Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
When it comes to weight loss, most people focus on calories, workouts, or portion sizes. Water often gets left out of the conversation. Yet research shows that drinking water before meals can help reduce calorie intake, which may contribute to weight loss and lower body measurements. That’s a powerful tool hiding in your water glass.
Proper hydration doesn’t just keep your body functioning; it can also boost metabolism, support fat breakdown, and make your workouts more effective. But how much water do you really need if weight loss is your goal?
Water is the most essential nutrient for life. It makes up about 60% of the human body and is critical for digestion, circulation, temperature regulation, and energy production. Without enough fluids, even mild dehydration can lead to fatigue, brain fog, and poor exercise performance.
Research highlights that proper hydration supports nearly every function of the body, including maintaining a healthy weight. Drinking more water also naturally reduces your intake of sugary drinks, which are one of the leading sources of excess calories in modern diets.
Yes, water does more than just quench your thirst. According to a study, drinking 500 ml of water increases metabolic rate by about 30% for up to 40 minutes. This effect is known as water-induced thermogenesis. Your body burns extra calories as it warms up the water to match your core temperature.
While this doesn’t mean water is a miracle fat burner, it does mean that staying hydrated can give your metabolism a small but helpful boost. Combined with other healthy habits, it can make a noticeable difference over time.
Hydration impacts weight loss in several interconnected ways. Here are the key benefits:
As mentioned earlier, water can slightly increase your resting energy expenditure. Even if the calorie burn isn’t massive, every little bit adds up and contributes to long-term weight control. By staying hydrated, you’re giving your metabolism the best chance to work efficiently day in and day out.
Sometimes the body confuses thirst with hunger, which leads to unnecessary snacking. A study found that young adults who drank water before a meal ate significantly less food compared to when they ate without water, yet they didn’t feel less full afterwards. This suggests that drinking water before meals can help reduce appetite without affecting satiety, making it a smart strategy for managing portions.
Water has zero calories, making it the perfect replacement for sugary drinks. Swapping just one can of soft drink (around 160 calories) per day for water could save you over 58,000 calories a year. That’s roughly 7.5 kg of body fat. Over time, these choices make a big difference in weight management.
Water is necessary for lipolysis, the process which your body breaks down fat for energy. Without adequate hydration, fat metabolism slows down, which can make weight loss harder than it needs to be. Staying hydrated ensures your body can tap into fat stores effectively.
Dehydration as little as 2% of body weight can decrease exercise performance. Drinking enough water helps you train harder, recover faster, and burn more calories during workouts. In other words, water keeps your fitness sessions productive.
Ironically, drinking more water helps your body retain less of it. When you’re dehydrated, your body clings to fluids, which can cause bloating and puffiness. Consistent hydration balances your system and helps you feel lighter.
Sugary drinks like juice, soda, or energy drinks are packed with calories that add up quickly. Swapping them for water significantly lowers your daily calorie intake without leaving you hungry. It’s one of the easiest and most effective ways to cut calories without effort.
There isn’t a single ‘magic number’ for everyone, but nutrition guidelines provide useful targets based on age and gender. The Nutrient Reference Values for Australia and New Zealand recommend how much water adults should aim to drink each day:
Men (19–70+ years) – 3.4 L total water per day, including 2.6 L from fluids (about 10 cups)
Women (19–70+ years) – 2.8 L total water per day, including 2.1 L from fluids (about 8 cups)
These amounts account for water from both beverages and food sources like fruits and vegetables. If you’re trying to lose weight, staying within these ranges, and sometimes slightly more if you exercise or live in a hot climate, can support hydration, appetite control, and fat metabolism.
Whether you’re a pro athlete, a gym regular, or someone who loves long runs or intense fitness classes, hydration plays a huge role in performance and recovery. According to the National Athletic Trainers’ Association (NATA), the goal is to stay ahead of fluid loss, aiming to keep body-weight reduction from sweat to under 2%. This means starting workouts well hydrated, sipping consistently during activity, and replacing what you lose afterwards.
Timing | Recommendation | Typical volume | Why / notes |
2–3 hours before exercise | Drink water or a light sports drink to begin well hydrated. | 500–600 ml | Gives the body time to absorb fluids and prevents starting in a dehydrated state. |
~10–20 minutes before exercise | Top up hydration with a small amount of fluid. | 200–300 ml | Prepares the body for exertion without causing stomach heaviness. |
During exercise | Sip at regular intervals to replace sweat losses. | 200–300 ml every 10–20 minutes | Adjust based on intensity, environment, and sweat rate. For long or very sweaty sessions, choose drinks with electrolytes. |
After exercise | Rehydrate gradually to restore balance. | Replace what was lost (weighing before and after can help estimate). | Fluids with electrolytes or mineral water may help restore hydration faster. |
Everyone’s hydration needs are unique. These factors play a big role:
Body weight and composition – Larger bodies and more muscle mass require more water.
Activity level and exercise routine – Active individuals need higher fluid intake.
Climate and environment – Hot and humid weather increases fluid loss through sweat.
Diet and salt intake – High-sodium or high-protein diets demand more water to balance electrolytes and support digestion.
Individual health conditions – Illness, pregnancy, or medications can increase hydration needs.
Drinking enough water daily can be a challenge, but small strategies make it easier.
Having water first thing in the morning helps kickstart hydration after hours of sleep. It also supports digestion and may give you a natural energy boost before reaching for coffee. Over time, this habit sets a healthy tone for the rest of your day.
A water bottle within reach is a constant reminder to drink more. Many people find they naturally sip more often when water is easily accessible. Choosing a fun or stylish bottle can also make the habit more enjoyable.
Apps and alarms can be handy nudges when life gets busy. A reminder every hour ensures you’re drinking regularly rather than forgetting for half the day. Over time, you’ll train yourself to reach for water without needing the alarm.
If plain water feels boring, infuse it with lemon, cucumber, or berries. This adds a refreshing taste without sugar or artificial additives. Experimenting with flavours can make hydration more exciting and sustainable.
A pre-meal glass of water may reduce overall calorie intake. It also helps with digestion and gives you a sense of fullness that prevents overeating. Making it a routine before breakfast, lunch, and dinner can lock in this healthy habit.
Workdays can fly by without enough hydration, especially if you’re focused on tasks. A glass or bottle at your desk encourages steady sipping throughout the day. It’s a simple way to boost both hydration and productivity.
Sparkling water gives the fizz without the added sugars and calories. It can be a satisfying swap for soft drink lovers who struggle with cutting soda completely. Adding a splash of lemon or lime can make it feel even more indulgent.
Foods like watermelon, cucumber, and celery contain up to 90% water. They’re tasty, hydrating, and packed with vitamins and fibre. Incorporating them into meals or snacks supports both hydration and nutrition.
Wondering if you’re meeting your needs? Here are some common indicators:
Light-coloured or clear urine
Rarely feeling thirsty
Steady energy levels
Fewer headaches
Healthy skin appearance
Good digestion and regular bowel movements
Reduced cravings for sugary snacks
Improved focus and concentration
If you’re ticking most of these boxes, chances are your hydration is on track.
Water isn’t a magic pill for weight loss, but it’s one of the simplest and most effective tools to support your goals. From boosting metabolism to reducing cravings and improving exercise performance, proper hydration helps every step of the way.
Aim for around 2.2 litres daily if you’re female and 3 litres if you’re male, adjusting for exercise and lifestyle. By making small daily choices, like swapping soda for water or starting your morning with a glass, you’ll not only stay hydrated but also make weight loss easier and more sustainable.
Hydration helps, but food choices matter too. If you want practical, science-backed ideas for what to eat when hunger strikes, read What Should I Eat When I’m Hungry But Trying To Lose Weight?.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.