Keto Diet Weight Loss: Why Early Pounds Come Off Fast
A fast drop on the scale after starting keto does not mean the same amount of body fat disappeared. When carbohydrate intake falls sharply, the body uses stored glycogen and releases some of the water stored with it. This can make weight fall quickly during the first several days.
South Korean actress Lim Ji-yeon gave a useful example. In a 2023 SBS clip, she said she had tried a keto-style diet by cutting carbohydrates and eating more meat and fat. She stopped after about 10 days because she said she had lost too much weight. However, she did not disclose exactly how much weight she lost or provide body-composition measurements.
Her experience raises an important question: When weight drops quickly on keto, how much of it is actually fat?
Why Keto Can Make the Scale Drop So Quickly
Your liver and muscles store carbohydrate in the form of glycogen. Glycogen is stored along with water.
When carbohydrate intake becomes very low, glycogen stores fall. As that glycogen is used, some of its associated water is released and excreted. Endotext notes that roughly 3 grams of water are stored with each gram of glycogen. Very-low-carbohydrate diets can therefore produce noticeable changes in body water during the early stages of weight loss.
This is why losing several pounds quickly after starting keto should not automatically be interpreted as losing several pounds of body fat.
Fat loss can occur if the diet creates an energy deficit, but early scale changes may reflect both fat loss and water loss. Once the initial glycogen and fluid changes have occurred, the early rate of weight loss usually does not continue at the same pace.
Keto and Low Carb Are Not the Same Diet
People often use “keto” and “low carb” as if they mean the same thing, but the degree of carbohydrate restriction can be very different.
Common research definitions help show the difference:
| Eating pattern | Typical carbohydrate intake | Main feature |
|---|---|---|
| Very-low-carb or ketogenic | About 20–50 g/day or under 10% of calories | Restrictive enough to promote nutritional ketosis |
| Low carbohydrate | Less than 130 g/day or under 26% of calories | Reduces carbohydrates without necessarily producing ketosis |
| Moderate carbohydrate | About 26–44% of calories | More flexible carbohydrate intake |
These ranges are commonly used in medical literature, although there is no single universal definition for every low-carb diet.
That distinction matters. Simply eating less bread, pasta, sweets, or rice does not necessarily mean you are following a ketogenic diet.
A true keto diet usually requires much more aggressive carbohydrate restriction.
You Do Not Have to Go Full Keto to Cut Carbs
For many adults, reducing lower-quality carbohydrate sources may be easier to maintain than immediately cutting carbohydrates to 20–50 grams per day.
A practical place to start is with foods that provide a lot of refined carbohydrate or added sugar without much fiber. Examples include sugar-sweetened drinks, candy, pastries, highly refined snack foods, and large portions of refined grains.
Then build meals around foods that still provide fiber and nutrients:
- nonstarchy vegetables
- beans or lentils when they fit your carbohydrate target
- smaller portions of minimally processed whole grains
- fish, poultry, eggs, tofu, or other protein foods
- nuts, seeds, avocado, and plant oils as fat sources
- water or unsweetened beverages instead of sugary drinks
The American Diabetes Association’s 2026 Standards of Care emphasizes minimally processed, nutrient-dense, high-fiber carbohydrate sources and reducing foods and drinks high in added sugar.
Fat quality matters too. A keto diet built largely around butter, fatty processed meats, and other foods high in saturated fat is not nutritionally equivalent to one that relies more heavily on olive oil, nuts, seeds, avocado, and fish.
The American Heart Association notes that very-low-carb and keto diets can be high in saturated fat, which may raise LDL cholesterol in some people.
What Side Effects Can Happen When Carbs Drop Sharply?
Very-low-carbohydrate diets can produce symptoms during the early adjustment period.
Reported short-term effects include nausea, constipation, diarrhea, headache, fatigue, dizziness, vomiting, and temporary hypoglycemia. Changes in fluid and electrolyte balance may contribute to some of these symptoms.
That does not mean everyone who tries keto will experience these problems. It does mean that rapid weight loss accompanied by persistent vomiting, dehydration, severe weakness, or significant blood-sugar changes should not simply be treated as proof that the diet is “working.”
Food quality can also become an issue when carbohydrate restriction removes fruits, legumes, whole grains, and other fiber-rich foods without replacing their nutrients appropriately.
Diabetes Medications Can Change the Safety Picture
Extra caution is needed if you have diabetes.
People using insulin or medications that can cause hypoglycemia may experience a significant change in blood glucose when carbohydrate intake suddenly falls. Medication decisions should be made with the clinician who manages the diabetes rather than by independently stopping or reducing a prescription.
There is an additional concern with SGLT2 inhibitors. The 2026 American Diabetes Association Standards of Care identifies very-low-carbohydrate eating patterns, prolonged fasting, and dehydration as risk factors for diabetic ketoacidosis in people taking SGLT inhibitors and specifically advises discouraging a ketogenic eating pattern in people at risk.
This is especially important because SGLT2 inhibitor-associated ketoacidosis can sometimes occur without extremely high blood glucose.
If you have type 1 diabetes, take an SGLT2 inhibitor, use insulin or another glucose-lowering medication, or have significant kidney, liver, or pancreatic disease, discuss major carbohydrate restriction with your health care professional before starting.
What a Fast Keto Weight Drop Really Tells You
Lim Ji-yeon’s experience illustrates why short-term keto weight loss needs context. A rapidly changing scale can tell you that body weight is changing, but it cannot tell you how much of that change is fat, glycogen, water, or lean tissue.
If your goal is weight management rather than nutritional ketosis itself, you do not necessarily need to eliminate nearly all carbohydrate-containing foods.
Start by reducing added sugars and highly refined carbohydrates, choose higher-fiber foods you can sustain, pay attention to protein and fat quality, and track more than the scale. Waist measurements, hunger, energy, digestive symptoms, and how consistently you can maintain the eating pattern can provide useful information alongside body weight.
Source:
SBS Entertainment News — Lim Ji-yeon ketogenic diet interview coverage
NCBI Bookshelf, Endotext — Dietary Treatment of Obesity
NCBI Bookshelf, StatPearls — Low-Carbohydrate Diet
NCBI Bookshelf, StatPearls — The Ketogenic Diet: Clinical Applications, Evidence-based Indications, and Implementation
American Diabetes Association — Standards of Care in Diabetes—2026
American Heart Association — Prevention and Treatment of High Cholesterol
