Understanding the Negative Effects of a Keto Diet

October 21, 2025 •

4 min read

Over 50% of people who attempt the keto diet experience a constellation of short-term side effects known as the 'keto flu' as their body adjusts to a new metabolic state. While often praised for weight loss, it's crucial to understand the full scope of negative effects of a keto diet before starting.

Quick Summary

The ketogenic diet can cause several adverse effects, including the short-term 'keto flu' and long-term health risks like kidney stones, liver issues, and nutrient deficiencies. Certain health conditions also contraindicate the diet.

Key Points

Initial 'Keto Flu': Many users report experiencing temporary flu-like symptoms, including fatigue, headaches, and nausea, as their body adjusts to a new metabolic state.
Kidney and Liver Strain: Long-term adherence can put stress on the kidneys, increasing the risk of kidney stones, and may contribute to fatty liver disease.
Nutrient Deficiencies: The strict elimination of many fruits, grains, and legumes can lead to deficiencies in essential fiber, vitamins, and minerals.
Cardiovascular Health Risks: Some individuals may see an increase in LDL ('bad') cholesterol, raising the risk for heart disease, especially with high saturated fat intake.
Electrolyte Imbalances: Rapid water and glycogen loss during the initial phase can flush out electrolytes, causing dehydration, muscle cramps, and headaches.
Not for Everyone: The keto diet is not recommended for people with certain medical conditions, including kidney, liver, or pancreatic issues, as well as pregnant women.
Sustainability Issues: The restrictive nature makes the diet difficult to maintain long-term for many, often leading to cycles of weight loss and regain.

The Initial Shock: Navigating the 'Keto Flu'

When transitioning into a ketogenic state, where the body burns fat for fuel instead of carbohydrates, many people experience a set of temporary, flu-like symptoms collectively known as the 'keto flu'. These effects occur as the body adapts to running on ketones instead of glucose. Symptoms typically emerge within the first few days and can last for a week or more.

Common 'Keto Flu' Symptoms

Headaches and Brain Fog: Reduced carbohydrate intake and changes in blood sugar can trigger headaches and make it difficult to concentrate.
Fatigue and Lethargy: Low energy is common as the body's primary fuel source shifts. Many report a decrease in exercise tolerance during this period.
Nausea and Digestive Issues: Gastrointestinal upset, including nausea, constipation, or diarrhea, can occur. Constipation is often linked to the reduction of high-fiber foods.
Irritability and Mood Swings: The metabolic shift can lead to changes in mood, causing irritability or anxiety.
Dehydration and Electrolyte Imbalance: The body excretes stored glycogen, releasing a significant amount of water and crucial electrolytes like sodium and potassium. This can cause increased thirst and dizziness.
'Keto Breath': The body's production of ketones, specifically acetone, can cause a distinct, fruity-smelling bad breath.

Long-Term Health Risks Associated with the Keto Diet

While the initial discomfort of the keto flu is temporary, several potential long-term health risks warrant serious consideration, especially as evidence on the extended effects of the diet is still developing.

Potential Organ Damage and Disease Risk

Kidney Stones: High protein and animal fat intake can increase the acidity of urine, a risk factor for kidney stones. Some studies show a significantly higher incidence of kidney stones in individuals on a keto diet.
Liver Problems: The high fat content in a keto diet, particularly from sources rich in saturated fats, can lead to the accumulation of fat in the liver, known as hepatic steatosis or fatty liver disease.
Cardiovascular Disease: The diet's emphasis on fatty foods, some of which are high in saturated fat, can increase levels of LDL ('bad') cholesterol in some individuals, elevating the risk of heart disease and related cardiovascular events.

Nutritional and Metabolic Deficiencies

Nutrient Deficiencies: The severe restriction of fruits, whole grains, and starchy vegetables can lead to deficiencies in essential vitamins, minerals, and fiber. Important micronutrients like potassium and magnesium, often lost during the initial phase, may remain depleted if not properly managed.
Osteoporosis: The metabolic acidosis induced by the diet can cause the body to pull minerals from bones to neutralize acidity, potentially weakening bone density over time and increasing fracture risk.
Muscle Loss: Some studies suggest that the keto diet, especially when not paired with adequate protein intake, may lead to a loss of muscle mass alongside fat loss.

Comparison of Short-Term vs. Long-Term Keto Effects


Aspect	Short-Term Effects (Initial Weeks)	Long-Term Effects (Months to Years)
Symptom Type	Temporary, metabolic adjustment symptoms.	Persistent, chronic health issues.
Primary Cause	Body's shift from using glucose to ketones for energy.	Cumulative impact of restricted nutrition and high-fat intake.
Common Symptoms	'Keto flu' (fatigue, headache, nausea), dehydration, mood swings.	Kidney stones, fatty liver, cardiovascular risk, nutrient deficiencies.
Duration	Self-limiting; typically resolves within a few days to weeks.	Persistent and potentially worsening over time.
Management	Stay hydrated, replenish electrolytes, ease into the diet.	Requires medical supervision, supplementation, and careful monitoring.

Who Should Avoid the Keto Diet?

Due to its high-fat content and metabolic demands, the keto diet is not safe or suitable for everyone. Medical consultation is essential before starting. Individuals with certain pre-existing conditions should steer clear of this diet.

High-Risk Individuals and Conditions

Kidney Disease: The increased demand on kidneys to process protein and manage acid load can exacerbate existing kidney problems.
Pancreatic, Liver, or Gallbladder Conditions: These organs are heavily involved in fat digestion, and the high-fat intake can put undue stress on them.
Type 1 Diabetes: The risk of diabetic ketoacidosis, a life-threatening condition, is heightened. Anyone taking SGLT2 inhibitor medication should also avoid the diet.
History of Eating Disorders: The restrictive nature of the diet can trigger or worsen disordered eating patterns.
Pregnancy and Breastfeeding: These periods require a wide array of nutrients that a restrictive diet may not provide.

Conclusion: Informed Decisions and Professional Guidance

While the ketogenic diet can produce rapid weight loss, the potential for significant negative side effects, both short-term and long-term, is substantial. The initial 'keto flu' is a common hurdle, but more serious concerns regarding kidney health, heart disease risk, and nutritional deficiencies arise with prolonged adherence. The diet is not a one-size-fits-all solution and is explicitly contraindicated for individuals with certain health conditions. Making an informed decision and consulting with a healthcare provider or a registered dietitian is crucial to safely assess whether the benefits outweigh the risks for your individual health profile. For more information on the ketogenic diet, consult authoritative health sources such as the article from Medical News Today detailing its potential risks.

Keto's Demerits: A Closer Look

Keto Flu: The transition to ketosis can cause fatigue, headaches, and nausea as your body adapts to burning fat instead of carbs for fuel. Kidney and Liver Stress: The high fat and protein content in many keto diets can increase the risk of developing kidney stones and fatty liver disease. Nutrient Deficiencies: Restricting high-carb foods like fruits and whole grains can lead to a lack of fiber, vitamins, and minerals essential for long-term health. Increased Heart Disease Risk: For some individuals, high intake of saturated fats can elevate LDL ('bad') cholesterol, increasing cardiovascular disease risk. Bone Health Concerns: Long-term metabolic changes can lead to weakened bones and a higher risk of fractures due to potential acidosis. Unsustainable for Many: The diet's highly restrictive nature makes long-term adherence challenging, often leading to yo-yo dieting and weight regain.

What are the negative effects of a keto diet?

Frequently Asked Questions

The 'keto flu' refers to a collection of temporary, flu-like symptoms experienced by some people when their bodies first enter ketosis. Symptoms include headaches, fatigue, nausea, and irritability. It can be managed by staying well-hydrated, replenishing electrolytes (sodium, potassium, magnesium), and gradually easing into the diet.

Yes, studies have shown an increased risk of kidney stones on a ketogenic diet. This is often linked to an increase in urinary acidity from high animal protein consumption and potential dehydration, which can lead to the formation of crystals.

Long-term risks include potential for increased LDL ('bad') cholesterol and cardiovascular events, development of fatty liver disease, bone density reduction due to metabolic acidosis, and nutrient deficiencies from restricted food groups.

Excessive intake of saturated fats, common in some versions of the keto diet, can lead to the accumulation of fat in the liver, increasing the risk of fatty liver disease. Individuals with existing liver conditions should be especially cautious.

Yes, because the diet severely restricts or eliminates many fruits, whole grains, and legumes, it can result in inadequate intake of essential vitamins, minerals, and dietary fiber. Supplements are often needed to counteract these deficiencies.

The effect on heart health varies by individual, but concerns exist. Some people experience elevated levels of LDL ('bad') cholesterol, particularly if they consume large amounts of saturated fat. This can increase the risk of heart disease.

Constipation is a common side effect because the diet significantly reduces or eliminates many high-fiber carbohydrate sources like fruits, whole grains, and starchy vegetables. Fiber is essential for maintaining regular bowel movements.