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What does it mean to lose 'water weight'?

9Honey Coach logo 9Honey Coach 12/01/2019 Kimberly Gillan
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The common warning against low- or no-carb diets is that the weight which rapidly falls off when you start out is just "water weight" — so it doesn't really count as weight loss.

For many, any reduction in the number on the scales is motivating. So if you start a keto or low-carb challenge, you might feel like you're having big weight loss wins as you drop fast kilos. 

The trouble, according to accredited practising dietitian Dr Alan Barclay, is that you're not losing body fat in the initial stages — you're just losing water stores. And if you start eating carbs again, your weight will bounce straight back up.

If you want the health and longevity benefits that come with weight loss, it's body fat you need to lose — not water. 

"You'll weigh less but if you have a lot of fat around the tummy [that's not healthy]," Dr Barclay explains. 

When we eat carbohydrates like grains and fruit, our body converts it to glycogen, a form of glucose that can be turned into energy wherever and whenever we need it.

"Glycogen is stored in granules in our muscles, liver and kidneys," says Dr Barclay, who is a spokesperson for the Dietitian's Association of Australia. 

"It is surrounded by water [which is required by] the enzymes that break it down into glucose so they can be released into the blood or muscles."

For each gram of glycogen we store in our body, we also store around three to four grams of water. So the average person on a very low-carb diet would lose around 2-2.5kg when they first start out, as they deplete their glycogen and the water stored with it.

"It will stay off as long as you stay on the diet," Dr Barclay explains.

If you go back to eating carbs, you'll likely notice a rapid spike in the scales, which some people point to as evidence that a low-carb diet keeps your weight down. 

"[People need to understand] that going back to carbs doesn't suddenly put on body fat – they've just regained the glycogen stores and associated water," Dr Barclay points out. 

The good news is that when you bring carbs back in — which you're very likely to do given evidence of how difficult it is to maintain a strict deprivation diet — you'll likely feel way more energetic.

"One of the things that people say with these very low-carb diets is that they feel tired and lethargic," Dr Barclay says.

"They can't think straight because the brain and the nervous system prefer glucose [as an energy source], so your energy levels should return to normal [when you eat carbs]."

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