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There have been many posts on this blog about diet, fiber, microbes, and the association of diet with various diseases, such as cancer. A recent journal article by M. Song and A. Chan reviewed studies that looked at the link between diet, gut microbes (the gut microbiota or gut microbiome), and colorectal cancer (what we typically call colon cancer).

In summary, research from the last 20 years has found that diet and colorectal cancer (CRC) go hand in hand, and that diet determines the microbes (microbiota) living in the gut - that is, what you feed the microbes determines what microbes will live and thrive in the gut. Also, certain microbes in the gut are linked to inflammation and cancer formation, and others to its prevention. In other words, there is potential to prevent colorectal cancer with certain diets, and to increase the odds of colorectal cancer with other diets.

What are main dietary factors linked to colorectal cancer? Western diet (lots of processed foods, red and processed meat, low in fiber, refined grains), low levels of dietary fiber, low intake of omega-3 fatty acids from seafood (or fish oil), and obesity. The researchers point out that a Western diet is associated with gut dysbiosis (microbial imbalance), loss of gut barrier integrity, and increased levels of inflammation. What should one do? Basically think to yourself: "I need to feed the beneficial microbes in my gut, so I need to eat lots of fruits, vegetables, whole grains, and seafood (omega-3 fatty acids)" - this is what the researchers call a "prudent pattern diet". And try to maintain a normal weight. Some excerpts from Current Colorectal Cancer Reports:

Diet, Gut Microbiota, and Colorectal Cancer Prevention: a Review of Potential Mechanisms and Promising Targets for Future Research

AbstractDiet plays an important role in the development of colorectal cancer. Emerging data have implicated the gut microbiota in colorectal cancer. Diet is a major determinant for the gut microbial structure and function. Therefore, it has been hypothesized that alterations in gut microbes and their metabolites may contribute to the influence of diet on the development of colorectal cancer.We review several major dietary factors that have been linked to gut microbiota and colorectal cancer, including major dietary patterns, fiber, red meat and sulfur, and obesity

Colorectal cancer (CRC) is the third most commonly diagnosed cancer and the fourth leading cause of cancer death in the world. Over the past few decades, numerous epidemiologic studies have identified a range of dietary factors that may potentially promote or prevent CRC. Likewise, increasing evidence has implicated the gut microbiota in CRC development. Biological plausibility is supported by habitation of numerous gut microbes in the large intestine and the functional importance of the gut microbiota in maintenance of the gut barrier integrity and immune homeostasis, the disruptions of which are among the most important mechanisms in colorectal carcinogenesis. Given the critical role of diet in the configurations of gut microbial communities and production of bacterial metabolites, it has been proposed that diet may influence CRC risk through modulation of the gut microbial composition and metabolism that in turn shape the immune response during tumor development.

Although gut bacterial abundance may respond rapidly to extreme changes in diet, predominant microbial community membership is primarily determined by long-term diet, and substantial inter-individual variation persists despite short-term dietary change. .... Thus, this review focuses on the dietary factors that have strong mechanistic support, including dietary pattern, fiber, red meat and sulfur, and omega-3 fatty acid. Given the close link between diet and obesity and the predominant role of obesity in CRC as well as the substantial data linking the gut microbiome to obesity, we also include obesity at the end of the review.

DIETARY PATTERNS: Convincing data indicate that a “Western dietary pattern,” characterized by high intake of red or processed meat, sweets, and refined grains, is associated with higher risk of colorectal neoplasia; in contrast, diets that are rich in fruits, vegetables, and whole grains (“prudent pattern diet”) are associated with lower risk of CRC. Western diets are associated with gut dysbiosis (microbial imbalance), loss of gut barrier integrity, increased levels of inflammatory proteins, and dysregulated immune signatures.

A potential role of the gut microbiota in mediating the dietary associations with CRC risk is suggested by the dramatic difference of the gut microbial structures between populations consuming different diets. Rural Africans, whose diet is high in fiber and low in fat, have a strikingly different gut microbial composition than urban Europeans or African Americans consuming a Western diet, which parallels the lower CRC rates in Africa than Western countries. For example, the African gut microbiota is characterized by a predominance of Prevotella genus that are involved in starch, hemicellulose, and xylan degradation, whereas the American microbiota is predominated by Bacteroides genus with a higher abundance of potentially pathogenic proteobacteria, such as Escherichia and Acinetobacter. .... Moreover, a crossover study indicates that switching African Americans to a high-fiber, low-fat diet for 2 weeks increases production of SCFAs, suppresses secondary bile acid synthesis, and reduces colonic mucosal inflammation and proliferation biomarkers of cancer risk.

Fiber: Numerous prospective studies have linked higher fiber intake to lower risk of CRC. The most recent expert report from the World Cancer Research Fund and the American Institute for Cancer Research in 2011 concludes that evidence that consumption of foods containing dietary fiber protects against CRC is convincing. Besides systemic benefits for insulin sensitivity and metabolic regulation, which have been implicated in colorectal carcinogenesis, fiber possesses gut-specific activities, such as diluting fecal content, decreasing transit time, and increasing stool weight, thereby minimizing exposure to intestinal carcinogens.

Moreover, soluble fiber can be fermented by bacteria in the lumen of the colon into SCFAs [short-chain fatty acids], including butyrate, acetate,and propionate. Higher fiber intake has been shown to enrich butyrate-producing bacteria in the gut, such as Clostridium, Anaerostipes, Eubacterium, and Roseburia species, and increase production of SCFAs. SCFAs have been suggested as the key metabolites linking the gut microbes to various health conditions, especially CRC

Red Meat and Sulfur: There is convincing evidence that red and processed meats are associated with increased risk of CRC. Recently, the Int. Agency for Research on Cancer has classified processed meat as a carcinogen to humans. Mechanisms underlying the pro-cancer effects of red or processed meats include heme iron, N-nitroso compounds, or heterocyclic amines, and hydrogen sulfide production. Hydrogen sulfide has been implicated in inflammatory disorders associated with risk of CRC, such as ulcerative colitis, and directly with CRC.

Omega-3 Fatty Acid: Marine omega-3 polyunsaturated fatty acid, including eicosapentaenoic acid, docosahexaenoic acid, and docosapentaenoic acid, possesses potent anti-inflammatory activity and may protect against CRC. Fish oil, a rich source of omega-3 fatty acid, is the most popular natural product used by US adults. Substantial data support the beneficial effect of omega-3 fatty acid on CRC prevention and treatment.

Dietary fat composition is a major driver of the gut microbial community structure. Compared to other types of fat, omega-3 fatty acid have been associated with higher intestinal microbiota diversity and omega-3 fatty acid-rich diet ameliorates the gut dysbiosis induced by omega-6 polyunsaturated fatty acid or antibiotics.

Obesity: Since the 1970–1980s, the prevalence of obesity has markedly increased worldwide. The obesity epidemic is believed to be largely driven by global westernization characterized by overconsumption of easily accessible and energy-dense food and a sedentary lifestyle. Obesity is an established risk factor for CRC and several other cancers. Possible mechanisms include increased insulin levels and bioavailability of insulin-like growth factor 1, altered secretion of adipokines and inflammatory cytokines, and changes in sex hormone levels.

 Two new papers just published in the British Journal of Nutrition are meta-analyses of existing studies that compare conventional vs organic milk, and conventional vs organic red meat. Both studies found clear differences between organic meat and milk compared to conventional milk and meat, with the organic milk and meat best health-wise, especially due to differences in fatty acids. The researchers stated: "organic bovine (cow) milk has a more desirable fatty acid composition than conventional milk". Some of the differences may be due to organic milk and beef coming from cattle that graze on grass (organic farming standards require  grazing/forage-based diets) , while most conventional milk and beef come from cows subsisting on grain. Beneficial omega-3 is much more prevalent in grass than in grain, which is why organic livestock and milk also contain higher levels, while omega-6 levels were lower in organic meat and dairy.

The researchers did not look at antioxidant, vitamin and mineral concentrations between the meat groups because there weren't enough studies to look at. Two years ago, Dr. Leifert led a similar review for fruits and vegetables that found organic produce had higher levels of some antioxidants and less pesticide residue than conventionally grown crops. From Medical Xpress:

New study finds clear differences between organic and non-organic milk and meat

In the largest study of its kind, an international team of experts led by Newcastle University, UK, has shown that both organic milk and meat contain around 50% more beneficial omega-3 fatty acids than conventionally produced products. Analyzing data from around the world, the team reviewed 196 papers on milk and 67 papers on meat and found clear differences between organic and conventional milk and meat, especially in terms of fatty acid composition, and the concentrations of certain essential minerals and antioxidants.

Publishing their findings today in the British Journal of Nutrition, the team say the data show a switch to organic meat and milk would go some way towards increasing our intake of nutritionally important fatty acids.Chris Seal, Professor of Food and Human Nutrition at Newcastle University explains: "Omega-3s are linked to reductions in cardiovascular disease, improved neurological development and function, and better immune function.

The systematic literature reviews analysed data from around the world and found that organic milk and meat have more desirable fat profiles than conventional milk and meat. Most importantly, a switch from conventional to organic would raise omega-3 fat intake without increasing calories and undesirable saturated fat....Other positive changes in fat profiles included lower levels of myristic and palmitic acid in organic meat and a lower omega-3/omega-6 ratio in organic milk. Higher levels of fat soluble vitamins such as vitamin E and carotenoids and 40% more CLA in organic milk were also observed. The study showed that the more desirable fat profiles in organic milk were closely linked to outdoor grazing and low concentrate feeding in dairy diets, as prescribed by organic farming standards.

The two new systematic literature reviews also describe recently published results from several mother and child cohort studies linking organic milk and dairy product consumption to a reduced risk of certain diseases. This included reduced risks of eczema in babies.

"Several of these differences stem from organic livestock production and are brought about by differences in production intensity, with outdoor-reared, grass-fed animals producing milk and meat that is consistently higher in desirable fatty acids such as the omega-3s, and lower in fatty acids that can promote heart disease and other chronic diseases." The study also found 74% more iodine in conventional milk....Iodine fortification of cattle feeds is also widely used to increase iodine concentrations in both organic and conventional milk.

The work builds on a previous study by the team - involving experts from the UK, US, France, Italy, Switzerland, Norway and Poland - investigating the composition of organic and conventionally-grown crops. This previous study - also published in the British Journal of Nutrition - showed that organic crops and crop-based foods are up to 60% higher in a number of key antioxidants than conventionally-grown crops and contained less of the toxic metal cadmium.

"We have shown without doubt there are composition differences between organic and conventional food. Taken together, the three studies on crops, meat and milk suggest that a switch to organic fruit, vegetables, meat and dairy products would provide significantly higher amounts of dietary antioxidants and omega-3 fatty acids," concludes Professor Leifert. (The 2 studies: the milk study, the meat study)

To celebrate National Nut Day, two articles about health benefits of nuts. From Medical Daily:

National Nut Day 2014: Peanuts, Tree Nuts, And How Each Helps Your Health

For people who already eat plenty of meat and dairy products…nuts and ‘nutty’ legumes, like Brazil nuts, cashews, peanuts and walnuts, are a good nutritional alternative to meat,” Dr. Donal Murphy-Bokern, independent agri-environmental scientist and author of several studies on food system impacts, said in a statement. Heeding this advice means people can reap the benefits that come with eating nuts — Protein! Fiber! Omega-3 fatty acids! 

Nuts fall into two categories: peanuts (which are really legumes) and tree nuts. The latter includes Brazil nuts, cashews, hazelnuts, macadamias, pecans, pine nuts, pistachios, walnuts and America’s beloved almonds. ...” And existing research generalizes that eating nuts does everything from reduce risk for a slew of diseases, maintains weight, boosts gastrointestinal and bone health, even adds years to a person’s life.

As previously mentioned, nuts are pretty much equal in terms of calories. There are, however, some nuts that have more heart-healthy nutrients and fats than others. See: pistachios. This particular tree nut is high in healthy fats called monounsaturated fats (MUFA). MUFAs are often associated with belly fat.

One study published in the journal Nutrition found that when middle-aged adults at risk for heart disease and diabetes incorporated more pistachios into their diet, they weighed less and lessened their cholesterol and blood sugar levels after just six months. And a separate study from UCLA found people who regularly ate pistachios lost an average of 10 to 12 pounds. Almonds and cashews are additional nuts high in MUFAs. 

The Harvard School of Public Health reported, “several of the largest cohort studies, including the Adventist Study, the Iowa Women’s Health Study, the Nurses’ Health Study, and the Physicians’ Health Study have shown a consistent 30 percent to 50 percent lower risk of myocardial infarction, sudden cardiac death, or cardiovascular disease associated with eating nuts several times a week.”

Though almonds tend to be associated most with heart health, it’s actually walnuts that take the number one spot. ...Health reported a 2006 Spanish study, which “suggested that walnuts were as effective as olive oil at reducing inflammation and oxidation in the arteries after eating a fatty meal.”

Folate, as defined by Harvard Medical School, is “the naturally occurring form of the vitamin that is in foods or in the blood.” It’s also the vitamin that staves off brain atrophy, or the progressive loss of brain cells over time... A study published in the American Journal of Psychiatry found folate may ward off depression, too. And which nut is super rich in folate? Unsalted peanuts...peanuts are also high in vitamin E and niacin, both of which boost brain health. Hazelnuts and almonds are known to have concentrated amounts of E, too, so either nut is bound to help your noggin.

Study done in mice, but shows benefits of walnuts to brain. From Science Daily:

Fight against Alzheimer's disease: New research on walnuts

A new animal study published in the Journal of Alzheimer's Disease indicates that a diet including walnuts may have a beneficial effect in reducing the risk, delaying the onset, slowing the progression of, or preventing Alzheimer's disease. Research led by Abha Chauhan, PhD, head of the Developmental Neuroscience Laboratory at the New York State Institute for Basic Research in Developmental Disabilities (IBR), found significant improvement in learning skills, memory, reducing anxiety, and motor development in mice fed a walnut-enriched diet.

The researchers suggest that the high antioxidant content of walnuts (3.7 mmol/ounce) may have been a contributing factor in protecting the mouse brain from the degeneration typically seen in Alzheimer's disease. Oxidative stress and inflammation are prominent features in this disease, which affects more than five million Americans.

Walnuts have other nutritional benefits as they contain numerous vitamins and minerals and are the only nut that contains a significant source of alpha-linolenic acid (ALA) (2.5 grams per ounce), an omega-3 fatty acid with heart and brain-health benefits. The researchers also suggest that ALA may have played a role in improving the behavioral symptoms seen in the study.