The ketogenic diet, or keto diet, was first used to help treat childhood epilepsy more than 100 years ago. Today, a less strict version of the diet has become more widely popular. Scientists continue to study its potential use in treating or preventing a variety of diseases, including a range of neurological disorders, cancer and glucose management in type 2 diabetes. More commonly, however, people use the keto diet to lose weight. In this article, we’ll focus on how the keto diet affects your gut microbiome – the collection of bacteria and other microbes that live in your gut.
First, let’s briefly explain the keto diet.
What is the Keto Diet?
The keto diet is a high-fat, very low-carbohydrate diet. The meals are 70-80% fat and about 5-10% carbohydrates. Typically, your body breaks down carbohydrates in your body into glucose, which provides energy.
If you don’t eat a lot of carbohydrates, your body will turn to burning ketones, which are made from fat. This is called ketosis.
Because the keto diet forces your body to burn fat instead of glucose, it can help you lose weight. However, because it is a difficult diet to stick to, the weight may not stay off for long.
Importantly, there is little information about the long-term effects of following a keto diet – in part because it is difficult to maintain.
The Keto Diet and Gut Bugs
Because the foods we eat affect the composition of our gut microbiome, it’s perhaps not surprising that a strict diet may affect our resident bacteria.
Although research on the effects of keto diets on gut bacteria is fairly limited, the available studies do shed some light on the situation.
A study published in 2020 took a multi-pronged approach to the issue. The authors recruited 17 men who spent 2 months in a facility where their diet and exercise levels could be closely monitored.
All participants were overweight or obese, but did not have type 2 diabetes. Participants either ate a keto or “standard” diet for 4 weeks. Then, for the last 4 weeks, they switched to another diet, so that all participants tried both diets.
The scientists found that switching between the two diets led to shifts in actinomycetes, bacillus-like bacteria, and bastards.
In particular, the reduction in beneficial bifidobacterial species was greatest in those who adopted the keto diet.
The decrease in bifidobacterial species was in response to a decrease in carbohydrates, rather than a decrease in fat intake. It is possible that consuming less fiber, which promotes gut bacteria, caused this change.
Keto and Epilepsy
Although doctors first used the keto diet to treat epilepsy in the 1920s, scientists are still unsure why it works. Could its effectiveness be due to changes in the microbiome?
An intriguing study, albeit in mice, offers some hints.
The researchers used mice that were raised in a special way so they had no gut bacteria. The team found that the keto diet did not protect these “germ-free” mice from electrically induced seizures.
When the scientists colonized the germ-free mice with a bacterial species associated with following a keto diet, it protected the mice from seizures.
Thus, changes in gut bacteria associated with the keto diet appear to be an important factor in producing antiepileptic benefits.
In another part of their study, they transplanted the gut microbiome of mice eating a keto diet to mice on a standard diet. Again, this influx of gut bacteria provided protection against seizures in a second mouse.
Keto, Epilepsy, and Gut Bacteria
Epilepsy is a complex disease, but there is growing evidence that the microbiome may play a role. The ability of ketones to affect gut bacteria may be at least one reason why it is so effective in reducing seizures in some people.
One study uncovered some additional complications.
Some people’s seizures respond well to the keto diet, but it doesn’t help others. In this study, scientists compared responders and non-responders. They recruited 20 children with epilepsy who followed a keto diet for 6 months.
They found no significant difference in the gut microbiome between the two groups before starting the keto diet.
And after 6 months, both groups had a decrease in microbial diversity – a sign that the gut microbiome was less healthy.
However, there were differences between the two groups: the non-responders had higher levels of some species than the responders, including Clostridium perfringens.
Scientists believe that Clostridium difficile are important for gut health, but there is also evidence that they may contribute to an imbalance in the gut microbiome, which experts call a dysbiosis.
So while researchers have again identified changes, it’s unclear what they might mean for long-term gut health.
Interestingly, the authors of a study of young children with epilepsy found significant differences in gut bacteria between children with and without epilepsy (prior to trying the keto diet).
After following the keto diet for only 1 week, the gut bacteria in children with epilepsy were more similar to those in children without epilepsy, and most children had substantially fewer seizures.
The researchers suggest that the keto diet may have helped “correct” their initial gut bacterial imbalance.
Other Microbiome Changes
One problem with the available evidence is that many studies have focused on people with epilepsy.
And because the microbiome of people with epilepsy may be different to begin with, it is difficult to know whether any changes in gut bacteria during the study period are associated with people without epilepsy.
Several studies have recruited people without epilepsy. For example, one study looked at elite athletes. Among other changes, the scientists found that athletes on a keto diet had lower levels of fecal bacteria.
These bacteria are common in the gut microbiome and are associated with a decrease in inflammatory markers. Some studies have also linked lower levels of these bacteria to a higher risk of obesity and type 2 diabetes.
However, the gut microbiome of elite athletes differs from that of less active individuals, so it’s difficult to know if these findings are relevant to the population as a whole.
Sometimes the results are mixed – a small Italian study found that the keto diet did not significantly alter levels of Firmicutes and Bacteroidetes – two major players in a healthy gut microbiome.
But they did show that the keto diet was associated with increased numbers of Desulfovibrio, which is associated with inflammatory bowel disease (IBD).
What does It All Mean?
IIn short, it appears that the keto diet does affect gut bacteria, but it’s less clear what these changes mean for health.
If you use this diet to treat epilepsy, some of the changes may be beneficial. Some changes may also be helpful if you’re trying to lose weight or control your blood sugar.
However, at this stage, scientists don’t know the long-term effects of these changes in the gut microbiome.
Understanding the complex network of interactions between food, gut bacteria and the rest of the body will require some nitpicking.
As interest in the keto diet and microbiome rises, researchers are sure to continue their research on this interesting topic.