What happens if I stop carbs for a week?

November 12, 2025 •

4 min read

When you first stop eating carbs, your body can lose several pounds of water weight almost immediately. But what happens if I stop carbs for a week beyond just the initial water loss? The body undergoes a series of significant metabolic and symptomatic changes in this short timeframe, as it adjusts to a new primary fuel source.

Quick Summary

Stopping carbs for a week triggers an initial loss of water weight and can cause side effects like the 'keto flu,' fatigue, and brain fog, as your body begins converting fat into ketones for energy.

Key Points

Initial Water Weight Loss: In the first week, rapid weight loss is primarily water, as your body depletes its stored glycogen, which is bound to water.
Keto Flu Symptoms: Many people experience flu-like symptoms such as fatigue, headaches, and irritability as the body transitions away from using glucose for energy.
Metabolic Switch: After a few days, your body shifts into ketosis, using fat for fuel instead of glucose, a key metabolic change.
Increased Mental Clarity: Once fat-adapted, some individuals report enhanced focus and mental clarity, often accompanied by more stable energy levels.
Digestive Changes: Cutting high-fiber carb sources can lead to temporary constipation or bloating, requiring increased intake of low-carb vegetables.
Appetite Suppression: Many find that their appetite and cravings for carbs decrease as the week progresses and they feel fuller for longer.
Not a Long-Term Verdict: The experience of one week does not reflect the long-term effects or sustainability of a low-carb diet.

The First Few Days: The Carb Withdrawal and "Keto Flu"

Upon severely restricting carbohydrate intake, your body is suddenly deprived of its primary, fast-acting energy source: glucose. This metabolic change can shock your system, leading to a cluster of unpleasant symptoms commonly known as the "keto flu". These effects typically last for a few days as your body adapts. As your body uses up its stored glucose (glycogen), it also flushes out the water bound to it, which is the reason for the initial rapid weight loss often seen in the first week.

Common 'Keto Flu' Symptoms:

Fatigue and Low Energy: With no glucose for quick fuel, your energy levels can plummet, affecting daily tasks and workouts.
Headaches: A lack of glucose and changes in electrolyte balance can trigger headaches.
Irritability and Mood Swings: Your brain relies on glucose, and the abrupt deprivation can affect mood and mental state.
Brain Fog: Many report feeling mentally sluggish or having difficulty concentrating as the brain adjusts to a new fuel source.
Digestive Issues: Constipation or bloating can occur due to a sudden decrease in dietary fiber, which is common when eliminating grains and many fruits.
Cravings: Psychological and physiological cravings for high-carb comfort foods are common in the initial days.

Staying well-hydrated and replenishing electrolytes (sodium, potassium, magnesium) can help alleviate many of these symptoms. Eating nutrient-dense, low-carb vegetables can also help with fiber intake.

The Metabolic Shift: From Glucose to Ketones

After the first 3-5 days, your body's glycogen stores are largely depleted, and it enters a state of nutritional ketosis. In this state, your liver starts breaking down fat into molecules called ketones, which are used as an alternative fuel for your body and brain. This metabolic switch is a fundamental goal of very low-carb diets like the ketogenic diet. Once fat-adapted, many people report feeling a more stable, sustained energy level throughout the day, without the energy crashes associated with high carbohydrate intake.

What You Can Expect: Benefits and Changes

By the end of the week, as your body becomes more adapted to running on fat, you may start to experience some of the reported benefits of a low-carb diet. These changes can be motivating, but it's important to differentiate between temporary effects and long-term results.

Comparison: Day 1-3 vs. Day 4-7 on a Low-Carb Diet


Feature	Day 1-3	Day 4-7
Energy Level	Often low, accompanied by fatigue	Starts to stabilize; many report higher, more consistent energy levels
Weight Change	Rapid water weight loss; mainly due to glycogen and water depletion	Slower, more sustainable fat loss may begin; water loss stabilizes
Appetite & Cravings	Strong cravings for carbs and sugary foods	Appetite often decreases, and carb cravings subside significantly
Mental Clarity	High risk of brain fog and difficulty concentrating	Many report increased mental clarity and focus
Physical Performance	May feel sluggish and have reduced strength/endurance	Endurance can improve, though high-intensity performance might still be affected
Digestive System	Potential for constipation due to reduced fiber intake	Digestion may start to regulate with careful fiber management from low-carb sources

Potential Side Effects and Precautions

While many of the initial symptoms are temporary, there are other potential side effects to consider, especially concerning overall nutrient intake. Eliminating entire food groups can lead to nutrient deficiencies if not managed properly. Additionally, some people experience “keto breath,” a fruity or metallic odor caused by acetone, a type of ketone, being released through the breath. For individuals with specific health conditions like diabetes, it is critical to consult a healthcare professional before making drastic dietary changes, as medication may need to be adjusted.

A Week Without Carbs vs. Long-Term Low-Carb

For most healthy individuals, a single week without carbs is a short-term metabolic experiment rather than a dangerous endeavor. However, the long-term effects of very low-carb or ketogenic diets are more complex and require careful consideration. Long-term studies have shown mixed results regarding cardiovascular health and lipid profiles, with some participants seeing increases in LDL cholesterol. The source and quality of the fats and proteins used to replace carbohydrates are crucial for long-term health. A single week is a starting point, not a complete picture of the long-term impact. For a detailed review of low-carbohydrate diets in a clinical context, see this resource on the National Institutes of Health website: Low-Carbohydrate Diet - StatPearls - NCBI Bookshelf.

Conclusion: Is One Week Worth It?

Stopping carbs for a week can be an insightful and challenging experience. It allows you to feel the direct effects of a metabolic shift, including rapid water weight loss and the initial "keto flu" symptoms. For many, this short period can reset their relationship with food, particularly highly processed carbohydrates and sugar. However, it is not without its side effects and requires careful management of hydration and electrolytes. The benefits—like increased mental clarity and stable energy once adapted—can be promising. Ultimately, a week without carbs is a temporary window into a very different way of fueling your body. The most sustainable approach for lasting health is to focus on a balanced diet rich in whole, nutrient-dense foods, and to consult with a healthcare professional before any significant dietary change.

Frequently Asked Questions

The 'keto flu' is a collection of flu-like symptoms, including headaches, fatigue, and brain fog, that can occur during the first week of stopping carbs. It happens as your body adjusts to switching its fuel source from glucose to ketones derived from fat.

In the first week, most weight loss is water weight, with figures often ranging from a few to several pounds, depending on the individual. This is due to the depletion of glycogen stores, which release water. Fat loss happens later.

Yes, it is very common to feel low on energy, tired, and sluggish in the first few days. This is part of the 'keto flu' as your body adapts to using fat for energy instead of glucose.

For most healthy people, cutting carbs for a week is generally safe, though it can cause temporary discomfort. However, individuals with existing medical conditions, such as diabetes, should consult a doctor before making this change, as medication adjustments may be necessary.

Focus on nutrient-dense, low-carb options to get your vitamins and minerals. These include leafy greens, broccoli, avocados, and other non-starchy vegetables, as well as lean proteins and healthy fats.

A low-carb diet restricts carbohydrate intake, while ketosis is a metabolic state where the body uses ketones for energy. Not all low-carb diets lead to ketosis; a very low-carb intake (typically under 50g per day) is needed to induce ketosis.

A common side effect of ketosis is 'keto breath,' which can have a fruity or metallic odor. This is caused by the release of acetone, a type of ketone, as a metabolic byproduct.