Microbes, Carbs, Fiber and Height
The human body is a repository of microbial cells that outnumber the cells of their human host by a factor of ten. Many of these microbes – bacteria, fungi, and protozoans – live on our skin and in our eyes, nose, and lungs. But most are found in the intestinal tract where they are collectively referred to as the gut microbiota.
A mounting body of evidence suggests gut microbiota can contribute to both acute and chronic disease as well as certain metabolic conditions, many of which link to cancer risk. At the annual Experimental Biology (EB) conference last week in San Diego, scientists presented the recent findings.
The human body is a super-organism, a multispecies consortium composed of both microbial and human parts, said Jeffrey Gordon, MD, Director of the Center for Genome Sciences and Systems Biology at the University of Washington at St. Louis, during his presentation at EB. No two individuals share the same microbiota but there are similarities across family members, as well as age and cultural groups.
Most of our lives we live in happy coexistence with our microbial partners in what often is described as a symbiotic relationship: host and microbes benefit one another. The human host provides a warm, oxygen-free environment conducive to microbial growth and in turn, the microbes help maintain intestinal and immune health and play important roles in nutrient synthesis and absorption.
Scientists study the effects of the gut microbiota on health by transplanting the microbiota from animals with particular physical and metabolic characteristics into animals that are bred to be microbe-free. This allows scientists to study the intersection of diet and the microbiota and determine how much of the animals' characteristics are attributed to their microbiota.
The numbers of microbes grow along our gastrointestinal tract, Gordon noted, with the fewest found in the mouth and stomach and the largest numbers found in the colon.
A growing body of evidence suggests there may be a link between one's microbiota and the tendency toward obesity, a known risk factor for cancer. The mechanisms by which the microbiota influence one's risk for obesity are not well understood. Recent findings from Gordon's lab have shown that lean mice have far more microbes than obese mice. This may indicate that a lean mouse's microbiota metabolizes more nutrients.
Another hypothesis presented at EB is that our microbes or their metabolic byproducts affect they way our body senses nutrients and feelings of fullness.
In one study, presented at a poster session at EB, researchers at the French Institute for Agricultural Research (INRA) transplanted the gut microbiota from obesity-prone and obesity-resistant rats into germ-free mice. Mice in each group were fed either a high fat diet or a standard-calorie diet.
When eating a high-fat diet, the animals that received the obesity-prone microbiota ate more and gained more weight than both their obesity-resistant peers and the comparison group. The mice that received the obesity-resistant microbes also gained weight, but not as much. These mice gained mostly lean body mass, not fat. All of the mice that received the obesity-prone microbiota demonstrated an increase in inflammatory markers and a reduction in key hormones that signal feelings of fullness when compared to the obesity-resistant mice.
These findings suggest, the study concludes, that certain types and numbers of microbes have the potential to increase one's risk of weight gain when overeating.
Like many studies in the field of microbiota and heath, results are preliminary and more studies are needed. And as scientists noted, the research in the microbiome field is only beginning to answer the many questions about our microbiome's role in human health.
Residents of rural area are not feeling well, when compared to those living in cities or on the outskirts, according to a recent government report.
Overall, the Centers for Disease Control and Prevention report found that residents of non-metropolitan areas were more likely to report ill health than those living in cities. The lowest percentage of adults reporting ill or poor health came from those living in large fringe metropolitan counties. The highest percentage of residents reporting ill or poor health – at almost 16 percent – came from the most rural areas.
Evidence links excess body fat and belly fat to increased risk of pancreatic cancer, which has led scientists to focus on the hormone insulin as a possible culprit. Obesity can lead to insulin resistance, and high levels of insulin play a role in several cancers. The key nutrient that affects insulin is carbohydrates, but studies have produced conflicting findings on carbs link to pancreatic cancer.
A new review of the research now suggests that the amount of total carbohydrates consumed does not affect the development of pancreatic cancer, but evidence points to one form of carbs – fructose – as possibly increasing risk.
The study was funded by the World Cancer Research Fund as part of AICR/WCRF's Continuous Update Project (CUP).
For the analysis, researchers looked at the 10 relevant population studies. All studies were prospective, asking participants about their dietary habits and then tracking incidence of pancreatic cancer over time.
The studies investigated pancreatic cancer risk related to total carbohydrates and the glycemic index, a measure of the effect of a food's carbohydrates on blood sugar levels. The review also looked at different types of carbohydrates, table sugar (sucrose) and fructose, a natural sugar in fruit.
The analysis found no link between pancreatic cancer risk and total carbohydrates, sucrose, or glycemic index. For fructose, every 25 grams a day linked to a 22 percent increased risk.
Because research points to high fruit intake linking with lower risk, the authors note, its possible the fructose link may reflect participants eating or drinking foods high in fructose other than fruit. Many processed foods, for example, contain high fructose corn syrup. The link may also be due to other factors. For example, there was no association between fructose and pancreatic cancer in the few studies that accounted for alcohol, diabetes, and physical activity. More, and stronger studies, are needed, the authors conclude.
Sources: Aune D, Chan DS, Vieira AR, Navarro Rosenblatt DA, Vieira R, Greenwood DC, Cade JE, Burley VJ, Norat T. "Dietary fructose, carbohydrates, glycemic indices and pancreatic cancer risk: a systematic review and meta-analysis of cohort studies." Ann Oncol. 2012 Apr 26.
Americans are eating about the same amount of fiber as a decade ago, according to a new study, but it's only about half the amount recommended for overall good health and cancer protection. The study was published in the early online May issue of the Journal of the Academy of Nutrition and Dietetics.
From 1999 to 2008, adults on average ate about 16 grams of fiber per day, shifting slightly higher or lower over the years. US guidelines recommend at least 14 grams of fiber for every 1000 calories. AICR's expert report and its continuous updates recommend 32 grams of fiber per day for cancer prevention. (A piece of whole wheat toast has about 3 grams of fiber.)
For the study, researchers pulled data from the National Health and Nutrition Examination Survey and grouped dietary fiber intake every two years, starting in 1999.
When looking at distinct populations, the study did see variation in fiber intake. Obese participants reported consuming less fiber than normal or overweight participants. Mexican Americans are eating slightly more fiber than white Americans. Blacks are eating approximately 13 grams of fiber a day, an increase of only half a gram from ten years earlier.
Sources: Dana E. King, Arch G. Mainous III, Carol A. Lambourne. "Trends in Dietary Fiber Intake in the United States, 1999-2008." Journal of the Academy of Nutrition and Dietetics. Volume 112, Issue 5, Pages 589-776 (May 2012).
Ovarian cancer causes the most deaths of all gynecological cancer, with the disease often going undiagnosed until its advanced stages. Currently, the only established risk factor for this cancer relating to diet, weight, and physical activity is our adult height, which has an indirect connection.
Now a new analysis of all the studies – both published and unpublished – adds to the evidence that tallness may increase a women's risk. The analysis also found that for women who have never used hormone therapy, being overweight increases the risk for this cancer. The study was published in PLoS Medicine last month.
For the analysis, researchers identified 47 relevant population studies that included approximately 25,000 women with the cancer and 81,000 cancer-free women as comparison groups. Only about half of the studies had published their results, according to the authors, with those findings inconsistent.
For weight, every 5-unit increase in BMI linked to a 10 percent increased risk among women who had never taken hormone therapy, a recognized risk factor for this cancer. For example, if a 5'2" women who weighed 130 pounds gained 30 pounds her BMI would increase 5 units.
For height, the researchers found that risk increased for every 5 cm increase in height (almost 2 inches). Height is unlikely to directly modify risk for cancer, but it is a marker for hormonal, nutritional and other factors that can play a role in risk. As the authors note, the average height of women has increased by about 1 centimeter per decade in high-income countries such as the United States.
Source: Collaborative Group on Epidemiological Studies of Ovarian Cancer (2012). "Ovarian Cancer and Body Size: Individual Participant Meta-Analysis Including 25,157 Women with Ovarian Cancer from 47 Epidemiological Studies." PLoS Med 9(4).