Researchers discovered that the ketogenic (keto) diet doesn’t work the same way for everyone. Using mice and studying people with liver disease, scientists found that a specific protein in the liver called FGF21 controls how well your body handles the keto diet. When this protein doesn’t work properly—especially in people with certain health conditions—the keto diet can actually cause weight gain and liver problems instead of helping. The study suggests that your body’s internal clock (circadian rhythm) plays an important role in whether the keto diet will be beneficial for you.
The Quick Take
- What they studied: Whether the keto diet works the same way for all people and what controls whether it helps or hurts your body
- Who participated: Laboratory mice with and without genetic changes, plus patients with alcoholic fatty liver disease
- Key finding: The keto diet only works well when a liver protein called FGF21 can respond properly. When this protein is broken or doesn’t work right, the keto diet can cause weight gain and liver damage instead of weight loss
- What it means for you: Before starting the keto diet, especially if you have liver disease or metabolic problems, you may want to talk to your doctor. The keto diet isn’t a one-size-fits-all solution, and your individual body chemistry matters a lot
The Research Details
Scientists conducted experiments using specially bred mice that had metabolic problems similar to human diabetes and obesity. They fed some mice a keto diet for 8 weeks while keeping the calories the same as a regular diet. They also studied a group of patients with alcoholic fatty liver disease who tried a keto diet for a short period. The researchers measured changes in weight, liver function, fat metabolism, and the activity of specific proteins in the liver.
The key innovation was examining two specific proteins: BMAL1 (which controls your body’s internal clock) and FGF21 (which helps regulate fat burning). The team created mice missing these proteins to understand their role in how the body responds to keto diet.
Understanding why the keto diet works for some people but not others is crucial because it’s a popular diet that many people try. If we can identify which people will benefit and which might be harmed, doctors can give better personalized advice. This research suggests that your body’s circadian rhythm (24-hour internal clock) is more important for diet success than previously thought.
This study combined animal research with human patient data, which strengthens the findings. The researchers used multiple approaches (different types of mice and human patients) to confirm their results. However, the human portion was limited to patients with liver disease, so results may not apply to healthy people. The study was published in a peer-reviewed scientific journal, meaning other experts reviewed it before publication.
What the Results Show
In normal, healthy mice, the keto diet worked as expected: it caused weight loss and maintained good metabolic health. However, in mice with metabolic problems (similar to type 2 diabetes), the keto diet had the opposite effect—it caused weight gain and made their fat metabolism worse.
The researchers discovered that this difference came down to a liver protein called FGF21 and its connection to BMAL1 (the circadian rhythm protein). In the metabolically unhealthy mice, BMAL1 wasn’t working properly, which meant FGF21 couldn’t respond to the keto diet correctly. When FGF21 couldn’t do its job, the body couldn’t properly handle the high-fat keto diet.
When scientists removed the FGF21 or BMAL1 genes from normal mice, those mice also had problems with the keto diet—showing weight gain and metabolic problems. This proved that these two proteins are essential for the keto diet to work well. Interestingly, when researchers gave the unhealthy mice extra FGF21 as a supplement, it fixed many of the problems caused by the keto diet.
The study also found that patients with alcoholic fatty liver disease showed the same problem as the unhealthy mice: their FGF21 protein didn’t respond well to the keto diet, and they experienced liver damage. Additionally, the unhealthy mice on the keto diet had reduced exercise capacity, meaning they couldn’t perform physical activity as well as they normally could.
Previous research has shown that the keto diet works well for weight loss in many people, but this study explains why it doesn’t work for everyone. Earlier studies didn’t focus on the role of circadian rhythm proteins like BMAL1. This research adds an important new piece to the puzzle by showing that your body’s internal clock affects how well you can handle a keto diet.
The main limitation is that most of the research was done in mice, not humans. While mice are useful for understanding how the body works, results don’t always transfer directly to people. The human portion of the study only included patients with liver disease, so we don’t know if these findings apply to healthy people trying the keto diet. Additionally, the study doesn’t tell us how to test whether someone’s FGF21 or BMAL1 are working properly before they start a keto diet. The sample size of human participants wasn’t specified in the available information.
The Bottom Line
If you have metabolic problems, liver disease, or diabetes, talk to your doctor before starting a keto diet. This research suggests the keto diet may not be safe or effective for you without medical supervision. For healthy people, the keto diet appears to work as expected, but maintaining a regular sleep schedule and circadian rhythm may be important for success. Consider working with a healthcare provider or registered dietitian who can monitor your progress.
This research is especially important for people with type 2 diabetes, obesity, fatty liver disease, or alcoholic liver disease. If you have any of these conditions, you should be cautious about starting a keto diet without medical guidance. Healthy people considering keto may also benefit from understanding that their body’s internal clock matters for diet success. Healthcare providers should consider this information when recommending diets to patients with metabolic problems.
In this study, changes appeared within 8 weeks. However, individual results vary. If you’re considering a keto diet, give it at least 4-6 weeks while monitoring how you feel and tracking your weight and energy levels. If you experience weight gain, fatigue, or worsening symptoms, stop and consult your doctor.
Want to Apply This Research?
- Track your weight, energy levels, and sleep schedule daily. Also note any digestive changes or how you feel during exercise. This data will help you and your doctor determine if the keto diet is working for your body.
- Set a consistent sleep schedule (going to bed and waking up at the same time daily) while following a keto diet. This supports your body’s circadian rhythm and may improve how well the diet works. Also, schedule regular check-ins with your doctor if you have metabolic health concerns.
- Weekly weigh-ins, daily energy level ratings (1-10 scale), sleep duration tracking, and monthly liver function tests if you have risk factors. If weight increases or energy decreases after 4 weeks, consult your healthcare provider about whether keto is right for you.
This research is preliminary and was conducted primarily in laboratory mice. While it provides important insights, it should not replace professional medical advice. If you have diabetes, liver disease, obesity, or other metabolic conditions, consult your doctor or registered dietitian before starting a ketogenic diet. This is especially important if you’re taking medications or have existing health conditions. The findings about FGF21 and BMAL1 are not yet routinely tested in clinical practice, so personalized testing is not currently available for most people. Always work with qualified healthcare professionals when making significant dietary changes.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.