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There's an old dieter's adage that you should drink a full glass of water before a meal, to reduce your appetite and prevent yourself from eating too much.

There are also claims that drinking water during meals is a bad idea, because it may have negative effects on digestion.

Medical professionals, on the other hand, keep telling us to chug down all the water we can, no matter what time of day.

When it comes to water and meals, what's true, and what's a myth?

Let's start with that sage advice from dieters, because it's actually based firmly in scientific research.

Drinking two glasses (around 500ml in total) of water before mealtimes has been proven by numerous studies as a weight loss aid. A 2016 study published in Obesity journal found overweight adults ate 40 less calories per meal after 500ml of H2O "pre-loading", and other research has shown slightly higher results.

In fact, two studies (both from the Journal of Clinical Endocrinology and Metabolism) have found that your metabolic rate and energy expenditure are increased by 30 per cent and 24 per cent (respectively) within 10-60 minutes of drinking 500ml of water.

Weight loss

Using the same metrics, another study by the University of Birmingham found the average weight loss over a course of three months was between two and four kilograms.

That's without changing your diet at all, although there's some suggestion that because high water consumption requires more frequent bathroom breaks, study participants could be walking more, and thus burn more calories that way.

The suggestions that drinking water and eating simultaneously during one meal could negatively affect your health are misleading.

There's the myth that drinking water dilutes the digestive enzymes and acid in the stomach, making it more difficult for to process what you're eating. This claim populates natural health and beauty blogs and spouted by some dieticians.

Moreover, there's also the misguided argument that drinking water while eating speeds up the exit of foods (and their nutrients) through the body, thus disallowing maximum nutritional benefit and enabling poorer digestion.

According to the journals Digestive Diseases and Sciences and Clinical Nuclear Medicine, both claims are not scientifically sound. There's no reliable evidence-based proof to support either argument.

The takeaway here is actually a nice little lesson in human biology: your digestive system simply and efficiently adapts its secretions to best suit a food's consistency, and will digest as appropriate for the conditions it has been given.

There's one exception where this doesn't necessarily happen, but all it tells us is that there are some people who should take sips of water throughout their mealtimes, not that they shouldn't.

The chew factor

Those that don't chew their food thoroughly enough often end up swallowing large chunks, which makes digestion harder and leads them to feelings of pain and bloating. Water breaks these chunks up as soon as they go down the throat and into the stomach, meaning water can help digest food.

What's more, water is essential in softening stools and helping them glide through the body. This means you're less likely to experience constipation.

The only scientific evidence that suggests people should not drink water with their food concerns those with gastric reflux (also known as acid reflux). As a study in Surgical Endoscopy journal confirmed, extra liquid in the stomach emulates the feeling of being over-full, and may trigger their reflux symptoms. Such people may feel more comfortable drinking and eating separately.

We must note that there is no scientific evidence to say that people who chew adequately and eat at a regular (i.e. not Labrador-like) pace must drink water with meals. There's no data to confirm that water consumed with food interferes with your digestive enzymes, neither positively or nor negatively.

It's up to you and your personal choice. As such, unless you're one of the previously-mentioned exceptions, you can drink your required daily dose of water – which still remains at eight glasses/two litres – whenever you want throughout the day.

Written by Lee Suckling. Republished with permission of Stuff.co.nz.

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