Saturday, July 8, 2017

Good Fiber, Bad Fiber:What's the Recommended Dietary Fiber?

Fiber is an essential part of a good diet. But fiber isn't essential for you. It's essential for the 20 to 50 trillion probiotic bacteria that live in your colon.

The intestines of healthy people usually have about 50 trillion bacteria—tens of millions in every drop of fecal matter—of 1000 to 2000 different species. People who have bowel disease typically 700 to 800 different species of bacteria in their guts, because their disease-causing bacteria have driven out their healthy bacteria. The balance among the different species of bacteria in the small intestines and colon has a powerful influence over health. How can you build up the "good" bacteria in your lower digestive tract? Feed them! Feed your healthy bacteria fiber.

Fiber from fruits and vegetables can't be broken down by enzymes released by the human body, but can be broken down by enzymes released by bacteria. And what do bacteria make from fiber? The surprising answer is, fat!

The intestines are devoid of free oxygen. This makes it impossible for bacteria to feed on the fat in the food we eat, because burning fat for fuel requires oxygen. However, the bacteria can ferment fiber and make carbohydrate for their own energy needs, with the process also releasing short-chain (chemically simple) fatty acids such as acetate, propionate, and butyrate. These free fatty acids are the main food for certain cells in the lining of the colon called colonocytes, and may provide up to 6 or 7% of the entire body's energy needs. Fiber becomes fat that bacteria can't burn for energy, but the human body can. This fat, however, is not the kind of fat that gets stored in fat cells.

Of special importance is the short-chain fatty acid known as butyrate. The butyrate that bacteria release from plant fiber has a number of beneficial effects on the human body.


Relieves constipation. It is not the fiber in food that relieves constipation. It’s the butyrate that bacteria release by fermenting fiber that relieves constipation. The fiber from rye—which is OK in small amounts even on paleo diets—is especially useful for feeding the bacteria that make the butyrate that makes stools easier to pass and increases the frequency of bowel movement.
Improves gut barrier strength. The lining of the intestines can become “leaky,” allowing toxins and allergens to pass into the bloodstream. Butyrate feeds colonocytes and helps keep the lining of the gut strong.
Heals inflammatory bowel disease. Butyrate supplements have been successfully used to treat Crohn's disease and ulcerative colitis.
Prevents colon cancer. Butyrate helps ensure that colon cells differentiate, or mature, into normal forms. It helps prevent mutations. The cancer-protective effect of butyrate is enhanced by docosahexaenoic acid (DHA), an omega-3 essentially fatty acid that should only be consumed in small amounts (no more than 1 gram per day).
Lowers LDL cholesterol.
• Lowers triglycerides.
• Lowers fasting insulin levels (so fat is more easily burned and less easily stored).
Helps stabilize blood sugars.
• Reduces inflammation in other parts of the body. Certain healthy bacteria, especially Lactobacillus, have a calming effect on the central nervous system by sending a message to the brain to produce fewer stress hormones through their production of butyrates.
Fosters tissue healing elsewhere in the body. A laboratory study with rats found that butyrate, vitamin A, and hyalouran accelerated tissue repair after experimentally induced heart attack.
Delays degeneration of the brain. Butyrate is chemically similar to ketone bodies. The brain can use butyrate to make energy when other energy sources are deficient.
Helps you lose weight. Butyrate increases sensitivity to insulin, so the body produces less insulin, stores less fat, and releases fatty acids more quickly when you cut back on your eating and your body needs energy.

So fiber is great for us and we should all eat more, more, more, right? Wrong! Actually, certain kinds
of plant food fibers are harmful to the gut, and there are limits to how much fiber we should eat.

Harmful Fiber

Fibers from cereal grains, especially wheat, often contain potentially toxic proteins such as gluten and gliadin. Whole wheat (although not rye or oats) contains insoluble fiber that can irritate the lining of the digestive tract and cause the passage of food from the stomach to slow down so much that heartburn results.

Many natural health experts, of course, disagree. They generally believe that since fiber can swell with water from digested food and “scrub” the digestive tract, all that scrubbing has to be a good thing. After all, when the lining of the bowel is irritated it releases healing mucus.

Or maybe not. In the 1980s, British researchers tracked 2,033 men in England, Scotland, and Wales who had had a heart attack. They identified men who ate a high-fiber diet, and men who ate a low-fiber diet. The men in the high-fiber group consumed nearly double the amount of whole grains eaten by the men in the low-fiber group, 17 versus 9 grams per day.

And 22 percent more men in the high-fiber group died of second heart attacks over the two years of the study compared to the men in the low-fiber group. It may be an exaggeration to say “high fiber kills,” but it's apparently not what it's cracked up to be for heart health.

Helpful Fiber

Although the fibers in whole grains are helpful, there are other kinds of fiber that are usually helpful—and that typically generate the most butyrate. These good fibers are pectin and resistant starch.

Pectin is a group of mucilages and gums also known as viscous or water-soluble fiber. Because this kind of fiber is water-soluble, it doesn't cause the stomach to “back up” with burping, belching, or heartburn the way whole wheat fiber can. Pectin is common in stone fruits (apples, peaches, cherries, pears, and the like), and berries. The pectins in berries (and some herbs, such as echinacea) are selectively antibacterial. They reduce the population of harmful bacteria, but they feed probiotic bacteria. Blueberry fiber—you'd need to eat the whole blueberry, not just drink the juice—is actually a better food for the bacteria that produce butyrate than oat or wheat brain.

Resistant starch is a kind of “tough” carbohydrate that the human body does not produce enzymes to digest. There is a great deal of resistant starch in potatoes and some kinds of rice (which we will describe a little later on). Slow cooking plant foods that contain resistant starch in water causes the starch to become kind of gelatin that the enzyme amylase (released by the pancreas) actually can digest, but the starch becomes indigestible as soon as the food cools. If you eat your rice or potatoes with colder foods, and in smaller amounts, they will cool off to the point their resistant starch becomes indigestible by the time they reach your gut.

Resistant starches are just as useful for bacterial production of butyrates as fiber. They are probably the reason there are lower rates of many kinds of cancer in India, China, Japan, and other rice-eating countries than in the US and Canada.

Another useful form of fiber is cellulose. Squashes and pumpkins are particularly concentrated sources of cellulose, as are celery and bok choi.

Cellulose feeds a variety of probiotic bacteria, and also contributes to the production of butyrates. And if irregularity is a problem, cellulose is the form of fiber that works best while you are still building up probiotic bacteria to healthy levels.

The Rule for Recommended Dietary Fiber: Not Too Much, Not Too Little

Fiber is food for the bacteria that live in the intestines. The more fiber you eat, the more bacteria you will have. However, there is an upper limit to how many bacteria are healthy for you. That is because bacteria not only generate beneficial short-chain fatty acids, they also generate complex carbohydrates known as lipopolysaccharides that can activate the immune system to attack healthy tissues. These lipopolysaccharides are known as endotoxins, or toxins generated inside the body.

The human body takes a Goldilocks approach to the number of bacteria in the digestive tract, regulating bacterial growth so there are neither too many nor too few. When endotoxin levels go up, the immune system attacks bacteria in the gut to reduce, but not eliminate, their population. When endotoxin levels are low, a little bit of endotoxin a tolerable tradeoff for the other benefits of bacteria, then the immune system lowers its defenses to allow bacteria to multiply.

If you eat a lot of fiber, your immune system has to generate a lot of its own natural antibiotics, and the bacteria feeding on the fiber generate not just helpful butyrates but also endotoxins. Too much fiber is as bad as too little.

Bacteria Don't Need Just Fiber

Probiotic bacteria feed on prebiotics, the complex carbohydrates found in various kinds of fiber, gums, mucilages, pectins, cellulose, and resistant starches. But just like other organisms, bacteria need protein and minerals, too. Well-nourished bacteria are better able to interact helpfully with their hosts.

This is the reason peanuts and tree nuts help control a variety of chronic health conditions, and multiple studies find that eating about 3-1/2 oz (100 grams) of almonds every day helps with losing weight, despite the extra calories. (Most studies find that the effect of adding 100 grams of almonds to the daily diet is about 500 grams, or a little more than a pound, of effortless weight loss every month. ) The fat in almonds helps probiotic bacteria thrive. The benefits of almonds are canceled out if the fat is removed. Eating too much carbohydrate and not enough fat starves probiotic bacteria of the fat they need. When it comes to eating certain kinds of healthy fat, eating more results in weighing less, and when it comes to eating fiber, sometimes eating more is counterproductive to achieving health goals.

Some Bacteria Don't Need Fiber At All

So, how much fiber is enough? Interestingly, some strains of probiotic bacteria, such as Bifidus bifidum, don't need fiber at all. They seem to be able to extract all the energy they need from the mucus the human body generates to lubricate the digestive tract. Many experts believe that getting just 10 to 15 grams of fiber per day is all the body's bacteria really need, and that eating little more, or a little less, won't really make any difference if bacteria are in good balance. Eating a lot more, or a lot less, however, causes imbalances in the digestive tract.

This means that if you eat even 5 servings of fruit and/or vegetables every day you really get enough fiber for optimum health. Eating 3 or 4 servings of fruits or vegetables will also be enough, and eating up to 10 will be OK. More or less than these extremes, however, isn't healthy. Fiber supplements aren't necessary—and remember, they won't help constipation unless the colon has already been seeded with the bacteria that process them.

Photo credits:
By NobbiP - Own work, CC BY-SA 3.0,

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