Flush Fat

Now that the Bush administration has declared all ephedrine and mahuang products taboo, the scramble to find other natural fat-burning substances is on. May I suggest hydrogen dioxide? Readers with a passing knowledge of high school chemistry may recognize that what I’m suggesting here is nothing more than ordinary water.

That isn’t as farfetched as you might think. Diet gurus have long advocated a generous intake of water. Since some popular diets, such as the low-carb versions, enhance diuresis, or water loss, due to breakdown of stored glycogen, dehydration can be a concern. Glycogen, the storage form of carbohydrates, is stored with 2.7 grams of water per gram of glycogen. When the glycogen is broken down’as occurs when you delete carbs from your diet’you lose water too. Water is also thought to ‘flush’ toxins stored in fat that are released when fat oxidizes.

While those notions about water aren’t exactly esoteric, other aspects of water metabolism may prove surprising. For instance, drinking moderate amounts of water increases blood pressure in healthy people by increasing the flow of sympathetic hormones, such as norepinephrine. Those same hormones are involved in the release and oxidation of fat in the body. In fact, much of the effectiveness of ephedrine is due to its structural resemblance to sympathetic hormones, allowing it to interact with the beta-adrenergic receptors responsible for the cells’ release of fat into the blood.

To test the thermogenic, or conversion of fat calories into heat, effect of water, a recent study featured seven men and seven women, all healthy, with an average age of 27, who drank 500 milliliters, or about half a quart, of water.1 That caused a metabolic increase of 30 percent over resting levels. The increase occurred within 10 minutes, reaching a maximum 30 to 40 minutes following the water intake. It lasted for more than an hour, and it led the authors to suggest that drinking 1.5 liters of water daily (just over a quart) would augment daily energy expenditure by 200 kilojoules. That’s like taking a dose of 50 milligrams of ephedrine three times daily, which results in an increased energy expenditure of 320 kilojoules. Admittedly, that adds up to only about 100 extra calories burned daily, but it does add to weight loss when coupled with diet and exercise.

When the male subjects drank water, it led to a marked increase in fat oxidation with no change in carbohydrate oxidation. In female subjects the increase in metabolic rate after they drank water was fueled mainly by carbs. The difference is thought to result either from differences in body composition or hormones. In men the upgraded fat oxidation was generated through stimulation of beta-receptors’exactly the way thermogenic supplements such as ephedrine work.

Why does water promote this apparent increase in sympathetic hormones? Scientists aren’t sure. One suspected mechanism involves the metabolic cost of heating ingested water to body temperature, but that didn’t play a significant role in the new study. Gastric distension, or filling the stomach with water, can also promote the flow of these hormones, but again, the subjects didn’t drink enough water to cause that effect. The actual mechanism behind the thermogenic response water promotes remains subject to speculation.

The one aspect that I find troubling about the new study is this: Now that water’s been shown to have thermogenic effects, will the government remove it from store shelves for being a hazard to human health’as it did ephedrine? After all, some people have also died from ingesting too much water.

1 Boschmann, M., et al. (2003). Water-induced thermogenesis. J Clin Endocrinol Metab. 88:6015-6019.