Wednesday, 26 August 2009

Fitness Tip or Fitness Myth – Sweating and Weight Loss

Back in the late 80’s and early 90’s it wasn’t uncommon to see people out exercising wearing suits made of PVC. These suits, normally with elasticated cuffs, ankles and neck, were designed to promote weight loss by increasing the amount of sweat produced by the wearer and were made very popular by those funky kids from the New York School for the Performing Arts in Fame but then so were leg warmers! Anyway…

The ‘’Sauna Suit’’ as it was known has almost all but disappeared but recently I spotted a “sauna vest” being promoted at a big UK leisure show so it looks like the misconception that sweating excessively causes fat loss is still alive and well. The theory that sweating causes increased fat loss has been around for a VERY long time – the history of saunas having contributed much to this mistaken opinion. It is an irrefutable fact that excessive sweating does indeed cause WEIGHT loss, but sadly, this weight is NOT fat!

Many sports use sweating as a way to “make weight” and get athletes into their required weight category. For example, a fighter who weighs 82kg could sweat off 2.5kg of weight to fight in the under 80kg division. The boxer would attempt to rehydrate after the weigh-in and, as a result, fight in a weight division below their current weight. Whilst this is an effective way of reducing scale weight, there is a possibility that the fighter may fail to be fully rehydrated by the start of the bout and this may result in a poor performance due to being still dehydrated. Essentially any hoped - for advantage would be lost. Jockeys often use a similar practice to ensure they are as light as possible to minimise the weight their horse will have to carry during a race and bodybuilders also try to “dry out” to maximise their muscular appearance for competition...

We can divide our scale weight broadly into two components…Fat Mass (FM) and Fat Free Mass (FFM). FFM is made up of water, muscle, bone and connective tissues like ligaments and tendons and we should always aim to preserve our FFM as it is quite literally the “good stuff” So really, we’re not correct when we talk about losing weight – we should be saying losing fat instead.

During exercise, or any other activity that causes a rise in body temperature (?!!) sweat lost can equal or even exceed one litre (just under 2 pints) in an hour. One litre of water weighs 1 kilogram (2.2 lbs) so quite possible to lose a substantial amount of weight during one hours exercise – especially in a warm climate. We sweat to reduce our body’s core temperature and prevent hyperthermia – the excessive build up of heat which may, if left unchecked, result in serious health problems. Water comes to the surface of our skin, evaporates, and takes with it some of the excess heat and as a result, we cool down.

The thing is, as soon as we drink water or our post- exercise beverage of choice, this weight will be put back on as soon as the fluid is back in our bodies…weight lost from dehydration is a very short term weight loss indeed! So clearly the degree of sweating while exercising has very little to do with long term fat loss.

In addition to having nothing to do with healthy weight loss, dehydration (the state of being deficient in water) also actually slows the burning of fat. The body perceives this reduction in water intake/increase in water expenditure as a possible drought, and drought is the natural pre-curser of famine. As a result, the age old “starvation response” kicks in and the body does all it can to preserve fat stores to keep us alive and well in periods of restricted food supplies! This is obviously not conducive to our goal of fat loss. We should do everything we can to avoid getting into a dehydrated state and this means we need to adopt a sensible approach to our water consumption…

1)Drink at least 2 litres of water a day

2)Drink more if living in a warm climate

3)Drink more still if lots of tea and coffee are consumed

4)Consume an extra 250ml of water per 15 minutes of exercise performed

5)Never wait to get thirsty – this means you are already 5-10% dehydrated

6)Watch out for high calorie sports and soft drinks which may well rehydrate you but will add extra energy to your energy intake and may interfere with fat loss - water is best!

It’s also worth remembering that water is ESSENTIAL to our health and well being. Just about every organ and process within our bodies relies on copious amounts of water...if water was on the healthy eating pyramid, it would make up the base because without sufficient water consumption our bodies will fail to function properly. We can survive a fairly long time without food but only a matter of days without water...

The main factor to consider when we try to losing weight is that to burn fat, we need an energy deficit – which means less food energy in, and more activity energy out. The negative energy balance will result in fat loss, whereas losing water will merely result in weight loss.

So, in our quest to get slimmer for the coming summer - ditch the sweat suits and extra layers of clothing, don’t worry about trying to “sweat the weight off”, drink plenty of water, eat a little less while exercising a little more.


  1. One litre of water weighs 1 kilogram (2.2 lbs) so quite possible to lose a substantial amount of weight during one hours exercise – especially in a warm climate.

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  3. This was a really great contest and hopefully I can attend the next one. It was alot of fun and I really enjoyed myself..weight lifting