Fiber- How it Prevents Certain Cancers and Heart Disease

I am sure almost all of you have heard of fiber but may not be sure exactly what it is. The most common definition is that fiber is essentially a starch (found in plants, beans, and legumes) that cannot be digested by the enzymes in our small colon (1). We cannot break down fiber. Japan has a more encompassing definition, labeling fiber as all indigestible materials regardless of whether they are carbohydrate, fat, or protein (1). Now that you know what fiber is, I will tell you about the amazing effects fiber has on disease prevention and colon health. Let’s first discuss the two types of dietary fiber found in plants: soluble and insoluble fiber.

Soluble and insoluble fiber

Water-soluble, or simply soluble fiber, is believed to work primarily in the upper gut, where it slows down digestion and absorption, making it very helpful for people with diabetes and those who have weight issues. Because digestion and absorption are slowed down, diabetics can eat foods without experiencing a drastic spike in blood sugar. Water insoluble, or simply insoluble fiber, tends to act more in the lower gut, where it helps create bulky stools that aid in producing regular and smooth bowel movements. Most plant foods contain a mixture of soluble and insoluble fiber, so I would not obsess over how much of either one you are getting. Rest assured, we will get a good mixture of both.

Role of Bacteria in Our Colon

Fermentation is a metabolic process that converts sugars to acids, gases, or alcohol. Process used to brew beer

Gut Microbiota: all of the various bacteria living together in our colon. We have between 300 and 1000 different bacteria species.

How is fiber digested in our body since we are not capable of breaking it down? Luckily, we have the little guys to thank. Our colon is full of good bacteria that are able to ferment fiber. I know most people hear the word bacteria and think of disease, but the bacteria in our colon offer us numerous health benefits from the fermentation of fiber. When soluble fiber is fermented, short-chain fatty acids are produced. A few health benefits associated with short-chain fatty acids include stabilizing blood glucose levels, suppressing cholesterol production by the liver, reducing blood levels of LDL cholesterol (“bad”) and triglycerides, and improving the barrier protection of the lining in our colon.

One of the unfortunate side effects of this fermentation is gas, but your body adjusts after a few weeks of eating a high-fiber diet. Intestinal health is increased, our colon microbiota is renewed, and there is a reduction in intestinal inflammation, all achieved through the fermentative effects of dietary fiber (2). Fiber appears to be able to alter the bacteria (microbiota) of the colon for the better.

How fiber works in our body: lowering cholesterol and removing carcinogens

Bile acids promote digestion and absorption of dietary fat (including cholesterol) and may have hormonal effects on our body.

It has been suggested that dietary fiber may absorb carcinogens (substances that cause cancer) and remove them from the body before they have a chance to initiate cancer (3). Fiber may also remove secondary bile acids, which are thought to be tumor promoters. Bile salts are bound by plant fibers (1). As fiber intake is increased, bile salt lost through fecal matter is also increased (1). This may reduce cholesterol, as bile acids are made of cholesterol, and their excretion would lower the amount of cholesterol in our blood.

A 2003 study that added barley to the diet of subjects found that the addition of barley to the diet lowered plasma total cholesterol, plasma LDL (bad) cholesterol, and lowered triglycerides (2). Fiber may also soak up estrogens and remove them from the body. Excess estrogen, which is a hormone, has been linked to cancer development.

Fiber may help with weight loss. High-fiber foods typically have a high volume with few calories and can help promote fullness and decrease hunger. Fiber may help lower LDL cholesterol (the bad type of cholesterol) by absorbing it and expelling it from the body in feces. Clinical studies have shown that LDL cholesterol can be decreased through the intake of soluble dietary fiber (3).

Fiber moves stools.

It has been proposed since as early as the 1970s that high-fiber diets tend to move fecal matter along relatively quickly. The faster fecal matter moves along the colon, the less of a chance of carcinogenic (cancer-causing) interaction with the colonic mucosa (4). Basically, the less time fecal matter remains in our body, the less time it has to turn into something that causes disease. On the opposite end, low-fiber diets would cause fecal matter to move slowly through the colon, thereby drying up and causing constipation. It was also proposed that slow movements of fecal matter may be related to higher rates of cancer.

Fibers are related to colorectal cancer (CRC).

The literature on the relationship between dietary fiber and colorectal (colon) cancer was recently reviewed for the American Gastroenterological Association (4). The review concluded by saying that dietary fiber may offer protection against colorectal cancer, but that the daily fiber intake to offer this protection must be set much higher than it is in the intervention studies. Kim looked at the epidemiological evidence on the effect dietary fiber has on colorectal cancer. He concluded that there is an inverse relationship (as one variable goes up, the other goes down) between dietary fiber and the risk of colorectal cancer. Most case-control studies on this issue have shown that the risk of colorectal cancer is closely linked to the amount of fiber one eats daily.

The European Prospective Investigation of Cancer and Nutrition (EPIC) study involved ten European countries and looked at the association between fiber intake and the incidence of colorectal cancer in 519,978 individuals aged 25–70 years of age (5). The results showed that high fiber intake was associated with a reduced risk of colorectal cancer. Those with the lowest fiber intake had the highest incidence of colorectal cancer. (5). In the EPIC study, a 13% lower colorectal cancer risk per 10 g/day increase in total fiber intake was yielded (5). So for every 10 grams of fiber that you add to your diet, your risk of getting colorectal cancer is lowered by 13%.

The relationship between fiber, coronary heart disease, and diabetes

Inversely, this means that as one variable goes up (or increases), the other variable goes down (or decreases). In our example, as fiber intake increased, the risk of coronary heart disease decreased, meaning that as fiber intake decreased, the risk of coronary heart disease increased.

Glycemic Response: how much your blood sugar increases after a meal. The higher the glycemic response, the more likely the food is to cause diabetes. Sweets like table sugar cause a drastic spike in blood sugar. 

Dietary fiber intake is inversely associated with the risk of coronary heart disease (CHD) (6). In a pooled analysis of ten prospective cohort studies, a 14% decrease in CHD risks for each 10 g/day increase in dietary fiber and a 27% decrease in risk of coronary death were reported (6). A high intake of cereal fiber has been shown to have a role in the prevention of diabetes through its role in improving glycemic control (6). A study showed that fiber in oats and legumes significantly reduced glycemic response (6).

A study in Japan looked at the fiber intake of 86,000 Japanese subjects. (7). They looked at the relationship between fiber intake and cardiovascular disease, which for the purpose of this study was defined as stroke or coronary heart disease. They found inverse associations between fiber intake and the incidence of cardiovascular disease, stroke, and other cerebral infarctions (as fiber intake increased, the incidence of these events decreased), but not coronary heart disease (7). In prospective studies, fiber intake was inversely associated with blood pressure and hypertension; the more fiber eaten, the better the blood pressure and hypertension became (7).

Why fiber supplements are not the same as eating whole plants

It appears that extracting fiber from the cell wall or part of the cell wall of plants is not the same as eating the whole plant. The components in cell walls are held together by crosslinks (8). Besides cellulose, these components are water-insoluble when inside the cell wall but may be water-soluble when extracted. As noted earlier, water-soluble and water-insoluble fiber behave differently in the body, so observing the properties of whole plant cell walls and extracted components of plant walls is very important.

Even though pectin preparations are extracted from plant cell walls, during their extraction they are chemically modified (8). Lignin preparations (another type of fiber), usually extracted from wood in a variety of different ways, are sold commercially (8). The properties of these extracted lignins are likely very different from the properties of lignins still inside the intact cell wall (8). The properties of lignins also differ depending on their extraction methods (8). For all of the reasons talked about above, fiber extracted from the plant may behave quite differently in our bodies than fiber inside the walls of a whole plant.

My fiber recommendation

Most government organizations advise consuming 25–30 grams of fiber a day. The average American consumes about 11 grams a day. I believe we should get about 50 grams a day. Sounds impossible? Speaking from personal experience, I have no problem getting close to 80 grams a day. But I tend to eat differently than the average American, so I am not the best example. The easiest way to increase fiber is to eat two servings of beans or lentils a day. Buy the dry-bagged beans, not the cans, as the cans have way less fiber. Lentils have about 70 calories and 14–15 grams of fiber! So for 140 calories, you get nearly 30 grams of fiber. Mix it with brown rice, and you have 4 more grams. Eat a piece of fruit or two in the morning, and you have 8 more grams. Make a smoothie with vegetables and fruit. Eat whole-grain bread. Snack on fresh fruit throughout the day.

It really is not that hard if you replace your processed foods with fruits and vegetables. If someone is only getting 11 grams of fiber a day, that means they are eating almost no plant foods, which means they are missing out on all of the anti-cancer, blood pressure-lowering, etc. effects that plant foods have. Getting 50 grams of fiber a day means much more than the fiber; it means that you are eating nutrient-dense plant foods whose many health benefits far outweigh the benefits of their fiber. Plus, you will be having more regular bowel movements than you have ever had in your life. Some people in parts of Africa eat 100 grams of fiber a day, and there seems to be no negative effect on their bodies from eating this large amount.

Fiber Supplements

I am sure you have guessed by now that I advocate getting fiber from food sources and not supplements. Part of this is because I believe that it may not just be the fiber in plant foods that offers all of these health benefits. It is possible that other chemicals in the plant are actually responsible for some of the health benefits. If you are unwilling to add plant foods to your diet, taking a fiber supplement is better than nothing. I would go to a health food store and get psyllium husk. 100% psyllium husk with no other ingredients.

It has no taste, but you can feel the texture. You can mix it with water or juice. When you first get it, add a teaspoon to the water and see what happens. The fiber soaks up nearly all of the liquid until it becomes gel-like. This shows why fiber is so effective at removing waste and cholesterol from our bodies. This is also why you need to drink a glass of water with each serving of fiber. If you take a lot of fiber and do not drink water, you will likely become constipated as the fiber has no water to soak up and thus no bulk to the stool, so it leaves the body slower and the stool dries out. Start with a teaspoon or two a day. Give your body time to adjust.

Discussion

Fiber, without a doubt, is one of my favorite nutrition topics to talk about. I actually wrote the bulk of this paper a few years ago just out of curiosity, but the original was much longer, so I trimmed it down some for this blog. I know fiber is talked about, but I feel like people largely neglect it. I do not subscribe to the idea of “super” foods (including supplements, vitamins, minerals, etc.) as I feel the overall diet is what matters, but if I did, fiber would be up there.

With nutrition, no topic goes undisputed. There are debates over every possible topic in nutrition. This is great. We need people to always question the foundations of nutrition. We can never be certain, as there are always new studies and more advanced scientific methods coming out. Despite this, most, but not all, scientists would agree that fiber has been shown to: remove cholesterol from the body (mainly the bad cholesterol), offer control in blood sugar for diabetics, reduce the risk of colon cancer, reduce the risk of heart disease, move stools smoothly through the colon, and remove excess hormones from the body.

While dietary fiber appears to have impressive health benefits, keep the big picture in mind, which is that eating a varied and whole-food diet has been shown to have anticancer effects, lower blood pressure, lower cholesterol, and even reverse diabetes, and that we should emphasize the benefits of the whole plant instead of focusing on individual parts of it (sorry for the run-on sentence or paragraph!).

Remember, animal foods will never have fiber, as they don’t have cell walls that we are unable to digest. So the only way to increase fiber intake is to eat more plants or take a fiber supplement from a plant.

Below is a chart I made to show the fiber content of commonly eaten foods:

Foods                                         Amount                  Fiber (grams)

FruitOrange	1 Medium	3.1
Banana	1 Medium	3.1
Strawberry	1 Cup	3
Kiwi	2 Small	4.5
Pear w/skin	1 Medium	5.5
Vegetables
Broccoli	1 Cup	5.1
Carrot	1 Medium	1.7
Brussels Sprouts	1 Cup	4.1
Sweet Corn	1 Cup	4
Baked Potato w/ skin	1 Small	3
Tomato Paste	1/4 Cup	2.7
Legumes, Nuts, Seeds
Cooked Lentils	1 Cup	15.6
Cooked Black Beans	1 Cup	15
Cooked Lima Beans	1 Cup	13.2
Vegetarian Baked Beans	1 Cup	10.4
Sunflower Seeds	1/4 Cup	3.9
Almonds	23 nuts	3.5
Pistachio Nuts	49 nuts	2.9
Pecans	19 halves	2.7
Grains, Cereal, Pasta
Whole Wheat Pasta	1 cup	6.3
Bran Flakes	3/4 Cup	5.3
Instant Oatmeal	1 Cup	4
Popcorn Air Popped	3 Cups	3.5
Brown Rice	1 Cup	3.5
Whole Wheat Bread	1 Slice	1.9

Sources

1. Leeds, A. R., & Hussain, K. (1998). A review of the effects of dietary fibre and their potential benefits for health. International Journal of Food Sciences and Nutrition (United Kingdom).
2. Li, J., Kaneko, T., Qin, L. Q., Wang, J., & Wang, Y. (2003). Effects of barley intake on glucose tolerance, lipid metabolism, and bowel function in women. Nutrition, 19(11), 926-929.
3. Sánchez-Muniz, F. J. (2012). Dietary fibre and cardiovascular health. Nutr Hosp, 27(1), 31-45.
4. Ferguson, L. R., Chavan, R. R., & Harris, P. J. (2001). Changing concepts of dietary fiber: implications for carcinogenesis. Nutrition and cancer, 39(2), 155-169.
5. Buttriss, J. L., & Stokes, C. S. (2008). Dietary fibre and health: an overview. Nutrition Bulletin, 33(3), 186-200.
6. Bingham, S. A., Day, N. E., Luben, R., Ferrari, P., Slimani, N., Norat, T., … & Riboli, E. (2003). Dietary fibre in food and protection against colorectal cancer in the European Prospective Investigation into Cancer and Nutrition (EPIC): an observational study. The Lancet, 361(9368), 1496-1501.
7. Kokubo, Y., Iso, H., Saito, I., Yamagishi, K., Ishihara, J., Inoue, M., & Tsugane, S. (2011). Dietary fiber intake and risk of cardiovascular disease in the Japanese population: the Japan Public Health Center-based study cohort. European journal of clinical nutrition, 65(11), 1233-1241.
8. Ferguson, L. R., & Harris, P. J. (2003). The dietary fibre debate: more food for thought. The Lancet, 361(9368), 1487-1488.