Oct 05 2011

Do Cold Drinks Alter Digestion?

A common theme of this blog is that there is a great deal of misinformation out there. The internet is a double-edged sword, providing tremendous access to useful information, but increasingly buried in a mountain of bad, poorly sourced, and often just incorrect information. So the savvy internet user needs to develop the skills necessary to distinguish reliable information from misinformation.

Here is just the latest example – I was recently sent a link to this article on Discover Fit & Health – Stop Drinking Water With Meals–Seriously. The articles carries the “Discover” brand, and many readers might confuse this for an indicator of reliability. The author, Sara Novak , is described as:

…writes about health and wellness for Discovery Health. Her work is also regularly featured in Breathe Magazine and on SereneKitchen.com. She has written extensively on food policy, food politics, and food safety.

So she is not some anonymous blogger, nor does she appear to be selling dubious supplements or some multi-level marketing scheme. She is a health journalist writing for a health magazine. And yet she gives her readers this whopper:

The ancient science of Ayurveda says that drinking water during meals, specifically cold water, puts out our digestive fire so that our bodies don’t properly digest the foods we eat. As a result, it’s recommended that you avoid drinking water at least 30 minutes before and 30 minutes after your meal. If you must have a drink, sip on a room temperature beverage.

The “science of Ayurveda?” I think she means the ancient superstition of Ayurveda. Calling something a science does not make it so. I get the sense that Novak has no idea what the definition of “science” is – it’s not any body of beliefs, it refers to the methods by which a body of knowledge is built.

Her only reference for this claim is an article on NaturalNews by Elizabeth Walling – essentially we have one uninformed health writer referencing another uninformed health writer. Also, NaturalNews is a notorious crank site, in my opinion, with no scientific credibility.

The article above is also not an isolated incident. The claim that water, particularly cold water, impairs digestion is common on the web, especially in nutrition circles. I found many sites repeating this myth, including this Nutrition Counseling site, which writes:

If the stomach’s content is colder than body temperature, then foods such as meat, fish, poultry, cheese, beans, nuts, and seeds, which are normally predigested in the stomach for 4-5 hours, are pushed out of the stomach to the small intestines in only 20 min.

Author, Marta Tereshchenko, gives no references for this claim.

None of this sounded right to me, so I did some searching to see what has been published with regard to these two claims – that water dilutes gastric enzymes and acid and impairs digestion, and that cold temperature meals accelerate gastric emptying.

The first claim flies in the face of basic human physiology (despite the quaint notion that water puts out our digestive “fires” – seriously?). Digestion is a water-intensive process. Some of the chemical reactions that digestive enzymes engage in actually require water. For this reason the stomach will secrete water, along with the gastric acid and digestive enzymes, to make the gastric juice that breaks down food for later further digestion and absorption in the intestines.

Water (or any drink that is mostly water) serves several functions during meals. It helps to wash food particles down the esophagus and into the stomach. It also helps to break apart large chunks of food and actually helps acids and enzymes get access to the food particles. Drinking a lot of water during a meal will dilute the enzymes in the gastric juice, but this is irrelevant to its function. The stomach is quite capable of regulating its own gastric juice content, and taking water during meals is helpful to this process. (This is textbook stuff – there are a couple of references in this overview.)

So Novak’s advice, based upon superstition and dubious crank web sites, is the opposite of the truth.

What about the claim that the temperature of food affects digestion, specifically gastric emptying? I was able to find a number of published studies that directly addressed this claim. In one study (Mishima 2009) hot meals increased gastric emptying, while cold meals did not. Another (Troncon 1988) found that meals colder or warmer than body temperature delayed gastric emptying (so food stayed in the stomach longer – the opposite of what  Tereshchenko and many others claim?).

This latter study also highlights another variable – liquid vs solid meals. They found a variable response depending on whether or not the meal was liquid or solid and the total volume (which might relate to gastric tone).

A study by Bateman in 1982 found that results were variable, and concluded that they were determined by individual physiology, and not universal. Sun 1988 found a delay in gastric emptying with cold or warm liquids. But McCarther in 1989 found no difference in gastric emptying over a wide range of temperatures.

Interestingly, in 2000 Nakae published a study that found that cold pain delayed gastric emptying – even from dipping one’s hand in cold water. This was probably mediated through a vagal nerve response. This might introduce an artifact into studies whereby the trauma of studying gastric emptying, or the cold stimulus itself (whether or not it is consumed) might delay gastric emptying.

To summarize all of this – the various studies that directly look at this question found variable responses to warm or cold liquid or solid meals, but with a tendency to find delayed gastric emptying in response to food at other than body temperature. This effect, if real, may be a nonspecific vagal response, which can either be due to temperature or any pain or trauma.

What not a single study found, however, was accelerated gastric emptying in response to cold water or food. The actual scientific results, if anything, are the exact opposite of what many of the nutrition sites are claiming.

Conclusion

With regard to the specific questions raised in the above articles, the scientific data indicates that water, of any tolerable temperature, does not have an adverse effect on digestion. Water, in fact, is critical for digestion. So, drink as much as you want (within reason, of course) during meals. If you are thirsty – drink. Thirst is the best indicator that your body wants more water.

It feels good to wash down food with water – and in this case there is a good reason. Liquids help wash down the food, they help break up the food, and aid in digestion.

All of this information is freely available on the internet. It did take some effort and searching for me to find sufficient reliable sources to flesh out this issue, however. But isn’t that the job of a health journalist – to do the leg work to find reliable information?

I get the sense that ideology, and not just laziness, is playing a role here. Both of the articles I referenced above also went further to say that poor digestion caused by cold water will cause “toxins” to build up in the body, and cause many specific health problems. This claim was also unreferenced, and is also completely bogus. Both authors appear to be buying into the “alternative” nutritional propaganda. The positive reference to the “science of Ayurveda” is also another clue that we are dealing with an ideologue, not a diligent broker of legitimate scientific information.

This is part of a disturbing trend – the substitution of carefully referenced scientific information with ideologically motivated “alternative” beliefs. There are common themes to these beliefs – they often follow the naturalistic fallacy (“natural” is always better), and often make vague references to “toxins” as a cause of illness. It is also common to grossly overestimate the role of nutrition in illness, and therefore as an intervention to deal with illness.

In this case the “alternative” approach to information led to specific recommendations (avoid water, especially cold water, during meals) that is the opposite of what scientific information tells us – that drinking water of any comfortable temperature during meals is good for digestion, and certainly is not a problem.

We also learn from this episode to be skeptical not only of information we read on the internet (yes, including this blog – don’t just believe anything I write, check out the references if you are interested), but also of sources that appear trustworthy. Just because a big media company (in this case Discover) is behind an article or an online magazine does not mean that the information or the author has been vetted and is reliable.

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