You started creatine on Monday. By Friday the scale reads higher than it has in weeks, and you have not eaten more than usual. The obvious question is whether that is fat already.
Usually it is not. Creatine is stored in your muscles and draws water into the muscle cells. Your trend weight therefore steps up after the start and then runs flat again. Fat gain looks different: it needs a sustained calorie surplus, and the curve keeps climbing week after week.
What creatine does in the body
Creatine is a building block in the energy supply of muscle. When you take it as a supplement, you fill the stores in your muscles. Water enters the cells along with it, and that water has weight. It sits inside the muscle, not in fat tissue, and it does not mean your body is storing surplus energy. The rise starts while the stores fill and ends when they are full. After that, creatine holds your weight at the new level without pushing it further.
Safety often comes up next. The International Society of Sports Nutrition position stand describes creatine supplementation as safe and well tolerated in healthy people. That applies to healthy people. If you have kidney disease or take medication regularly, talk to your doctor first.
How large the step is differs from person to person. The sources behind this article give no reliable figure in kilos or pounds, so this article names none. You measure it best on yourself.
Water step or fat gain: how to tell
The shape of the curve says more than its height. A comparison:
| Creatine water step | Fat gain | |
|---|---|---|
| Course of the trend | Rises after the start, then flat | Keeps rising |
| Trigger | The day you start taking it | A calorie surplus over weeks |
| Eating | Unchanged | More than you burn |
| After stopping | Trend drops back to the earlier level | Stays until you create a deficit |
The last row follows from the mechanism: water bound in the muscles leaves when the stores empty. Fat leaves only through a deficit.
A worked example
Your trend weight sits at 80.0 kg (176.4 lb) before you start, and the daily values scatter between 79.6 and 80.4 kg (175.5 to 177.2 lb). After the start the trend climbs to 80.9 kg (178.4 lb) and stays there. These numbers are an arithmetic example, not an expectation.
If those 0.9 kg (2.0 lb) were fat, the usual approximation of about 7,700 kilocalories per kilogram of body weight would require roughly 6,900 kilocalories of surplus. Spread over four weeks, that is around 250 extra kilocalories every day. If you have neither eaten more nor moved less since the start, the water step fits what you see better. You can run the same sum with your own numbers: multiply the step in kilograms by 7,700 and you know the surplus that fat would have needed.
If the rise instead continues for two or three months, the sum points the other way. A surplus has joined the step, and your trend shows it long before the mirror does.
Reading the question in the trend curve
Single daily values do not help here. After the start they scatter as they always did, as described in Why your weight fluctuates daily, and a high Friday says nothing about fat. Trend weight smooths that scatter, so the step shows up as a step. How the smoothing works is explained in Trend weight instead of the daily number.
Lean is law gives you three tools for this, all under "Settings & more" → "Experiments and markers":
- Set a marker (free). Create a marker on the start day, for example with the type "Supplement" and the label "Creatine". It appears in the history and as a line in the chart. Later you can see that the rise begins at the marker and not at a weekend with pizza.
- Restart the trend (Pro). The "Restart trend" switch in the same dialog begins the trend anew on the start day. Weekly rate and 7 day change then refer only to the time with creatine and are not pulled along by the old level. The first weeks of the new segment contain the step. Judge the flat part that follows.
- Evaluation (Pro). If you set a duration, Lean is law compares the weekly rate before and during the marker. Each section needs at least 7 days and 4 weigh-in days. The card carries a fixed note, "Correlation, not cause", and it applies here too: it shows what happened, not why.
Lean is law is not a medical device and does not judge whether you should take creatine.
If you are losing weight on creatine
This is where the step hurts most. You hold a deficit and the scale still goes up. Your fat loss continues in the meantime, but the water step covers it. You expect falling values, get the opposite for a few weeks and take it for a plateau.
Three things help. First, set the marker so you can attribute the step to the start day later. Second, judge your rate after the step and not from the start day. Third, look at values that do not depend on water in the muscles. Your waist is one. In Lean is law you log it under body measurements (Pro), on iPhone also from Apple Health. If your waist shrinks while the trend is flat or slightly higher, that points to fat loss.
If you want to gain weight instead, for example to build muscle, the step works in your favor. The trend rises faster at the beginning than your plan, and that is expected. Check your weekly rate after the step, not in the first days.
If you stop creatine, the trend falls again. Set a marker for that too, so you do not mistake the drop for fat loss.
What to do now
Before the first dose, create a marker: "Settings & more" → "Experiments and markers", type "Supplement", label "Creatine", start day today. Then weigh yourself as usual and read only the trend. Judge your progress once the curve runs flat again.