Archives July 2024

If you’ve ever tried to lose excess weight, you’ve probably gotten this advice: drink more water. Or perhaps it was more specific: drink a full glass of water before each meal.

The second suggestion seems like a reasonable idea, right? If you fill your stomach with water before eating, you’ll feel fuller and stop eating sooner. But did that work for you? Would drinking more water throughout the day work? Why do people say drinking water can help with weight loss — and what does the evidence show?

Stretching nerves, burning calories, and thirst versus hunger

Three top theories are:

Feel full, eat less. As noted, filling up on water before meals has intuitive appeal. Your stomach has nerves that sense stretch and send signals to the brain that it’s time to stop eating. Presumably, drinking before a meal could send similar signals.

• The evidence: Some small, short-term studies support this idea. For example, older study subjects who drank a full glass of water before meals tended to eat less than those who didn’t. Another study found that people following a low-calorie diet who drank extra water before meals had less appetite and more weight loss over 12 weeks than those on a similar diet without the extra water. But neither study assessed the impact of drinking extra water on long-term weight loss.

Burning off calories. The water we drink must be heated up to body temperature, a process requiring the body to expend energy. The energy spent on this — called thermogenesis — could offset calories from meals.

• The evidence: Though older studies provided some support for this explanation, more recent studies found no evidence that drinking water burned off many calories. That calls the thermogenesis explanation for water-induced weight loss into question.

You’re not hungry, you’re thirsty. This explanation suggests that sometimes we head to the kitchen for something to eat when we’re actually thirsty rather than hungry. If that’s the case, drinking calorie-free water can save us from consuming unnecessary calories — and that could promote weight loss.

• The evidence: The regulation of thirst and hunger is complex and varies over a person’s lifespan. For example, thirst may be dulled in older adults. But I could find no convincing studies in humans supporting the notion that people who are thirsty misinterpret the sensation for hunger, or that this is why drinking water might help with weight loss.

Exercise booster, no-cal substitution, and burning fat demands water

Being well-hydrated improves exercise capacity and thus weight loss. Muscle fatigue, cramping, and heat exhaustion can all be brought on by dehydration. That’s why extra hydration before exercise may be recommended, especially for elite athletes exercising in warm environments.

• The evidence: For most people, hydrating before exercises seems unnecessary, and I could find no studies specifically examining the role of hydration to exercise-related weight loss.

Swapping out high calorie drinks with water. Yes, if you usually drink high-calorie beverages (such as sweetened sodas, fruit juice, or alcohol), consistently replacing them with water can aid weight loss over time.

• The evidence: A dramatic reduction in calorie intake by substituting water for higher-calorie beverages could certainly lead to long-term weight loss. While it’s hard to design a study to prove this, indirect evidence suggests a link between substituting water for high-cal beverages and weight loss. Even so, just as calorie-restricting diets are hard to stick with over the long term, following a water-only plan may be easier said than done.

Burning fat requires water. Dehydration impairs the body’s ability to break down fat for fuel. So, perhaps drinking more water will encourage fat breakdown and, eventually, weight loss.

• The evidence: Though some animal studies support the idea, I could find no compelling evidence from human studies that drinking extra water helps burn fat as a means to lose excess weight.

The bottom line

So, should you bump up hydration by drinking water before or during meals, or even at other times during the day?

Some evidence does suggest this might aid weight loss, at least for some people. But those studies are mostly small or short-term, or based on animal data. Even positive studies only found modest benefits.

That said, if you think it’s working for you, there’s little downside to drinking a bit more water, other than the challenge of trying to drink if you aren’t particularly thirsty. My take? Though plenty of people recommend this approach, it seems based on a theory that doesn’t hold water.

About the Author

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD

As the adage goes, the eyes are the windows to the soul. So what does it mean to wish yours were a different color?

Apparently enough people share this desire to create a bustling market for color-changing eye drops, which are making the rounds through social media and online retailers.

Personalizing eye color might sound tempting, especially for younger people and those who enjoy experimenting with elements of fashion or style. But are over-the-counter, color-changing eye drops safe? The answer is a hard no, according to the American Academy of Ophthalmology (AAO), which recently issued a warning against “eye color-changing solutions.”

Why shouldn’t you try color-changing eye drops?

Color-changing eye drops aren’t approved by the FDA, haven’t been tested for safety or effectiveness, and could potentially damage people’s eyes, the AAO warns.

“It might seem benign when you see a product like this online,” says Dr. Michael Boland, an associate professor of ophthalmology and glaucoma specialist at Harvard-affiliated Mass Eye and Ear. “People think, ‘Why not try it?’.” “But there’s no way to know what’s in these bottles and no oversight over how they’re being made.”

How do the eye drops work?

That’s not clear. Companies manufacturing the drops claim the products adjust levels of melanin in the iris, the colored portion of the eyeball. Purportedly, the effects begin to be visible within hours and can last for a week or longer. If a user wants enduring results, they’ll need to continue using the product.

But these claims skirt a complete lack of evidence that the drops have any effects on the iris, much less the desired effects, Dr. Boland says.

“I’ve found zero descriptions of how they work in terms of a plausible mechanism,” he says. The ingredients list includes things that might be found in other eye drops or drugs or even cosmetics, but nothing that would actually change your eye color.”

How might the drops hurt your eyes?

The AAO lists a variety of potential safety risks from using these products or any other unregulated eye drops, including:

• inflammation
• infection
• light sensitivity
• increased eye pressure or glaucoma
• permanent vision loss.

“All of those problems are possible, since we don’t have any real idea what’s in these bottles,” Dr. Boland says. “The biggest concern is damage to the cornea, the clear part of the front of the eye. If the cornea is damaged by the chemicals in those bottles, you might lose vision.”

Are there safe alternatives to change eye color?

Still hankering for a way to get, say, Taylor Swift’s electric blue eyes or Julia Roberts’ golden brown peepers? There is a trustworthy option, Dr. Boland says: colored contact lenses. But he recommends choosing that option with caution.

“Professionally prescribed and dispensed contact lenses are a safe way to change your eye color,” he says. “But don’t buy them online. Get them from a reputable source to make sure they’ve been regulated and evaluated as safe, because contacts can damage the eye if they’re not designed properly or kept clean.”

About the Author

Maureen Salamon, Executive Editor, Harvard Women's Health Watch

Maureen Salamon is executive editor of Harvard Women’s Health Watch. She began her career as a newspaper reporter and later covered health and medicine for a wide variety of websites, magazines, and hospitals. Her work has … See Full Bio View all posts by Maureen Salamon

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD