What will happen if I eat no carbs for 2 weeks?

January 5, 2026 •

4 min read

According to a 2021 review, a very low-carbohydrate ketogenic diet can produce significantly greater short-term weight loss than a low-fat diet, but a restrictive diet also brings notable side effects. Understanding what will happen if I eat no carbs for 2 weeks involves preparing for your body’s metabolic shift, shedding water weight, and potentially experiencing the 'keto flu' as you transition to burning fat for fuel.

Quick Summary

This article details the initial physiological and psychological changes your body undergoes during a 14-day period of severe carbohydrate restriction, including water weight loss, ketosis induction, and common temporary side effects. It also covers the shift in energy source, impact on mental clarity and athletic performance, and important considerations before adopting such a restrictive eating plan.

Key Points

Water Weight Loss: You will lose several pounds of water weight initially as your body depletes its glycogen stores.
Ketosis Induction: Your body will enter a metabolic state called ketosis, burning fat for energy instead of glucose.
'Keto Flu' Symptoms: Expect temporary side effects like fatigue, headaches, and irritability as your body adapts during the first week.
Increased Fat Burning: By the second week, your body becomes more efficient at burning fat, potentially leading to more consistent fat loss.
Reduced Appetite: Many people experience a decrease in hunger and cravings due to the satiating effect of fats and proteins.
Potential Nutrient Deficiencies: Eliminating carbs removes many sources of essential vitamins, minerals, and fiber, risking deficiencies and digestive issues.
Impact on Performance: Athletic performance may temporarily decline during the adaptation phase until your body fully adjusts to a fat-based fuel system.

The Metabolic Switch: From Carbs to Ketosis

When you stop eating carbohydrates, your body's primary and most readily available fuel source, it must find an alternative to power its functions. This metabolic shift typically occurs within 3 to 4 days of consuming fewer than 50 grams of carbs daily. Your body first burns through its stored glucose, known as glycogen, which is stored in the liver and muscles. Since glycogen also holds a significant amount of water (about 3 grams of water per gram of carbohydrate), you'll experience a rapid loss of water weight during the first week.

After depleting its glycogen stores, the body enters a metabolic state called ketosis. In ketosis, your liver begins breaking down fat into molecules called ketones, which are then used as the primary fuel source for your body and brain. This process is the foundation of the ketogenic diet and is the reason many people experience increased fat burning.

Week 1: The 'Keto Flu' and Initial Changes

The first week of zero-carb eating is often the most challenging due to what's known as the 'keto flu'. These flu-like symptoms are caused by a combination of carbohydrate withdrawal and changes in fluid and electrolyte balance as your body adapts.

Common Week 1 Side Effects:

Headaches: Caused by dehydration and mineral loss.
Fatigue and irritability: A result of your brain adjusting to a new energy source.
Brain fog: Difficulty concentrating as your body re-regulates blood sugar levels.
Constipation: A common symptom due to the sudden reduction in dietary fiber.
Sugar cravings: Intense cravings can occur as your body withdraws from carbohydrates.

Week 2: Adaptation and Stabilization

By the second week, most individuals begin to feel better as their body becomes more efficient at using ketones for energy. The initial side effects of the 'keto flu' typically subside, and other changes become more apparent.

Common Week 2 Developments:

Increased energy and mental clarity: Many people report more stable energy levels throughout the day without the peaks and crashes associated with high-carb diets.
Reduced appetite: Ketones and a higher intake of fat and protein can have an appetite-suppressing effect, leading to fewer cravings and a feeling of fullness.
Keto breath: Your breath may develop a distinct, fruity odor as your body releases excess acetone (a type of ketone) through the lungs.
Steady fat loss: After the initial water weight is shed, more consistent fat loss can occur, provided you maintain a calorie deficit.

Comparison: No-Carb vs. Balanced Diet (2 Weeks)


Feature	No-Carb Diet (2 Weeks)	Balanced Diet (2 Weeks)
Initial Weight Loss	Rapid, primarily water weight due to glycogen depletion.	Slower and more gradual, focusing on fat loss through a sustainable calorie deficit.
Energy Source	Shifts from glucose to fat/ketones, leading to potential 'keto flu' symptoms during adaptation.	Primarily glucose from a variety of carbohydrate sources, providing consistent, stable energy.
Satiety	Increased feelings of fullness due to higher intake of fats and proteins.	Balanced approach to hunger management, using a mix of fiber, protein, and healthy fats.
Micronutrients	Potential deficiencies in fiber, vitamins, and minerals found in fruits, grains, and some vegetables.	Greater nutrient diversity from a wider range of food groups, including whole grains and fruits.
Athletic Performance	May be temporarily reduced during the adaptation phase as muscles adjust to fat as a primary fuel.	Supports optimal performance and glycogen stores for high-intensity exercise.

Important Considerations and Risks

While a short-term, no-carb diet can lead to initial weight loss and a shift to fat burning, it is not without risks. Nutrient deficiencies are a significant concern, as eliminating entire food groups removes essential vitamins, minerals, and fiber. A lack of fiber, in particular, can cause digestive issues like constipation. Very low-carb diets may also increase the risk of heart disease if healthy fats are not prioritized over saturated fats. Long-term adherence can be difficult and is often unsustainable.

It is always recommended to consult a healthcare professional or registered dietitian before beginning a restrictive diet. For example, individuals with underlying health conditions, especially diabetes, should not attempt this without strict medical supervision.

How to Safely Approach a Low-Carb Period

If you choose to experiment with a two-week low-carb period, it's crucial to mitigate the risks. Ensuring proper hydration is key, especially during the first week when you lose a lot of water. Supplementing with electrolytes like sodium, potassium, and magnesium can help minimize 'keto flu' symptoms. You should also prioritize nutrient-dense, keto-friendly foods to avoid deficiencies. Focus on leafy greens, cruciferous vegetables, and healthy fats from avocados, nuts, and olive oil. This balanced approach can help make the experience safer and more productive.

Conclusion

For the first two weeks of eliminating carbohydrates, your body undergoes a dramatic metabolic adjustment, transitioning from glucose to fat burning (ketosis). This period is marked by initial rapid water weight loss, followed by the temporary discomfort of the 'keto flu'. By the second week, most people experience a stabilization of energy levels and a decrease in appetite. While a short stint can jumpstart weight loss and may offer benefits like improved blood sugar control, it's a restrictive approach with potential downsides, including nutrient deficiencies and short-term side effects. It is critical to manage these risks and, for long-term health, to transition back to a more balanced and sustainable eating pattern that includes healthy carbohydrates, fiber, and diverse nutrients. Consulting a healthcare professional before making such a significant dietary change is strongly advised.

Frequently Asked Questions

The 'keto flu' refers to flu-like symptoms, such as headaches and fatigue, that can occur during the first week of a low-carb diet as your body adapts. You can manage it by staying well-hydrated and replenishing electrolytes like sodium, potassium, and magnesium.

The rapid weight loss seen in the first week is mostly water weight. When you restrict carbs, your body uses up its glycogen stores, which hold a lot of water. Significant fat loss typically occurs more steadily after this initial phase.

During the first week, many people experience 'brain fog' as their brain adjusts to using ketones for fuel. However, by the second week, many report increased mental clarity and more stable energy levels.

The biggest risks include dehydration, electrolyte imbalances, nutrient deficiencies (especially fiber), and potential digestive issues like constipation. It can also be unsustainable for many people.

You should focus on nutrient-dense, low-carb foods such as leafy greens, cruciferous vegetables (broccoli, cauliflower), healthy fats (avocado, olive oil, nuts), and protein sources like meat, eggs, and fish.

When you reintroduce carbohydrates, your body will replenish its glycogen stores, and you will likely regain the water weight you initially lost. Long-term results depend on whether you adopt a healthy, sustainable eating pattern afterward.

Focus on consuming a variety of non-starchy vegetables, healthy fats, and protein sources. Consider supplementing with electrolytes to maintain proper balance. Consulting with a dietitian can also help create a safe, nutrient-adequate plan.