A ketogenic diet is not inherently dangerous long term, but it does carry real tradeoffs that become more significant the longer you follow it. The short version: keto can be effective for weight loss and certain medical conditions, but sustained use raises legitimate concerns about kidney stones, nutrient gaps, thyroid hormone shifts, and potentially higher mortality when the diet leans heavily on animal fats. Whether those risks outweigh the benefits depends largely on how you construct the diet and what you’re using it for.
Weight Loss Fades Over Time
Keto’s reputation as a weight loss powerhouse holds up in the short term but becomes less impressive over longer periods. A systematic review of 13 randomized controlled trials, covering over 1,500 participants, found that people on ketogenic diets lost only about 0.9 kg (roughly 2 pounds) more than those on low-fat diets when followed for 12 to 24 months. Another review of 11 trials found a slightly larger gap of 2.2 kg, but the results were inconsistent across studies.
This doesn’t mean keto doesn’t work for weight loss. It does, especially early on. But the data suggest that by the one- to two-year mark, the advantage over other approaches narrows considerably. If long-term sustainability is your goal, the best diet is whichever one you can actually stick with, and keto’s restrictiveness makes adherence a common problem.
What Happens to Your Cholesterol
This is where the keto conversation gets complicated. Many people on long-term keto see a dramatic rise in LDL cholesterol, the type most strongly linked to heart disease. A subset of lean, metabolically healthy people experience especially extreme spikes, a pattern researchers have labeled the “lean mass hyper-responder” phenotype. These individuals develop LDL levels above 200 mg/dL alongside very high HDL and very low triglycerides, a combination that doesn’t fit neatly into conventional risk models.
A one-year study tracked 100 of these hyper-responders using CT scans of their coronary arteries. Despite average LDL levels of 242 mg/dL and elevated apoB (a marker of particles that drive plaque), most participants had low absolute plaque volumes. Fifteen percent actually showed plaque regression. Neither apoB levels nor cumulative LDL exposure predicted who got worse. Baseline plaque was the strongest predictor of progression.
That’s a provocative finding, but it comes from a single study of a very specific population: lean, otherwise healthy people with a particular lipid pattern. It doesn’t mean sky-high LDL is harmless for everyone on keto. If you have existing heart disease, a family history of early cardiovascular events, or other risk factors, sharply elevated LDL still warrants a conversation with your doctor regardless of your triglyceride levels.
Kidney Stone Risk Increases
Kidney stones are one of the better-documented complications of long-term keto. A meta-analysis found a pooled incidence of about 5.9% in people following ketogenic diets, with an average follow-up of nearly four years. Adults had a slightly higher rate at 7.9%. For context, the annual incidence of kidney stones in the general population is roughly 1-2%.
The risk climbs after the two-year mark and can lead to more serious complications, including urinary obstruction, acute kidney injury, and in rare cases, chronic kidney disease. The likely culprits are a combination of higher protein intake, lower urine pH from ketosis, and reduced intake of fruits and other alkalizing foods. Staying well hydrated and including potassium-rich vegetables in your meals can help offset this, but the elevated risk is real and worth monitoring if you plan to stay on keto for years.
Nutrient Gaps You Might Not Notice
Cutting out grains, most fruits, and many starchy vegetables means cutting out major sources of certain vitamins and minerals. The most concerning deficiency identified in research is thiamine (vitamin B1). In a cross-sectional study comparing people following low-carb or ketogenic diets to controls, 43% of the keto group failed to meet the recommended intake for thiamine from food alone, compared to 14% of controls. Blood levels of thiamine were also significantly lower in the keto group, and three participants met the threshold for outright biochemical deficiency.
Thiamine deficiency is no small thing. Severe cases can cause neurological damage, heart failure, and a condition called Wernicke’s encephalopathy that affects memory and coordination. Case reports of life-threatening thiamine deficiency have been documented in people on strict low-carb diets. The good news: participants who took a multivitamin or micronutrient supplement showed no biochemical deficiency. Low intakes of B vitamins, iron, magnesium, and fiber have also been reported, though blood levels of magnesium, zinc, copper, and selenium didn’t differ significantly between keto followers and controls in the same study.
The takeaway is straightforward. If you’re on long-term keto, a basic multivitamin and a deliberate effort to eat nutrient-dense vegetables can close most of these gaps.
Your Thyroid Hormones Shift
Carbohydrate restriction consistently alters the balance of thyroid hormones in your blood. Multiple studies show that nutritional ketosis lowers T3, the active form of thyroid hormone your cells use, while raising T4, the inactive precursor. In one randomized crossover trial, T3 dropped significantly after the ketogenic phase compared to pre-diet levels, falling from baseline to about 4.1 pmol/L, while T4 rose significantly. TSH, the signal your brain sends to your thyroid gland, typically stays unchanged.
What this means in practice is debated. Some researchers believe the drop in T3 is an adaptive response, a way the body conserves energy and muscle glycogen during carbohydrate scarcity rather than a sign of thyroid dysfunction. Others point out that chronically low T3 can contribute to fatigue, cold intolerance, and sluggish metabolism. If you’ve been on keto for months and feel increasingly tired or cold, this hormonal shift is worth investigating with a blood test that includes free T3, not just TSH.
Gut Bacteria Diversity Declines
Your gut microbiome thrives on fiber, and keto diets tend to be low in it. Research shows that ketogenic diets reduce overall microbial diversity, a metric generally associated with better digestive and immune health. One notable change is an increase in a bacterium called Akkermansia muciniphila, which has been linked to improved metabolic health and a stronger gut lining. So the picture isn’t entirely negative, but the overall reduction in diversity is a pattern that, sustained over years, could have consequences for immune function and digestive resilience that aren’t yet fully understood.
Including low-carb, high-fiber foods like leafy greens, avocados, nuts, seeds, and fermented vegetables can help maintain a healthier microbial ecosystem without breaking ketosis.
Bone Density Appears Stable
One concern you can largely set aside: long-term keto does not appear to significantly harm your bones. A systematic review found no meaningful changes in bone mineral density or bone mineral content after ketogenic dieting. Markers of bone breakdown and bone formation both remained stable. The one exception was women who lost 10% or more of their body weight, who showed increased bone resorption and decreased bone formation, but this pattern occurs with significant weight loss on any diet and didn’t reach the threshold for osteoporosis risk. One study noted reduced bone mineral content in participants who didn’t supplement with calcium, reinforcing the importance of adequate calcium intake on a restrictive diet.
Mortality Data Depends on Food Choices
The most sobering long-term data comes from two large cohort studies that tracked tens of thousands of people over decades. An overall low-carbohydrate eating pattern was associated with a 12% higher risk of dying from any cause. But the details matter enormously. When the low-carb diet was built around animal fats and proteins (think bacon, butter, and red meat), all-cause mortality risk jumped to 23% higher. When it was built around plant-based fats and proteins (nuts, avocados, olive oil, seeds), mortality risk dropped by 20%.
These are observational studies, not controlled experiments, so they can’t prove cause and effect. People who eat lots of processed meat may differ from plant-forward eaters in dozens of ways beyond their macronutrient ratios. Still, the pattern is consistent and large enough to take seriously. A keto diet centered on olive oil, nuts, fatty fish, avocados, and non-starchy vegetables looks very different, from a longevity standpoint, than one built around processed meats and cheese.
Liver Fat May Improve
For people with non-alcoholic fatty liver disease, keto shows genuine promise. Research has found that low-carbohydrate diets can reduce liver fat stores roughly three times more effectively than low-fat diets in the short term. The mechanism makes physiological sense: when you stop flooding the liver with glucose and fructose, it draws down its fat reserves for fuel. However, long-term comparative data on different weight loss approaches for fatty liver disease is virtually nonexistent, so it remains unclear whether keto maintains this advantage over months and years or whether any sustained calorie deficit would produce similar results.
Who Benefits Most From Long-Term Keto
The risk-benefit calculation looks different depending on your situation. People using medical keto for drug-resistant epilepsy have the strongest case for long-term use, as the neurological benefits can be life-changing and outweigh the dietary risks. People with type 2 diabetes or significant insulin resistance often see meaningful improvements in blood sugar control that persist as long as the diet is maintained.
For the average person using keto purely for weight management, the data suggest diminishing returns over time. The weight loss advantage over other diets shrinks to near-negligible levels by two years, while the risks of nutrient deficiencies, kidney stones, and hormonal shifts accumulate. If you do stay on keto long term, the evidence consistently points toward a few practical strategies that reduce risk: emphasize plant-based fats over animal fats, eat plenty of low-carb vegetables, take a multivitamin that includes B vitamins, stay well hydrated, and get periodic blood work to monitor your lipids, thyroid hormones, and kidney function.