Can Drinking a Glass of Water Before a Meal Enhance Weight Loss?

April 25, 2021

by Cathe Friedrich

You may have heard that drinking water before a meal can help you eat less, and possibly even curb those cravings for junk foods. Who wouldn’t want to get slimmer by drinking a glass of water before a meal? But as you know, there’s a lot of weight loss advice that isn’t backed by science. Is this one of them?

Hydration Matters

Water contains no calories and supplies no energy, so it’s not a substitute for food, but it’s necessary for life and is involved in every chemical process in your body. So, you need it in substantial quantities just to survive.

Studies also show that people don’t consume enough water, but hydration needs vary between individuals and the environment they’re in. The quantity of water you need depends on age, diet, the medications you take, how physically active you are, and the environment you live in. If you live in a hot environment and sweat a lot, you’ll need more fluid than someone who lives in a cool climate and is sedentary.

But can drinking water before meals help you eat less and lose weight?

Some People Confuse Thirst and Hunger

Are you hungry or thirsty? According to the Polycystic Kidney Disease Foundation, 37% of people confuse thirst signals with hunger. It seems our brains aren’t skilled at distinguishing between the two.

So, you might head to the refrigerator for a snack rather than rehydrating with a glass of water. Thirst and hunger signals get crossed in your brain. That’s where the advice to drink a glass of water if you feel hungry comes from. There’s a chance that the ‘hunger’ you feel is really thirst!

It also shows why it’s important to question whether you’re thirsty before biting into a snack. Also, don’t wait until you’re thirsty to drink water. Studies show you can be 1-2% dehydrated before you feel thirsty. Therefore, thirst isn’t a good indicator of whether you’re hydrated.

Does Drinking Cold Water Before a Meal Boost Resting Metabolic Rate?

Another way water may help with weight control is the effect it has on metabolism. Research shows drinking a half-liter of water boosts resting metabolic rate by an average of 20% for up to an hour after you drink it.

If you drink very cold water, it causes a modest bump up in resting metabolic rate since your body has to work harder to warm the water to body temperature. This alone isn’t enough to cause significant weight loss, but in the context of a healthy diet and physical activity, it may have modest benefits. Therefore, drinking a glass of ice-cold water before a meal could give you a slight weight loss advantage.

Water Expands Your Stomach

When you drink a glass of water, your stomach distends a bit because of the added volume. This stretching phenomenon can increase satiety enough to reign in the number of calories you eat. Some studies show that people who drink water before a meal eat fewer calories and that’s an advantage if you’re trying to lose weight.

Drinking Water Works Best as a Substitute for Sugary Beverages

One of the best ways to reduce calorie intake and your risk of weight gain is to drink water with a meal rather than a sugary beverage. The sugary beverage will raise blood sugar and cause an insulin surge that makes it easier for your body to store fat. In contrast, water is sugar and calorie-free. If you drink soda or sugary drinks with meals, drinking water instead could have a significant impact on your weight over time.

Is There Scientific Proof that Drinking Water Before Meals Boosts Weight Loss?

A 2015 study of 84 obese adults carried out by researchers at the University of Birmingham in the United Kingdom found that participants who drank 16 ounces of water 30 minutes before a meal lost more weight than those who didn’t. In fact, the water drinkers lost an average of 2.87 pounds more than those who didn’t down a glass of water before meals. It’s a finding that needs more research but it’s a small step anyone can take. At the very least, it will improve hydration.

Other Reasons to Drink Water

Beyond weight control, drinking more water will help you feel more energized since even mild dehydration causes fatigue, lack of motivation, and headache. You’ll simply feel better if you hydrate, especially if you replace sugary beverages with water. Another bonus: Some studies show that drinking more water may lower the risk of certain cancers.

According to a study in the Journal of Clinical Oncology, drinking more water may reduce the risk of cancers of the colon, rectum, bladder, and breast. The evidence is strongest for bladder cancer. Drinking water dilutes the urine. When your urine is more dilute, fewer toxins and carcinogens in your urine contact the bladder wall and cause damage or inflammation.

The Bottom Line

Drinking water before meals is unlikely to have a huge impact on your weight, but it all counts. The best approach may be to substitute water for the current beverages you drink, since the sugar and calories in other beverages add up quickly. If you do that, you’ll likely lose a few pounds. Plus, there are other reasons to make sure you’re drinking enough water and aren’t walking around in a dehydrated state. Skip the sugary drinks, and sip on water!

References:

org. “Hunger vs. thirst: tips to tell the difference”
com. “Does Drinking Cold Water Burn More Calories than Warm Water?”
Boschmann M, Steiniger J, Hille U, Tank J, Adams F, Sharma AM, Klaus S, Luft FC, Jordan J. Water-induced thermogenesis. J Clin Endocrinol Metab. 2003 Dec;88(12):6015-9. doi: 10.1210/jc.2003-030780. PMID: 14671205.
DOI: 10.1200/JCO.2004.99.245 Journal of Clinical Oncology 22, no. 2 (January 15, 2004) 383-385.
“Water consumption increases weight loss during a ….” https://pubmed.ncbi.nlm.nih.gov/19661958/.
“Drink Water Before Meals to Lose Weight?.” 28 Aug. 2015, https://www.webmd.com/diet/obesity/news/20150828/water-weight-meals-obesity.