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The Downside of Keto and Intermittent Fasting

author avatar Dr. Eric Berg 01/10/2025

I've been there. You're excited about the keto diet, ready to lose weight and boost your energy. But then you start hearing whispers about the keto diet's side effects, making you question if the diet is right for you.

Let's talk frankly about potential side effects. This isn't to scare you, it's about being prepared.

Understanding Common Keto Diet Side Effects


Many keto beginners experience the "keto flu." This isn't the actual flu but a group of symptoms like headache, fatigue, and nausea. It happens as your body transitions from using glucose to ketones, an alternate energy source.

Short-Term Keto Diet Side Effects

Besides the keto flu, other short-term side effects can occur. You might experience constipation due to decreased fiber intake. Dehydration can also happen as ketones have a diuretic effect.

Don't be surprised if your breath has a fruity odor—it's acetone, a ketone body, being released. These initial side effects can be uncomfortable. But they usually subside within a few weeks as your body adapts.

Staying hydrated, eating fiber-rich, keto-friendly foods, like fresh fruits, and good oral hygiene help minimize these issues. These symptoms will resolve on their own as you adjust to burning fat and achieve ketosis.

Healthy keto-approved food spread

Long-Term Keto Diet Side Effects

While less common, there are some long-term keto diet side effects to be aware of. If you follow keto long-term without proper nutrition, you could develop nutrient deficiencies because the diet restricts certain food groups.

In rare cases, high amounts of ketones might increase kidney stone risk. Electrolyte imbalances can occur from fluid loss. Many manage this by consuming electrolyte-rich foods and staying hydrated.

A high-fat keto diet, without careful management of saturated fat intake, might raise the risk of cardiovascular disease.

Monitoring your cholesterol levels is essential. In rare cases, some experience liver problems with prolonged keto if not managed carefully.

This is a serious concern that might require medical attention. For some, keto restrictions might trigger disordered eating patterns, as noted in some studies about restrictive diets.

Mood swings can also be a significant factor, especially for those starting with high-carb diets or mental health considerations.

Managing Keto Diet Side Effects


Now that we’ve covered potential keto diet side effects let's explore how to keep your body healthy while on keto.

Smart Keto Strategies

Focus on a healthy, sustainable keto diet emphasizing whole, unprocessed foods. Prioritize nutrient-dense foods with high fiber content to maintain regularity. Drinking enough water is crucial. Don't hesitate to use electrolyte supplements.

Talk to your doctor about blood sugar testing and insulin management. Consult with your doctor before and during your keto journey for guidance. They can discuss the potential effects of a low-carb diet on managing blood sugar levels.

Supplements

While a balanced ketogenic diet aims to provide all nutrients from food, supplements can help with proper guidance.

Consult a healthcare professional or clinical dietitian on appropriate dietary approaches before implementing changes on your own.

This may help with reducing symptoms of the so-called keto flu and may make your initial experience less jarring as you induce ketosis in the beginning.

These supplements might include calcium, magnesium, potassium, sodium, omega-3 fatty acids, MCT oil, fiber supplements, and a multivitamin.

Intermittent fasting illustration

Keto Diet Side Effects and How They Vary


Keto's results and keto diet side effects vary greatly depending on the individual. Pay attention to how your body responds.

It is vital to be cognizant of changes in your health status as a low-carbohydrate diet can impact health conditions like metabolic syndrome or insulin resistance.

Consult a healthcare professional, such as a physician, registered dietitian, or certified diabetes educator, before initiating any significant dietary adjustments.

This is especially relevant for individuals with chronic conditions, like those seeking to manage blood sugar and who need assistance determining if this type of diet, whether high fat or not, fits their lifestyle and individual preferences.

Partnering with your doctor during your keto journey is essential.

Navigating Protein Choices and Their Impact on Keto Side Effects


One common side effect of starting a keto diet is the “keto flu,” characterized by fatigue, headaches, and nausea as the body adapts to fat as its primary energy source.

To minimize these effects, ensuring balanced protein intake is essential. While animal proteins are a staple of keto, some individuals explore alternative options and may ask, is plant based meat healthy for this diet?

Plant-based meats can offer variety, but many are processed and contain added carbs, which may disrupt ketosis. For those seeking plant-based options, focusing on whole, low-carb sources like tofu or tempeh is a better fit.

By carefully selecting your proteins and maintaining an adequate balance of fats and electrolytes, you can reduce side effects and transition smoothly into ketosis.

Conclusion

 

Keto offers potential benefits but also has potential keto diet side effects. A well-informed approach can minimize and manage these challenges, helping you achieve ketosis and reap the weight loss and wellness rewards of keto.

Following a low carbohydrate high-fat regimen can support fat loss goals and contribute to other intended metabolic impacts such as on blood sugar levels, blood pressure and insulin resistance.

Ensure you choose healthy fats and a sustainable dietary approach overall, incorporating diverse nutritious foods, including those containing healthy unsaturated fats.

Consult your doctor before making any dietary or lifestyle changes, including those discussed here. Remember that others' experiences are not a guarantee of your own outcome.

Each individual's results and experience on the keto diet varies, which can make it challenging to predict specific individual reactions, benefits, and potential risks.

FAQs about keto diet side effects


What are the negative effects of keto?

Negative keto diet side effects include the "keto flu" (fatigue, headache, nausea), constipation, dehydration, and bad breath initially.

Long-term risks include nutrient deficiencies, kidney stones, and electrolyte imbalances. In rare cases, cardiovascular disease or liver issues can occur.

Some may experience fatigue and, rarely, a condition called keto rash. For severe symptoms, expert medical advice is essential.

Videos by Dr. Berg on keto rash and fatigue can provide further insight. This is because a high-fat diet like this is meant to use fats, rather than carbs, as an energy source.

What happens when you stop keto?

Weight regain is possible after stopping keto. The rate and extent of any weight regained are subjective.

Maintaining a healthy lifestyle with moderate activity, protein intake, and a proper diet consisting of things like red meats, olive oil, canola oil, fatty fish, and nuts can help maintain weight.

What happens on day 3 of keto?

By day 3, some individuals may begin entering ketosis as the body’s carbohydrate stores deplete and your carb intake has been low enough.

"Keto flu" symptoms might intensify around this time as your body adjusts to this shift from primarily glucose to fat metabolism.

Attaining and maintaining ketosis is important for achieving desired outcomes from a low-carbohydrate, high-fat dietary pattern like the keto diet.

How long does it take to get out of ketosis?

Increasing carb intake typically shifts the body back to using glucose as the primary fuel source, bringing you out of ketosis within 1–3 days.

In doing so, the body starts relying more on carbs and stops using fats for energy production to such a large extent.

To understand better the ketosis diet in more depth and it's effect on conditions like metabolic syndrome and how the brain works in conjunction with blood sugar levels, consider learning from reliable health platforms or review articles by experts.

Consulting a pediatric patient's dietician can also offer more insights if you have any specific needs and/or concerns.

Healthy Keto Guide for Beginner

FREE Keto Diet Plan