The human body is teeming with microbes, outnumbering human cells ten to one. The emerging science of the microbiome, featured at AICR’s Research Conference, revealed that diet’s link to cancer prevention may, in part, depend upon the trillions of microbes living in our gut.
The microbes in the human gut – the microbiome – weigh in at about three pounds and carry out a range of functions essential to human health. Gut microbes manufacture some vitamins, break down toxins and produce necessary metabolites. But only in recent years, with the aid of advanced technologies, have scientists begun to unravel the key role of the microbiome in human health and cancer.
"We’ve always known [the microbiome] was there but just within the last 10 years we’ve developed the tools to be able to characterize the microbiome and that’s what’s making it hotter," said Cindy Davis, PhD, Program Director in the Nutritional Sciences Research Group at the National Cancer Institute, and chair of the recent AICR Annual Research Conference session on the microbiome.
Studies are just now beginning to show the diversity and makeup of individuals’ microbiome. Earlier this year, for example, a study published in Nature catalogued the gut microbiome at 3.3 million microbial genes, outnumbering previous estimates for the whole of the human body. Over 99 percent of the genes were bacterial. Patients with inflammatory bowel disease (IBD), which is linked with an increased risk of colon cancer, contained an average of 25 percent fewer microbiome genes than individuals without IBD.
Our microbiome starts forming at birth and by the time we are adults, the community of gut microbes is in place. But foods can lead to shifts in the microbial community and its metabolic activity, studies show. For example, consuming probiotics – bacteria beneficial to human health – can temporarily change the composition of the microbiome, and the effects may improve digestion and immune function.
Research presented by Wendy R. Russell, PhD, Principal Investigator in Molecular Nutrition at the University of Aberdeen Rowett Research Institute of Nutrition and Health, is showing that manipulating the microbiome through diet leads to significant changes in metabolites that play a role in inflammation, a condition linked to increased risk for many cancers.
In intervention trials, Russell and her colleagues have focused on testing diets related to protein and carbohydrates. The researchers knew the major metabolites in the gut and had identified that certain metabolites were particularly anti-inflammatory. In one intervention, test participants consumed an Atkins-style, high protein, low-carbohydrate diet; in another study, two groups of participants consumed similar diets except one group took in their protein from meat sources and the other from soy.
After three to four weeks on the diet, biological samples showed changes in the gut microbes and their activity. "With certain diets, the anti-inflammatory metabolites were significantly affected," said Russell. In the meat versus soy protein diet, there was an increase in the inflammatory molecules for the meat eaters. The types of carbohydrates also seem to be important.
"I think metabolites are the best picture of health status," said Russell. "We’re now getting a much clearer picture of what the diet and gut bacteria are doing and how it relates to inflammation, one of the most important endpoints of health."
Individual differences in microbiomes may also help explain findings seen in population studies relating to diet and cancer prevention. In some cases, understanding microbiomes may help explain findings seen in population studies. For example, studies of Asian populations show a more consistent, protective effect of soy foods against breast and prostate cancer compared to Western populations. Soy isoflavones are extensively metabolized in the gut and one of the isoflavones scientists are studying is daidzein.
"When it was recognized that a lot of the daidzein gets converted to equol or another metabolite, there was this recognition that what we’re looking at is not in effect daidzein but it may be the metabolites," said Johanna Lampe, PhD, Associate Division Director at the Fred Hutchinson Cancer Research Center who presented her research at the conference.
Studies by Lampe and others have shown that not all people can produce equol. About 50 to 60 percent of Asians and 30 percent of Caucasians have the bacteria to produce equol. Early studies suggested equol-producer status may be responsible for some of the discrepant cancer preventive findings related to soy, but research is ongoing.
For soy and other constituents of the diet, identifying the active metabolites may provide a clearer understanding of diet’s role in cancer prevention. "We rely on our gut bacteria to make many of these compounds available to us from precursors in vegetables [and other foods]. And we have only begun to explore the impact of these bacterial metabolites on human health from bacterial action that we haven’t figured out yet," said Lampe.
Excerpted from ScienceNow.
Public Health Nutr. 2010 Nov 12:1-9
Although Americans are shifting toward eating more poultry, red meat still ranks as the largest proportion–58 percent–of total meat consumed, according to a new study analyzing data of meat intake among developed countries in the last century.
Overall meat consumption in the United States, the European Union, and the developed world as a whole has increased relatively steadily from 1961 to 2003, with the U.S. steadily consuming the highest amounts. Total U.S. meat consumption has nearly doubled in the last century.
Using 24-hour dietary recall data from National Health and Nutrition Examination Survey 2003-2004, study researchers found that of the total 128 grams/day of average total meat Americans consumed, 58 percent was red meat, 32 percent poultry, and 10 percent fish. Processed meat made up 22 percent of total, from either red meat or poultry categories. And while fish consumption has remained relatively steady since 1909, poultry consumption begins to increase steadily beginning in the 1950s and red meat consumption appears to decrease slightly beginning in the 1980s.
Source: Daniel CR, et al. Trends in meat consumption in the USA. Public Health Nutr. 2010 Nov 12:1-9
Consuming relatively large amounts of red meat may increase the risk of esophageal cancer and possibly stomach cancer, suggests a new study of almost half a million Americans published in the American Journal of Gastroenterology.
The study used data from 494,979 Americans ages 50 to 71. After ten years of follow up, researchers found that those in the top fifth category of red meat consumption had a 79 percent higher risk of developing esophageal squamous cell carcinoma compared to those who ate the least meat. Researchers also found a link between a type of compound found in red meat after it is cooked at high temperature. Those who consumed the highest amount of the compound, called DiMelQx for short, were linked with an increased risk of stomach cancer compared to those who consumed the least. Neither white meat nor processed meat was associated with any of the cancers investigated.
AICR’s expert report found that consuming high amounts of red meat (over 18 ounces) per week and processed meat is a cause of colorectal cancer. The evidence linking red and processed meat intake to esophageal cancer was limited suggestive. For stomach cancer, the link between processed meat was also limited suggestive, with insufficient data for a red meat finding.
Source: Cross, Amanda J. et al. Meat Consumption and Risk of Esophageal and Gastric Cancer in a Large Prospective Study Am J Gastroenterol. 2010 Oct 26 [Epub ahead of print].
Drinking approximately half a cup of coffee or tea per day may decrease the risk of the most common type of brain tumor, suggests a large new study of Europeans. The study, published in the November issue of American Journal of Clinical Nutrition, supports an earlier study of Americans linking total coffee and tea consumption with lower risk of the brain tumor.
Study researchers evaluated data from approximately 400,000 participants from nine European countries. After an average of 8.5 years, the study found that drinking 100 mL or more of coffee or tea a day was linked to a 34 percent reduced risk of glioma brain tumors compared to those who drank less than 100 mL. Men who were coffee and tea drinkers had a slightly greater reduced risk of glioma than women. No link was found between coffee and tea intake and the other type of brain tumor studied, meningioma.
Coffee and tea contain caffeine and many other compounds, many of which are antioxidants, which may explain the possible protective effect against some types of brain tumors, note the authors. Yet brewing methods and intake patterns varies greatly by country, which could affect estimating the amount of caffeine or other coffee and tea compounds people consumed. For example, coffee consumption was highest in Denmark and lowest in Italy. Tea consumption was highest in the U.K. and lowest in Spain.
Source: Michaud, Dominique S. et al. Coffee and tea intake and risk of brain tumors in the European Prospective Investigation into Cancer and Nutrition (EPIC) cohort study. Am J Clin Nutr 92: 1145-1150, 2010.
In an average day, only 6 percent of individuals consume the recommended amount of vegetables and 8 percent the recommended amount of fruit, according to new report released by the Produce for Better Health (PBH) Foundation, the non-profit educational foundation of the fruit and vegetable industry. The 2010 State of the Plate Report found that fruit and vegetable consumption has remained relatively stable over the past decade, hovering at just under two cups per person per day. Highlights of the report’s major findings include:
You can read the entire report at the PBH Website.
Source: Produce for Better Health Foundation. 2010 State of the Plate Report - Study on America's Consumption of Fruits & Vegetables.