The Details Behind Digestion

"DIGESTION" is a simple term for a complicated sequence of events that involves numerous systems working together to ensure the proper utilization of nutrients and the efficient disposal of waste products. Digestion begins in the mouth, where enzymes initiate the process of softening and breaking down food. The process continues through the combined efforts of the esophagus, stomach, small intestine, pancreas, liver, gallbladder and large intestine (colon).

Because digestion entails proper functioning of various systems, there are numerous conditions and diseases that can interfere with digestive health. According to the National Institute of Diabetes & Digestive & Kidney Diseases (NIDDK), an arm of the National Institutes of Health (NIH), there are more than 60 digestive disorders -- ulcers, constipation and irritable bowel syndrome (IBS), to name a few.

Combined, digestive disorders affected 60 million to 70 million people in 1985, the most recent statistics available from NIDDK. Additionally, NIDDK noted digestive diseases accounted for 50 million doctor's office visits and cost $107 billion in 1992.

Women are 34 percent more likely to suffer from digestive disorders than men, according to the Natural Marketing Institute's (NMI) Health & Wellness Trends Database -- three years of trended data of more than 2,000 household respondents. NMI's report also indicated 10 percent of women and 8.1 percent of men suffer from constipation, and 7.7 percent of women and 8.3 percent of men have intestinal irregularity.

While digestive disorders are widespread, there are natural options available to maintain a healthy digestive system and address many of the concerns that arise in digestive health. For example, if the body's digestive system is overtaxed because of a lack of ingested enzymes, supplemental enzymes can assist the body's system to reduce the strain on the body's enzyme-producing organs. Similarly, probiotics and prebiotics can enhance smooth functioning in the gastrointestinal (GI) tract and colon. And, natural fiber supplements and botanicals can promote colon health and improve regularity.

ENZYMES

Enzymes are protein-based substances comprised of chains of amino acids, and they exist in every cell of every living organism. With more than 3,000 kinds known to exist in the human body alone, enzymes are needed to support life, energy production and numerous bodily functions, including digestion.

Hydrolase is one of six classes of enzymes and is known for utilizing water molecules to break down proteins, carbohydrates and fats. More specifically, proteases break down protein, amylases break down carbohydrates and lipases break down fats or lipids.

In the mouth, chewing assists the digestive process by softening food and increasing its surface area. Saliva contributes ptyalin, or salivary amylase, to begin breaking down carbohydrates before they are swallowed.

The body's enzymatic system continues the digestive process in the stomach, which contains pepsin, an enzyme that breaks down proteins. The stomach also contains lipases to break down fats.

By adding enzymes and breaking food down into small particles, the stomach creates chyme, which is then pushed into the small intestine for further enzymatic processing. The intestinal wall is covered with villi -- small, projected cells -- which are, in turn, covered with microvilli. "The villi and microvilli are only one cell layer thick but perform multiple functions of producing digestive enzymes, absorbing nutrients and blocking absorption of substances that aren't useful to the body," wrote Elizabeth Lipski, MS, CCN, author of Digestive Wellness (Keats Publishing, 2000).

Like villi and microvilli, the pancreas also produces digestive enzymes. When food passes from the stomach to the duodenum (the first 12 inches of the small intestine), the pancreas neutralizes the acidic chyme, and then it secretes lipases, proteases and amylases. However, if the pancreatic duct becomes blocked or the pancreas is damaged, the body's enzymatic system can become less efficient.

"Some of the enzymes ... are secreted from the pancreas in their inactive form--these are called proenzymes," wrote Anthony Cichoke, DC, in The Complete Book of Enzyme Therapy (Avery Publishing Group, 1999). "When the pancreatic juice reaches the small intestine, the inactive forms of the enzymes are converted to their active forms. ... If activated while still in the pancreas, they would digest the organ. To assure this does not happen, the pancreas secretes a substance called trypsin inhibitor."

Trypsin inhibitor prevents proenzymes from becoming active enzymes too early. However, this system is sometimes damaged. "In these instances, the proenzymes will overwhelm the inhibitor, causing large amounts of [enzymes] to become active in the pancreas," Cichoke continued. "This condition, called acute pancreatitis, can result in a lifetime of pancreatic insufficiency, a condition in which the pancreas does not produce an adequate amount of enzymes."

Supplementing with pancreatic tissue from pigs is known to supply missing pancreatic enzymes and combat pancreatic insufficiency. A vegetarian alternative can be derived from a fungus called Aspergillus oryzae. Vegetarian enzymes work in a wider pH range than pancreatic enzymes, according to Lipski, and they enhance digestion in the stomach and intestines. When taken with meals, these enzyme supplements are also said to reduce gas and flatulence.

In addition to the pancreas, the liver is also an integral part of the body's enzymatic system. This 4.5-pound organ contains more than 2,000 enzyme systems that are necessary for breaking down and processing nearly every nutrient that is ingested. It also produces bile, which is stored in the gallbladder and emulsifies fats, breaking them down so enzymes can split them for cellular use.

Probably the most well-known enzyme-related digestive disorder is lactose intolerance. This occurs when the body fails to produce sufficient lactase, the enzyme that digests lactose (milk sugar).

According to a research review out of Rigshospitalet, Denmark, seven studies involving a total of 131 lactose intolerant subjects indicated that adding lactase to milk improved lactose absorption. Researchers only found one study with a total of 10 subjects that contradicted this finding.¹

There is some contention among the scientific community of whether supplemental enzymes can be absorbed in the body compared to those that are derived from food. "Growing amounts of research by a number of highly respected scientists have shown that a significant amount of enzymes are, in fact, absorbed intact," Cichoke wrote. "The absorption rate of orally ingested enzymes is about 20 percent within six hours."

PROBIOTICS

There are between 400 and 500 types of bacteria present in the human digestive system, each with numerous strains. The most common types are Bacteroides, Bifidobacteria, Eubacteria Fusobacteria, Lactobacilli, Peptococcaceae, Rheuma-nococcus and Streptococcus, according to Lipski. These bacteria are present in the mouth and small intestine, but the majority resides in the colon.

Of the so-called "friendly bacteria," the most important groups are Lactobacilli, which are found mainly in the small intestine, and Bifidobacteria, which are found mainly in the colon. Both of these secrete lactic acid, which is required to increase absorption of minerals such as calcium, copper, magnesium and iron. Those bacteria that produce lactic acid also help acidify the intestinal tract to protect against harmful bacteria.

Lactobacillus acidophilus (L. acidophilus) is one of the most prominent strains of beneficial bacteria, a deficiency of which can result in the growth and proliferation of pathological organisms in the intestinal tract. This can decrease digestion and absorption of nutrients, as well as increase production of gas, bloating and toxins. The most common cause of L. acidophilus deficiency is the use of antibiotic drugs, although prescription drugs, stress, diarrhea and intestinal infections can also be factors.

L. acidophilus supplementation has been indicated for relieving lactose intolerance. The same researchers from Rigshospitalet, Denmark who determined supplemental lactase was beneficial for lactose intolerance also reviewed the evidence supporting L. acidophilus for improving the condition. Researchers uncovered eight studies with a total of 78 patients that demonstrated lactase-deficient subjects absorbed lactose in yogurt better than lactose in milk, although two studies with a total of 25 patients did not support this. Additionally, researchers noted finding two studies with a total of 22 patients that showed unfermented acidophilus milk was absorbed better than milk, although six similar studies with a total of 68 patients found no significant differences.²

L. acidophilus has also been indicated for treating diarrhea. Researchers from Universidad de Buenos Aires in Argentina randomly assigned 22 patients with diarrhea caused by bowel bacterial overgrowth to take either placebo or a probiotic regimen consisting of L. acidophilus and Lactobacillus casei (L. casei) for three weeks. Subjects taking the Lactobacilli exhibited a significant reduction in mean daily number of stools at 15 days and 21 days, and the effect was sustained for two weeks after ceasing treatment.³

Another strain of Lactobacilli, Lactobacillus GG (LGG), was found in an open-label, pilot study out of the University of Chicago's Children's Hospital to improve symptoms of Crohn's disease, a form of inflammatory bowel disease (IBD) that most commonly occurs in the colon and ileum. Four children with mildly to moderately active Crohn's disease were given LGG twice daily for six months, and significant improvement was noted after one week and lasted the duration of the study period.⁴

Lactobacillus plantarum (L. plantarum) is thought to be useful for relieving the symptoms of IBS. A research review written by investigators at the University of California, Los Angeles, stated probiotic therapy with L. plantarum was superior to placebo for improving pain, regulating bowel habits and decreasing flatulence in IBS.⁵

Lactobacilli, when combined with Bifidobacteria, are also beneficial for digestive health. For example, L. acidophilus combined with Bifidobacterium infantis (B. infantis) effectively treated acute diarrhea in children. Researchers from Cathay General Hospital in Taipei, Taiwan, randomly assigned 100 children with acute diarrhea to one of two groups: rehydration (control) or rehydration plus probiotics (L. acidophilus and B. infantis). Subjects in the treatment group improved on the first and second day of hospitalization, and had a decreased duration of diarrhea during hospitalization.⁶

The prevalence of Bifidobacteria is important for preventing flare-ups of IBD and related symptoms, according to researchers at the Academic Hospital Vrije Universiteit Amsterdam in The Netherlands. They noted that in Crohn's disease, the inflamed parts of the gut were those with the highest bacterial concentrations made up of Bacteroides, Eubacteria and Peptostreptococcus, although Bifidobacteria were markedly deficient. Researchers concluded that manipulating colonic bacteria with antibiotic drugs and probiotics may be more effective treatments and better tolerated than pharmaceutical immunosuppressants for IBD.⁷

Also classified under the umbrella of probiotics is Saccharomyces boulardii (S. boulardii), a friendly yeast known to kill Clostridium difficile, which can infect the small intestine and lead to IBS. S. boulardii is also recommended for preventing antibiotic-induced diarrhea. Researchers conducting a meta-analysis reviewed four trials that compared antibiotic therapy alone to antibiotics combined with S. boulardii. They concluded S. boulardii is a promising option for preventing diarrhea during a treatment regimen that includes antibiotics.⁸

S. boulardii may also prevent recurrences of IBD. Researchers at the Gastroenterology Unit at Raffaele Hospital in Milan randomly assigned 32 patients with Crohn's disease in clinical remission to either traditional therapy or a combination of traditional therapy and S. boulardii. Clinical relapses were observed in 37.5 percent of patients in the traditional therapy regimen, while only 6.25 percent of patients taking a combination of S. boulardii and traditional therapy relapsed.⁹

According to Daniel J. O'Sullivan of the Department of Food Science and Nutrition at the University of Minnesota, St. Paul, there are many factors to consider in choosing a probiotic supplement. For example, the strain or species of the probiotic should be of human origin, he said, because "human intestines are sufficiently different from those of animals such that the isolates suited to those environments would not necessarily be suited to the human intestine." O'Sullivan also recommended considering the selection of an isolate that can survive the transit to its intestinal target via the stomach and duodenum, as well as those that are tolerant to bile.¹⁰

PREBIOTICS

Prebiotics are non-digestible fibers that enhance the beneficial intestinal flora in the gut. Because they work synergistically in the body, prebiotics and probiotics are often used concurrently--their combined use is sometimes referred to as synbiotics, according to Lipski.

One of the most well-documented prebiotic groups is oligosaccharides. "Most oligosaccharides are fermented in vitro by Bifidobacterium species, though not by B. bifidum," wrote Tomotari Mitsuoka, professor emeritus at the University of Tokyo, in a 2002 paper. "The oral administration of oligosaccharides enhances the proliferation of intestinal Bifidobacteria, improving the properties of the host's stool and scavenging the intestine, thereby altering host lipid metabolism in a beneficial way."¹¹

Fructooligosaccharides (FOS) are a class of soluble, non-digestible carbohydrates, ingestion of which provides almost no calories. Although FOS occur naturally in many foods, a large proportion of these products are now synthesized commercially by reacting glucose with beta-fructofuranosidase enzymes, which are obtained from Aspergillus niger.

FOS pass through the GI tract into the colon where they are used by Bifidobacteria as a preferential source of food and energy. This tends to inhibit the number and growth of pathological bacteria, thereby improving overall health. FOS are thought to normalize bowel function, maintain bowel integrity, restore colonization resistance, alter nitrogen excretion and improve calcium absorption, according to researchers at Abbott Laboratories in Cleveland.¹²

When used in combination with galactooligosaccharides (GOS), FOS have been shown to improve intestinal flora and stool consistency in formula-fed infants. Researchers at the Center for Infant Nutrition in Milan randomly supplemented infants' formula with either a mixture of oligosaccharides (GOS and FOS) or placebo (maltodextrin) for 28 days. At the end of the study period, infants taking the prebiotics had significantly increased Bifidobacteria and Lactobacilli, as well as improved stool consistency.¹³

Because of their ability to stimulate a healthy intestinal flora, FOS have been suggested for improving conditions such as IBS. However, a study out of Copenhagen County Hospital in Hellerup, Denmark, indicated while 58 percent of patients in the FOS group exhibited improved symptoms, 65 percent of the placebo group also exhibited an improvement.¹⁴

FOS may reduce the risk of colon cancer, according to research presented at the International Symposium on Fructooligosaccharides held in Tokyo July 3, 2001. Researchers from Nutri-Health S.A. in Rueil-Malmaison, France, noted that short-chain FOS are mostly fermented to lactate, short-chain fatty acids and gas in the colon. Butyrate is one such short-chain fatty acid believed to regulate cell growth in the colon. Short-chain FOS, in animal models, reduced colon tumor development by enhancing colon butyrate concentrations and immune system function, according to researchers.¹⁵

Similar to FOS, maltodextrin-like oligosaccharide is also known for its ability to promote healthy intestinal flora. Researchers from Abbott Laboratories conducted a series of experiments and determined maltodextrin-like oligosaccharide (as Fibersol-2™, manufactured by Matsutani America) may act as a "dietary fiber-like" ingredient. In vitro, Fibersol-2 fermentation increased total short-chain fatty acid production compared with gum arabic. In an animal experiment, researchers noted Fibersol-2, as well as GOS, supplementation led to higher total fecal weight and increased fecal concentrations of Bifidobacteria.¹⁶

According to human research conducted in Japan, Fibersol-2 may be able to relieve constipation. Eighty female volunteers were given 40 g/d of rice crackers, containing a total of 5 g/d Fibersol-2. This regimen was seen to increase defecation frequency and fecal amount.¹⁷

Soy protein and isoflavones may also have a beneficial effect on enhancing intestinal flora. According to company-sponsored research, a soy germ ingredient (as SoyLife™, manufactured by Acatris USA Inc. in Minneapolis, Minn.) demonstrated prebiotic effects by increasing the presence of Lactobacillus sp. and reducing the amount of damage to intestinal walls by bile acid stimulators.

Additional prebiotics recognized for their ability to enhance intestinal flora are insulin and oligofructose, both of which are extracted from chicory root. Researchers at England's University of Reading noted that as food ingredients, inulin and oligofructose are known to stimulate Bifidobacteria, which would in turn prevent infections.¹⁸ And, according to research conducted with birds, dietary insulin induced a more than three-fold increase in the concentration of Bifidobacteria in the cecum (opening of the large intestine).¹⁹

Because of its ability to stimulate the growth of Bifidobacteria, inulin has also been indicated for colon cancer prevention.²⁰ An animal study conducted at Mississippi State University demonstrated a significant reduction in the number of aberrances in the colons of mice fed either of the prebiotic diets (inulin or oligofructose) compared to the control diet.²¹

Researchers from Flamm Associates in Vero Beach, Fla., conducted a research review on the evidence surrounding inulin and oligofructose, and determined both should be defined as dietary fiber because of their pathway and actions in the body. In particular, researchers noted when oligofructose and inulin reach the colon, they induce a bulking effect.²²

FIBER, ETC.

Second only to water, fiber is one of the most important factors in protecting bowel health. "Proper functioning of the colon requires a high-fiber diet," Lipski wrote. "Without adequate fiber, we starve the colonic cells and weaken the integrity of the colon."

The colon's job is to take the nutrients that remain in the chyme it receives, absorb water and form stool. About two-thirds of stool is composed of water, undigested fiber and food products. When bowel transit time--the time it takes between ingestion and excretion--is longer than 12 to 18 hours, constipation is probably the reason.

Constipation affects an estimated 4 million people each year--twice as many women as men. The single-most common cause of constipation in America is arguably a lack of fiber in the diet, although dehydration can also be a factor. According to NMI, 19.8 percent of men and 16.6 percent of women have recently purchased fiber supplements.

Americans spend an estimated $725 million each year on laxatives, according to a 1991 National Health Interview survey. While most laxative products--including herbals--are generally believed to be safe, it is thought overuse may cause the bowel to become reliant upon them; however, this link between laxatives and the "cathartic colon" is not well established, according to a research review out of the Cleveland Clinic Foundation.²³

Aside from the discomfort it can cause, constipation raises the risk of colon disease and contributes to other health concerns by allowing toxins to be reabsorbed into the body. Fiber is suspected to help prevent colon cancer because of its ability to increase the incidence of short-chain fatty acids, including butyrate, according to researchers from Flinders University of South Australia in Adelaide. They conducted a study using mice that demonstrated a diet high in fermentable fiber (wheat bran fiber) regulated carcinogenic cell death, thereby preventing the incidence of colon cancer.²⁴

In addition to fiber, there are numerous other bulking agents that can assist normal bowel transit time and prevent constipation. Psyllium (Plantago ovata), for example, is thought to act as a stool softener and ease constipation. A research review out of Czechoslovakia noted that psyllium, as a natural fiber, effectively alleviated constipation by increasing stool volume and weight, as well as improving bowel transit time.²⁵ Similarly, Swiss researchers who conducted a Cochrane Database Review found four trials involving psyllium and noted it was associated with increased stool frequency in people with Parkinson's disease.²⁶

A randomized, clinical trial of psyllium seeds indicated the natural fiber may be as effective as pharmacological treatment for maintaining remission of ulcerative colitis. The Spanish Group for the Study of Crohn's Disease and Ulcerative Colitis involved 105 patients with ulcerative colitis. For 12 months, patients took psyllium, mesalamine or a combination of the two. Researchers reported an increase in fecal butyrate levels in the psyllium groups compared to having taken the pharmaceutical alone.²⁷

A natural fiber extracted from kombu, a seaweed popularly eaten in Japan, may be helpful for promoting regularity. According to OptiPure Chemco Industries, manufacturers of a kombu fiber extract, kombu is non-toxic and promotes regularity. Company-sponsored toxicity and safety research indicated the extract did not produce hematological or histological abnormalities. And a company-sponsored clinical study indicated the kombu extract increased bowel movement frequency by one and a half times.

Aloe is also thought to improve a number of gastrointestinal conditions, according to a 1985 study conducted by Jeffrey Bland, PhD, of the Linus Pauling Institute of Science and Medicine. Ten healthy subjects consumed 6 ounces of aloe vera juice in 2-ounce increments three times daily. After seven days, tests indicated improved digestion of protein, decreased bowel transit time and improved water-holding characteristics of stool. Aloe vera also improved the balance of gastrointestinal symbiotic bacteria.²⁸

Another plant-derived extract well known for its ability to relieve constipation is Cascara sagrada. Cascara has been an approved treatment for constipation in the U.S. pharmacopoeia since 1890. Cascara has been used traditionally to treat sluggish gallbladder, digestive problems, hemorrhoids, skin problems, intestinal parasites, jaundice and colitis.²⁹ However, cascara is contraindicated for people with Crohn's disease, an intestinal obstruction or appendicitis. Long-term use is also contraindicated, as it may weaken natural bowel function.

While laxative abuse has been linked to an increased risk of colon cancer, cascara does not appear to induce colon tumor growth, according to animal research out of the University of Naples in Italy.³⁰

Early in 2002, the Food and Drug Administration (FDA) reclassified aloe and cascara sagrada ingredients as category II (nonmonograph), and added them to a list of stimulant laxative ingredients that have inadequate data for general recognition of safety in over-the-counter (OTC) drug products. The FDA's final ruling on aloe and cascara in OTC drug products was published in the May 9, 2002 Federal Register.

In response to FDA's final ruling, the American Herbal Products Association (AHPA) and the International Aloe Science Council (IASC) filed a petition with FDA on June 10 requesting a stay and reconsideration of the ruling. "There is a wealth of well-documented evidence to support their safety, which the agency either overlooked or chose to ignore," says Michael McGuffin, AHPA president. "The main point of this petition is that AHPA and IASC do not believe FDA has the authority by the process they used to remove these ingredients from OTC drugs."

There are dozens of supplements and food products that can be used to establish and maintain a healthy digestive system. Enzymes are the backbone of the digestive system and participate in nearly every step of the way. Similarly, probiotics are essential for maintaining a healthy digestive system, and prebiotics are known for enhancing probiotic health. Natural fiber and other plant-derived compounds are known for their ability to improve colon health. With tens of millions of Americans suffering various digestive disorders every year, digestive supplements are an integral part of the marketplace.

Editor's notes: Some content for this story provided by Intramedicine (www.intramedicine.com).

DID YOU KNOW?

The Digestive Benefits of Honey
HONEY has been traditionally used for numerous health conditions, particularly wound healing. According to Synergy Production Laboratories, a special honey derived from Manuka trees in New Zealand has been clinically tested in hospitals for healing burns and wounds. As a stomach ulcer is basically an internal wound, it goes to follow that honey would be effective for relieving ulcers as well. According to the company, Manuka Honey is currently being tested in humans for treating stomach ulcers.

Honey is also noted for its antibacterial properties. Manuka Honey is said to possess the same antibacterial effects as a 10 percent phenol solution, and it has been shown to eradicate infections and stop the growth of many bacteria, including E. coli, Staphylococcus, Streptococcus, Helicobacter pylori, Pseudomonas and Klebsiella pneumoniae, according to Synergy Production Laboratories. This is perhaps due to honey's ability to promote beneficial bacteria.

Researchers from Michigan State University in East Lansing cultured five strains of Bifidobacteria--B. longum, B. adolescentis, B. breve, B. bifidum and B. infantis--and reinforced them with either a control medium or the control plus 5 percent honey, fructooligosaccharides (FOS), galactooligosaccharides (GOS) or inulin. Honey was found to enhance the growth of all five cultures in a similar manner as that of the prebiotics FOS, GOS and insulin.³¹

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