What Happens the First Week on Paleo?

October 27, 2025 •

4 min read

Many people experience what is often dubbed the 'Paleo Flu' during their first week, characterized by fatigue, headaches, and irritability as the body adapts. Understanding what happens the first week on paleo is crucial for navigating this transition successfully and sticking with your new lifestyle.

Quick Summary

The first week of a Paleo diet involves significant body adaptation as it switches energy sources, leading to temporary side effects like fatigue, cravings, and digestive changes. Planning meals and managing expectations are key to navigating this initial adjustment period effectively.

Key Points

Paleo Flu is Normal: Experience temporary fatigue, headaches, and irritability during the first week as your body adjusts to burning fat instead of glucose.
Expect Cravings: You will likely have strong cravings for sugar and carbs, but these will subside as your body adapts to the new eating pattern.
Hydration is Key: Drink plenty of water and replenish electrolytes, especially sodium and potassium, to mitigate flu-like symptoms.
Mind Your Digestion: The shift to higher fiber intake can cause temporary digestive issues like bloating or constipation.
Weight Loss is Common: Many see an initial drop of 5-10 pounds, which is primarily water weight from reduced carb intake.
Plan Ahead for Success: Meal prepping and stocking up on Paleo-friendly foods are crucial for staying on track and avoiding temptation.
Listen to Your Body: Prioritize rest and avoid intense exercise during the initial adaptation period to manage fatigue and reduce stress.

The transition to a Paleo diet represents a major shift in how your body sources and uses energy. For most people, this means moving away from a modern diet high in processed foods, refined sugars, grains, and legumes to one based on whole, unprocessed foods like lean meats, fruits, vegetables, and healthy fats. The initial week is often the most challenging, but understanding the biological changes at play can help you prepare and push through to the long-term benefits.

The First 7 Days: Navigating the Paleo Flu

For many, the first three to seven days are dominated by the so-called 'Paleo Flu' or 'Carb Flu,' which is the body's reaction to carbohydrate withdrawal and the shift to a new fuel source. Before this change, your body likely relied on glucose from carbohydrates for quick energy. With that source now restricted, it must adapt to burning stored fat and ketones.

Day 1-3: The Initial Shock

Fatigue and Low Energy: This is one of the most common complaints. The body is used to a constant supply of easily accessible glucose and can feel sluggish as it searches for a new energy source. You may feel tired, foggy, or just generally off.
Headaches and Irritability: The brain's reliance on glucose can cause mood swings and headaches as it adjusts. For those who also cut out caffeine, these symptoms can be compounded.
Intense Cravings: Expect powerful cravings for sugar, bread, and other high-carb foods. These are signs of your body's old habits fighting for their familiar comfort foods.
Digestive Adjustments: Depending on your prior diet, you may experience bloating, gas, or a change in bowel movements. This is often due to a sudden increase in fiber from vegetables and a change in gut bacteria.

Day 4-7: The Body Adapts

As the week progresses, many people notice a shift for the better.

Energy Stabilization: Energy levels often start to stabilize and even increase as the body becomes more efficient at using fat for fuel. Many report waking up feeling more refreshed and having fewer energy dips throughout the day.
Cravings Subside: The intense cravings for non-Paleo foods typically begin to fade as your body and mind adjust.
Mental Clarity: The 'brain fog' often associated with the initial days begins to lift, leading to greater mental clarity and focus.
Initial Weight Loss: Rapid initial weight loss of 5-10 pounds is not uncommon in the first week. This is primarily water weight, not body fat, but it can be a motivating sign of progress.

Managing the Transition: Practical Strategies

To make your first week on Paleo as smooth as possible, focus on smart preparation and self-care.

Plan and Prep Meals: A lack of planning is a primary reason people give up. Cook meals in batches, chop vegetables in advance, and have portable Paleo-friendly snacks ready.
Embrace Healthy Fats: Don't be afraid to consume healthy fats from avocados, nuts, seeds, and oils (olive, coconut, avocado). These provide a sustained energy source that helps manage fatigue and cravings.
Increase Hydration and Electrolytes: Drink plenty of water throughout the day. The drop in carbs can cause the body to excrete more water and electrolytes. Supplement with sources of sodium and potassium, like bone broth, to combat headaches and muscle cramps.
Listen to Your Body: Take it easy on strenuous exercise during the first few days if you feel tired. Instead, opt for light activities like walking or yoga. Prioritizing rest and adequate sleep is crucial for a successful transition.

What to Eat: A Week 1 Focus

Keep it simple and focus on nutrient-dense foods.

Proteins: Grass-fed beef, pastured chicken, wild-caught salmon, and eggs.
Vegetables: Load up on all vegetables, especially leafy greens (spinach, kale), cruciferous veggies (broccoli, cauliflower), and root vegetables (sweet potatoes, carrots).
Fruits: Enjoy berries, apples, and bananas in moderation.
Fats: Use olive oil for dressings and coconut or avocado oil for cooking.

Paleo Week 1 vs. Standard Diet: A Comparison


Aspect	Paleo Week 1	Standard Diet
Primary Fuel Source	Transitioning from glucose to fat/ketones.	Primarily relies on glucose from carbohydrates.
Processed Food Intake	Zero processed foods, added sugars, and refined oils.	Can be high in processed foods, refined sugars, and unhealthy fats.
Common Side Effects	Fatigue, headaches, cravings, digestive changes.	Typically none, unless transitioning from a very unhealthy diet.
Energy Levels	May fluctuate early on, but stabilizes and can increase by week's end.	Often marked by energy spikes and crashes due to blood sugar fluctuations.
Hydration	Increased need for water and electrolytes.	Standard hydration needs.
Nutrient Density	Extremely high due to focus on whole, unprocessed foods.	Varies widely, often lower due to refined ingredients.

Conclusion: Pushing Through for Long-Term Benefits

The first week on Paleo is a period of adjustment, not a permanent state of discomfort. While the 'Paleo Flu' can be challenging, it is a temporary phase as your body re-learns how to efficiently burn fat for fuel. The initial rapid water weight loss and potential improvements in sleep and mental clarity are powerful motivators to continue. The Paleo diet promotes nutrient-dense, whole-food eating, which can be highly beneficial for overall health. By staying hydrated, prioritizing rest, and focusing on quality foods, you can navigate this introductory period and set the stage for sustained wellness. For more in-depth nutritional information and diet reviews, resources like those from the Harvard T.H. Chan School of Public Health can provide further context(https://hsph.harvard.edu/news/paleo-diet-health-benefits-complicated/).

Frequently Asked Questions

The 'Paleo Flu' is a term for the flu-like symptoms—including fatigue, headaches, and irritability—that some people experience during the first week of transitioning to a Paleo diet. It's caused by the body withdrawing from its reliance on sugar and processed carbs for energy and switching to burning fat.

For most people, the symptoms of the Paleo Flu are temporary and can last anywhere from a few days to a week. In some cases, it may extend for a couple of weeks, but symptoms generally subside as the body adapts.

Yes, it is very common to experience quick weight loss in the first week or two on Paleo. However, this is largely due to shedding water weight from the reduction of carbohydrates and not fat loss. Long-term, more sustainable weight loss will follow.

Intense cravings for sugary or carb-rich foods occur because your body is accustomed to using glucose as its primary fuel source. As you eliminate these foods, your body signals for its usual energy supply, but these cravings typically lessen as you become fat-adapted.

To fight fatigue, ensure you are eating enough healthy fats and protein to provide sustained energy. Staying well-hydrated, replenishing electrolytes, getting enough sleep, and avoiding overly strenuous exercise can also help.

Yes, changes in digestion like bloating, gas, or changes in bowel movements are normal. They are usually caused by a significant increase in fiber from vegetables and a shift in your gut microbiome as it adjusts to your new diet.

Focus on a variety of whole, unprocessed foods like lean meats, a wide range of vegetables, some fruits, nuts, seeds, and healthy fats. Planning simple, go-to meals and having easy snacks on hand can prevent frustration.