Despite what you may have heard from dogmatic nutritionists, low-carb diets are not inherently bad for the gut. However, the way that most people do lower carb diets leaves a lot to be desired when it comes to gut function. This is a big problem because the bacteria that live in our gastrointestinal tracts have a profound impact on all aspects of health.
Therefore, it’s worth making the effort to optimize gut function if you are on lower carb diet. Doing so will pay off in numerous ways, including improved body composition, better brain function and mood, easier sleep, greater appetite control, faster recovery from exercise, improved metabolic function, lower cancer risk, and better cardiovascular health.
Why Lower Carb Ketogenic & Paleo Diets Are So Popular
Lower carb ketogenic and paleo-style diets have surged in popularity due to their ability to reduce body fat and overcome the most common lifestyle diseases, diabetes, heart disease, and cancer. These diets help people take control of what they are eating by removing refined carbs and other processed foods that “hijack” the brain and lead to overconsumption.
Ketogenic diets are designed around MACRONURIENT composition, with followers eating a higher fat, moderate protein, and lower carb dietary profile. The typical keto diet is about 75 to 80 percent fat, 15 to 20 percent protein, and about 5 percent or less carbohydrate from low glycemic sources. The goal of the ketogenic diet is to lower blood glucose levels to allow for the production of ketones via the liver.
Ketones are a byproduct of fat burning that the body can use for energy. By reducing carbohydrates, the body is forced to increase reliance on body fat for energy, which makes the ketogenic diet useful for solving metabolic problems (such as prediabetes) and reducing body fat. The ketogenic diet tends to be designed around whole foods, particularly meat, fish, nuts, seeds, low-carb vegetables, whole fat dairy, eggs, and other fat sources. Sometimes lower carb fruits or beans may be included, depending on the individual situation.
The Paleo diet also tends to be higher in protein and lower in carbohydrates, however, the main defining factor is that it is designed around WHAT you eat, rather than strict macronutrient guidelines. Paleo diets are aimed at eating whole foods that have undergone minimal processing, with followers choosing foods that our ancestors ate, such as meat, fish, vegetables, fruit, and nuts. In some cases dairy products, eggs, seeds, and some grains may be allowed, whereas in others they avoided.
The Paleo diet is unlikely to be a ketogenic diet, unless especially designed to raise blood ketone levels. Although the Paleo diet removes added sugar, refined carbs, and processed foods, it can provide higher carb fruits and vegetables, which are not appropriate on a ketogenic diet. In fact, many ancestral diets get a substantial proportion of calories from whole carb sources, such as fruit and starchy vegetables like sweet potatoes and other root vegetables.
Both diets are popular because they can aid with reduction in body fat and improve blood sugar balance, while lowering insulin. The blood sugar benefits pay off in improved mood and fewer peaks and valleys in energy levels. For example, followers often report sustained energy throughout the day instead of afternoon tiredness or post-workday exhaustion. There’s also the fact that these eating styles allow people to get their eating under control so that they are no longer at the will of their environments. By going lower carb keto or paleo, you take responsibility for your health and food choices, which makes it easier to avoid the guilt and self-loathing that comes with a food hangover.
Because these diets tend to be higher in protein, they are compatible with body composition and fitness goals, allowing for optimal muscle recovery and lean mass gains. Higher protein lower carb diets are also great for bone health with followers typically having better bone density throughout the lifespan.
Watch Out For Common But Dangerous Pitfalls To Lower Carb Eating Plans
Unfortunately, most people who adopt a lower carb diet put themselves at risk of problems with gut health. This is a complicated issue, but here’s the deal in a nutshell:
The gut is populated with billions of bacteria that are known as the “microbiome,” which dictate health and well-being. Research into the microbiome is still in the early stages but we do know that certain bacteria are beneficial and others are harmful. Additionally, it appears that having a greater diversity of beneficial bacteria in the gut is associated with fewer health problems.
Because gut bacteria live off of what you eat, nutrition has a major impact on the type and number of bacteria in the GI tract. For example, an interesting new study looked at the impact of dietary fat on the population of bacteria in the gut. Researchers found that compared to a typical western diet that is high carbohydrates, a high-fat diet altered the microbiota, resulting in lower diversity and fewer beneficial bacteria, namely Bacteroides, Clostridium, and Roseburia. These bacteria are responsible for metabolism of protein and carbohydrates.
Interestingly, there was also a 70 percent decrease in production of protective short chain fatty acids and antioxidants. Short chain fatty acids, such as butyric and propionic acid, are important because they promote the health of the intestinal cell layer in the gut. Antioxidants are important because they neutralize reactive oxygen species that cause inflammation and damage cells and DNA.
The study authors cautioned that shifting to a high-fat, low-carb diet such as the ketogenic diet could put dieters at risk of lower levels of protective gut bacteria and antioxidants that fight DNA damage and aging if done incorrectly.
Something similar happens on diets high in protein, but low in carbs. A 2014 study found that although people who have a higher intake of protein foods have more lean mass, they also have higher levels of inflammation in the gut. These inflammatory markers are considered metabolic toxins that have been linked with adverse health conditions including gastric cancer, obesity, and type 2 diabetes. The study authors recommend taking advantage of the lean mass benefits of a higher protein diet by planning the diet to include protective levels of low-carb plants, which will feed the beneficial gut bacteria and prevent inflammation.
Carb Up With Low-Carb Fibers
In an ideal world, lower carb diets would provide naturally occurring fiber. Fiber is a component of carbohydrate foods that is not digested or absorbed in the intestinal tract. Instead, it travels to the intestines and is metabolized by our gut bacteria. Almost all plant foods contain some fiber, including grains, vegetables, fruits, nuts, and seeds, though the type and concentration differ greatly.
Another difference in fiber-containing foods is how they impact blood sugar and insulin release. Fiber itself does not stimulate insulin release since it has no impact on blood sugar, however, the different fiber-containing foods vary in terms of insulin and blood sugar response (also known as the glycemic response).
Grains tend to stimulate the largest glycemic response and they are much more calorie dense than starchy vegetables or fruit, which lead to a moderate increase in blood sugar and insulin.
Low-carb vegetables have the lowest glycemic response, while also supplying minimal calories but abundant nutrients and fiber.
Nuts and seeds have a low glycemic response due to their lack of digestible carbs but high concentration of fats.
Refined carbs and processed foods may contain fiber; however, these foods have several drawbacks: First, they are high in calories, often contain added sugar, and have a large glycemic response, spiking blood sugar and insulin. Second, they tend to be made from refined grains that have had the naturally occurring fiber removed. If they do contain any fiber, it is added fiber, which has not been shown to produce the same health benefits as naturally occurring fiber in fruits, vegetables, intact grains, nuts, and so on.
Ideally, a low-carb diet would provide plenty of low glycemic, high fiber foods, including nuts, seeds, leafy greens, cruciferous vegetables, spices, and low-carb fruits. However, surveys show that most low-carb diets are largely absent of naturally occurring fiber. One survey of British low-carb dieters found that 20 percent of people ate zero vegetables and 45 percent ate no fruit. Another study found that average fiber intake was less than 10 grams per day in low-carb dieters, which is abysmally low.
The solution is to support the growth of beneficial anti-inflammatory gut bacteria by including low glycemic plant sources. This approach is supported by what we know about present day hunter-gatherers such as the Kitavans in Oceania who eat an incredible 50 to 100 grams of fiber a day, all from natural sources that fuel the beneficial bacteria in the gut. The Kitavans eat no western foods (grains, flours, sugar, oil) and are lean and virtually free of heart disease, obesity, and diabetes.
Here is a sample list of fibrous, low-glycemic carbs that are compatible with a very low-carb ketogenic diet:
Leafy Greens: Dandelion greens, collards, chard, mustard greens, beet greens, kale, arugula, lettuce, spinach, parsley, basil
Roots: Jicama, chicory, Jerusalem artichoke
Alliums: Garlic, onion, scallion, leeks
Peppers: Green, yellow, red, and orange bell peppers, chili peppers
Fruits: Olives, avocado, coconut
Spices: Nutmeg, cumin, paprika, curry, cinnamon
Nuts: Almonds, walnuts, pistachio
Seeds: Chia, flax, sesame
Cruciferous vegetables: Broccoli, cauliflower, cabbage, bok choy, brussels sprouts
Other low-carb vegetables: Eggplant, zucchini, asparagus, cucumbers, celery, mushrooms
There are also numerous fiber containing foods that are higher in carb content and may not be appropriate for a very low-carb diet. These foods can provide variety on a paleo diet, or may be useful for a re-feed higher carb meal:
Fruits: Bananas, apples, pears, grapes, melons, mango, peaches, plums
Legumes: Lentils and beans (pinto, black, white, red, garbanzo, etc.)
Roots: Carrots, sweet potatoes, potatoes, turnips, beets
Grains: Oats, millet, buckwheat, amaranth
Another great source of fuel for healthy gut bacteria is resistant starch. Resistant starch passes through to the intestine undigested so that the anti-inflammatory flora can use the fiber it contains as fuel to proliferate. Resistant starch can be found in foods such as bananas, oats, peas, maize, and potatoes, however, these foods do contain insulin-raising carbs. Resistant starch can be supplemented by taking 20 to 30 grams of unmodified potato starch, either dissolved in water or added to food, such as a protein shake or Greek yogurt.
Additional Strategies To Optimize Gut Health On A Lower Carb Diet
The good news about lower carb, higher fat diets, is that there are certain ways they are favorable for gut health compared to a western high-carb diet.
First, they eliminate the two favorite food sources fueling inflammatory gut bacteria: Sugar and artificial flavorings. Since sugar and processed foods are pretty much off the table with paleo and keto diets, you don't have to worry about undermining your efforts to protect gut by accidentally overfeeding the bad bacteria.
Second, most lower carb diets eliminate many of dietary components that harm the gut lining. A healthy gut is composed of tight junctions connecting the single cell layer that protects the body from waste products in the GI tract. The tight junctions can be damaged by a whole slew of things, including medications, gluten, antibiotics, and high levels of cortisol. When this happens, anything and everything that passes through your GI system can escape into your bloodstream, including undesirable bacteria, tiny pieces of food, and toxins. These can have negative effects on hormone balance, brain function, and skin.
Here are some additional strategies you can take to protect the gut on a lower carb diet:
Reduce medication use. Medications (especially antibiotics and painkillers like ibuprofen and acetaminophen) and alcohol harm the tight junctions in the gut.
Identify any food intolerances. Though soy, peanuts, and gluten may be the most common food intolerances that harm the tight junctions, you can develop an intolerance to any food. Addressing food intolerances is out of the scope of this article, but the main point is to eliminate any offending foods, heal the gut, and then attempt to reinstate those foods, monitoring any symptoms and adjusting accordingly.
Eat probiotic foods or consider supplementing. Probiotics are the term for the beneficial bacteria that promote a healthy microflora in the gut. They can be consumed in fermented foods such as sauerkraut, kim chi, and dairy, however, to truly impact the gut, it is likely that you need to supplement with a high powered probiotic. Part of the problem with relying on food for probiotics is that the live bacteria are unlikely to survive the food production and storage process. Additionally, the concentration of live bacteria is often too low to have an impact on the gut, and the type of bacteria used in many of these foods has not been shown to have beneficial effects on human health.
Chew your food. The intestines don’t deal well with incompletely digested food. In fact, when large food particles hit the intestines, harmful bacteria feed on them, which can lead to an overgrowth of these bacteria.
Cope with your stress: Stress does a number on the gut by leading to the release of cortisol, which stimulates histamine, a compound that revs up your immune system. Histamine increases release of compounds that damage the tight junctions protecting the gut lining.
Final Words: By adopting a lower carb diet, you set yourself up for better health if you design your nutrition around a balanced array of whole foods in their most natural state. Hopefully, the strategies presented in this article will allow you to avoid undermining your efforts and optimize gut health.