A low carb diet is always grain free. It may be high fat ketogenic, vegan low glycemic, ovo-lacto low carb, or more omnivore in how it is eaten, but it is always grain free. Grains are innately a healthy part of our diet, and cultures throughout the world have regularly included whole grains in their meals.
Removing grains removes a type of fiber that seems particularly beneficial for the human intestinal microbiome, the beneficial bacteria that thrive in our small and large intestines. Considering we have around 40 trillion bacteria in our intestines, we have a lot of bugs to keep happy! We now know that the gut bacterial health has influence over the rest of our body and mind, so having a strong microbiome is vitally important.
Fiber is a key food for beneficial bacteria—they eat it and ferment it into short chain fatty acids (SCFA). SCFA is the food for the colon cells and in fact, removing SCFA from colon cells can cause atrophy and death within days in a laboratory setting. They reduce inflammation in the colon and are used clinically to help patients with inflammatory bowel disease. SCFA may be particularly helpful for diabetes patients; they have also been show to decrease the levels of serum glucose, reduce insulin resistance, reduce systemic inflammation, and increase the secretion of Glucagon-like peptide one, a hormone which is so beneficial for diabetes control it has been made into an injectable diabetic drug.
In one study in people eating a low carb grain free higher protein fat diet, a negative change in the intestinal microbiome was noted, possibly leading to systemic ill health. Their bacteria produced less butyrate, a key SCFA, reduced antioxidant compounds, and increased certain amines associated with increasing the risk of colon cancer.
As a result, for patients eating a low carb grain free diet, the LCDA strongly recommends adding in 1-2 TBSP of a fiber powder daily into your supplement regimen, as long as your medical practitioner approves. Adding fiber in will feed the microbiome, protect against any negative changes in intestinal health, and also be helpful in reducing or eradicating a tendency to constipation that some people have eating a grain free diet.
There are many good types of fiber: flax seeds, chia seeds, psyllium, oat or rice brain, carrot or prune powder, apple pectin, guar gum, and so forth. A good fiber powder should have a nice little mixture of different types of fiber.