Evidence suggests that one way to lose fat is to drink more water

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I was out of the UK two weeks of January, but if I’d been here I have a feeling I’d have witnessed a fair few magazines touting healthy regimes for the New Year on the ‘detox’ theme. A key element of such regimes is usually a good intake of water. This, it is often said, can help to flush out ‘toxins’ from the body, and so improve general energy levels and wellbeing. Detox regimes often get a withering reaction from the scientifically inclined, even though there is not enough evidence in the area to conclude whether they ‘work’ or not. My experience in practice, I have to say, is that generally individuals generally feel much better for the experience. For more on detox regimes, see here.

Detox regimes are often recommended as a path to weight loss. One of theories circulating here is that toxins in the body can be stored in the fat cells, and as toxins are released, so is fat. However fat-fetched this may seem to some, to my knowledge this proposed mechanism has not be subjected to systematic study, so we’re not really in a position to dismiss it. Also, I came across a letter in the International Journal of Obesity this week which outlined mechanisms and some evidence which appears to support the concept that drinking more water might indeed stimulate fat loss.

The letter was written in connection with a previously published study in the same journal. The original research treated rats with ‘angiotensin-converting enzyme inhibitors (ACE-inhibitors). Angiotensin is a hormone that increases blood pressure, and ACE-inhibitors can therefore reduce blood pressure and are a popular treatment for hypertension (raised blood pressure). In this study, it was noted that treating rats with an ACE-inhibitor led to a reduction in the fat mass of these rats. Despite eating the same amount of food, ACE-inhibitor treated rats ended up with 26 per cent less fat in their bodies then those not receiving the treatment.

The study also cited other evidence of inhibition of angiotensin (perhaps in conjunction with inhibition of a related hormone known as renin) led to weight loss in animals. The authors of the latest article suggest that this means inhibition of the so-called ‘renin-angiotensin system’ might be unblocking fat-metabolising mechanisms. But they suggest another mechanism too:. The original study found that rats treated with the ACE inhibitor drug drank twice as much water as untreated rats. Could it be this, the authors ask, that is responsible for the improved fat loss in these animals? Could increased water intake hydrate cells better, and allow them to regulate fat metabolism better too?

In support of this theory they explore findings in a type of rat which fails to produce a hormone called vasopressin (also known as anti-diuretic hormone). As a result of this abnormality, these rats cannot concentrate their urine. They pee and drink a lot, and their blood is relatively dilute. Physiologically, this essentially mimics what happens when rats (or humans for that matter) drink more water.

Compared to other animals, these rats are lean. Also, their ability to metabolise glucose in nerve cells is enhanced. The relative absence of fat in these rats and enhanced metabolism of glucose suggest improved metabolic function. Perhaps most importantly, the leanness of these rats in particular suggests that their fat metabolism is that much more efficient.

The authors also cite evidence which shows that dehydration of cells reduce their capacity to take up glucose [3]. This, in theory, could cause metabolism to stall. Put another way, improved cell hydration might help ensure normal metabolic functioning, which has implications for all sorts of things including energy production and body weight.

All this work in animals is interesting enough, but is there any human research which supports the idea that drinking water might stimulate fat loss? Actually, yes. The authors of this week’s letter cite two studies which found that in humans, when the blood is made more dilute (hypoosmolar), fatty breakdown in the body (also known as ‘lipolysis’) is enhanced.

This evidence does not prove that drinking more water helps us shed excess fat. However, it does at least support this concept. It’s also something that certainly appears to be worthy of further study. In the meantime, my advice remains for individuals to drink enough water to ensure that their urine remains pale yellow in colour throughout the course of the day.


1. Thornton SN, et al. Hydration increases cell metabolism. International Journal of Obesity [epub ahead of print publication 20 January 2009]

2. Mathai ML, et al. Selective reduction in body fat mass and plasma leptin induced by angiotensin-converting enzyme inhibition in rats. Int J Obes (Lond) 2008;32:1576″1584.

3. Schliess F, et al. Cell hydration and mTOR-dependent signalling. Acta Physiol (Oxf) 2006;187: 223″229.

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