When you first start a new diet or exercise program, you may notice a quick drop in weight on the scale. This is often attributed to water weight, not fat loss. So how much of that initial weight loss is actually from water versus fat?
What causes water weight gain?
Water weight refers to the amount of water stored in your body tissues and bloodstream. Your body needs to maintain a certain level of hydration, so it will hold on to water when necessary. Here are some of the main causes of excess water retention or bloating:
- Eating a diet high in sodium
- Hormonal changes like menstruation
- Medications like corticosteroids or NSAIDs
- Being sedentary
- Excess stress
- Dehydration – counterintuitively, dehydration triggers the body to retain more water
- High carb intake – carbs require water to be stored in the body
Consuming excess sodium is one of the biggest culprits of water retention. Processed and restaurant foods tend to be very high in sodium. The more salt you eat, the more water your kidneys need to hold onto to maintain fluid balance in the body. This leads to swelling or bloating.
Why do you lose water weight first?
When you make changes to your diet, exercise regimen, or fluid intake, your kidneys respond by flushing out excess water. Here’s why water weight drops rapidly at the start of a diet or fitness program:
- Reduced sodium intake – eating less processed foods and salt causes you to excrete more water
- Lower carb intake – reducing starchy carbs causes you to store less water since carbs attract water
- Increased exercise – sweating from exercise removes both water and electrolytes like sodium from your body
- Drinking more water – counterintuitively, being better hydrated signals your kidneys to release unneeded water
In addition, calorie restriction itself can lead to water loss because your body breaks down stored glycogen in the muscles and liver. Glycogen is basically the stored form of carbohydrates, and it’s bound to water. So depleting glycogen leads to additional water loss early on in a diet.
How much water weight do you lose initially?
It’s difficult to provide an exact number on how much water weight you’ll lose right away when starting a diet, because it depends on several individual factors. However, experts estimate the average water weight loss in the first week of a diet is around 2-5 pounds (0.9-2.3 kg).
Studies have looked at this initial water weight fluctuation in people on weight loss diets. Here’s some of what they’ve reported:
- Over 7 days, water loss accounted for 91% of the weight lost on a very low calorie diet (1).
- Water loss averaged 1.6 pounds (0.7 kg) in the first 5 days of a low calorie diet (2).
- Low carb diets lead to an average water loss of 5 pounds (2.3 kg) in the first week (3).
As you can see, cutting carbs tends to have the biggest impact on initial water weight loss. Very low calorie diets will also lead to more water loss at the start.
When do you start losing fat?
Fat loss occurs more slowly than water loss. You can start losing small amounts of fat in the first 1-2 weeks of a diet. However, noticeable fat loss usually doesn’t happen until after the 2 week mark.
That’s because it takes time for fat cells to release their stored triglycerides and shrink in size. Fat cells don’t like to give up their fat! The longer you stick with a reduced calorie diet and exercise plan, the greater the fat loss will be.
One study in obese women compared water vs fat loss over 6 weeks on a low calorie diet (4):
| Week | Total weight lost | % from water | % from fat |
|---|---|---|---|
| 1 | 3.6 lbs (1.6 kg) | 89% | 11% |
| 2 | 1.4 lbs (0.6 kg) | 72% | 28% |
| 3-6 | 5.4 lbs (2.4 kg) | 31% | 69% |
As shown, the majority of weight lost in the first 1-2 weeks is water. Fat loss becomes more prominent starting around week 3. This study demonstrates that you need to be patient and stick with your plan consistently in order to lose fat.
Tips to lose fat faster
Here are some tips to ramp up fat burning after you’ve dropped that initial water weight:
- Be consistent – stick with your diet and exercise plan day in and day out
- Cut calories moderately – aim for a 500-750 calorie per day deficit
- Eat plenty of protein – aim for 0.7-1g per pound of body weight
- Lift weights – lifting helps retain and build calorie-burning muscle
- Do HIIT – incorporate high intensity interval training to rev up metabolism
- Get enough sleep – lack of sleep increases hunger hormones
- Manage stress – high cortisol slows fat loss
Should you be discouraged by initial water weight loss?
Losing water weight first is actually a good sign that the diet is working! Although the number on the scale may go down rapidly at first, this shouldn’t discourage you.
Remind yourself that this initial drop is just water, and fat loss will occur more gradually over the coming weeks. Stick with your plan and be patient.
Additionally, getting rid of excess water has benefits for reducing bloating and puffiness. You may start looking slimmer right away even if you haven’t lost much fat yet.
Can you prevent water weight regain?
It’s common to regain some water weight after ending a diet, especially if you go back to eating a lot of salty, processed foods or carbs. However, you can take steps to minimize water weight regain:
- Continue eating plenty of nutrient-rich, unprocessed foods
- Limit sodium intake by cooking at home more often
- Choose complex, fiber-rich carbs over refined carbs
- Drink water as your primary beverage
- Weigh yourself regularly to catch any fluctuations
Making sustainable, healthy eating patterns part of your regular routine can help maintain results long-term.
The bottom line
It’s typical to lose more water weight than fat within the first 1-2 weeks of starting a new diet or exercise regimen. Water fluctuations account for most of the initial weight you see come off on the scale.
Significant fat loss tends to kick in after a couple of weeks. For the best chance of success, stick with your program consistently and be patient as your body adapts.
Although water weight will inevitably fluctuate day-to-day, you can take steps to prevent excessive rebound. Focus on sustainable, healthy eating habits that nourish your body and support your fitness goals.
