If you have struggled with chronic GI problems, you have probably noticed that low carb and high fat diets are often promoted as the best diets for gut healing. Carbs are vilified as feeding SIBO, candida and other bad gut bugs. Healthy fats olive oil and butter are encouraged as they do not feed gut bugs and provide calories and nutrients.

I personally went lower carb when I first received my SIBO diagnosis under the advisement by my practitioner at the time. I was told to eat primarily veggies with just a few measly servings of fruit a day. But, he encouraged me to eat added fats like coconut, olive oil and ghee liberally. I was also encouraged to eat fattier cuts of beef.

Most of my clients are eating a very similar diet as I was for my SIBO. This low carb/higher fat and sometimes even keto style diets are popular among functional and integrative docs. Many docs will even bully their patients and say things like you “’will never heal their gut unless you follow a strict keto style diet”. But, is gut healing dependent on a keto diet?  

No it certainly is not! I often cringe when I hear my client’s tell me about the strict dietary pressure they have endured from practitioner in the past. Low carb/high fat did not work for me and it doesn’t work for 95% of my clients.

I was more constipated and under nourished on this diet. Plus, as a carb lover, life without potatoes, fruit and rice was unbearable! Sorry to my friends and family who had to put up with my grumpy attitude during this time.

When my clients come to me after working for months and often times years attempting to repair their guts, they are usually following these strict higher fat and lower carb diets. Their gut health usually continues to decline on these diets.  

I want to make something very clear before you continue reading this article. Certain people may do better on lower carb diets like those with diabetes, epilepsy or neurological disorders. So, I am not trying to say that low carb/high fat and keto styles are bad.

But if the goal is to repair the gut, low carb is NOT effective as a long term strategy to “heal the gut”. There is some evidence that keto short term may help the gut, but long term it FAILS to produce relief. It is impossible to repair the microbiome if carbs intake is too low.

In this post, I want to highlight the problems with going low carb and high fat for gut healing. I will also describe some general guidelines that I use with my clients for fat and carbs.

Low carb diets starve your good gut bugs

When you first go low carb, it can initial reduce symptoms. I hear this all the time from my clients. They went low carb and symptoms improved. Almost always these improvements are fleeting.

Going low carb typically reduces the amount of soluble fibers that you are eating. Soluble fibers are what your gut bugs eat. When your gut microbes break down these fibers, they produce gas. If you lower the fibers, then you lower gas, bloating and discomfort. Sounds good, right?

This reduction in fermentation can help in short term to calm things in an imbalanced gut, but at the same time it also starves your good gut bugs. When you don’t feed gut microbes, you will have a reduction in production of compounds called SCFAs (short chain fatty acids). These acids help to regulate the environment making it more hospitable for good gut bugs and less hospitable for bad gut bugs.

The SCFAs thickens the mucosal layer, which sits on top the gut lining and serves as a shield between the delicate gut lining and gut bacteria/toxins. This mucosal layer also serves as a habitat and food source for our gut bacteria.

When your mucous layer is thin, bacteria and toxins will come into contact with the epithelial lining and elicit an inflammatory immune response. This inflammation can lead to more permeability AKA leaky gut.

Without fermentable fuel to produce adequate mucous, the bacteria become ravenous, eating through all the mucosa and they will eventually start consuming your gut lining. This degradation of the gut barrier will not only lead to gut dysfunction, but system wide inflammation.

From working with 100s of IBS and SIBO clients, I often see inflammation, immune dysregulation and imbalances with my clients labs who were low carb for a long time before coming to see me. Their gut health suffers as their diet has been insufficient in soluble fibers for so long.

I do want to clarify that low carb does not necessarily mean lower fiber. But, cutting out carbs makes it much hard to eat enough fiber. Typically in my gut healing clients, low carb almost always becomes lower in fiber. You have to actively work on meeting fiber needs when you are lower carb.

To sum up, while starving the gut of fermentable carbs be a helpful initial strategy, I would not do this long term. For long term gut repair and healing, it takes eating enough carbs and fiber to keep your good gut bugs happy, to prevent inflammation and to build a strong gut barrier.

Low carb slows down thyroid function and motility

Thyroid hormones are crucial for optimizing digestion and motility. Thyroid issues are a root cause of SIBO because insufficient thyroid hormones will slow down gut function leaving you susceptible to overgrowths. Thyroid hormone activation is highly dependent on carb intake. Failing to meet proper carb intake will lead to lower thyroid hormones.

I constantly see low thyroid hormone in my clients eating low carb. Specifically, I see low levels of free T3 (the active thyroid). The inactive thyroid hormone T4 has to be activated to T3 so that thyroid hormones can be used by your cells. How do carbs increase this activation? It all has to do with how carbs stimulate a robust insulin response.

Insulin is needed to activate thyroid hormones. Insulin gets a bad wrap, but it plays valuable role in communicating to your body that you have adequate short term fuel. A strong insulin signal when you eat carbs will activate thyroid hormones.

When you eat high fat and low carb, insulin levels drop. Lower insulin means less free T3.

With less T3, your gut function suffers. Symptoms of low T3 are constipation, fatigue, hair loss, dry skin, weight instability, depression, brain fog, low body temps and more . If you have had an uptick in these symptoms, it would be worth getting a full thyroid panel run by your primary care doctor.

I usually like free T3 in the upper half of the lab range (above 3 at least). If it is in the low end of range, I would try adding some additional carbs back in and see if it goes up.

Basal body temps can be an indirect measure of thyroid status. Low basal temps can mean low thyroid function. Basal body temps under 97 degrees Fahrenheit would likely indicate low thyroid function and could also warrant bumping the carbs.

Low carb enlists more cortisol which hinders digestion

Low carb diets can also cause cortisol dysregulation. Cortisol is your body’s stress hormone and is activated in response to a dip in blood sugar.

Your body is skilled at maintaining your blood glucose levels, because you need a certain level of blood glucose to efficiently fuel your brain. When you eat carbs, your body uses those carbs to maintain a good blood sugar balance. You body shuttles those carbs to the blood after you eat to keep levels stable.  

When you go low carb and you don’t have enough glucose coming from your diet to feed into the blood stream, your body has to adapt and find a new way to maintain blood sugar levels. Enter cortisol!

When blood sugar dips on low carb, cortisol kicks off a process called gluconeogenesis where the body starts to break down protein into glucose. On low carb diets, cortisol is chronically being activated to keep blood sugar levels from falling too low.

Cortisol is not just a blood sugar regulating hormone, like I mentioned earlier, it is your stress hormone. It puts your body in a fight or flight state. Digestion takes a back seat when cortisol is activated. Here are the effects of cortisol on gut function:

  • Reduced blood flow to the gut which can lead to intestinal permeability (leaky gut)
  • Reduced digestive enzymes and stomach acid
  • Reduced motility and MMC activity
  • Enhanced pathogenic bacterial growth and virulence
  • Inhibited immune function in the gut
  • Increased blood glucose which can damage nerves in the GI tract (leading to further reduction in MMC activity

When you have SIBO, you want to avoid constant cortisol activations as it really harms digestion. Optimizing your carb intake can help prevent cortisol activations all the negative gut reactions that come along with higher cortisol.

High fat can lead to more endotoxemia and more gut slow downs.

Many low carb diets seem to promote that a plate of bacon and unlimited coconut oil is totally ok to heal your gut, but a banana has too much sugar and should be avoided. There is this idea that you can not go overboard with the fats, but you have to keep a tight rein on the carbs.

While I think fat is certainly a valuable nutrient and should be incorporated into your diet, eating too much fat especially saturated fat can lead to more LPS permeability. LPS is an endotoxin that is released by gut bugs. LPS becomes bad news in high quantities and when it seeps into the blood stream. This elevation of LPS in the blood is called endotoxemia.

Endotoxemia activates the immune system and promotes system wide inflammation. Elevated LPS has detrimental effects on the nervous system. Because digestion relies on a healthy autonomic nervous system, endotoxemia disrupts many digestive processes by stimulating neuroinflammation.  In particular, LPS can shuts down motility by acting on the brain stem and vagus nerve.

When your diet is high in coconut oil, butter, bacon, lard and other saturated fats, your digestion and motility can take a hit. And that is not to say that these foods are bad! I want to make that very clear. I use butter when I cook most days. Usually I probably use about 1 TBSP daily with my cooking.

But, when you are on a low carb diet you often have to rely on eating large amounts of added fats to keep your calories up.  Keto and low carb communities promote VERY liberal use of all fats. Adding extra coconut oil and butter to meals is promoted. This exorbitant amount of saturated fat could lead to greater amounts of endotoxemia and all the negative gut consequences as a result.

How low is too low carb? How much is too much fat?

Before I dive into this, I do want you to state that everyone’s needs for fat and carbs are going to vary. Working with a dietitian to figure out where your macronutrients should fall is really valuable. Your goals, activities, genetics and history all need to be analyzed to figure out what your optimal carb and fat levels are. Experimentation is also important too.

In general, most of my clients do better gut wise when we can work up their carbs to 30-40% of total calories. Usually, I am trying to ensure that my clients are consuming at least 150 grams daily. But, many do best with even more than this. I am always trying to find a carb level where we can adequately support hormones and also feed enough good gut bugs.  

I would say most of my SIBO/IBS clients come to me eating around 75-125 grams of carbs daily. Usually this is not enough carbs to support hormones or optimal gut health. Clients eating too few carbs feel sluggish, foggy, constipated, depressed and more.

Every one is going to be a little different when it comes to optimizing their carb intake. It takes experimentation to figure out exactly where your optimal carb intake should fall. Tracking your intake for a few days is a great idea to see where your carbs are falling.

For fat, I am all for using it when you cook. I would be a little more cautious with saturated fats. I would in most cases limit added saturated fats like butter and coconut oil to 1 TBSP per meal. Olive oil can be used a bit more liberally since it has less saturated fats. I would also encourage mixing in different types of fats from nuts, seeds, avocado and fish.

Swapping out more carbs instead of loading up on fat can be a process that takes times. Mentally, you may need to move through fears that you have about carbs. I like to help my clients develop new beliefs around carbs so they feel confident in the reintro process.

Physically, your body also may need to adjust to higher carb intake. Your body needs to increase enzymes that breakdown carbs. Your microbiome will also need some time to adjust to more carbs. Sometimes there can be some symptoms during this transition process. Going slow can keep transitional symptoms to a minimum.

Bottom Line:

If a lower carb and higher fat diet is not providing relief, add in some more carb to optimize hormones and digestion.