I was discussing Keto with a doctor (who was not a fan). He said, “You may lose weight quickly, but it’ll just be water weight.” The implication was that the second you eat an extra bread crumb, you’ll gain it all back.
True?
Like most of us, I certainly lose a lot of water weight every day (even though I try to consume a ton of sodium). Is this “real” weight loss, i.e., lasting weight loss?
Generally you’ll lose a few pounds of water weight in the beginning of keto (or more if you have a lot of inflammation going on or are very big to begin with) and after that, it’s fat. Yes, if later you have more carbs than your system can handle, you’ll add that water back on (and take it off again when you stop the carbs).
You can think of the water weight as the first 3 or 4 pounds that come off (or on) when you stop/start carbs. The effective part of keto with weightloss is the fat loss part. If he’s not a fan of keto I wouldn’t debate it with him!
In my case, it lasts as long as you keep keto/low carb going. I’m a little over 6 months into weight loss, and the only time I saw a major jump on the scale was when I had a cheat weekend of carbs, resulting in a 10lb water weight gain, which took a week to lose.
If I had 95 pounds of water weight to lose, I would have had severe lung issues or lymphedema. I had neither. That dr can bite my now much smaller ass.
This is an exaggeration but essentially true. The truth is if you adopt keto as a lifestyle which means a commitment to low carbs, no grains etc. then you’ll have lasting results.
If you look at keto as a short term weight loss diet and go back to eating carbs they will affect you and your body the same way when you add them back into your food.
The underlying and unspoken truth is that one would assume that carbs aren’t good for long term health and keto is. He’s implying that carbs are a necessity of life and keto will fail you in the end, completely ignoring that the carbs were the source of people’s metabolism disorder that led to weight gain in the first place. He probably also thinks you eat too much and don’t move around enough, completely ignoring the hormonal driven reason too much weight stems from. Get a new doctor that supports keto. 
in week one it is water weight. After that it will be fat or we would all be raisins by now. And yes if you go back to that old way of eating you will have the same weight gain you had before.
At first you lose water weight quickly, yes. But over time, you lose fat. I’ve lost 70ish lbs in 8 months. That’s not all water 
and I’m at a point now where if I eat some carbs every now and then, I don’t typically gain much. Maybe a pound or even less. And I get back on the horse and Keto on.
I lost 18 lbs in the first two weeks that I imagine was water. The next 40ish pounds came off slower and i doubt it was water. I can tell you that a few heavy binges over 2 or 3 consecutive days blow me up like a water balloon.
Sounds like an ignorant doctor fearing over possibly losing his job if he gave out guidance not approved by big pharma. Him implicating ull only lose the water weight and then itll be the same as trying to lose weight on sad diet almost sounds like he thought beforehand of stuff to say to anyone who confronts him with keto or he literally doesnt know anything else about keto but the water weight loss in absence of carbs (which was taught to him in school).
Carbohydrate (broken down into its constituent glucose) causes water retention, about 3 grams of water for each gram of glucose, as I recall, so yeah, we lose some water at first, as we burn off the glucose. But once that’s done, it’s fat from then on. But since fat is metabolized into water and carbon dioxide, your doctor is, in some very technical sense, right. 
If losing weight were as simple as draining the water out of me, I’d just put a spigot on my belly and butt. When I feel myself getting too heavy, I could go outside, turn on both spigots and spin in circles so I water my lawn. 
Lol - that’s excellent. I think he meant that it was “only water weight,” as in, you’d gain it back in a hot second. His assumption is that keto is a diet, that it will eventually end and that when you return to “normal” eating, you’ll gain back every last pound you lost and then some.
Ironically, this was not my doctor - it was my mother’s. I was talking to him about the possibility of her going on Keto for Parkinson’s. All 3 of her doctors have treated me like I’m from Mars for suggesting it.
Well I lost more than just water weight. 80 pounds and I only weigh 120 now.
Everyone who loses weight runs the risk of gaining it back if they go back to eating the way they were when they gained. The bias against this way of eating is real.
What he’s saying is pretty basic. We are designed to store excess sugars as glycogen in our muscles and liver for a rainy day. Like @PaulL says, water is stored along with that glycogen. Going low carb depletes these stores and enables lipolysis. There is no sin in this process. The problem occurs when our hormones run amok because we constantly make the wrong response to hunger. If our hormones are healthy, we all should have some degree of metabolic flexibility, meaning we can switch from a fat burning state to a glucose burning state when necessary.
