells go through a process of using up minor stores of ATP and then move to carbs before fat is burned. Only after a low effort exercise becomes constant will the cells switch into the last fat burning gear.
 

Generally the fitter a person the quicker they can reach the last gear, also a fit person can exercise at a slightly higher level of effort and still burn mostly fat. An experienced swimmer has had many years to develop fitness. It means that the energy system can easily cruise at a level where muscle cells can take full advantage of fat stores for fuel. If all people had equal abilities then swimming would be ideal to lose weight, the trouble is we all have different levels of fitness.

Another difference comes with swimming experience, some can swim well and others can only just get by. This can make a big difference because someone who can’t swim well will expend more energy thus pushing the exercise towards the anaerobic end of the spectrum. A good swimmer will be able to sustain an effective rhythm to help fat burning. You only need to watch a professional swimmer to see the perfect exercise technique, as she gracefully glides through the water every movement is gentle and consistent yet strong enough to pull the body through the water without effort. That’s where the difference lies; more practice and greater fitness gives the energy system a chance to switch into that important gear.

For those who are good swimmers and can glide through the water without becoming out of breath then swimming may be a very good exercise to burn the fat. If you tend to create big splashes and clumsily drive through the water while struggling to complete a full length of the pool, then it may be best to try another exercise to lose weight.