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Revisiting Fiber and Colorectal Cancer

By Kevin Klatt

Colorectal cancers are the third most common worldwide, and represent one of the major areas of prevention research. Rates of these cancers increase with industrialization, and are uncommon in Africa and much of Asia. A number of potential nutritional targets have been posited, based on preclinical and epidemiological data; however, these remain controversial. The American Institute of Cancer Research’s 2011 report (1) on Colorectal Cancer states that there is convincing evidence that foods high in fiber decrease risk and red and processed meats increase risk of colon cancer. However, there are few controlled feeding studies in humans have corroborated these associations; indeed, a large body of literature (2-7) focusing on dietary fiber supplementation back in the late 90’s and early 2000’s did not show any support for any positive effects of high fiber/low-fat diets on recurrent adenomas . However, these studies can/have been criticized for: 1. not being long enough 2. fail to capture of a window of true prevention (as subjects already had adenomas) 3. The dose/type of fiber. Since these trials, considerable experimental data (8,9) has been generated to suggest that the type of fiber, its dose, and the type/amount of short chain fatty acid fermentation products likely add some complexity to the inconsistent epidemiological associations between fiber intake and colorectal cancer risk.

A recent study published in Nature Communications (10) provides a novel perspective on this contentious topic of high-fiber diets and colon. The study employed a food-based dietary intervention in 2 populations: African Americans and rural South Africans (a sensible population to study given Burkitt’s original observations that rural Africans are nearly free of large bowel diseases). Twenty healthy, middle-aged African Americans and 20 rural Africans were first examine in their home environments for 2 weeks, to examine their normal food intake, before being housed in their respective research facilities for the 2 weeks of the dietary intervention (to ensure compliance). African Americans were given the ‘African style’ diet that was low in fat (16% kcals) and high in fiber (55g/day). Participants from Africa were given a western style diet that was higher in fat (52% kcals) and lower in fiber (12g/day). Notably, the high fiber diet was achieved using HiMaize, a purified resistant starch product. The authors look at outcomes related to mucosal epithelial cell proliferation (Ki67 staining) and markers of inflammation (CD3+ intraepithelial lymphocyte and CD68+ lamina propria macrophage staining), to examine the effect of diet on predicted neoplastic change and increased risk of colon cancer. They further look at alterations in microbial composition, highlighting changes in microbes with the baiCD gene, responsible for the deconjugation of bile acids and production of their carcinogenic, secondary metabolites. Their results quite nicely show that the high fiber intervention alters biomarkers in directions that suggest a protective effect against colorectal cancer, while also finding some interesting nuances related to amino acid and choline metabolism.

While providing encouraging results for the role of nutrition in colorectal cancer development, the study leaves us with more hypotheses to test, and a renewed interest in the way in which fiber and its fermentative products might act to buffer against colorectal cancer. Without hard clinical outcomes, it’s difficult to get too excited about the results in light of the multiple fiber interventions that have failed in the past. The biomarkers chosen are not without their scrutiny, as it has been noted that decreases in apoptosis rather than increased cell proliferation better predict tumorigenesis in animal models of colorectal cancer (11). Regardless of one’s enthusiasm about biomarker changes over 2 weeks, it does force us to critically think about previous study designs that have cast doubt on fiber’s role in colon cancer. The authors in this current study employ highly butyrogenic starches, at doses not tested in the trials that have failed before. There is consistent molecular evidence that butyrate works in a paradoxical manner, both stimulating cell proliferation at low concentrations and inhibiting it at high (12), leaving open the possibility that the previous doses of fiber were too low to see a beneficial effect.

Given the Western diets low concentrations of dietary fiber, particularly resistant starches (13), as well as the increased enthusiasm to fortify the food supply with added fibers, further research examining the role of particular fibers, their appropriate doses, and their relationship to clinical outcomes appear warranted. The type 2 resistant starch utilized in this study is uncommon in the food supply, coming largely from raw potatoes, unripe bananas, and some legumes and represents a potential area for food technologists to significantly alter the food supply for better health (14).



Added Fiber: The Answer to Our Weight Problems?


By Sarah Gold

Determining how to stave off hunger while on a reduced calorie diet is the million-dollar question in the world of weight management. While there are many theories on how to increase satiety, slowing gastric emptying rate, or the rate at which food leaves the stomach, is a common tactic among many weight loss plans. Fiber, a carbohydrate found mostly in plant foods, is known to slow digestion and is often touted as the not-so-secret ingredient to weight loss.

Diets that contain fiber-rich foods such as fruits, vegetables, whole foods, and legumes have been associated with a decreased risk of obesity among other health benefits. In addition, a significant amount of research over the last 30 years has linked fiber-rich foods to improved glycemic control, increased production of hunger-suppressing hormones in the hours after a meal, reduced production of hunger hormones, and overall increased satiety. In theory, reduced hunger should lead a person to eat less, and ultimately lose weight.

For this reason, fiber has received a lot of attention from dietitians and weight management counselors to food companies and health journalists. And it has begun to show up in unlikely places. A 90-calorie brownie with 20% of your daily fiber needs – who would have thought it possible? Food scientists, that’s who! Food companies are adding synthetic, or functional, fiber to anything from white bread to sugary breakfast cereals and even baked goods. You can now get 100% of the recommended 25-30g of dietary fiber per day without ever eating a fruit, vegetable, or whole grain. However, the question that remains is, does this added fiber actually aid weight-loss?

There are two types of naturally occurring fiber: soluble and insoluble. Both are found in plant foods, insoluble in the skins of fruits and vegetables, and soluble found in oats, legumes, and whole grains. Researchers have tested the effect of synthetic soluble and insoluble fibers on satiety with mixed results. For example, beta-glucan (the kind of fiber found in oats) has been shown to have some effect on satiety, while inulin (found in plant roots) has been ineffective. There are a number of different synthetic fibers that food companies use to boost the fiber content of food, so it’s difficult to know if the product your buying will actually offer any benefit.  In addition, studies that have tested the effect of supplemental fiber on weight management have been less than promising.

When it comes to weight management, fiber-rich foods certainly play a role. But is fiber the magic ingredient we’ve all been looking for? Probably not.  Much of the research that links fiber-rich diets to lower weight are population studies, which are not able to completely control for other lifestyle factors that play a role in weight management such as physical activity and presence of other foods in the diet. In addition, many foods that naturally contain fiber also have a high percentage of water, which can also play a role in satiety. If you’re looking to reduce calories and control hunger, stick with whole foods that contain fiber such as whole-grains, fruits, vegetables, and legumes.

Bolton, R., Heaton, K., Burroughs, L. (1981). The role of dietary fiber in satiety, glucose, and insulin: studies with fruit and fruit juice. American Journal of Clinical Nutrition; 34(2): 211-217.

Kristensen, M., Georg Jensen, M. (2011). Dietary fibers in the regulation of appetite and food intake. Importance of viscosity. Appetite; 56(1): 65-70.

Lyon, M. & Kacnik, V. (2012). Is there a place for dietary fiber supplements in weight loss? Current Obesity Reports; 1(2): 59-67.

The Real Scoop on Chia Seeds

By Jessica Currier

I’m sure most of you remember the chia pet, the clay figurines with sprouts of chia to resemble hair or fur, or at least the jingle on their advertisement, “Chi-Chi-Chi-Chia!” If you haven’t heard already, you probably will soon, people are now consuming chia seeds for the added health benefits. Who would have thought that a garden ornament could be ingested to promote health and vitality?

Chia seeds are from the desert plant Salvia hispanica, a member of the mint family, and can be eaten raw or added to dishes (1). Consumers add chia to baked goods, breads, porridges, smoothies, and can be ground and added to water or milk. The seeds can be purchased at local health food stores or online. The familiar chia hair or sprouts can also be eaten and added to salads, sandwiches, and other dishes (1). Numerous claims can be found in the media concerning chia. Chia being an excellent source of fiber, omega-3 fatty acids, protein, and antioxidants are some of the proposed claims. The media also claims that chia can help cut cravings, balance blood sugar levels, improve cardiovascular disease, lower cholesterol, triglycerides, blood pressure, and can promote weight loss. This exceptional list of health benefits really peaked my interest to find out the real scoop concerning chia seeds.

It is true that chia seeds do provide omega-3 fatty acids and contain fiber, antioxidants, protein, and minerals (1). While claims of weight loss and decreases in daily cravings may be a bit far fetched, increases in satiety due to the fiber and protein content may be valid. A study conducted by Nieman and Colleagues concluded that ingestion of 50g/d of chia seeds for 12 weeks did not influence body mass, composition, or disease risk factors in overweight/obese men and women (2). A recent study published in The Journal of Nutrition viewed the effects of a specific dietary pattern on Metabolic Syndrome (3). Sixty-seven participants with Metabolic Syndrome were involved in the study and were given a mixture to drink twice a day. The mixture chosen was based on antihyperglycemic, antihyperinsulinemic, hypolipidemic, anti-inflammatory, and antioxidants effects (3). Chia seeds were included in this mixture because of the presence of fatty acids and antioxidants that promote a reduction in the inflammatory response (3). This study concluded that a dietary pattern of nopal, chia seed, soy protein, and oat showed a reduction in serum triglyceride levels, serum CRP (C-Reactive Protein test, indicates acute inflammation or infection), and insulin AUC (3).

Although this study does provide encouraging outcomes, more research needs to be done with the conjunction of chia seeds helping to improve cardiovascular disease, lowering cholesterol, triglycerides, blood pressure, and weight loss promotion (1). Little published research concerning chia exists, and most information available is based on lab animals not humans (1). So remember, be an informed consumer with a critical eye when reviewing media claims. If you are looking for fiber or antioxidants, chia seeds would be a great addition to your diet; but for weight loss, stick with good old exercise and healthy food choices!


1) Academy of Nutrition & Dietetics. What are Chia seeds? Are There Health Benefits?

2) Nieman DC, Cayea EJ, Austin MD, Henson DA, McAnulty SR, Jin F. Chia seed does not promote weight loss or alter disease risk factors in overweight adults. Nutr Res. 2009;29:414- 418.

3) Guevara-Cruz M, Tovar A, Aguilar-Salinas C, Medina-Vera I, Gil-Zenteno L, Hernandez-Viveros I, Lopez-Romero P, Ordaz-Nava G, Canizales-Quinteros S, Guillen Pineda L, Torres N. A Dietary Pattern Including Nopal, Chia Seed, Soy Protein, and Oat Reduces Serum Triglycerides and Glucose Intolerance in Patients with Metabolic Syndrome. J. Nutr. 2012;142:64-69.