Rehmannia, Diabetes, Obesity, and the Microbiome

Prepared Rehmannia (Shu Di Huang) is one of the most well-known herbs in Chinese medicine. It is the emperor of the famous Six Ingredient Rehmannia Pill or liu wei di huang wan. It is also one of the most extensively studied Chinese herbs in laboratory and clinical research over the past 70 years. Much of the research over the years has focused on its blood-sugar regulating effect, initially inspired because it was indicated frequently over the centuries for what appears to have been a diabetic condition. This condition was called wasting and thirsting syndrome or xiao ke.

Although prepared Rehmannia is classified as a Blood tonic in standard modern materia medica, it is often used to treat patterns of Yin deficiency. However, as most experienced clinicians have observed, Spleen Qi deficiency, damp heat, and phlegm often present as the more predominant patterns in the early stages of modern type 2 diabetes patients. I have written about this at length elsewhere on this site, including here. Rehmannia is generally contraindicated in the presence of such symptoms and patterns. Nevertheless, much research has shown Rehmannia to be useful in the treatment of patients with type 2 diabetes, metabolic disorder, and general blood sugar regulation. Much of this research has shown a benefit without regard to the traditional TCM diagnoses the herb is most typically associated with. How can this be?

The mechanism for Rehmannia’s blood-sugar regulating effect has not been well understood. As reported here, some recent research in Korea showed very promising results in the use of Rehmannia in the treatment of obesity:

The clinical study reported here was conducted in order to analyze the anti-obesity effect of the steamed root of Rehmannia glutinosa Libosch (Shu Dihuang), a Chinese herbal medicine widely used for the treatment of metabolic diseases. To understand the mechanism(s) underlying the beneficial effects of R. glutinosa, we investigated the changes in gut microbiota after herbal intervention through 16S rRNA gene-based pyrosequencing analyses. Twelve female middle-aged subjects (40–65 years old) with body mass index (BMI) over 25 kg m−2 were included in this study which involved intake of steamed roots of R. gluti- nosa for eight weeks. The subjects were visited for anthropometric measurements every two weeks and fecal samples were collected before and after the intervention. All subjects showed a significantly decreased waist circumference following the herbal treatment. The relative abundances of fecal microbiota suggested an association of intake of R. glutinosa with increases in phylum Actinobacteria and genus Bifidobacterium, while phylum Firmicutes and genus Blautia were decreased in response to the herbal treatment. Based on these findings, it is conceivable that a decrease in the waist circumferences after R. glutinosa intake may be related to alteration of intestinal microbiota and the herbal intervention has the potential as a prebiotic.

What caught my eye about this study was the role that it indicated for changes in microbiota composition as a factor in the mechanism of Rehmannia’s effect on obesity. There’s other research coming out of China that also indicates that imbalances in the microbiome are a major factor in diabetes and that there are range of Chinese herbs that positively impact the condition of diabetics by regulating the microbiota composition. All of which begs the question as to what is going on from a traditional Chinese medical perspective that makes Rehmannia so valuable in conditions that appear to be predominantly those of Spleen Qi deficiency, damp heat, and phlegm accumulation.

The legendary Bob Flaws co-authored a comprehensive textbook on the traditional Chinese medical treatment of diabetes. He explained that the benefit of Rehmannia in such conditions was because the Yin had actually been damaged by prolonged brewing of damp heat in the lower burner that consumed vital fluids. At least, that is my elevator speech version of the hypothesis. That may be satisfying enough for many people. Obviously, from the perspective of herbal formulation, it becomes a delicate balancing act. This diagram from Bob’s book shows the complex dynamics of diabetes from a TCM perspective.

As you can see, Yin deficiency occurs at a later stage of a process that, not surprisingly, begins in the digestive system. Yet, the herb appears to be beneficial for general blood sugar regulation in an otherwise healthy person to full-blown diabetes.

Lest we think this is a new or new-ish idea, Flaws includes this passage from the Nei Jing about xiao ke:

This [condition] occurs in those who are fat and beautiful. This person must [eat] many sweet, fine [foods] and too many fats. Fats all cause heat inside humans, and sweets all cause center fullness. Therefore, the Qi spills over above, transforming into wasting and thirsting

This was a rich person’s diet back in the time of the yellow emperor. Today, it is the standard American diet. It is generally understood that too much sweet is not just sugar-sweet but also energetically “sweet” foods that are starchy. In other words, the term “fine foods” refers, at least in part, to refined carbohydrates. Although white rice and white flour did not become widely available until the 19th century, partially milled products were available to the wealthy since ancient times. The reference to fats is most likely referring to saturated fats. Cooking oil was expensive and not widely available. The rich could afford it, but they preferred to cook in lard (who wouldn’t?). Now that we all eat like the kings of old, we get their diseases, too. It is always striking how the words of Qi Bo to Huang Di ring so true at least 2200 years later.

Reading the Korean research study quoted above also reminded me of something I learned from the renowned herbalist Michael Tierra. Some of Tierra’s students over the years were vegans, and he advised in his writings that it may be difficult to adequately supplement kidney Yin on a vegan diet. He recommended the use of herbs like Rehmannia as a substitute for animal flesh. I never explored whether this idea is grounded in traditional Chinese medical nutrition or if it was an innovation of Tierra’s own making. However, in light of what we know about the benefits of Rehmannia on various metabolic disorders and blood sugar regulation in general, as well as the recent research from Korea, it does make me wonder if consumption of Rehmannia may function in part through a substitution effect. (Given that Google Scholar has 15,000 results for “Rehmannia Glutinosa,” I suspect what I am about to write has been considered by others.)

Does the consumption of Rehmannia results in a feeling of satiety that reduces appetite? Where I would differ with Mr. Tierra is that the consumption of Rehmannia appears to reduce the craving for refined carbohydrates more than animal fat. Either way, I would expect that the mucilaginous fiber of the plant would play a significant role in the effect. However, in the Korean study referenced above, the preparation method for the herb is described and it would not appear to contain any fiber when all is said and done:

The extracts were freeze-dried and finally converted to granular form. Four grams of the granules were packed in each medi- cine packet. The packets were distributed to the subjects by the pharmacist in the dispensary of the hospital per two weeks at every visit. The subjects were asked to take one packet of medicine at a time with warm water, twice a day after the meal.

So, the effect on the microbiota from this form of preparation would be from components of the plant other than prebiotic fiber. Rehmannia contains a large number of chemical constituents, some of which fit into categories of biochemicals that are known to have an effect on microbiota composition. There has been some specific research in this area, which I will explore in a future post. 

The traditional six-ingredient pill would have contained the mucilaginous prebiotic fiber of the plant. According to Bensky (1990), the traditional preparation was to grind the ingredients into powder and form into small pills with honey. The recommended dosage was 9 g three times per day. To put this in a scale that will make sense to most readers, many encapsulated herbal products are dosed at 500 mg per capsule. To consume 9 g prepared in this fashion, you would need to take 18 capsules per dose or 54 g per day. Setting aside the fact that very few people would actually do that, what really strikes me about this is that this is much closer to a food-level dose of plant material than what we typically think of as medicine.

When herbs are consumed from ground whole plants, they contain everything that was part of the original plant. Decoctions leave behind the vast bulk of plant matter and extract various chemical constituents for the most part. I believe both forms of preparation have their place in medicine. However, I think it is becoming indisputable that one can reasonably expect that the whole plant form of medicinal herbs might have a range of effects and benefits not found in extracts. Extracts typically only contain the chemical constituents and do not contain what had been previously thought of as inert material (fiber, etc.). We now know those “inert” materials are far from it.

Here’s a few final thoughts:

Let’s not forget about the other herbs in the six-ingredient Rehmannia pill: one is a fungus, another is a fruit, and a third is a yam. All of these are certainly the types of plants one might expect to have a beneficial effect on the gut microbiota.

Modern pills made from extracts, which although they would appear to be similar or same as traditional Chinese prepared medicines, may be lacking something vital that was present in the traditional preparations.

Since it is much easier to grind herbs than it is to make them into pills, the use of drafts is worthy of consideration. If you make a draft from ground powdered herb and consume the powder when consuming the liquid, you have taken a whole plant preparation, fiber and all.