Short chain fatty acids, e.g. acetate, propionate, and butyrate, are produced by the fermentation of dietary fibers in the colon.
The ability of two different fermentable carbohydrates (inulin and β- glucan) to effect body composition and central appetite regulation in high fat fed mice was examined by Arora and coworkers (2012). A fermentation of wheat or rye bran with probiotic intestinal bacteria of the Lactobacillus genus may be a way by producing short chain fatty acids long before the colon. Perhaps such a brew or vegan yogurt could work in the opposite direction of an appetizer before entering a setting in which one has the potential to eat out of control. This was my plan as I read the paper.
Thirty six C57BL/6 male mice were randomized and maintained for 8 weeks on a high fat
- 0% (w/w) fermentable carbohydrate,
- 10% (w/w) inulin
- 10% (w/w) β-glucan
Note that inulin is a polymer of glucose and five membered ring fructose. β-glucan is a polymer of glucose with 1,3 and 1,6 linkages (mushrooms and sea weed) or β-1,3 and β-1,4 in grains. (Nakashima 2018).
Fecal and cecal microbial changes were measured using fluorescent in situ hybridization (FISH)
Note the abundance of intestinal bacteria in the mouse caecum, bold pink line.
- Fecal metabolics weremesured with proton nuclear magnetic resonance (1H NMR)
- Colonic short chain fatty acids were measured by gas chromatography.
- Body composition and hypothalamic neuronal activation were measured using magnetic resonance imaging (MRI) and manganese enhanced MRI (MEMRI), respectively.
- PYY (peptide YY) concentration was determined by radioimmunoassay. PYY is a saeity hormone secreted by the ileum to proximal colon in humans.
- Adipocyte cell size and number were also measured.
Mice eating a diet rich in β -glucans gained less weight
Figure 2. The effect of inulin and β-glucan supplementation over the 8-week dietary interventional period (a) weekly cumulative body weight gain, n = 12 per group (b) weekly cumulative food intake over the 8 week dietary intervention period, n = 12 per
group. * p<0.05, ** p<0.01, *** p<0.001.
It would appear that both β-glucan and inulin suppress weight gain and food intake. β-glucan appears to be a little more effective than inulin in decreasing food intake.
The really significant changes were seen in the caecum
Superscipt (*) shows the significant difference between HFD-I or HFD-BG vs. HFD-C.
Superscipt (#) shows the significant difference between HFD-I vs. HFD-BG.
The β-glucans do not promote cecal growth itself or the bacteria therein as much as inulin. This will be revisited in the discussion
The cecal short chain fatty acid profile
Acetate and propionate levels were significantly increased in HFD-BG and HFD I compared with HFD-C, p<0.05
total SCFA p<0.05
HFD-BG 34.462.5 mmol/mg
HFD-I 27.862.1 mmol/mg
HFD-C 17.764.1 mmol/mg
HFD-BG 30.262.4 mmol/mg;
HFD-I 25.163.1 mmol/mg
HFD-C 16.763.1 mmol/mg
HFD-BG: 3.061.2 mmol/mg
HFD-I 2.060.9 mmol/mg
HFD-C: 0.660.3 mmol/mg, .
butyrate, not significant
HFD-BG 1.160.3 mmol/mg
HFD-I 0.760.2 mmol/mg HFD-C 0.460.1 mmol/mg
β-glucan and inulin in feeding associated brain activity
UT-Health has a nice has a nice tutorial on feeding circuits in the mouse brain.
In Manganese enhanced MRI, Manganese ions (Mn2+) enter into the excitable neuronal cells in the brain producing contrast in the MRI images. The appetite centers are located in the hypothalamus. This figure combines material from the UT website and Arora (2016).
The arcuate nucleus is comprised of neurons expressing orexigenic (neuropeptide Y, agouti related peptide) and anorexigenic (proopiomelanocortin, melanocyte stimulating hormone) peptides, which project into other areas like VMH and PVN.
paraventricular hypothalamic nucleus receives input from NPY-containing neurons in the arcuate nucleus. It coordinates metabolism and energy intake.
nucleus of solitaries tractus receives baroreceptor (pressure) information from the gut wall.
Arora and coworkers also profiled classes of intestinal bacteria in the feces over the course of the study. They reviewed the work of others and the role that these bacteria may play in satiety.
Just my opinion
Overall, I really like this study. A control group of an indigestible (to bacteria) carbohydrate like cellulose was not included in this study. Such a carbohydrate would have provided bulk and the sense of fullness. Arora and coworkers also saw a larger decrease in veriventricular nuclei activity in the β-glucan fed versus inulin fed mice. The inulin fed had larger ceca and more cecal contents. In some rodent ceca I’ve encountered are distended with gases from fermentations. Cellulose may not have produced distension via gas production. The authors had no easy way of measuring fermentation gases in addition to the short chain fatty acids.
I left out figures on bacteria in rectal contents and the fecal NMR spectra. How much are the SCFA products of these bacteria absorbed in the colon? Did any of these short chain fatty acids make their way into the blood of these mice? I wanted to know if there are transporters for short chain fatty acids in the colon since most of the nutrient absorption occurs in the small intestine. Al-Mosauwi and coworkers addressed this in a 2016 study. They used real time (quantitative) PCR to assess the MCT1 proton monocarboxylate cotransporter thoruut the human GI tract: : colon > small intestine > stomach. Immunolocalization of human tissue revealed MCT1 to be abundant in the basolateral membranes of epithelial cells of the ascending, transverse, and descending colon, but significantly less prevalent in the sigmoid colon.
A diagram of some very common transporters selected from a random cartoon on the Internet and colorized. On the apical side, short chain fatty acids may diffuse through the membrane in the protonated state. SCFA may also pass through a bicarbonate/anion exchanger.
Arora and coworkers just reported MRI results for the hypothalamus and surrounding regions. The hypothalamus is a region of the brain that lacks a very tight blood brain barrier. This Wikipedia link contains all sorts of interesting information. See the blood borne signal section in particular. As interesting as this paper is, the possibility remains that some other product of inulin and/or β-glucan are responsible for the changes in feeding behavior. Perhaps these products require access to regions of the brain not protected by the blood brain barrier.
Borş the brew for appetite control?
An Internet search was perform for beta-glucan and lacto fermentation, inspired by the Lactobacilli in the Arora study. Though not specifically a lacto fermentation, Borş is a Hungarian fermentation of wheat bran. The link provides a recipe for fermentation with natural bacteria as well as a starter. I’m using the starter recipe with a commercial yogurt starter.
My brew, in all of its glory, fermenting by Lactobacilli in my window seal. After two days it had a very fruity smell, not at all like the gym sock, vinegar, and rotten butter smell I was expecting. The taste was rather sweet and fruity. A quick search of PubMed for borş revealed one publication by Pasqualone and coworkers (2018). I was way off base. Phenolics, ferulic acid in particular, esters (fruity notes) , and ” pungent-sour and goat milk-cheese odor notes” at higher temperatures were reported. I’m also wondering about the role of oxygen tensions for achieving the “pungent-sour and goat milk cheese odor notes.”
My suggestion for further studies would be to test a brew made by fermenting inulin or β-glucan with some of the Lactobacilli and other bacteria Arora (2016) reported being increased in their study. Give this brew, or vegan “yogurt” to rodents or ourselves as a possible means of appetite control.
Al-Mosauwi H, Ryan E, McGrane A, Riveros-Beltran S, Walpole C, Dempsey E, Courtney D, Fearon N, Winter D, Baird A, Stewart G.(2016) Differential protein abundance of a basolateral MCT1 transporter in the human gastrointestinal tract. Cell Biol Int.40(12):1303-1312
Arora T, Loo RL, Anastasovska J, Gibson GR, Tuohy KM, Sharma RK, Swann JR, Deaville ER, Sleeth ML, Thomas EL, Holmes E, Bell JD, Frost G.(2012)Differential effects of two fermentable carbohydrates on central appetite regulation and body composition. PLoS One. 7(8):e43263 free paper
Logsdon AF, Erickson MA, Rhea EM, Salameh TS, Banks WA.(2018)Gut reactions: How the blood-brain barrier connects the microbiome and the brain. Exp Biol Med (Maywood). 243(2):159-165.
Nakashima A, Yamada K, Iwata O, Sugimoto R, Atsuji K, Ogawa T, Ishibashi-Ohgo N, Suzuki K.(2018) β-Glucan in Foods and Its Physiological Functions. J Nutr Sci Vitaminol (Tokyo). 64(1):8-17.
Pasqualone A, Summo C, Laddomada B, Mudura E, Coldea TE. (2018) Effect of processing variables on the physico-chemical characteristics and aroma of borş, a traditional beverage derived from wheat bran. Food Chem. 265:242-252.