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Dietary Fiber and Cancer

August 27, 2009 Written by JP       [Font too small?]

Some types of foods are easier to incorporate into one’s diet than others. If your doctor advises you to eat more fruits or vegetables, you can quite easily select the varieties that you like best and up your intake. The same can be said for other commonly recommended health foods such as fish, nuts and seeds. But adding more fiber into your daily routine requires some planning because not all fruits and vegetables contain much and animal based foods are completely devoid of it. In my opinion, being reminded of the importance of fiber, while becoming more aware of foods that are abundant in this dietary component is the key to making it a priority.

A recent summary in the journal Nutrition Review suggests that optimal levels of dietary fiber may help prevent a wide array of health conditions, including several cancers, cardiovascular conditions, diabetes, gastrointestinal diseases and, even, obesity. The recommended target is roughly 14 grams of fiber per every 1000 calories consumed. Ideally, the majority of this fiber should come from nutrient rich foods. But fiber supplements can also be utilized if your diet regularly falls short of your fiber goals. (1)

When I reviewed the 2009 medical literature relating to fiber, two key areas of health care were most prominently featured: cancer and cardiovascular disease. Today I’ll focus on the cancer protective role of these bulking agents. Next week, I’ll devote a separate column to the cardiovascular part of the equation.

  • A 4 year dietary intervention examined the effects of a strict high fiber diet (rich in fruits and vegetables) in a group of patients at an increased risk for colon polyps. A 35% reduction in polyp recurrence was found in those deemed as “super compliers” to the menu plan. This emphasizes the need for a consistently healthy diet. (2)
  • A very large population trial entitled the “National Institutes of Health – AARP Diet and Health Study” investigated the role that dietary fiber may play in breast cancer (BC) rates. Over 185,000 postmenopausal women were followed for 7 years. Food frequency questionnaires were used to assess typical food selection and macronutrient status. The researchers determined that the women consuming the most fiber were afforded significant protection against BC. Their concluding remarks were as follows: “Our findings suggest that dietary fiber can play a role in preventing breast cancer through non-estrogen pathways among postmenopausal women.” (3)
  • The August 2009 issue of the journal Cancer Causes and Control provided very strong evidence that a high fiber diet can reduce the likelihood of stomach cancer occurrence. More importantly, the Italian scientists behind this trial actually looked at what forms of fiber appear to be most beneficial for stomach cancer prevention. Their overall conclusion was that total fiber consumption did demonstrate a protective effect. But only fiber from vegetables and, to a lesser extent, fruit yielded positive results. Fiber rich grains did not afford any benefit at all in this investigation. (4)
  • Reflux esophagitis and Barrett’s esophagus are inflammatory conditions that can increase the risk of developing esophageal cancer. A new study from the Netherlands determined that the intake of starchy carbohydrates increased the risk of these forms of pre-cancerous inflammation. But, higher intake of roughage was inversely related to esophageal inflammation and the related cancer. The reduced risk was noted as 56% based on a comparison of those with the highest vs. lowest dietary fiber intake. This is yet another example of how good carbs (fiber) can benefit health and bad carbs (starches and sugar) can endanger it. (5)

Fiber Rich Foods and Supplements

Food Serving Size Fiber Content (grams)
Almonds 2 oz 6
Avocado 100 g 7
Blackberries (Frozen) 100 g 5
Broccoli (Cooked) 1 cup 6
Chia Seeds 1 oz 12
100% Cocoa Powder 1 oz 9
Coconut Flour 1 oz 12
Collard Greens 1 cup 5
Flax Seeds 1 oz 8
Red Raspberries (Raw) 100 g 6
Note: 100 grams = 3.5 ounces

One concern that I’ve personally had about dietary fiber is whether its bulking action may impede the absorption of other healthy components found in foods. This issue was recently addressed in a study presented in the June issue of the journal Plant Foods for Human Nutrition. 10 volunteers were provided with an antioxidant rich fiber supplement. The product contained a total of 15 grams of dietary fiber per serving. The researchers then tested the blood of the volunteers at various points following the fiber consumption. Significant elevations in serum antioxidant status were found 8 hours after the ingestion of the antioxidant/fiber blend. This indicates that “antioxidants associated with dietary fiber are at least partially bioavailable in humans, although dietary fiber appears to delay their absorption”. (6)

One the easiest and healthiest ways to boost fiber intake is to make a fiber rich smoothie. I regularly include berries, pure cocoa powder and flax seeds in my protein shakes to increase fiber content. I can now do so with the added knowledge that the naturally occurring antioxidants in these fiber sources will sustain my good health for several hours after I drink them. In effect, this may help provide valuable protection over the course of the day and night. I hope that this information and my upcoming column about fiber and cardiovascular disease will help inspire you to include more fiber in your diet. I believe the effort will be well worth it.

Note: Please check out the “Comments & Updates” section of this blog – at the bottom of the page. You can find the latest research about this topic there!

Be well!

JP

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13 Comments & Updates to “Dietary Fiber and Cancer”

  1. Girl Gone Primal Says:

    Hey JP,

    The problem with the studies you cite are that they are usually observational, don’t include groups that do not consume any fiber, and are already assuming that fiber intake is necessary. However, when you consider the carnivorous diets of our ancestors (and some traditional peoples today, such as the Inuit that have not been corrupted by the SAD), and the very low levels of cancer, it certainly makes you wonder whether fiber is necessary at all…

    Here’s a great blog post exploring the issue and linking to the thoughts of many experts on the subject:

    http://www.carnivorehealth.com/main/2009/4/17/screw-you-fiber.html

  2. JP Says:

    Howdy, Girl Gone Primal.

    Thank you for visiting!

    It’s true that these studies are not randomized and placebo controlled. That would, of course, be ideal. In my dreams, I’m a billionaire capable of sponsoring such research. :)

    This is a complex topic indeed. Some civilizations who do not consume much fiber appear to thrive. On the other hand, others do very well eating plenty of unprocessed, fiber rich foods.

    I eat a relatively low carb diet which is pretty much devoid of grains. But I do find that including plenty of fiber helps me to feel healthy – in terms of my digestive health. This is just my own anecdotal observation.

    I’m going to go check out the link you’ve shared. Thanks for posting it!

    Be well!

    JP

  3. Nina K. Says:

    JP and all others,

    i sufferd very bad from pms, eat always low carb and did lot of sports, cut out caffeine for a while, took vitamin b6 but nothing helped really. so i read recs in a breast cancer forum from women: they include oat bran in their breakfast, coconut flower is also helpful. that did the job. it seems that i have to much estrogen and that fiber rich breakfast resorbs that to much estrogen. theres a lot of research, that shows that fiber can bond free estrogen from the intestinum. if i drink too much caffeine, that pushes my estrogen. I don’t know why these sorts of fibers are working better than only apples, green leaves etc. but it works. despite that i have never had any carb cravings.

    Nina K.

  4. JP Says:

    Thank you for sharing that, Nina.

    It’s important to get these kinds of “field reports”. I value them very much. :)

    PS – A new study in the American Journal of Clinical Nutrition backs up your experience:

    http://www.ajcn.org/cgi/content/abstract/ajcn.2009.27990v1

    Be well!

    JP

  5. Ken Shim, RMT Says:

    Personally I find that about once or twice a week I just feel my body’s need to have a high fibre meal. I kind of fluctuate between eating healthy and hedonistic. After too much junk, my body just tells me that I am in dire need of a big old plate of spinach or leafy greens. Like it literally craves it. I am sure there are studies to prove whatever your opinion is, but my best advice is to get in touch with your body and its rhythms and needs and you can never go wrong

  6. JP Says:

    Thanks for your input, Ken.

    I agree that it’s important to listen to your body.

    Some cravings may indeed indicate a nutritional requirement in the body that isn’t being met. On the other hand, other cravings can be self-destructive. An example of this would be a compulsive desire for junk food – such as what we see in binge-eating disorders and morbid obesity.

    The trick is to determine which body signals are constructive and which are hurtful, IMO.

    Be well!

    JP

  7. Nina K. Says:

    JP, thanks for the link. A question: My normal foodintake consists of tons of vegetables, some fruits (in the morning) and fish and meat. Only at breakfast i eat some starchy fibers like one tablespoon oat bran, one oat flakes and one tbs spelt flakes and one tbs wheat germs, toghether with a fresh apple, blueberries and raspberries (if available). Sometimes i put one or two tbs natural yoghurt on it. i dont use milk, i use almondmilk.

    Do you think my carbload is to high, do you think my eating habits are more a high carb diet? I thought not, but my breakfast has some carbs in.

    Stay healthy,
    Nina K.

  8. JP Says:

    Nina,

    Is the almond milk you use unsweetened? That would be the most important consideration, IMO. The carbs I’m most concerned with are “empty calories” (such as sugar and other sweeteners).

    Adding some stevia to unsweetened almond milk may be a suitable alternative to the sweetened variety.

    If your blood sugar and triglycerides aren’t offended by your breakfast choices, then you’re probably okay, IMO.

    Most of your morning carbs are fiber-rich and have a pretty low glycemic index and load. Your fruit choices are also rich in antioxidants and phytochemicals which tend to reduce the negative impact of carbohydrates.

    BTW, I regularly have a morning protein shake that contains blueberries, raspberries and flax. All of these contain carbs but they’re also fiber-rich and highly nutritious. The trick is that I also make sure to add a good source of protein (usually natural egg white protein powder) and fat (typically coconut milk). As you know, protein and fat also dampen the blood sugar/insulin response to carb intake.

    I hope this helps!

    Be well!

    JP

  9. Nina K. Says:

    JP,
    me again :-)

    yes my almond milk is unsweetened. sometimes i add some protein powder. its a simple pure protein from milk. do you think its ok?
    its that:

    http://www.dr-ritter.de/produkte/bio-eiweiss-konzentrat.html

    it has 81 g protein / 5,5 g carbs / 2g fat / 2,4g calcium / 364 kcal/100g

    thanks for your advices
    Nina K.

  10. JP Says:

    Nina,

    Good news about the almond milk.

    I couldn’t get much additional information about the protein powder as my German’s a bit rusty. :)

    But, based on the macro-nutrient breakdown you and the site presented, it looks like a pretty solid high protein, lower-carb powder. In short, I think it looks ok.

    I personally switch between a natural (vanilla) egg white protein and a natural (vanilla) whey protein (dairy derived). I think that egg and whey protein are probably the top two protein powder sources available.

    Be well!

    JP

  11. JP Says:

    Update: Higher fiber diets linked to lower mortality risk …

    http://ajcn.nutrition.org/content/100/6/1498.long

    Am J Clin Nutr. 2014 Dec;100(6):1498-507.

    Fiber intake and all-cause mortality in the Prevención con Dieta Mediterránea (PREDIMED) study.

    BACKGROUND: Few observational studies have examined the effect of dietary fiber intake and fruit and vegetable consumption on total mortality and have reported inconsistent results. All of the studies have been conducted in the general population and typically used only a single assessment of diet.

    OBJECTIVE: We investigated the association of fiber intake and whole-grain, fruit, and vegetable consumption with all-cause mortality in a Mediterranean cohort of elderly adults at high cardiovascular disease (CVD) risk by using repeated measurements of dietary information and taking into account the effect of a dietary intervention.

    DESIGN: We followed up 7216 men (55-75 y old) and women (60-75 y old) at high CVD risk in the Prevención con Dieta Mediterránea (PREDIMED) trial for a mean of 5.9 y. Data were analyzed as an observational cohort. Participants were initially free of CVD. A 137-item validated food-frequency questionnaire administered by dietitians was repeated annually to assess dietary exposures (fiber, fruit, vegetable, and whole-grain intakes). Deaths were identified through the continuing medical care of participants and the National Death Index. An independent, blinded Event Adjudication Committee adjudicated causes of death. Cox regression models were used to estimate HRs of death during follow-up according to baseline dietary exposures and their yearly updated changes.

    RESULTS: In up to 8.7 y of follow-up, 425 participants died. Baseline fiber intake and fruit consumption were significantly associated with lower risk of death [HRs for the fifth compared with the first quintile: 0.63 (95% CI: 0.46, 0.86; P = 0.015) and 0.59 (95% CI: 0.42, 0.82; P = 0.004), respectively]. When the updated dietary information was considered, participants with fruit consumption >210 g/d had 41% lower risk of all-cause mortality (HR: 0.59; 95% CI: 0.44, 0.78). Associations were strongest for CVD mortality than other causes of death.

    CONCLUSION: Fiber and fruit intakes are associated with a reduction in total mortality.

    Be well!

    JP

  12. JP Says:

    Updated 09/08/16:

    http://www.ncbi.nlm.nih.gov/pubmed/27599758

    Int J Cancer. 2016 Sep 6.

    Fiber intake modulates the association of alcohol intake with breast cancer.

    Alcohol intake has been related to an increased risk of breast cancer (BC) while dietary fiber intake has been inversely associated to BC risk. A beneficial effect of fibers on ethanol carcinogenesis through their impact on estrogen levels is still controversial. We investigated the role of dietary fiber as a modifying factor of the association of alcohol and breast cancer using data from the European Prospective Investigation into Cancer and Nutrition (EPIC). This study included 334,850 women aged 35-70 years at baseline enrolled in the ten countries of the EPIC study and followed up for 11.0 years on average. Information on fiber and alcohol intake at baseline and average lifetime alcohol intake were calculated from country-specific dietary and lifestyle questionnaires. Hazard ratios (HR) of developing invasive breast cancer according to different levels of alcohol and fiber intake were computed. During 3,670,439 person-years, 11,576 incident breast cancer cases were diagnosed. For subjects with low intake of fiber (<18.5 g/day), the risk of BC per 10g/day of alcohol intake was 1.06 (1.03-1.08) while among subjects with high intake of fiber (>24.2 g/day) the risk of BC was 1.02 (0.99-1.05) (test for interaction p=0.011). This modulating effect was stronger for fiber from vegetables. Our results suggest that fiber intake may modulate the positive association of alcohol intake and BC.

    Be well!

    JP

  13. JP Says:

    Updated 01/16/17:

    http://apjcn.nhri.org.tw/server/APJCN/26/1/89.pdf

    Asia Pac J Clin Nutr. 2017 Jan;26(1):89-96.

    Dietary fiber intake is inversely associated with risk of pancreatic cancer: a meta-analysis.

    BACKGROUND AND OBJECTIVES: The association between fiber intake and pancreatic cancer risk is conflicting and poorly explored. The aim of study was to investigate the association between dietary fiber intake and the risk of pancreatic cancer by conducting a meta-analysis of epidemiological studies.

    METHODS AND STUDY DESIGN: Systematic search of PubMed and Embase databases up to April 2015 were conducted to identify relevant studies. Adjusted odds ratios (ORs) were combined using random-effects models to assess the risk of pancreatic cancer when comparing extreme categories of fiber intake. Dose-response meta-analysis was performed for studies reporting categorical risk estimates for at least 3 exposure levels.

    RESULTS: One cohort and thirteen case-control studies were identified. The overall analysis revealed a strong inverse association between risk of pancreatic cancer and high fiber intake (OR 0.52; 95% CI 0.44-0.61). No publication bias was detected by Egger’s or Begg’s test. The dose-response analyses showed that the summary OR for an increment of 10 g daily intake of fiber was 0.88 (0.84 to 0.92).

    CONCLUSION: A high intake of dietary fiber was associated with a reduced risk of pancreatic cancer. Further well-designed prospective studies are warranted to confirm the inverse association and to identify the dietary fiber types involved.

    Be well!

    JP

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