In a world of misinformation, Fitness Pudding is here to separate fact from fallacy, and science from fiction.

Sweating Fat Away?

Sweating Fat Away?

Sweating off fat is 'hot' again. As typical, such fallacies receive ample help from media outlets featuring 'hot' products, such the Zaggora Hot Pants, which claim to target trouble areas, enhance metabolism, and drench your bum in sweat. Other products, such as the traditional sauna suits and body wraps are also taking advantage of the 'what goes around comes around' swing of this fallacy. But, can we really sweat away fat?

saunasuits

History

Products have long claimed to promote weight loss through sweating (water loss), from sauna suits to the actual sauna (see blog on body wraps). Of course, 'sweat pants' have been used to help the muscles warm-up before activity, hence why the are also known as 'warm-ups'.

Good 'ol sauna suits have not changed much since the 70's.hot-pants-evolution

However, hot pants have seen a bit more of an evolution, from the famous inflatable versions to the hi-tech Verseo suana shorts.

Of course, the Zaggora Hot Pants are the latest addition, with its slimming feature, and luxury of being able to wear out in public without being laughed at (in exchange for buoyancy).

Metabolic Heat

Evaporation of sweat from the skin is the best way for the body to cool itself during exercise. However, these clothes inhibit evaporation, so we keep sweating, unable to cool down.

So, it is true that metabolic heat (measured in Calories) will very slightly increase while exercising in the heat or while wearing 'hot' clothing, but is due to the additional work of ventilation (breathing rate), enzyme activity and increase in sweat gland activity...not 'fat burning' of the muscles.

Zaggora Hot Pants' website claims an increase in energy expenditure during exercise up to 18%. However, this 18% was NOT the average, rather most likely represents a single person at the highest end of the range. The research actually tells us that exercising in the heat only produces 4% to 10% increase, on average, in metabolic heat release (measured in Calories).

Let me illustrate with a 150 lb person.

Aerobic Activity Intensity METs
Duration Calories Percent
Increase
Not in Heat or Hot Pants Moderate 3 30-min 102 --
In Heat or Hot Pants Moderate 3 30-min 112 10%

So, the same 30-minute exercise in the heat or with hot pants, with a 10% increase in metabolic heat, is only worth around 10 Calories for a 150 lb person (112 Calories versus 102 Calories). 10 Calories = 6.5 raisins

Exercise & Work Capacity

The inability to cool the body will subsequently hinder our ability to exercise at a higher intensity or for a longer duration. Muscles produce tons of heat (Calories), and keep making the body hotter! This is why experts promote movement as one of the best ways to fight off hypothermia in the cold. At the same time, the body must also deal with the water loss, which impacts blood volume, heart rate and muscle performance. These limitations support why millions of dollars are spent on specially-designed equipment and clothing to help keep the body cooler (not hotter) during exercise.

The Trade-Off

So, you have a trade-off:

  1. Exercise in hot clothing, get a very slight increase in energy expenditure and lose water weight, but limit performance and fat loss, or
  2. Keep cooler, so you can exercise for harder and longer, thus expending more energy from fat.

Clearly, if you want to lose fat (not just water weight), then stay cool and exerciser harder/longer. We want to use more muscle, not more sweat glands.

Take the same example from above:

Aerobic Activity Intensity METs
Duration Calories Percent
Increase
Not in Heat or Hot Pants Moderate 3 30-min 102 --
In Heat or Hot Pants Moderate 3 30-min 112 10%
Not in Heat or Hot Pants
(same intensity, 30-min longer)
Moderate 3 60-min 204 100%
Not in Heat or Hot Pants
(more intensity, same duration)
Vigorous 6 30-min 409 300%

As you can see, exercising in the heat can give a 4% to 10% boost in energy expenditure (Calories), but because we will have to exercise at a lower intensity we are potentially missing an opportunity to expend 100% to 300% increase in energy expenditure (from longer duration or higher intensity, respectively).

Water Loss

A review looking at weight cutting in wrestlers, who commonly use excess sweating and hypohydration as a tactic, reported up to 5% average weight loss from water alone.1 The American College of Sports Medicine's position stand on this issue of sweating and hypohydration report that it may take 24 to 48 hours to reestablish body fluid balance, up to 72 hours to replinish muscle glycogen, and even longer to replace lost lean tissue/muscle. As you would assume, weight cutting through these means are deemed unhealthy.

Muscle Loss

A study looking at triple iron triathletes found NO change in total body water after the grueling 2.4 mile swim, 112-mile bicycle ride, and 26.2 mile run.2 The athletes start as early as 7:00am and must finish by midnight!

You see, these athletes were able to replinish body water that was lost, but were unable to maintain their body weight. After the race, the athletes lost an average of 3.65 pounds of body weight, with the majority coming from losses in muscle mass. A loss in muscle will then negatively affect metabolism. Less muscle = less ability to use fat for energy.

Conclusion

Despite the small increase in energy expenditure, exercising in the heat or with 'hot' clothing does not mean we are sweating off fat. Keeping our bodies cooler, so that we can exercise harder/longer, will maximize our use of fat for energy.

 


References

1Buskerk, E. R., & Puhl, S. M. (1996). Body Fluid Balance: Exercise and Sport. Boca Raton, FL: CRC Press.

2Knechtle, B., Knecthtle, P., Rosemann, T., & Oliver, S. (2010). A triple iron triathlon leads to a decrease in total body mass, but not to dehydration. Research Quarterly for Exercise and Sport, 81(3), 319-327.

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