In an article published this week in the journalBioEssays, researchers from UC San Francisco, Arizona State University and University of New Mexico concluded from a review of the recent scientific literature that microbes influence human eating behavior and dietary choices to favor consumption of the particular nutrients they grow best on, rather than simply passively living off whatever nutrients we choose to send their way.

Bacterial species vary in the nutrients they need. Some prefer fat, and others sugar, for instance. But they not only vie with each other for food and to retain a niche within their ecosystem -- our digestive tracts -- they also often have different aims than we do when it comes to our own actions, according to senior author Athena Aktipis, PhD, co-founder of the Center for Evolution and Cancer with the Helen Diller Family Comprehensive Cancer Center at UCSF.

While it is unclear exactly how this occurs, the authors believe this diverse community of microbes, collectively known as the gut microbiome, may influence our decisions by releasing signaling molecules into our gut. Because the gut is linked to the immune system, the endocrine system and the nervous system, those signals could influence our physiologic and behavioral responses.

"Bacteria within the gut are manipulative," said Carlo Maley, PhD, director of the UCSF Center for Evolution and Cancer and corresponding author on the paper." "There is a diversity of interests represented in the microbiome, some aligned with our own dietary goals, and others not."

Fortunately, it's a two-way street. We can influence the compatibility of these microscopic, single-celled houseguests by deliberating altering what we ingest, Maley said, with measurable changes in the microbiome within 24 hours of diet change.

"Our diets have a huge impact on microbial populations in the gut," Maley said. "It's a whole ecosystem, and it's evolving on the time scale of minutes."

There are even specialized bacteria that digest seaweed, found in humans in Japan, where seaweed is popular in the diet.

Research suggests that gut bacteria may be affecting our eating decisions in part by acting through the vagus nerve, which connects 100 million nerve cells from the digestive tract to the base of the brain.

"Microbes have the capacity to manipulate behavior and mood through altering the neural signals in the vagus nerve, changing taste receptors, producing toxins to make us feel bad, and releasing chemical rewards to make us feel good," said Aktipis, who is currently in the Arizona State University Department of Psychology.

In mice, certain strains of bacteria increase anxious behavior. In humans, one clinical trial found that drinking a probiotic containing Lactobacillus casei improved mood in those who were feeling the lowest.

Maley, Aktipis and first author Joe Alcock, MD, from the Department of Emergency Medicine at the University of New Mexico, proposed further research to test the sway microbes hold over us. For example, would transplantation into the gut of the bacteria requiring a nutrient from seaweed lead the human host to eat more seaweed?

The speed with which the microbiome can change may be encouraging to those who seek to improve health by altering microbial populations. This may be accomplished through food and supplement choices, by ingesting specific bacterial species in the form of probiotics, or by killing targeted species with antibiotics. Optimizing the balance of power among bacterial species in our gut might allow us to lead less obese and healthier lives, according to the authors.

"Because microbiota are easily manipulatable by prebiotics, probiotics, antibiotics, fecal transplants, and dietary changes, altering our microbiota offers a tractable approach to otherwise intractable problems of obesity and unhealthy eating," the authors wrote.

The authors met and first discussed the ideas in the BioEssays paper at a summer school conference on evolutionary medicine two years ago. Aktipis, who is an evolutionary biologist and a psychologist, was drawn to the opportunity to investigate the complex interaction of the different fitness interests of microbes and their hosts and how those play out in our daily lives. Maley, a computer scientist and evolutionary biologist, had established a career studying how tumor cells arise from normal cells and evolve over time through natural selection within the body as cancer progresses.

In fact, the evolution of tumors and of bacterial communities are linked, points out Aktipis, who said some of the bacteria that normally live within us cause stomach cancer and perhaps other cancers.

"Targeting the microbiome could open up possibilities for preventing a variety of disease from obesity and diabetes to cancers of the gastro-intestinal tract. We are only beginning to scratch the surface of the importance of the microbiome for human health," she said.

The co-authors' BioEssays study was funded by the National Institutes of Health, the American Cancer Society, the Bonnie D. Addario Lung Cancer Foundation and the Institute for Advanced Study, in Berlin.

Story Source:

The above story is based on materials provided by University of California, San Francisco (UCSF). The original article was written by Jeffrey Norris. Note: Materials may be edited for content and length.

Journal Reference:

1. Joe Alcock, Carlo C. Maley, C. Athena Aktipis. Is eating behavior manipulated by the gastrointestinal microbiota? Evolutionary pressures and potential mechanisms. BioEssays, 2014; DOI: 10.1002/bies.201400071

Because ramen consumption is relatively high among Asian populations, the research focused primarily on South Korea, which has the highest per-capita number of instant noodle consumers in the world. In recent years, South Koreans have experienced a rapid increase in health problems, specifically heart disease, and a growing number of overweight adults. Such changes could lead to increased mortality due to cardiovascular disease, as well as increased health care costs.

Baylor's primary investigator on the study, Hyun Joon Shin, MD, is a clinical cardiology fellow at Baylor University Medical Center and a nutrition epidemiology doctoral student at Harvard School of Public Health.

"While instant noodle intake is greater in Asian communities, the association between instant noodle consumption and metabolic syndrome has not been widely studied," Dr. Shin said. "I decided to investigate in order to uncover more distinct connections."

Dr. Shin, who led the study on behalf of the Baylor Heart and Vascular Hospital (BHVH), found that eating instant noodles two or more times a week was associated with cardiometabolic syndrome, which raises a person's likelihood of developing heart disease and other conditions, such as diabetes and stroke.

Dr. Shin also found that those results were more prevalent in women. He said that can likely be attributed to biological differences (such as sex hormones and metabolism) between the sexes, as well as obesity and metabolic syndrome components. In addition, men and women's varied eating habits and differences in the accuracy of food reporting may play a role in the gender gap.

Another potential factor in the gender difference is a chemical called bisphenol A (BPA), which is used for packaging the noodles in Styrofoam containers. Studies have shown that BPA interferes with the way hormones send messages through the body, specifically estrogen.

Regardless of the gender-related findings or their causes, Dr. Shin said, the study represents the importance of understanding the foods we feed our bodies.

"This research is significant since many people are consuming instant noodles without knowing possible health risks," Dr. Shin said. "My hope is that this study can lay a foundation for future research about the health effects of instant noodle consumption."

Dr. Shin added that the study's health implications could be substantial -- particularly if it leads to people choosing healthier foods.

Story Source:

The above story is based on materials provided by Baylor Scott & White Health.Note: Materials may be edited for content and length.

Journal Reference:

1. H. J. Shin, E. Cho, H.-J. Lee, T. T. Fung, E. Rimm, B. Rosner, J. E. Manson, K. Wheelan, F. B. Hu. Instant Noodle Intake and Dietary Patterns Are Associated with Distinct Cardiometabolic Risk Factors in Korea. Journal of Nutrition, 2014; 144 (8): 1247 DOI: 10.3945/jn.113.188441

Paul T. Williams, PhD, of the Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, and Paul D. Thompson, MD, of the Department of Cardiology, Hartford Hospital, Hartford, CT, studied the relationship between exercise and cardiovascular disease-related deaths in about 2,400 physically active heart attack survivors. They conducted a prospective long-term study using the National Walkers' and Runners' Health Studies databases. This study confirmed previous reports indicating that the cardiovascular benefits for walking and running were equivalent, as long as the energy expenditures were the same (although when walking, as compared to running, it will take about twice as long to burn the same number of calories).

Remarkable dose-dependent reductions in deaths from cardiovascular events of up to 65% were seen among patients who were running less than 30 miles or walking less than 46 miles per week. Beyond this point however much of the benefit of exercise was lost, in what is described as a reverse J-curve pattern.

"These analyses provide what is to our knowledge the first data in humans demonstrating a statistically significant increase in cardiovascular risk with the highest levels of exercise," say Williams and Thompson. "Results suggest that the benefits of running or walking do not accrue indefinitely and that above some level, perhaps 30 miles per week of running, there is a significant increase in risk. Competitive running events also appear to increase the risk of an acute event." However, they point out that "our study population consisted of heart attack survivors and so the findings cannot be readily generalized to the entire population of heavy exercisers."

In the same issue, investigators in Spain report on a meta-analysis of ten cohort studies aimed at providing an accurate overview of mortality in elite athletes. The studies included over 42,000 top athletes (707 women) who had participated in a range of sports including football, baseball, track and field, and cycling, including Olympic level athletes and participants in the Tour de France.

"What we found on the evidence available was that elite athletes (mostly men) live longer than the general population, which suggests that the beneficial health effects of exercise, particularly in decreasing cardiovascular disease and cancer risk, are not necessarily confined to moderate doses," comments senior investigator Alejandro Lucia, MD, PhD, of the European University Madrid, Spain. "More research is needed however, using more homogeneous cohorts and a more proportional representation of both sexes."

"Extrapolation of the data from the current Williams and Thompson study to the general population would suggest that approximately one out of twenty people is overdoing exercise," comments James H. O'Keefe, MD, from the Mid America Heart Institute in Kansas City, MO, and first author of an editorial on "Exercising for Health and Longevity versus Peak Performance: Different Regimens for Different Goals," which appears in the same issue. Along with co-authors Carl "Chip" Lavie, MD, and Barry Franklin, PhD, he explains that "we have suggested the term 'cardiac overuse injury' for this increasingly common consequence of the 'more exercise is better' strategy." Even so, these authors state that about 10 out of every twenty people are not getting the minimum recommended amount of physical activity (>150 minutes/week of moderate exercise).

O'Keefe, Franklin and Lavie point out that a weekly cumulative dose of vigorous exercise of not more than about five hours has been identified in several studies to be the safe upper range for long-term cardiovascular health and life expectancy, and that it may also be beneficial to take one or two days a week off from vigorous exercise, and to refrain from high-intensity exercise on an everyday basis. They propose that individuals from either end of the exercise spectrum (sedentary people and over-exercisers) would probably reap long-term health benefits by changing their physical activity levels to be in the moderate range.

"For patients with heart disease, almost all should be exercising, and generally most should be exercising 30-40 minutes most days, but from a health stand-point, there is no reason to exercise much longer than that and especially not more than 60 minutes on most days," says Lavie, who is a cardiologist at the John Ochsner Heart and Vascular Institute, New Orleans, LA. "As Hippocrates said more than 2,000 years ago, 'if we could give every individual the right amount of nourishment and exercise, not too little and not too much, we would have found the safest way to health.' I and my co-authors believe this assessment continues to provide wise guidance," he concludes.

Story Source:

The above story is based on materials provided by Elsevier. Note: Materials may be edited for content and length.

Journal References:

1. Paul T. Williams, Paul D. Thompson. Increased Cardiovascular Disease Mortality Associated With Excessive Exercise in Heart Attack Survivors. Mayo Clinic Proceedings, 2014; DOI: 10.1016/j.mayocp.2014.05.006

2. Nuria Garatachea, Alejandro Santos-Lozano, Fabian Sanchis-Gomar, Carmen Fiuza-Luces, Helios Pareja-Galeano, Enzo Emanuele, Alejandro Lucia. Elite Athletes Live Longer Than the General Population: A Meta-Analysis. Mayo Clinic Proceedings, 2014; DOI: 10.1016/j.mayocp.2014.06.004

3. James H. O’Keefe, Barry Franklin, Carl J. Lavie. Exercising for Health and Longevity vs Peak Performance: Different Regimens for Different Goals.Mayo Clinic Proceedings, 2014; DOI: 10.1016/j.mayocp.2014.07.007