Is aquafaba readily digestible?

I have always drained and tossed the water from canned beans. My understanding has been that the water that canned beans are soaked and cooked in contains raffinose, the gas-causing sugars that humans can't digest. This University of Michigan page, referred to in the answer to an earlier question, says:

Rinse beans thoroughly and never cook beans in the water they've soaked in. It's loaded with the gas-causing raffinose sugars.

And also advises:

Drain and rinse canned beans. That will get rid of some of the gas-causing raffinose sugars (and almost half of the unwanted sodium).

Now that aquafaba is all the rage, though, I'm wondering whether my understanding is wrong. I understand that the bean water would taste mildly sweet and foam up so readily because of the raffinose. But it seems to me that aquafaba would lead to severe bloating and intestinal distress, as it relies for its properties wholly on the gassy and sugary nature of the bean water.

Am I mistaken in my understanding of the need to toss the water that one soaks or cooks beans in? Or is it just that fans consider the bloating and gas a price well paid for the delights of aquafaba?

Much of it is not readily digestible. According to this chemical analysis:

Finally the results presented here also indicate that the amount of digestible carbohydrates in aquafaba is minimal. For families with GLUT1 deficiency, where a diet with minimal amounts of glucose and carbohydrates digestible to glucose is required, aquafaba can represent an additional foaming or emulsifying ingredient, as an alternative to eggs.

It also contains proteins, presumably digestible. The carb and protein content is significant, according to the study, which implies a fairly decent proportion of undigestable carbs.


Unlike plants, which use carbon dioxide and light as sources of carbon and energy, respectively, fungi meet these two requirements by assimilating preformed organic matter carbohydrates are generally the preferred carbon source. Fungi can readily absorb and metabolize a variety of soluble carbohydrates, such as glucose, xylose, sucrose, and fructose. Fungi are also characteristically well equipped to use insoluble carbohydrates such as starches, cellulose, and hemicelluloses, as well as very complex hydrocarbons such as lignin. Many fungi can also use proteins as a source of carbon and nitrogen. To use insoluble carbohydrates and proteins, fungi must first digest these polymers extracellularly. Saprotrophic fungi obtain their food from dead organic material parasitic fungi do so by feeding on living organisms (usually plants), thus causing disease.

Fungi secure food through the action of enzymes (biological catalysts) secreted into the surface on which they are growing the enzymes digest the food, which then is absorbed directly through the hyphal walls. Food must be in solution in order to enter the hyphae, and the entire mycelial surface of a fungus is capable of absorbing materials dissolved in water. The rotting of fruits, such as peaches and citrus fruits in storage, demonstrates this phenomenon, in which the infected parts are softened by the action of the fungal enzymes. In brown rot of peaches, the softened area is somewhat larger than the actual area invaded by the hyphae: the periphery of the brown spot has been softened by enzymes that act ahead of the invading mycelium. Cheeses such as Brie and Camembert are matured by enzymes produced by the fungus Penicillium camemberti, which grows on the outer surface of some cheeses. Some fungi produce special rootlike hyphae, called rhizoids, which anchor the thallus to the growth surface and probably also absorb food. Many parasitic fungi are even more specialized in this respect, producing special absorptive organs called haustoria.

The Sugars

Sugars are the most basic form of carbohydrates. Simple sugars such as glucose and fructose are very small molecules, with a ring of carbon atoms providing structure for groups of hydrogen and oxygen atoms. More complex sugars such as lactose and sucrose -- table sugar -- are called disaccharides because they're made up of two sugars. Sucrose, for example, consists of one molecule of glucose and one molecule of fructose that have bonded together. Sugars are easily digested by the human body. Glucose molecules are small enough to pass directly through cell membranes and serve as fuel, while complex sugars are broken down into their respective simple sugars in the intestine and then used.


The mechanical and digestive processes have one goal: to convert food into molecules small enough to be absorbed by the epithelial cells of the intestinal villi. The absorptive capacity of the alimentary canal is almost endless. Each day, the alimentary canal processes up to 10 liters of food, liquids, and GI secretions, yet less than one liter enters the large intestine. Almost all ingested food, 80 percent of electrolytes, and 90 percent of water are absorbed in the small intestine. Although the entire small intestine is involved in the absorption of water and lipids, most absorption of carbohydrates and proteins occurs in the jejunum. Notably, bile salts and vitamin B12 are absorbed in the terminal ileum. By the time chyme passes from the ileum into the large intestine, it is essentially indigestible food residue (mainly plant fibers like cellulose), some water, and millions of bacteria.

Figure 5. Absorption is a complex process, in which nutrients from digested food are harvested.

Absorption can occur through five mechanisms: (1) active transport, (2) passive diffusion, (3) facilitated diffusion, (4) co-transport (or secondary active transport), and (5) endocytosis. As you will recall from Chapter 3, active transport refers to the movement of a substance across a cell membrane going from an area of lower concentration to an area of higher concentration (up the concentration gradient). In this type of transport, proteins within the cell membrane act as “pumps,” using cellular energy (ATP) to move the substance. Passive diffusion refers to the movement of substances from an area of higher concentration to an area of lower concentration, while facilitated diffusion refers to the movement of substances from an area of higher to an area of lower concentration using a carrier protein in the cell membrane. Co-transport uses the movement of one molecule through the membrane from higher to lower concentration to power the movement of another from lower to higher. Finally, endocytosis is a transportation process in which the cell membrane engulfs material. It requires energy, generally in the form of ATP.

Because the cell’s plasma membrane is made up of hydrophobic phospholipids, water-soluble nutrients must use transport molecules embedded in the membrane to enter cells. Moreover, substances cannot pass between the epithelial cells of the intestinal mucosa because these cells are bound together by tight junctions. Thus, substances can only enter blood capillaries by passing through the apical surfaces of epithelial cells and into the interstitial fluid. Water-soluble nutrients enter the capillary blood in the villi and travel to the liver via the hepatic portal vein.

In contrast to the water-soluble nutrients, lipid-soluble nutrients can diffuse through the plasma membrane. Once inside the cell, they are packaged for transport via the base of the cell and then enter the lacteals of the villi to be transported by lymphatic vessels to the systemic circulation via the thoracic duct. The absorption of most nutrients through the mucosa of the intestinal villi requires active transport fueled by ATP. The routes of absorption for each food category are summarized in Table 3.

Table 3. Absorption in the Alimentary Canal
Food Breakdown products Absorption mechanism Entry to bloodstream Destination
Carbohydrates Glucose Co-transport with sodium ions Capillary blood in villi Liver via hepatic portal vein
Carbohydrates Galactose Co-transport with sodium ions Capillary blood in villi Liver via hepatic portal vein
Carbohydrates Fructose Facilitated diffusion Capillary blood in villi Liver via hepatic portal vein
Protein Amino acids Co-transport with sodium ions Capillary blood in villi Liver via hepatic portal vein
Lipids Long-chain fatty acids Diffusion into intestinal cells, where they are combined with proteins to create chylomicrons Lacteals of villi Systemic circulation via lymph entering thoracic duct
Lipids Monoacylglycerides Diffusion into intestinal cells, where they are combined with proteins to create chylomicrons Lacteals of villi Systemic circulation via lymph entering thoracic duct
Lipids Short-chain fatty acids Simple diffusion Capillary blood in villi Liver via hepatic portal vein
Lipids Glycerol Simple diffusion Capillary blood in villi Liver via hepatic portal vein
Lipids Nucleic acid digestion products Active transport via membrane carriers Capillary blood in villi Liver via hepatic portal vein

Carbohydrate Absorption

All carbohydrates are absorbed in the form of monosaccharides. The small intestine is highly efficient at this, absorbing monosaccharides at an estimated rate of 120 grams per hour. All normally digested dietary carbohydrates are absorbed indigestible fibers are eliminated in the feces. The monosaccharides glucose and galactose are transported into the epithelial cells by common protein carriers via secondary active transport (that is, co-transport with sodium ions). The monosaccharides leave these cells via facilitated diffusion and enter the capillaries through intercellular clefts. The monosaccharide fructose (which is in fruit) is absorbed and transported by facilitated diffusion alone. The monosaccharides combine with the transport proteins immediately after the disaccharides are broken down.

Protein Absorption

Active transport mechanisms, primarily in the duodenum and jejunum, absorb most proteins as their breakdown products, amino acids. Almost all (95 to 98 percent) protein is digested and absorbed in the small intestine. The type of carrier that transports an amino acid varies. Most carriers are linked to the active transport of sodium. Short chains of two amino acids (dipeptides) or three amino acids (tripeptides) are also transported actively. However, after they enter the absorptive epithelial cells, they are broken down into their amino acids before leaving the cell and entering the capillary blood via diffusion.

Lipid Absorption

About 95 percent of lipids are absorbed in the small intestine. Bile salts not only speed up lipid digestion, they are also essential to the absorption of the end products of lipid digestion. Short-chain fatty acids are relatively water soluble and can enter the absorptive cells (enterocytes) directly. Despite being hydrophobic, the small size of short-chain fatty acids enables them to be absorbed by enterocytes via simple diffusion, and then take the same path as monosaccharides and amino acids into the blood capillary of a villus.

The large and hydrophobic long-chain fatty acids and monoacylglycerides are not so easily suspended in the watery intestinal chyme. However, bile salts and lecithin resolve this issue by enclosing them in a micelle, which is a tiny sphere with polar (hydrophilic) ends facing the watery environment and hydrophobic tails turned to the interior, creating a receptive environment for the long-chain fatty acids. The core also includes cholesterol and fat-soluble vitamins. Without micelles, lipids would sit on the surface of chyme and never come in contact with the absorptive surfaces of the epithelial cells. Micelles can easily squeeze between microvilli and get very near the luminal cell surface. At this point, lipid substances exit the micelle and are absorbed via simple diffusion.

The free fatty acids and monoacylglycerides that enter the epithelial cells are reincorporated into triglycerides. The triglycerides are mixed with phospholipids and cholesterol, and surrounded with a protein coat. This new complex, called a chylomicron, is a water-soluble lipoprotein. After being processed by the Golgi apparatus, chylomicrons are released from the cell. Too big to pass through the basement membranes of blood capillaries, chylomicrons instead enter the large pores of lacteals. The lacteals come together to form the lymphatic vessels. The chylomicrons are transported in the lymphatic vessels and empty through the thoracic duct into the subclavian vein of the circulatory system. Once in the bloodstream, the enzyme lipoprotein lipase breaks down the triglycerides of the chylomicrons into free fatty acids and glycerol. These breakdown products then pass through capillary walls to be used for energy by cells or stored in adipose tissue as fat. Liver cells combine the remaining chylomicron remnants with proteins, forming lipoproteins that transport cholesterol in the blood.

Figure 6. Unlike amino acids and simple sugars, lipids are transformed as they are absorbed through epithelial cells.

Nucleic Acid Absorption

The products of nucleic acid digestion—pentose sugars, nitrogenous bases, and phosphate ions—are transported by carriers across the villus epithelium via active transport. These products then enter the bloodstream.

Mineral Absorption

The electrolytes absorbed by the small intestine are from both GI secretions and ingested foods. Since electrolytes dissociate into ions in water, most are absorbed via active transport throughout the entire small intestine. During absorption, co-transport mechanisms result in the accumulation of sodium ions inside the cells, whereas anti-port mechanisms reduce the potassium ion concentration inside the cells. To restore the sodium-potassium gradient across the cell membrane, a sodium-potassium pump requiring ATP pumps sodium out and potassium in.

In general, all minerals that enter the intestine are absorbed, whether you need them or not. Iron and calcium are exceptions they are absorbed in the duodenum in amounts that meet the body’s current requirements, as follows:

Iron—The ionic iron needed for the production of hemoglobin is absorbed into mucosal cells via active transport. Once inside mucosal cells, ionic iron binds to the protein ferritin, creating iron-ferritin complexes that store iron until needed. When the body has enough iron, most of the stored iron is lost when worn-out epithelial cells slough off. When the body needs iron because, for example, it is lost during acute or chronic bleeding, there is increased uptake of iron from the intestine and accelerated release of iron into the bloodstream. Since women experience significant iron loss during menstruation, they have around four times as many iron transport proteins in their intestinal epithelial cells as do men.

Calcium—Blood levels of ionic calcium determine the absorption of dietary calcium. When blood levels of ionic calcium drop, parathyroid hormone (PTH) secreted by the parathyroid glands stimulates the release of calcium ions from bone matrices and increases the reabsorption of calcium by the kidneys. PTH also upregulates the activation of vitamin D in the kidney, which then facilitates intestinal calcium ion absorption.

Vitamin Absorption

The small intestine absorbs the vitamins that occur naturally in food and supplements. Fat-soluble vitamins (A, D, E, and K) are absorbed along with dietary lipids in micelles via simple diffusion. This is why you are advised to eat some fatty foods when you take fat-soluble vitamin supplements. Most water-soluble vitamins (including most B vitamins and vitamin C) also are absorbed by simple diffusion. An exception is vitamin B12, which is a very large molecule. Intrinsic factor secreted in the stomach binds to vitamin B12, preventing its digestion and creating a complex that binds to mucosal receptors in the terminal ileum, where it is taken up by endocytosis.

Water Absorption

Each day, about nine liters of fluid enter the small intestine. About 2.3 liters are ingested in foods and beverages, and the rest is from GI secretions. About 90 percent of this water is absorbed in the small intestine. Water absorption is driven by the concentration gradient of the water: The concentration of water is higher in chyme than it is in epithelial cells. Thus, water moves down its concentration gradient from the chyme into cells. As noted earlier, much of the remaining water is then absorbed in the colon.


Pea protein powders are hypoallergenic and easily digestible .

So brands really wanted to make it into an easily digestible , very clean and easy-to-understand experience.

Even if someone can’t attend a brainstorming session, they can access the board afterward to quickly review ideas and next steps in a digestible , visual way.

Co-created by Roy Schwartz, Jim VandeHei and Mike Allen, the idea of Axios was to publish the important information in an easily digestible format, rather than in the form of an 800-word article.

Several things make these flip-flops digestible to microbes.

This edition is definitely a digestible and informative dip into our past.

Whistle, available now, offers an easy and digestible way for owners to get the most relevant info on your dog's activities.

Breaking my fear into smaller, digestible portions by doing a little research each day made the whole situation more palatable.

Could you describe how you convert complex, intellectual concepts into a format digestible to popular readers?

The score, created by U2's Bono and The Edge, isn't made up of catchy, easily digestible pop songs in the "Hakuna Matata" vein.

Eat what is easily digestible before what is difficult of digestion.

Cereals and legumes are less digestible foods than are dairy products, meat, or fish.

The paws took longest of all to cook, but, treated to lengthy stewing, they became quite digestible .

Mothers have only to consult easily procured books to learn the kinds of food most easily digestible , and most nourishing.

Electronic supplementary material is available online at

Published by the Royal Society. All rights reserved.


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Biology of the Fowl

Let's take a look at the internal and external biology of the chicken. The chicken is an interesting creature when observed from a biological standpoint. The chicken has a comb, which is unique. It has a high rate of metabolism, is a rapid breather and digests its food relatively quickly. The body temperature varies, but averages around 106°F. Let's start with the terms for the chicken's exterior features.

Interesting Facts About The Exterior Features Of The Chicken

The Comb of a chicken functions as its cooling system. Chickens do not sweat like humans. The chicken cools itself by circulating its blood throughout its comb and wattles. The comb in ascent operates like the radiator in a car. There are seven different types of combs in chickens. The four most common types of combs are shown in Figure below.

The Earlobe color can tell you what color egg the chicken will lay. If the chicken has a white earlobe, it will lay a white-shelled egg. If it has a red earlobe, it will lay a brown-shelled egg. There is one exception of this rule: Araucana lay blue and green-shelled eggs.

By observing the Hackle (neck) and Saddle (back) feathers of an adult chicken, you can determine its sex. Male hackle and saddle feathers come to a distinctly pointed tip and are shinier. Female hackle and saddle feathers have rounded ends. The breeds of "Sebright" and "Campine" are the only exceptions. In these two "hen-feathered" breeds, the feathers are alike in both sexes.

Although feathers come in many color patterns (shown below are some feather patterns you will find in purebred chickens). Feathers basically serve as the bird's protection. They can insulate the bird from the cold, protect the bird's skin from getting wet and can help the bird fly or glide to safety. Although feathers cover most of a bird's body, they all grow from certain defined areas of the bird's skin called "feather tracts". The first indications of feather tracts appear during the fifth day of embryonic development when the feather papillae appear. Papilla is Latin for "pimples" and that is what they look like on a developing embryo.

The Skeleton of the fowl is compact, lightweight, and strong. Birds have many hollow bones that are connected to the respiratory system these are the bones of the skull, humerus, clavicle, heel, and lumbar and sacral vertebrae. Another interesting feature of chicken bones is called medullary bone. This bone fills the narrow cavity with a readily available source of calcium for eggshell formation when calcium intake is not sufficient. Medullary bone is found in the tibia femur, pubic bones, sternum, ribs, ulna, toes and scapula.

Chicken Digestive System

The chicken has a simple digestive system, with few to no microorganisms living in the digestive system to help digest food like in ruminants such as cattle. Chickens depend on enzymes to aid in breaking down food so it can be absorbed, much like humans.

The beak of the bird replaces the mouth and lips. The crop is a pouch formed to serve as a storage area for the food until it can be passed along for digestion in the gizzard and intestines. The proventriculus is the true stomach of the bird from which hydrochloric acid and pepsin (an enzyme) is secreted to aid in digestion. The gizzard is the oval organ composed of two pairs of thick red muscles. These muscles are extremely strong and are used to grind or crush the food particles. This process is aided by the presence of grit and gravel picked up by the bird. The digestion and absorption of food takes place primarily in the small intestine. It usually takes about 2.5 hours for food to pass through the digestive tract from beak to cloaca .

Is only unwanted material thrown out in exophers?

It would seem sensible to only throw trash out, leaving the functional non-aggregated materials behind in the soma to continue executing required neuronal functions. Indeed, if a touch neuron expresses both an aggregating mCherry protein and a simple soluble GFP protein, the exopher it generates contains primarily aggregating mCherry, while the sending soma retains most of the soluble GFP (Fig. 1c). Although one might be concerned that the GFP fluorescence could be preferentially degraded in the exopher compartment, polyQ128CFP and several other GFP tagged proteins can be observed in extruded exophers, suggesting preferential signal degradation is not the reason for the apparent dramatic sorting. This sorting reveals a capacity for the neuron to distinguish what it will throw away from what it will keep. The mechanism for sorting is not known, but can readily be interrogated using C. elegans genetic approaches. A reasonable hypothesis is that the aggregates might be recognized by heat shock chaperones and/or ubiquitin ligases and the associated signals may be recognized by motor proteins to initiate compartmentalization and the trip to the “extrusion site” of the cell.

Biologically Produced Methane as a Renewable Energy Source

Methanogens are a unique group of strictly anaerobic archaea that are more metabolically diverse than previously thought. Traditionally, it was thought that methanogens could only generate methane by coupling the oxidation of products formed by fermentative bacteria with the reduction of CO2. However, it has recently been observed that many methanogens can also use electrons extruded from metal-respiring bacteria, biocathodes, or insoluble electron shuttles as energy sources. Methanogens are found in both human-made and natural environments and are responsible for the production of ∼71% of the global atmospheric methane. Their habitats range from the human digestive tract to hydrothermal vents. Although biologically produced methane can negatively impact the environment if released into the atmosphere, when captured, it can serve as a potent fuel source. The anaerobic digestion of wastes such as animal manure, human sewage, or food waste produces biogas which is composed of ∼60% methane. Methane from biogas can be cleaned to yield purified methane (biomethane) that can be readily incorporated into natural gas pipelines making it a promising renewable energy source. Conventional anaerobic digestion is limited by long retention times, low organics removal efficiencies, and low biogas production rates. Therefore, many studies are being conducted to improve the anaerobic digestion process. Researchers have found that addition of conductive materials and/or electrically active cathodes to anaerobic digesters can stimulate the digestion process and increase methane content of biogas. It is hoped that optimization of anaerobic digesters will make biogas more readily accessible to the average person.

Keywords: Anaerobic digester BES Biogas DIET Methanogenesis.


George A. Brooks is Professor of Integrative Biology at the University of California, Berkeley and Docteur Honoris Causa de l'Université Montpellier. Dr Brooks has received Honor Awards from the American College of Sports Medicine and the Exercise and Environmental Physiology Section of the American Physiological Society. His research interests involve bioenergetics, mitochondrial morphology, energetics and biogenesis, and the regulation of energy substrate partitioning. His work on the lactate shuttle has influenced thinking in fields as diverse as brain and cancer metabolism. When not in the laboratory, his focus centres on interests of family and friends.

José Arevalo is a 3rd year PhD student at the University of California Berkeley investigating ageing mitochondrial fragmentation and what drives mitochondrial dysfunction with age progression in skeletal muscle. José was born in Guatemala and grew up in the Boyle Heights neighbourhood of East Los Angeles, California. José received his master's degree in kinesiology from California State University Fullerton. When not in the laboratory, his interests are football, rugby, trail running, and lifting weights.