With the renewed interest in the keto diet, many people regularly consume high fat food. But just because something gives you short term benefit doesn’t mean that there are no long term consequences. Overall, if a person loses weight on keto and can’t do so on a regular diet, it’s probably great for them.

Unfortunately, I don’t think people stick to the keto diet over the long term. Maybe they do it for a few months and diverge. Or maybe they do it on the weekdays and come off on the weekends. Either way, if you go keto you should stay keto.

A new study just published on high fat diets show that 5 days of a high fat diet increases absorption of LPS. LPS is a component of the cell wall of bacteria in our gut. So, this means that LPS is sneaking across the gut barrier. But I wouldn’t refer to this as leaky gut, as you’ll soon see.

High fat food increases endotoxin

In the study, participants consumed a weight maintenance control diet for 2 weeks. Consequently, they were fed a high fat meal and put on a high fat diet for 5 days that also maintained weight. Again, after 5 days, they consumed the high fat meal again. Macro ratios for the diet and meal were:

• Control diet was 55% carb, 30% fat, 15% protein
• High fat meal was 820 cals (25% carb, 63% fat, 12% protein)
• High fat diet was 30% carb, 55% fat, 15% protein

Researchers measured serum LPS prior to the high fat meal and 4 hours after during both high fat meal challenges. A 4 sugar intestinal permeability test was also performed. Since all participants followed the same protocol, each acted as their own control group.

Despite no change in intestinal permeability as measured by the 4 sugar test, serum endoxotin doubled. This is a bit troubling since all participants were healthy (BMI=23) and free of dyslipideia or other metabolic disease. In other words, overweight or obese people likely see greater problems.

But how does LPS get in to the blood without leaky gut? I discuss the 2 primary types of intestinal permeability in my free course 3 Common Causes of Leaky Gut. Check that out to get up to speed.

Not a leaky gut from high fat food

What most people think of as leaky gut is paracellular permeability. In it, the tight junctions that hold the cells in the gut together fail. The 4 sugar test will measure this, and people classically think of this as leaky gut. But since the 4 sugars didn’t cross the barrier, the gut wasn’t “leaky”.

However, there is another way to increase paracellular permeability. Passive absorption of a substance occurs when the concentration on one side of the barrier is higher than the other side. Things aren’t “leaking” in this form of permeability, they are let across.

So based on this study, 5 days of high fat feeding increases the amount of LPS in the gut. The concentration increases to the point that LPS passes from the gut to the blood.

What this means for keto dieters

So what does this mean for people doing the keto diet? I don’t think it means that going keto is bad, per se. However, increasing the amount of LPS in your gut and serum isn’t a gut thing. The biggest problem is when you decide to go off the diet.

Multiple lines of evidence point to increased fat intake altering the microbiota to favor an increase in gram–negative bacteria. This is the type of bacteria enriched with LPS. This jibes with the research above.

In the context of the keto diet, I don’t think this is a big issue. The problem comes when you do something else that increased permeability, particularly in the colon. Alcohol definitely does this, so people going keto probably want to abstain from alcohol.

But an even bigger issue is that hyperglycemia coupled with low insulin promotes paracellular permeability in the colon. This is the worst case scenario as most of your microbiome resides in the colon. Therefore, so does most of the LPS.

This assuredly happens to people when they abruptly come off keto. Don’t believe me, it’s simple enough to test. And people have reported it as “physiological insulin resistance”, a normal adaptation to a keto diet. But your colon doesn’t care about that, it only sees hyperglycemia and insulin resistance.

Boom, leaky gut in the worst of places. It’s interesting to point out that the results of the above study indicate the colon wasn’t involved. So this would likely lead to a far worse effect than a doubling of fasting endotoxin.

Conclusion

Based on the anecdotal evidence scattered about the internet, there is no doubt many see health benefits from a keto diet. Be that as it may, our gut responds in a consistent way to a chronic diet of high fat food consumption: increased LPS in the gut.

This doesn’t mean that you shouldn’t follow a keto diet. But it does indicate that if you are eating a keto diet, you should stay keto. Don’t diverge on the weekends and definitely reconsider alcohol intake.

Over time, if you plan to transition to a more balanced diet, take your time. Introduce carbs slowly, and measure your blood glucose. Many report they fell worse on carbs after following a keto diet long term. But this may have more to do with how rapidly they introduce carbs rather than an inherent intolerance to carbs.