A ketogenic diet can produce impressive short-term results for weight loss and blood sugar control, but the evidence for long-term safety is mixed and, in several areas, genuinely concerning. Most clinical trials on keto last only weeks to months, so much of what we know about staying in ketosis for years comes from observational data and studies of children treated with medical keto diets for epilepsy. The picture that emerges is one of real trade-offs: meaningful benefits for some conditions, but accumulating risks to your kidneys, nutrient status, gut health, and potentially your lifespan.
What Happens to Mortality Risk
The largest and most sobering data point comes from two major cohort studies that tracked tens of thousands of people over decades. When researchers pooled the results, people who followed a low-carbohydrate diet built around animal fats and proteins had a 23% higher risk of dying from any cause compared to those eating more carbohydrates. That’s a meaningful increase. People following a plant-based version of low-carb eating, replacing grains with nuts, vegetables, and plant oils, actually had a 20% lower risk of death.
This distinction matters enormously. The version of keto most people follow, heavy on bacon, butter, cheese, and red meat, is the version linked to higher mortality. Swapping animal sources for plant-based fats and proteins flipped the association entirely. So the question isn’t just whether keto is safe long term, but which version of keto you’re eating.
Kidney Stress and Kidney Stones
Keto diets are typically high in protein, and that protein load has consequences for your kidneys over time. A population study of over 1,500 adults found that those consuming more protein had lower kidney filtration rates after 12 years, regardless of whether they started with kidney disease. A separate six-year study of 1,800 people found that high protein intake carried a 48% increased odds of developing chronic kidney disease.
Kidney stones are one of the most well-documented side effects. The connection has been observed repeatedly in children treated with medical ketogenic diets for epilepsy, where kidney stones are listed as a recognized complication. The combination of higher animal protein intake and the mild, chronic acidosis that ketosis produces creates favorable conditions for stones to form. If you have any existing kidney issues, this risk is worth taking seriously.
Nutrient Gaps That Widen Over Time
Cutting carbohydrates below 20 to 50 grams a day means eliminating or drastically reducing fruits, most vegetables, legumes, and whole grains. These are the primary dietary sources of several essential nutrients. Research consistently shows that low-carbohydrate diets tend to fall short in thiamin, folate, vitamins A, E, and B6, as well as calcium, magnesium, iron, and potassium.
Even a carefully designed ketogenic diet with nutrient-dense foods still shows gaps. Analysis of a strict 4:1 keto ratio (four grams of fat for every one gram of protein plus carbs) found shortfalls in vitamin K, certain essential fatty acids, and most water-soluble vitamins. A few weeks of missing these nutrients won’t cause problems. Months or years of chronic deficiency can affect everything from bone strength to immune function to nerve health. Supplementation can help, but it requires deliberate planning that many people on keto don’t do.
Gut Health Takes a Hit
Your gut bacteria depend heavily on fiber and resistant starches, both of which plummet on a ketogenic diet. Studies show keto reduces overall bacterial diversity in the gut, which is generally considered a marker of poor gut health. Fecal short-chain fatty acids, the compounds your gut bacteria produce to nourish your intestinal lining and regulate inflammation, also decline.
One randomized trial of 91 overweight adults found that eight weeks on a very low-carb diet led to decreased stool mass, fewer bowel movements, and reduced butyrate, a short-chain fatty acid critical for colon health, compared to an equal-calorie higher-carb diet. Constipation is one of the most commonly reported side effects of keto, and it’s not just an inconvenience. It reflects a shift in your gut environment that, sustained over years, could have broader health implications. Researchers have noted that the long-term effects of keto on gut microbiome composition and function remain largely unstudied.
Liver Fat May Improve, at Least Initially
One area where keto shows a clear short-term benefit is liver fat. In people with fatty liver disease, a ketogenic diet reduced liver fat content by roughly 31% in just six days. Liver enzyme levels associated with inflammation also dropped. This makes physiological sense: when you starve the body of carbohydrates, the liver burns through its stored fat rapidly.
The caveat is that these results come from very short interventions. Whether the benefit holds over months or years, especially given the high fat intake that keto requires, is less clear. The liver is processing significantly more dietary fat on keto, and for people with liver conditions, that long-term burden hasn’t been well studied.
Bone Density: Uncertain but Not Alarming
There are theoretical reasons to worry about bones on keto. The mild acidosis from sustained ketone production could leach calcium, and the diet often falls short on calcium and vitamin D. However, a systematic review of seven trials found no significant changes in bone mineral density among people following ketogenic diets. Bone formation markers and bone breakdown markers both stayed stable in most subjects.
One exception: women who lost 10% or more of their body weight showed increased bone breakdown and decreased new bone formation. This is a known effect of significant weight loss on any diet, not unique to keto. Still, the review’s authors cautioned that no human studies with strong enough designs exist to give a definitive answer on keto and bone health. If you’re postmenopausal or already at risk for osteoporosis, this uncertainty is worth factoring in.
What Children on Medical Keto Tell Us
Some of the longest-running data on ketogenic diets comes from children with severe epilepsy, who may stay on medical keto for years under close supervision. These cases offer a window into what prolonged ketosis does to a growing body. Over 15 months, children on keto showed a significant decline in height-for-age scores, with 12 out of 15 participants falling behind in linear growth. Weight remained stable, meaning these children gained less height without losing weight, shifting their body composition.
Children’s nutritional needs differ from adults’, so these results don’t translate directly. But they do show that years of ketosis can affect fundamental biological processes like growth, even with medical monitoring. It’s a signal that the diet’s metabolic effects reach beyond fat burning.
The Practical Bottom Line
Keto works well as a short-to-medium-term intervention for specific goals: rapid weight loss, blood sugar reduction, and liver fat clearance. The evidence for keeping it going indefinitely is far less reassuring. The risks to kidney function accumulate with time. Nutrient deficiencies deepen. Gut health erodes. And if your version of keto leans heavily on animal products, the mortality data points in the wrong direction.
If you do choose to stay on keto long term, the research suggests two strategies that meaningfully change the risk profile. First, shift toward plant-based fat sources like olive oil, avocados, and nuts rather than relying on animal fats and processed meats. Second, work with a dietitian to identify and supplement the specific nutrients that keto diets consistently lack, particularly folate, magnesium, potassium, and vitamins A, E, and K. Many people treat keto as a simple formula of cutting carbs, but the longer you follow it, the more the details of what you’re actually eating start to matter.