Truth or Myth: Drinking Water Helps with Weight Loss

November 28, 2021

by Cathe Friedrich

Water is essential for life and makes up two-thirds of the human body, and it’s a substance every organism needs for survival and well-being. But can drinking more of it help you lose weight? The belief that drinking water helps with weight loss has been around for a while now. The idea is that drinking a big glass of water helps suppress appetite, so you eat less when you’re well hydrated. Does science support this idea?

Does Water Suppress Appetite?

Water isn’t as effective at suppressing appetite as food, but there is evidence that it modestly reigns in appetite and calorie intake. In one study, women who drank 500 milliliters of water 30 minutes before each meal felt less hungry. They also lost body weight and body fat. Another study found that subjects who drank 2 glasses of water before meals consumed 22% fewer calories.

Why might drinking water before a meal be effective for weight loss? The water expands your stomach and sends feedback back to your brain that your stomach is full. The mechanism appears to be stretching and expanding the stomach. But what about eating something high in fiber AND drinking water? Fiber absorbs the water in your stomach and causes the walls of your stomach to expand even more than drinking water alone. Plus, studies show that fiber has appetite-suppressing benefits.

Are there drawbacks to drinking water before meals? A downside is drinking large quantities of water before eating could hinder digestion by diluting digestive enzymes that break down food, but this is unproven.

Some People Mistake Thirst for Hunger

Could those hunger pangs be thirst? Research shows it’s not uncommon for people to think they’re hungry when they’re thirsty. So, it may be helpful to drink a glass of water when you’re tempted to eat a snack and see how you feel afterward. Quenching your thirst may be all you need to strike down that hunger pang or craving for something sugary.

Does Drinking Water Boost Your Metabolism?

Other people drink water because they believe it boosts their metabolism. There is scientific evidence that drinking ice-cold water gives a modest boost to resting metabolic rate. Your body must expend more energy to heat up the water, and that means more calories burned. However, this effect is modest enough that it’s not a strategy you can depend on for significant weight loss.

You might wonder why water modestly boosts resting metabolic rate? Research shows drinking cold water activates the sympathetic nervous system, the component of your nervous system that has an activating effect on your body. After drinking cold water, a more active sympathetic nervous system helps you burn more calories.

One study found that consuming 500 milliliters of water, the equivalent of a little more than 2 cups, boosted resting metabolic rate by 30%. The increase in metabolism lasted around 40 minutes. So, there is some truth to the idea that drinking water speeds up resting metabolism.

The Biggest Benefit? Substituting Water for Sugary Beverages

While there’s evidence that drinking water before meals and when you’re hungry helps with weight loss and weight control, the biggest benefit comes from switching sugary beverages for water. If you drink three soft drinks per day and replace those high-sugar drinks with water, you’ll consume 420 fewer calories per day, not to mention the sugar or high-fructose corn syrup that does nothing positive for your metabolic health. That step alone could have a significant impact on your body weight and your health.

Drinking More Water Can Improve Your Mental Health Too

There’s more than one reason to ensure you’re drinking enough water. Another surprising benefit of drinking more water is that it can improve your mental health and brain function. Even mild dehydration, at a level you don’t feel thirsty, can cause brain fog, a depressed mood, and a mild headache. One study involving 20 healthy young men found as little as 2% dehydration caused increased fatigue, anxiety, and impaired memory and cognitive function. When you’re feeling tired or hungry, rehydrate by drinking a glass of water or two and see if it helps.

The Bottom Line

Drinking more water, especially as a replacement for beverages with calories, is a small step you can take for healthier body weight. If you don’t like plain water, try adding cucumber slices, herbs, or fruit slices to your water glass. Infused water is a popular way to make water taste better, and you can infuse your water with many sliced fruits, berries, or herbs. You’ll feel better, your brain will function more efficiently, and you’ll have more clarity if you consume enough water, and not let your body’s water stores dwindle. Water is basic to life, and it makes up 60% of your body. Make sure you’re getting enough.

References:

“6 reasons why drinking water can help you to lose weight.” 28 Jun. 2018, medicalnewstoday.com/articles/322296.
“More Food, Fewer Calories? – WebMD.” webmd.com/diet/obesity/features/more-food-fewer-calories.
“Yes, drinking more water may help you lose weight | Hub.” 15 Jan. 2020, hub.jhu.edu/at-work/2020/01/15/focus-on-wellness-drinking-more-water/.
Ganio MS, Armstrong LE, Casa DJ, McDermott BP, Lee EC, Yamamoto LM, Marzano S, Lopez RM, Jimenez L, Le Bellego L, Chevillotte E, Lieberman HR. Mild dehydration impairs cognitive performance and mood of men. Br J Nutr. 2011 Nov;106(10):1535-43. doi: 10.1017/S0007114511002005. Epub 2011 Jun 7. PMID: 21736786.
Dennis EA, Dengo AL, Comber DL, Flack KD, Savla J, Davy KP, Davy BM. Water consumption increases weight loss during a hypocaloric diet intervention in middle-aged and older adults. Obesity (Silver Spring). 2010 Feb;18(2):300-7. doi: 10.1038/oby.2009.235. Epub 2009 Aug 6. PMID: 19661958; PMCID: PMC2859815.
Vij VA, Joshi AS. Effect of excessive water intake on body weight, body mass index, body fat, and appetite of overweight female participants. J Nat Sci Biol Med. 2014 Jul;5(2):340-4. doi: 10.4103/0976-9668.136180. PMID: 25097411; PMCID: PMC4121911.
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.
“Water | The Nutrition Source | Harvard T.H. Chan School of ….” https://www.hsph.harvard.edu/nutritionsource/water/.