A ketogenic diet cut liver fat by 67% in adults with obesity, prediabetes and fatty liver disease, according to a randomized clinical trial published Aug. 27 in the journal Cell Metabolism. Researchers at Washington University School of Medicine ran the test. They compared keto head-to-head against a Mediterranean diet and a low-fat, plant-forward diet. Notably, every group lost about the same amount of weight. Still, only the keto group saw those liver numbers move.

Moreover, the finding falls within a community that carries an outsized share of metabolic disease. The Centers for Disease Control and Prevention reports that 115.2 million U.S. adults have prediabetes and 40.1 million people have diabetes. National Institute of Diabetes and Digestive and Kidney Diseases data show that diagnosed diabetes reaches 12.1% of non-Hispanic Black adults, compared with 6.9% of non-Hispanic white adults.

Still, one trial does not settle a decade of argument. Researchers supplied every meal. Moreover, the study ran for five months. And separate research shows keto can push cholesterol the wrong way for some people.

The science behind the ketogenic diet

First, the ketogenic diet is not a wellness invention. Dr. Russell Wilder of the Mayo Clinic coined the term in 1921 and used it to treat epilepsy, according to StatPearls, a clinical reference hosted by the National Library of Medicine. He wanted the seizure-reducing effects of fasting without starving his patients. Doctors still use it for treatment-resistant epilepsy.

Nevertheless, the mechanism is straightforward. Your body normally runs on glucose from carbohydrates. Cut carbs low enough, and your liver breaks fat into compounds called ketone bodies instead. That state is ketosis. A 2026 systematic review in BMC Nutrition defines keto as a diet in which fat provides at least 60% of calories. Meanwhile, carbohydrates stay at or below 10%. In practice, that usually means roughly 50 grams a day.

What the new trial found

For this study, the Washington University team randomized 55 adults with obesity, prediabetes and fatty liver disease. Notably, participants received all their food and met a dietitian weekly. They logged more than 95% of study meals. Finally, 42 of those 55 completed the study.

In contrast, the three diets differed sharply. The ketogenic arm drew 4% of calories from carbohydrates and 73% from fat. The Mediterranean arm drew 50% of its calories from carbs and 35% from fat. The plant-forward arm drew 70% of its calories from carbs and 15% from fat. Researchers then adjusted calories so everyone lost about 10% of their body weight. That took four to five months.

Overall, all three groups improved muscle insulin sensitivity by roughly 50%. However, liver fat fell by 67% on keto versus 45% on the other two, and liver insulin sensitivity improved by two to three times. Additionally, about 50% of keto participants no longer met the criteria for prediabetes. On the Mediterranean diet, 29% reached that mark. On the plant-forward diet, only 7% did.

Nevertheless, cholesterol did not worsen. First author Max Petersen said the keto group “didn’t experience an increase in blood fat or cholesterol”. The published results showed no differences among groups in LDL cholesterol, apolipoprotein B or 24-hour triglycerides.

What food do you eat on the keto diet?

In short, keto centers on fat and protein while cutting starches and sugars. Typical foods include meat, fish, eggs, full-fat dairy, cheese, nuts, seeds and non-starchy vegetables.

However, researchers use a more precise term for the healthier version. Stanford’s Keto-Med trial, published in The American Journal of Clinical Nutrition, tested a “well-formulated ketogenic diet.” That version keeps non-starchy vegetables, restricts added sugars and limits refined grains. Even so, it still drops legumes, fruits and whole intact grains.

However, that exclusion carries a cost. Specifically, the Keto-Med researchers found the ketogenic arm delivered lower nutrient intake, including less fiber. Because those food groups were removed, the shortfall followed. The Mayo Clinic similarly warns that long-term carb restriction may leave you short on some vitamins and minerals.

Why safety is a concern

The findings are encouraging. Still, a few caveats matter before anyone overhauls their eating habits.

First, the authors flagged limits themselves. They noted the trial was small. They also could not determine whether a less extreme carbohydrate cut might work without full ketosis.

Second, participants neither shopped nor cooked. Dr. Dacia Russell Goman calls that the biggest gap between a nutrition study and real life. She is dual board-certified in emergency medicine and obesity medicine, and founded Apex Metabolic. At home, she noted, people make hundreds of decisions around work, children, travel, stress and convenience.

“The most common problem is that ‘low carbohydrate’ gradually becomes a very narrow diet high in calorie-dense foods and low in fiber, produce and overall nutritional quality,” she said. “The best diet on paper is not necessarily the best diet for the person who has to live with it.”

Who the results actually apply to

Indeed, participants shared a specific profile: obesity plus prediabetes plus fatty liver disease. They also lost 10% of their body weight, which does considerable work on its own. “Losing around 10% of your body weight can create meaningful improvements in insulin sensitivity, blood sugar, triglycerides and fatty liver disease regardless of the dietary strategy,” Russell Goman said.

“Keto is a tool, not the goal,” she said. “The goal is improved metabolic health through an approach someone can actually sustain.”

Why cholesterol results differ by person

Furthermore, the narrowness of that profile matters. A randomized crossover feeding trial published in Nutrients tested a ketogenic diet in healthy, young, normal-weight women. In that group, LDL cholesterol and apolipoprotein B nearly doubled. The authors called those lipid changes a cause for concern.

Russell Goman tells Blavity Health that such variation is expected. “People’s responses can vary to the same intervention,” she said. “We see this across many interventions in medicine.” “Changes in LDL and apoB can be influenced by many factors, including baseline body composition, genetics, weight loss, energy balance, the types of fat being consumed, and the overall quality of the diet,” she said.

“A patient actively losing weight with obesity or insulin resistance may have a very different response from a young, lean person whose weight is stable,” she said. “So I would never use one study to say that a ketogenic diet cannot raise cholesterol,” she added. “If someone chooses this approach, I still want to monitor their lipid profile, and particularly apoB when appropriate, rather than assuming their response.”

In fact, the clinical literature describes the same split. A 2026 review in Annals of Medicine notes that LDL and total cholesterol often fall in people losing excess body fat on keto. In some lean individuals, though, those numbers rise sharply. Researchers call this the lean mass hyper-responder phenotype.

Risks and side effects

Meanwhile, the BMC Nutrition systematic review offers the clearest picture of what goes wrong. Researchers analyzed 36 studies covering 42 ketogenic interventions and 1,162 participants.

In total, researchers documented at least one adverse event in 43% of participants. Gastrointestinal problems accounted for 40% of all reported events. Specifically, constipation alone made up roughly 24%, the single most common complaint. Neurological effects followed at 17%, then metabolic and nutritional problems at 11%. Meanwhile, stricter diets produced more frequent and more severe events. Dropout across studies averaged 17%.

As a result, the so-called “keto flu” often arrives within the first two to seven days, bringing fatigue and headaches. Overall, short-term adverse events lasted about three and a half weeks. The Mayo Clinic additionally lists muscle cramps, bad breath and weakness. Because carb restriction increases fluid loss, staying properly hydrated matters more than usual.

What happens to muscle on the ketogenic diet?

Meanwhile, lean mass deserves separate attention, and Russell Goman flagged it as a particular concern for women approaching midlife and beyond.

“Any significant weight loss can include some loss of lean mass,” she said. “Very low-carbohydrate eating does not automatically protect muscle.” “Adequate protein, progressive resistance training, sufficient overall nutrition, and avoiding unnecessarily aggressive weight loss are much more important,” she said.

“I want patients asking not only, ‘How much weight did I lose?’ but also, ‘What did I lose?'” she said. “Preserving muscle is part of preserving long-term metabolic health.”

Longer-term concerns

Beyond the adjustment period, the clinical literature reports several risks. Those include kidney stones, gallstones, osteopenia, pancreatitis, high cholesterol and hair loss. Importantly, the BMC Nutrition reviewers could not detect several of those outcomes in their own data. They attributed the gap to short study durations averaging about 19 weeks. Bone effects, for instance, generally take at least 12 months to appear.

An umbrella review of meta-analyses separately found that keto can raise LDL and total cholesterol. That same review also found it can lower total testosterone, which is worth knowing because low testosterone is one hormonal contributor to erectile dysfunction. A broader review in Frontiers in Nutrition concluded that for most people, the risks may outweigh the benefits.

Similarly, population research points in the same direction. A study of 15,428 adults in The Lancet Public Health found a U-shaped relationship between carbohydrate intake and death. The lowest risk landed at 50% to 55% of calories from carbs. However, the replacement mattered. Swapping carbs for animal fat and protein raised mortality risk. Swapping them for plant fat and protein lowered it.

Who should avoid keto?

Nevertheless, some people should not attempt keto at all. The Annals of Medicine review lists rare absolute contraindications. Those include porphyria and certain inborn errors of metabolism. The metabolic disorders affect pyruvate carboxylase activity, carnitine transport and fatty acid oxidation. Relative contraindications include acute pancreatitis, advanced liver or kidney disease, and familial hypercholesterolemia.

In addition, the same review flags situations requiring caution:

Diabetes treated with insulin, sulfonylureas, SGLT2 inhibitors, metformin or GLP-1 medications
Hypertension managed with medication
Gallbladder disease or prior gallbladder removal
Electrolyte disturbances and cardiac arrhythmias
Pregnancy and breastfeeding
Being underweight
Intense physical training or recovery from surgery

Meanwhile, people with chronic kidney disease face particular concerns. A paper in the Clinical Kidney Journal points to metabolic acidosis, rising LDL cholesterol and kidney stones. Its authors suggest considering Mediterranean or plant-dominant patterns first.

Similarly, anyone with a history of disordered eating should talk with a clinician before starting a highly restrictive plan. Similarly, loop in your doctor before cutting carbs sharply if you take prescription medication for blood sugar or blood pressure, including beta blockers. Dosages often need adjusting.

Fatty liver disease and Black patients

Notably, research on metabolic dysfunction-associated steatotic liver disease, or MASLD, holds an important wrinkle. However, it cuts against the obvious assumption. A narrative review in Digestive Diseases and Sciences found MASLD is less common in Black populations than in white and Hispanic populations. Even so, the same review found Black and Hispanic patients suffer worse outcomes. Those include higher rates of progression to steatohepatitis and higher mortality. Lower prevalence has not translated into better results.

Safer alternatives

Still, keto is one option among several, not the only route to better metabolic health.

For example, the Mediterranean diet performed well in the Washington University trial. There, participants lost comparable weight and improved insulin sensitivity. Stanford’s Keto-Med trial makes the comparison directly. There, 40 adults with prediabetes or type 2 diabetes followed both a ketogenic and a Mediterranean-style diet for 12 weeks each. HbA1c improved similarly on both. The ketogenic arm lowered triglycerides more. However, it also raised LDL cholesterol and delivered fewer nutrients. Follow-up data suggested the Mediterranean pattern was easier to sustain.

Therefore, Russell Goman resists ranking these options in a fixed order. “I don’t think of obesity treatment as a ladder where everyone has to start with the same diet and earn their way toward medication,” she said. Instead, she individualizes the plan. “A Mediterranean-style pattern has excellent evidence and is often easier to sustain,” she said. “A lower-carbohydrate or ketogenic approach can be very effective for the right person.” Moreover, when a GLP-1 medication is clinically appropriate, she said, nutrition and medication can work together rather than compete.

Best practices

Get baseline bloodwork first, including a lipid panel and liver enzymes, then recheck it
Choose unsaturated, plant-based fats over saturated animal fats where you can
Keep non-starchy vegetables in rotation to protect fiber intake
Stay hydrated and watch electrolytes
Work with a registered dietitian rather than following social media protocols
Treat it as a defined intervention with a check-in date, not a permanent default

Finally, Russell Goman had one more caution, this one about how keto gets sold. Marketing it as proof of one correct way to eat, she said, can imply that people struggling with obesity simply lacked discipline.

“Obesity is a complex chronic disease, not a character test, and no single macronutrient strategy changes that,” she said. “Ketogenic diets may be one effective metabolic tool for some people, but you do not have to eat keto to successfully treat obesity or improve your health. The right plan is the one that is medically appropriate, nutritionally sound and sustainable for you.”

Bottom line

In short, a 2026 clinical trial found the ketogenic diet beat Mediterranean and low-fat diets on liver fat and blood sugar in adults with obesity, prediabetes and fatty liver disease, without worsening cholesterol. But that trial was small, ran under five months and supplied every meal. Other research shows keto can raise LDL cholesterol in people who are not losing weight. Talk with your doctor before starting, especially if you take medication or have kidney, liver, pancreatic or metabolic conditions.

Frequently Asked Questions

What is a typical keto breakfast?

Typically, eggs cooked in olive oil with avocado, spinach and smoked salmon is standard, delivering fat and protein with almost no carbohydrates.

What is the most filling food on keto?

In general, protein-dense foods like eggs, fish and meat tend to be most filling, especially paired with non-starchy vegetables.

Citations

Petersen MC, Smith GI, Farabi SS, et al. Effect of diet macronutrient content on the cardiometabolic response to weight loss: a randomized clinical trial. Cell Metabolism. Published online August 27, 2026. https://doi.org/10.1016/j.cmet.2026.07.020

Centers for Disease Control and Prevention. National Diabetes Statistics Report. Updated January 21, 2026. https://www.cdc.gov/diabetes/php/data-research/index.html

National Institute of Diabetes and Digestive and Kidney Diseases. Diabetes statistics. https://www.niddk.nih.gov/health-information/health-statistics/diabetes-statistics

Masood W, Annamaraju P, Khan Suheb MZ, Uppaluri KR. Ketogenic diet. In: StatPearls. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK499830/

Schopf C, Assmann M, Wolke N, Frenser M, Marquardt T, Fischer T. Adverse events and tolerability of ketogenic diets: a systematic literature analysis. BMC Nutrition. 2026;12(1):44. https://doi.org/10.1186/s40795-026-01277-5

Cell Press. Keto diet has greater health benefits than other popular weight-loss diets, according to clinical trial. EurekAlert! Published August 27, 2026. https://www.eurekalert.org/news-releases/1140343

Gardner CD, Landry MJ, Perelman D, et al. Effect of a ketogenic diet versus Mediterranean diet on glycated hemoglobin in individuals with prediabetes and type 2 diabetes mellitus: the interventional Keto-Med randomized crossover trial. The American Journal of Clinical Nutrition. 2022;116(3):640-652. https://doi.org/10.1093/ajcn/nqac154

Mayo Clinic. Low-carb diet: can it help you lose weight? https://www.mayoclinic.org/healthy-lifestyle/weight-loss/in-depth/low-carb-diet/art-20045831

Buren J, Ericsson M, Damasceno NRT, Sjodin A. A ketogenic low-carbohydrate high-fat diet increases LDL cholesterol in healthy, young, normal-weight women: a randomized controlled feeding trial. Nutrients. 2021;13(3):814. https://doi.org/10.3390/nu13030814

Dynka D, Rodzen L, Rodzen M, et al. The ketogenic diet is not for everyone: contraindications, side effects, and drug interactions. Annals of Medicine. 2026;58(1):2603016. https://doi.org/10.1080/07853890.2025.2603016

Chen S, Su X, Feng Y, et al. Ketogenic diet and multiple health outcomes: an umbrella review of meta-analysis. Nutrients. 2023;15(19):4161. https://doi.org/10.3390/nu15194161

Crosby L, Davis B, Joshi S, et al. Ketogenic diets and chronic disease: weighing the benefits against the risks. Frontiers in Nutrition. 2021;8:702802. https://doi.org/10.3389/fnut.2021.702802

Seidelmann SB, Claggett B, Cheng S, et al. Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. The Lancet Public Health. 2018;3(9):e419-e428. https://doi.org/10.1016/S2468-2667(18)30135-X

Joshi S, Shi R, Patel J. Risks of the ketogenic diet in CKD: the con part. Clinical Kidney Journal. 2023;17(1):sfad274. https://doi.org/10.1093/ckj/sfad274

Miller KC, Geyer B, Alexopoulos AS, Moylan CA, Pagidipati N. Disparities in metabolic dysfunction-associated steatotic liver disease prevalence, diagnosis, treatment, and outcomes: a narrative review. Digestive Diseases and Sciences. 2025;70(1):154-167. https://doi.org/10.1007/s10620-024-08722-0

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