What Are The Side Effects Of The Keto Diet?

To help you become fitter and healthier than before, you might be interested in applying the keto diet to your daily regimen. This diet plan might be useful for losing excess body fat without hunger pangs. It might also have other health benefits, like improving type 2 diabetes. But this diet might not be for everyone, especially once you learn about its possible side effects.

What’s the Keto Diet?

The keto diet is a high-fat, very low-carbohydrate eating pattern that shifts the body’s main fuel source from glucose to ketones, molecules the liver produces when carbohydrate intake drops low enough to trigger fat breakdown. A typical keto plan draws roughly 70 to 75% of calories from fat, 20% from protein, and only 5 to 10% from carbohydrates — usually the 20 to 50 grams a day figure most keto guides cite. Most people enter ketosis within 2 to 7 days of starting.

The diet isn’t a recent invention. It was developed in the 1920s as a treatment for drug-resistant epilepsy in children, long before it became popular for weight loss, and it’s still used clinically for that purpose today (NIH: StatPearls, NIH: pediatric epilepsy diet therapy).

Who Shouldn’t Try Keto

Don’t start the keto diet if you:

• Take medicines for diabetes, particularly insulin, sulfonylureas, or SGLT2 inhibitors, which carry a risk of dangerously low blood sugar or diabetic ketoacidosis when combined with keto
• Have high blood pressure and take diuretics
• Are pregnant or breastfeeding
• Have kidney or liver disease
• Have a history of gallbladder disease, pancreatitis, or a cholecystectomy
• Have a history of disordered eating
• Have type-1 diabetes

A 2025 clinical review lists these among the diet’s key contraindications and cautions, alongside interactions with metformin, GLP-1 receptor agonists, and corticosteroids (NIH: contraindications, side effects, and drug interactions). Following this diet might also present side effects even for otherwise healthy people. Consult your doctor or nutritionist before attempting this eating plan — going in without medical guidance raises your risk of the adverse effects below.

What Are the Side Effects of the Keto Diet?

When you decide to go on a keto diet, you should also prepare for the potential adverse effects. These side effects may include the following:

Keto Flu

You might experience flu-like symptoms after a few days of following the keto eating regimen — brain fog, dizziness, fatigue, headache, and nausea are common. These symptoms are tied to fluid and electrolyte shifts as the body adjusts to burning fat rather than glucose, rather than to any actual virus.

While you have keto flu, you’ll also have a deep craving for sugar. The first few days might be the most critical period, since giving in to that craving can derail the diet early on.

Keto Breath

You can develop a condition called keto breath when you follow this eating plan closely. Your breath might smell similar to nail polish remover, and it may come with a metallic taste in your mouth that’s hard to remove. This comes from acetone, one of the ketone bodies the liver produces, being released through the lungs.

Vitamin and Electrolyte Deficiency

One of the most significant allures of the keto diet is the elimination of excess fat, but that weight loss might come with vitamin deficiency. You have a limited range of foods to eat on this plan, so you can’t eat specific fruits and vegetables while following the keto diet.

Also, your body sheds water and glycogen along with fat while on this diet, and you lose electrolytes as your body removes these substances. Other side effects, like headaches and fatigue, might occur because of this electrolyte loss. Replacing sodium, potassium, and magnesium — through broths, leafy greens, nuts, or a supplement — can help ease these symptoms while your body adjusts.

Constipation and Digestive Upset

Gastrointestinal side effects, including constipation, nausea, and bloating, are among the most commonly reported complaints on keto, affecting as many as half of people on the diet at some point (NIH: adverse effects of the ketogenic diet). The drop in fiber from cutting grains, legumes, and most fruit is the main driver. Leafy greens, chia seeds, and adequate water intake can help offset this.

Keto Rash

A less common but well-documented side effect is prurigo pigmentosa, nicknamed “keto rash” — an itchy, reticulated rash that typically appears on the neck, chest, and back within the first month of starting keto and resolves once carbohydrates are reintroduced or the diet is stopped (NIH: case report and literature review).

Weight Loss

Weight loss can be a benefit and a drawback for keto diet followers. Following this eating plan can produce both fast and gradual weight loss. Quick weight loss can bring on other issues, like fatigue and nausea, so gradual weight loss over time is the better outcome to aim for.

Cholesterol and Long-Term Considerations

The keto diet’s effect on cholesterol is one of the more debated areas of the science. A randomized controlled trial in healthy young women found that a ketogenic low-carbohydrate, high-fat diet nearly doubled LDL cholesterol and apolipoprotein B within four weeks (NIH: Burén et al., Nutrients 2021). Other trials in people with obesity have found the opposite — improved LDL and triglyceride numbers over 24 weeks. The honest read is that the effect appears to depend heavily on who’s following the diet, their starting weight, and how long they stay on it, so this is worth discussing with a doctor and monitoring through bloodwork rather than assuming either outcome.

Longer-term use has also been associated with kidney stones and reduced bone mineral density in some studies, which is another reason keto is generally recommended as a time-limited intervention rather than a permanent way of eating.

Related » Heart Disease Explained by an Interventional Cardiologist

What to Eat on a Keto Diet

Now that you know the risks, here’s how to approach the diet itself. Several nutritious foods are low-carb options, so hitting the 20 to 50 grams of carbohydrates a day isn’t as difficult as it might sound.

Seafood

Both fish and shellfish are ideal options on this dietary plan. Other seafood that might interest you includes clams, oysters, and squid — these options contain only 3 – 7 grams of carbohydrates per serving.

Cheese

This dairy product is delicious and an excellent choice for keto diet followers. An ounce of cheddar cheese may only contain about 1 gram of carbohydrates. As a bonus, you may also gain about seven grams of protein and approximately 20% of the Recommended Daily Intake (RDI) for calcium.

Meat and Poultry

You can still eat meat on a keto diet, within certain rules. Consider eating grass-fed meat as much as possible — grass-fed animals produce meat with higher amounts of omega-3 fats. Opt for lean cuts, and trim visible fat before eating.

Other foods to eat for keto diet practitioners may include avocados, eggs, and several types of nuts and seeds. Keep a list of keto-friendly foods handy to help guide your choices.

How Long Should You Stay on Keto?

The keto diet is generally meant as a short-term intervention rather than a permanent way of eating. Many nutritionists recommend cycling off after a few months and monitoring cholesterol levels, bone density, and kidney function along the way. Reintroducing carbohydrates gradually, rather than all at once, can also help avoid rapid weight regain.

Conclusion

In summary, you should now know more about the keto meal plan. Prepare yourself for the health benefits and concerns that come with the diet. Specific symptoms might occur when you start following this eating plan — signs like bad breath, digestive changes, and flu-like symptoms can surface once you begin the ketogenic diet, and cholesterol changes are worth tracking over the longer term.

Most importantly, consult a medical professional before you follow this eating plan. Otherwise, your body might be more susceptible to adverse health effects than it needs to be. Approach this diet carefully, and the benefits are more likely to outweigh the side effects.