The keto diet has become one of the most popular ways to lose weight, but it’s not as simple as cutting carbs and eating more fat. While some people thrive on keto, others experience side effects that can make the diet tough to stick with. If you’re thinking about going keto, it’s important to know what to expect so you can handle any challenges that come your way.
Keto Flu: The Rough First Week
One of the biggest complaints people have when starting keto is the “keto flu.” This isn’t an actual flu, but it can feel like one. Symptoms include:
- Fatigue
- Headaches
- Nausea
- Brain fog
- Muscle cramps
These symptoms happen because your body is adjusting from burning carbs to burning fat for fuel. A sudden drop in carbs causes water loss, which leads to dehydration and an imbalance in electrolytes. To lessen these effects, drink plenty of water and make sure you’re getting enough sodium, potassium, and magnesium.
Digestive Issues
Switching to keto can cause constipation or diarrhea, depending on how your body reacts to the change in fiber intake. Since keto limits high-fiber foods like whole grains and certain fruits, constipation is common. On the other hand, eating too much fat too quickly can lead to diarrhea.
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To help with digestion:
- Eat fiber-rich keto foods like avocados, nuts, and leafy greens
- Drink enough water
- Introduce fats gradually if your stomach feels off
Bad Breath (Ketosis Breath)
Many people notice a strange, fruity, or metallic smell in their breath when they first enter ketosis. This happens because your body is producing acetone, a type of ketone, and releasing it through your breath.
While ketosis breath isn’t harmful, it can be unpleasant. Drinking more water, chewing sugar-free gum, and brushing your tongue can help reduce the smell.
Sleep Problems
At first, keto may make it harder to fall or stay asleep. This is partly due to changes in blood sugar levels and a drop in serotonin, which comes from carb intake. Some people also feel extra alert on keto, which can make winding down at night more difficult.
If keto is affecting your sleep, try:
- Eating more healthy fats at dinner to keep blood sugar stable
- Taking magnesium before bed to relax muscles and nerves
- Making sure you’re getting enough calories throughout the day
Loss of Electrolytes and Dehydration
Since keto causes a rapid loss of water weight in the first few days, it also flushes out important minerals. If you don’t replace electrolytes, you might experience dizziness, muscle cramps, and weakness.
Make sure you’re getting enough:
- Sodium – Add salt to your food or drink bone broth
- Potassium – Eat avocados, spinach, and salmon
- Magnesium – Take a supplement or eat nuts and seeds
Increased Cholesterol Levels
Keto is high in fat, and for some people, this can lead to a rise in LDL (“bad”) cholesterol levels. While many people see an improvement in cholesterol over time, some may need to adjust their fat sources to avoid potential heart risks.
Focus on healthy fats like:
- Olive oil
- Avocados
- Fatty fish
- Nuts and seeds
If you have a history of high cholesterol, consider getting regular blood tests to track changes.
Possible Hormonal Changes
Keto affects hormones like insulin, cortisol, and thyroid hormones. Some women may notice changes in their menstrual cycle, especially if they drastically cut calories or carbs too quickly. Others may experience mood swings or increased stress levels due to the impact on cortisol.
To keep hormones balanced:
- Avoid extreme calorie deficits
- Eat enough protein and healthy fats
- Listen to your body—if keto doesn’t feel right, adjust your approach
The keto diet has benefits, but it also comes with side effects that can make the transition challenging. Knowing what to expect can help you manage these issues and decide if keto is right for you. If you experience severe side effects, it may be worth modifying your approach or considering a less restrictive low-carb diet.
Long-Term Side Effects to Watch For
While short-term keto side effects like keto flu and digestive issues tend to go away after a few weeks, long-term concerns should also be considered. Sticking to keto for months or years can impact different areas of health, so it’s important to monitor changes in your body.
Nutrient Deficiencies
Since keto restricts many fruits, grains, and some vegetables, it can be harder to get enough essential vitamins and minerals. Over time, this can lead to deficiencies in:
- Vitamin C – Found in many carb-rich fruits and vegetables, a lack of vitamin C can weaken the immune system and lead to fatigue.
- Folate – Essential for cell growth and brain function, folate is mainly found in beans, lentils, and whole grains, which are off-limits on keto.
- Calcium & Vitamin D – Dairy can be included on keto, but many people don’t consume enough to meet daily calcium and vitamin D needs, which can affect bone health.
To prevent deficiencies, focus on eating a variety of low-carb, nutrient-rich foods like leafy greens, fatty fish, and organ meats. You might also consider a high-quality multivitamin to fill any nutritional gaps.
Potential Bone Loss
Long-term keto diets have been linked to a decrease in bone mineral density, possibly due to lower calcium intake or changes in the way the body processes minerals. Some studies suggest that keto can lead to an increase in calcium excretion, which may contribute to weaker bones over time.
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To support bone health, make sure you’re eating foods rich in calcium, magnesium, and vitamin K2, such as:
- Sardines (with bones)
- Leafy greens like kale and spinach
- Cheese and full-fat dairy
- Nuts and seeds
Regular resistance training can also help maintain bone strength and prevent osteoporosis.
Gallbladder Problems
Since keto is a high-fat diet, your gallbladder has to work harder to release bile for fat digestion. For most people, this isn’t an issue, but for those prone to gallstones or gallbladder disease, a sudden increase in dietary fat can cause discomfort or even trigger gallbladder attacks.
Signs of gallbladder distress include:
- Bloating and gas after fatty meals
- Pain in the upper right abdomen
- Nausea or vomiting after eating high-fat foods
If you have a history of gallbladder issues, you may need to introduce fats more slowly or choose healthier fat sources like olive oil and avocado over heavy cream and butter.
Increased Risk of Heart Disease (For Some People)
Although keto can improve some heart health markers, like triglycerides and HDL cholesterol, some people experience a rise in LDL (“bad”) cholesterol and other risk factors for heart disease. This depends on individual genetics, the types of fats consumed, and overall diet quality.
If you’re following keto long-term, focus on heart-healthy fats such as:
- Extra virgin olive oil
- Avocados
- Nuts and seeds
- Fatty fish (like salmon and sardines)
Getting regular blood tests can help you track cholesterol and adjust your fat intake if needed.
Impact on Gut Health
A healthy gut relies on fiber and a diverse range of plant foods to support beneficial bacteria. Because keto limits many fiber-rich foods, gut health may suffer over time, leading to:
- Poor digestion
- Increased inflammation
- A weaker immune system
To support gut health on keto, eat plenty of prebiotic-rich foods like asparagus, onions, and garlic. Fermented foods like sauerkraut, kimchi, and kefir can also help maintain a healthy gut microbiome.
Is Keto Safe for Women?
Keto affects women differently than men due to hormonal differences. Some women do well on keto, but others experience negative changes in their menstrual cycle, energy levels, and overall well-being.
Irregular Periods
Since keto reduces insulin levels, it can impact reproductive hormones like estrogen and progesterone. Some women experience missed periods or cycle irregularities, especially if they:
- Eat too few calories
- Drop carbs too low for their body’s needs
- Exercise intensely while on keto
If your cycle becomes irregular, consider increasing your carb intake slightly or following a cyclical keto approach (including some carbs on certain days).
Thyroid Health
The thyroid plays a key role in metabolism, and some research suggests that very low-carb diets may lower thyroid hormone levels. Women are already more prone to thyroid issues, so this is something to watch if you experience symptoms like:
- Fatigue
- Hair thinning
- Feeling cold all the time
To support thyroid health, include iodine-rich foods like seaweed and seafood, and avoid excessive calorie restriction.
Increased Stress Levels
Carbs help regulate cortisol, the body’s main stress hormone. For some women, cutting carbs too low can lead to increased stress, anxiety, and sleep disturbances. If keto makes you feel overly stressed or moody, adding in more carbs from whole food sources like berries or sweet potatoes may help.
When Keto May Not Be the Best Choice
Keto works well for some people, but it’s not right for everyone. You might want to reconsider if you:
- Have a history of eating disorders (keto can encourage restrictive eating habits)
- Are pregnant or breastfeeding (carbs are important for fetal and infant development)
- Have adrenal fatigue or chronic stress (low-carb diets can increase stress hormones)
- Struggle with maintaining energy levels for workouts (especially high-intensity exercise)
If keto isn’t working for you, a more balanced approach, like a moderate low-carb diet, might be a better fit.
How to Transition Off Keto Safely
If you’ve been on keto for a while but want to reintroduce carbs, it’s best to do so gradually to avoid blood sugar spikes and energy crashes. Here’s how:
- Start with Whole Foods – Reintroduce slow-digesting carbs like sweet potatoes, quinoa, and legumes rather than jumping straight into processed foods.
- Increase Carbs Slowly – Add 20-30 grams of carbs per day over a few weeks instead of making a drastic jump.
- Keep Protein and Healthy Fats Stable – Maintain a balanced intake of protein and fats to avoid sudden hunger swings.
- Monitor How You Feel – Pay attention to energy levels, digestion, and mood as you transition.
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Here’s a great video to help you get started:
Final Thoughts
The keto diet can be a powerful tool for weight loss and metabolic health, but it comes with side effects that shouldn’t be ignored. While some side effects are temporary, others can impact long-term health, especially if the diet isn’t well-balanced.
If you decide to try keto, be mindful of how your body responds and make adjustments as needed. Keto isn’t the only way to lose weight or improve health—there are many ways to eat well without extreme carb restriction. The best diet is the one that fits your lifestyle and keeps you feeling your best.