Nobody knows for sure, because most research on the ketogenic diet lasts weeks or months, not years. The longer studies point to a few real risks: higher LDL cholesterol in many people, a higher chance of kidney stones, and meals that run short on fiber and some vitamins and minerals. Some people shouldn’t try keto at all without medical supervision. Here’s what the evidence shows, who should be careful, and how to lower the risks if you stay on it.
What counts as “long term” in keto research
A ketogenic diet cuts carbohydrate so far, usually under 50 g a day and sometimes as low as 20 g, that the body switches to burning mostly fat and making ketones for fuel. Popular versions get 70 to 80% of their calories from fat and only 5 to 10% from carbohydrate, according to Harvard’s Nutrition Source.
In nutrition research, “long term” usually means a year or more. Harvard’s review of the evidence notes that most keto weight-loss studies were small and lasted 12 weeks or less. That’s too short to show problems that build slowly, such as kidney stones or changes in bone strength. Trials that run for a year or longer do exist, but there are far fewer of them, and the same review points out that people tended to drift off the diet as time went on.
That last point matters when you read the results. A long keto trial usually tells you what happens to people who mostly stick with the diet for a year or two while researchers check on them. It tells you much less about following keto on your own for five or ten years.
What the longer trials found
The best summary of the longer evidence is a 2013 meta-analysis of 13 randomized trials, each lasting at least 12 months, that compared a ketogenic diet (no more than 50 g of carbohydrate a day) with a low-fat diet. People on keto lost slightly more weight: an average of 0.91 kg (about 2 lb) more after a year or longer. Their triglycerides fell and their HDL cholesterol rose, both welcome changes. But their LDL cholesterol rose as well, by an average of 0.12 mmol/L (about 4.6 mg/dL).
Harvard’s review reaches a similar conclusion: after one year, the effects of keto were not significantly different from those of conventional weight-loss diets. Put simply, over the long run keto works about as well as other diets for weight loss, while asking more of you and carrying a few extra risks (source).
A smaller, more recent trial adds useful detail. In the Keto-Med study, 40 adults with prediabetes or type 2 diabetes spent 12 weeks on a ketogenic diet and 12 weeks on a Mediterranean-style diet. Both diets cut added sugar and refined grains, but only the Mediterranean-style one kept legumes, fruit and whole grains.
In that trial, blood sugar control, measured as HbA1c, improved about equally on both diets. On keto, triglycerides fell further, but LDL cholesterol rose by about 10%, while it fell by about 5% on the Mediterranean-style diet. Twelve weeks after the study ended, people were keeping up the Mediterranean-style eating better than keto.
The main long-term risks
Higher LDL cholesterol
LDL is often called “bad” cholesterol, and the NHS explains that eating too much saturated fat can raise it, which can increase the risk of heart disease and stroke. Both trials above found LDL went up on keto, on average. Responses vary a lot from person to person, so the only way to know what’s happening to yours is a blood test.
The likely reason is the type of fat. Many keto meal plans lean heavily on butter, cream, cheese, fatty and processed meat and coconut oil, which are all high in saturated fat. According to the same NHS guidance, there’s good evidence that replacing saturated fats with some unsaturated fats can help lower cholesterol. You can make that swap and stay keto: olive oil, avocado, nuts, seeds and oily fish such as salmon, mackerel and sardines are all very low in carbohydrate.
People with familial hypercholesterolemia, an inherited condition that causes very high LDL from birth, are on the list of people who should only try keto under medical care, according to a 2026 review of the diet’s contraindications.
Kidney stones
A 2021 meta-analysis pooled 36 studies covering 2,795 people on ketogenic diets. Over an average of 3.7 years, 5.9% developed kidney stones, which is roughly 1 person in 17. The estimate was 5.8% in children and 7.9% in adults. About half were uric acid stones, and calcium-based and mixed stones made up most of the rest.
The US National Institute of Diabetes and Digestive and Kidney Diseases says drinking enough liquid, mainly water, is the most important thing you can do to prevent kidney stones. If you’ve had a kidney stone before, talk to your doctor before you start keto.
Low fiber and missing nutrients
Keto rules out most fruit, beans, lentils, whole grains and starchy vegetables, which are some of the main sources of fiber in a typical diet. In the Keto-Med trial, people ate less fiber, folate, vitamin C and magnesium on keto than on the Mediterranean-style diet, and the researchers linked this to cutting out legumes, fruit and whole grains.
Harvard’s review adds B vitamins, iron and zinc to the nutrients that can run short, and suggests working with a registered dietitian to plan around them. It also lists constipation among the common complaints, which isn’t surprising on a diet this low in fiber.
Bones, uric acid and gout
The same Harvard review lists osteoporosis (thinning, weaker bones) among the problems linked to long-term keto, along with kidney stones and higher levels of uric acid in the blood, which is a risk factor for gout (source). If you already have weak bones or have had gout, that’s another reason to involve your doctor before starting.
Sticking with it
A diet can only help while you follow it. In both the Harvard review and the Keto-Med trial, people found keto harder to keep up than less restrictive ways of eating. If you find you’re constantly starting and stopping, a less strict plan that you can follow for years may serve you better.
Who should not try keto without medical supervision
Safety note: A ketogenic diet isn’t safe for everyone. Don’t start one without medical supervision if you have type 1 diabetes, take insulin or other diabetes medicines (especially SGLT2 inhibitors such as empagliflozin or dapagliflozin), take medicine for high blood pressure, have kidney, liver, pancreas or gallbladder disease, are underweight or have had an eating disorder, or are pregnant or breastfeeding. Children should only follow keto as a medical treatment run by a specialist team. A 2026 review of keto’s contraindications lists these and other situations that need care, so talk to your doctor first if any apply to you.
Medicines are the biggest everyday risk. Cutting carbohydrate this far can make insulin and sulfonylureas push blood sugar too low. With SGLT2 inhibitors, it has been linked to euglycemic ketoacidosis, a dangerous build-up of acid in the blood that can happen even when blood sugar readings look normal. The 2026 review also flags blood pressure tablets and diuretics (“water pills”) as needing care. Doses often have to change before or soon after you start, and that’s a decision for your doctor, never something to adjust on your own.
How to lower the risks if you stay on keto
If you and your doctor decide keto suits you, these habits deal with the main risks above.
- Get a baseline blood test. Ask your doctor about checking your cholesterol, kidney function and, if it applies, blood sugar before you start and again a few months in, so you can see how your body is responding.
- Make unsaturated fats your main fats. Cook with olive oil, and build meals around avocado, nuts, seeds and oily fish. Treat butter, cream, cheese and processed meat as extras rather than staples.
- Eat non-starchy vegetables at most meals. Leafy greens, broccoli, cauliflower, cabbage, zucchini and peppers add fiber, folate, vitamin C and magnesium for very little carbohydrate.
- Drink plenty of water through the day. It’s the simplest protection against kidney stones.
- Consider a less strict version. In the Keto-Med trial, a Mediterranean-style diet with no added sugar or refined grains improved blood sugar about as much as keto did, without the rise in LDL, and people found it easier to keep up.
- Set review dates. Plan check-ins with your doctor or a dietitian at about 3 months and 12 months, rather than drifting on with no plan.
Planning meals is easier with a few go-to recipes. Our keto guides cover low-carb foods and meals, and leafy greens are one of the best low-carbohydrate sources of fiber, as our guide to leafy greens and inflammation explains.
Common questions
How long can you safely stay on keto?
There’s no agreed limit, because there are few studies lasting longer than a year or two. If you want to stay on it longer, regular blood tests and check-ins with your doctor are the safest way to do it.
Is keto bad for your heart?
It depends partly on what happens to your blood fats. Keto usually lowers triglycerides and raises HDL cholesterol, which are good changes, but it raises LDL cholesterol in many people, which isn’t. The trials so far haven’t followed people long enough to show what this means for heart attacks and strokes. If you have heart disease or high cholesterol, talk to your doctor before you start.
Does keto damage your kidneys?
The clearest kidney risk is stones, as described above. Advanced kidney disease is one of the reasons to avoid keto unless a specialist supervises it, according to the 2026 review.
This article is general information, not medical advice. Talk to your doctor or a registered dietitian before making big changes to how you eat, especially if you have a health condition, take regular medication, or are pregnant or breastfeeding.
