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Published on Leave a comment on Improve Knee Arthritis Pain With A High Fiber Diet?

Another study finding health benefits of a fiber rich diet, which means lots of fruits, vegetables, whole grains, legumes (beans), nuts, and seeds. This time, researchers doing an a analysis of 2 studies lasting over a number of years found that there was an association with more fiber in the diet and less risk of developing knee osteoarthritis pain and of knee osteoarthritis symptoms worsening. The highest fiber group reported eating a median (middle number) 25.5 grams of fiber per day, while the lowest fiber group had a median of about 9 grams of fiber per day. They found a dose dependent relationship - the more fiber, the less osteoarthritis knee pain, and vice versa (the less daily fiber, the more they reported knee pain worsening) - this is called a "dose-dependent inverse relationship". The average fiber intake for Americans is about 15 grams per day.

The researchers also found that the more fiber in the diet, the lower their Body Mass Index (less weight) - but they say they took that into account in the analyses, and found that the amount of fiber intake was the most important thing regarding knee osteoarthritis pain. Interestingly, they did not find an association of fiber intake and x-ray evidence of osteoarthritis.  Note that this was an observational study - it observed that certain things go hand in hand, but it doesn't prove causation.

Osteoarthritis (OA) is common among adults aged 60 years and older, and is sometimes called "wear and tear" arthritis because it affects the joints. It causes pain and limits a person's physical functioning. There is a strong association between obesity, inflammation, and knee osteoarthritis. Obesity causes both inflammation and puts extra weight on the knees, and inflammation results in more joint pain. On the other hand, a high fiber diet reduces inflammation. The researchers point out that the data shows "a consistent protective association" between fiber in the diet and symptoms of knee osteoarthritis (no matter if you're overweight or not). IN SUMMARY: Eat lots of fruits, vegetables, legumes, whole grains, and nuts! From Science Daily:

Fiber-rich diet linked to lowered risk of painful knee osteoarthritis

A fibre-rich diet is linked to a lowered risk of painful knee osteoarthritis, finds the first study of its kind, published online in the Annals of the Rheumatic Diseases. The findings, which draw on two different long term studies, are broadly in line with the other reported health benefits of a fibre-rich diet. These include reductions in blood pressure, weight, and systemic inflammation, and improved blood glucose control.

The researchers mined data from two US studies in a bid to find out if dietary fibre might have any bearing on the risks of x-ray evidence of knee osteoarthritis, symptomatic knee osteoarthritis (x-ray evidence and symptoms, such as pain and stiffness), and worsening knee pain. The first of these studies was the Osteoarthritis Initiative (OAI). This has been tracking the health of nearly 5000 US men and women with, or at risk of, osteoarthritis since 2004-6 (average age 61), to pinpoint potential risk factors for the condition.  The second was part of the Framingham Offspring cohort study, which has been tracking the health of more than 1200 adult children of the original Framingham Heart Study and their partners since 1971.

Analysis of the data showed that eating more fibre was associated with a lower risk of painful knee osteoarthritis. Compared with the lowest intake (bottom 25 per cent of participants), the highest intake (top 25 per cent) was associated with a 30 per cent lower risk in the OAI and a 61 per cent lower risk in the Framingham study. But it was not associated with x-ray evidence of knee osteoarthritis. Additionally, among the OAI participants, eating more fibre in general, and a high cereal fibre intake, were associated with a significantly lower risk of worsening knee pain.

This is an observational study, so no firm conclusions can be drawn about cause and effect. Nevertheless, the researchers say: "These data demonstrate a consistent protective association between total fibre intake and symptom-related knee [osteoarthritis] in two study populations with careful adjustment for potential confounders." [Original study.]

Published on Leave a comment on Should We Be Worried That Humans Are Losing Many Species of Gut Microbes?

An article was just published in a research journal to discuss the fact that humans - in part due to lifestyles which include less dietary fiber (due to eating fewer varieties and amounts of plants) and due to medical practices (such as frequent use of antibiotics) has resulted in gut "bacterial extinctions". In other words, humans (especially those living an urban industrialized Western lifestyle) have fewer gut bacterial species than those living a more traditional lifestyle, and this loss of bacterial species is linked to various diseases. Humans can increase the number of certain bacterial species, but the loss of some bacterial species is forever. 

The researchers discuss that humans have the "lowest level of gut bacterial diversity"  of any hominid and primate. They stated that the shrinking of the variety of microbial species in the human gut (the gut microbiome) began early in human evolution (as humans started eating more meat), but that it has accelerated dramatically within industrialized societies. And that evidence is accumulating that this gut bacterial "depauperation" - the loss of a variety of bacterial species - may predispose humans to a range of diseases.  Some of it is due to evolution (as humans ate more meat), and some to lifestyle changes. A term is used throughout this paper: depauperate - which means lacking in numbers or variety of species in the gut microbiome (the microbial community or ecosystem).

Other research has also shown that eating a highly processed Western diet results in gut microbial changes that are linked to various diseases (here, here, here) - that is, the microbes being fed are those associated with diseases. Also, certain diets encourage certain microbial species to flourish (here, here).  Bottom line: studies find health benefits from higher levels of dietary fiber - from fruits, vegetables, seeds, nuts, whole grains, and legumes (beans). From Current Opinion In Microbiology:

The shrinking human gut microbiome

Highlights: Humans harbor the lowest levels of gut bacterial diversity of any hominid. Humans in industrialized nations harbor fewer gut bacterial taxa than any primate. Medical practices and lack of dietary fiber may drive gut bacterial extinctions. Depauperate microbiotas may predispose entire human populations to certain diseases.

Mammals harbor complex assemblages of gut bacteria that are deeply integrated with their hosts’ digestive, immune, and neuroendocrine systems. Recent work has revealed that there has been a substantial loss of gut bacterial diversity from humans since the divergence of humans and chimpanzees. This bacterial depauperation began in humanity’s ancient evolutionary past and has accelerated in recent years with the advent of modern lifestyles. Today, humans living in industrialized societies harbor the lowest levels of gut bacterial diversity of any primate for which metagenomic data are available, a condition that may increase risk of infections, autoimmune disorders, and metabolic syndrome. Some missing gut bacteria may remain within under-sampled human populations, whereas others may be globally extinct and unrecoverable.

A typical human harbors on the order of 1013 bacterial cells in the large intestine. This gut microbiota, which can contain over a thousand species, is deeply integrated with virtually every tissue and organ system in the body. Gut bacteria process difficult to digest components of the diet, promote angiogenesis in the intestine, train the immune system, regulate metabolism, and even influence moods and behaviors.

In contrast to hunter–gatherer to agricultural transitions, adoptions of industrial and post-industrial lifestyles have led to massive reductions in bacterial richness within human gut microbiotas. Individuals living in urban centers in the United States harbor fewer gut bacterial species on average than do individuals living more traditional lifestyles in Malawi , Venezuela, Peru, and Papua New Guinea.....Industrialized and traditional lifestyles differ in many respects, confounding the identification of the specific practices that have led to decreases in gut bacterial diversity within industrialized societies. One potential cause is the rise of food processing and the corresponding reductions in the intake of dietary fiber in favor of simple sugars. Recently, studies in model systems have indicated that long-term reductions in dietary fiber can lead to the extirpation of gut bacterial taxa from host lineages. 

Other potential causes of reduced gut bacterial diversity within industrialized human populations include certain modern medical practices. For example, longitudinal studies in humans have shown that levels of gut bacterial diversity decrease drastically after antibiotic use. Although bacterial richness may recover after treatment is completed, the timeline and extent of the restoration is highly subject-dependent. The consequences of antibiotic use on gut bacterial diversity may be most severe when treatment is administered during the early years of life, before the adult microbiota has fully formed .

Published on Leave a comment on Eating Whole Grains Linked To Living Longer

A second study was just published about the benefits of eating whole grains daily - again a significantly lower risk of premature death, and again the effects were dose-related. That is, the more whole grains eaten daily, the lower the risk of early death. Like the first study, this also was a review study. This study (published in BMJ) found that whole grain consumption was associated with a reduction in the risk for death from cancer, coronary heart disease (heart attack and stroke), respiratory disease, infectious disease, and diabetes.

A slice of 100 percent whole grain bread contains about 16 grams of whole grains, and current U.S. dietary guidelines recommend 48 grams or more of whole grains daily, but this study suggests that eating even more whole grains daily is best (eating 90 grams of whole grains a day reduced the risk for mortality from all causes by 17 percent).

Grains are divided into two subgroups: whole grains and refined grains. Whole grains or foods made from them contain all the essential parts and naturally-occurring nutrients of the entire grain seed in their original proportions. This definition means that 100% of the original kernel – all of the bran, germ, and endosperm – must be present to qualify as a whole grain. Some whole grains are: whole wheat. barley. buckwheat, corn (including whole cornmeal and popcorn), millet, oats (including oatmeal), quinoa, brown rice, rye, sorghum, spelt, bulgur, and wild rice. From Eurekalert:

Seven servings of whole grains a day keep the doctor away

Eating three more portions of dietary fiber a day--say, two pieces of whole grain bread and a bowl of whole grain breakfast cereal--is associated with a lower risk for all cardiovascular diseases and for dying of cancer, diabetes, and respiratory and infectious diseases, a study just published in the BMJ has shown. The study is strong proof that consuming lots of whole grains is good for our health, says first author Dagfinn Aune, a PhD candidate at the Norwegian University of Science and Technology who is currently working at Imperial College, London.

....In general, the study showed that the higher the consumption, the better protected you are. "We saw the lowest risk among people who ate between seven and seven and a half servings of whole grain products a day, which was the highest intake across all the studies. This corresponds to 210-225 grams of whole grain products in fresh weight and about 70-75 grams of whole grains in dry weight, and is about the same as the health authorities in Norway and other Nordic countries recommend as the minimum daily allowance," says Aune.

The researchers' analyses showed fewer risk factors for people who consumed more bread and cereal with whole grains, as well as foods with added bran. On the other hand, people who ate a lot of white bread, rice or cereals with refined grains did not show reduced risk.

Nine studies with a total of more than 700,000 participants examined the risk for all types of cardiovascular disease and correlated cardiovascular deaths....The risk of dying prematurely from all causes was 18% lower for individuals who consumed a lot of whole grains compared to those who consumed lesser amounts, while three additional servings each day were associated with a 17% reduction in mortality. The risk for deaths associated with cancer (15%), respiratory diseases (22%), diabetes (51%) and infectious diseases (26%) was also lower the more whole grains individuals consumed.

Published on Leave a comment on Eat More Fiber to Improve Your Gut Microbiome

Another article commenting that increasing the amount of dietary fiber eaten by people eating a typical Western diet (which is low in fiber) will improve their gut microbiome (community of microbes). Research is finding that the added dietary fiber is food (nutrition) for microbes in the gut, and eating additional fiber daily will help restore or increase bacterial diversity, which then should lead to health benefits. Note: Easy ways to increase dietary fiber are increasing intake of whole grains, legumes, nuts, seeds, fruits, and vegetables. Think of food writer Michael Pollan's advice: "Eat food. Not too much. Mostly plants."

Researchers feel that fiber intake needs to be increased to more than current dietary guidelines, and that beneficial effects to the microbiome starts to occur rapidly (within 2 weeks) of changing to a higher fiber diet. This post from January 21, 2016 discussed the Sonnenburg research on gut microbe depletion (from a low fiber diet), and this April 28, 2015 post discussed the O'Keefe research (changing the diet has big effect on colon cancer risk) - both studies are mentioned below. See the page Feeding Your Gut Microbes for more information. From Science Daily:

Can more fiber restore microbiome diversity?

Scientists are pushing to restore human health in Western countries by changing our diet to restore the microbial species lost over the evolution of Western diet. Researchers advocate for strategically increasing dietary fiber intake as one path forward in regaining microbial biodiversity.

Insufficient nutrients for our gut microbes have been linked to a loss of certain beneficial bacterial species in industrialized societies and are likely impacting our immunological and metabolic health, although more data is needed. For example, most Westerners consume half of the amount of dietary fiber recommended by dietary guidelines, which nutritionists refer to as the "fiber gap," which is a problem because dietary fiber is the primary source of nutrition (e.g., carbohydrates) accessible to gut bacteria in humans.

"The idea to boost fiber levels is not new," says Jens Walter of the University of Alberta, Canada. "However, depletion of the microbiome adds a new perspective to this low-fiber Western diet that we are currently eating." Earlier this year, Stanford University's Justin Sonnenburg found that mice fed a typical Western diet (high in fat and carbohydrates and low in fiber) transferred a lower diversity of beneficial microbial species to future generations. The re-introduction of the microbes' preferred fiber at that stage did not result in a return of some (good) species, indicating that extinctions had occurred in only a few generations.

Walter and co-author Edward Deehan, his PhD student, are concerned that a dramatic shift away from a diet similar to the one under which the human-microbiome symbiosis evolved is a key factor in the rise of non-communicable disorders like obesity. "There is a lot of epidemiological evidence that fiber is beneficial, and food products containing dietary fiber have FDA-approved health claims for both colon cancer and coronary heart disease. There is also quite a bit of clinical evidence (although it is less consistent)," Walter says. "The most pressing issue at the moment that neither consumption of fiber in society nor the doses used in clinical research are high enough."

People living in non-industrialized societies have an average intake of fiber that is much higher than the low norms of Western societies. The authors note the recent work from the Stephen J.D. O'Keefe lab in Nature Communications in which modern African-Americans were given a traditional South-African diet that contained 55 grams of daily dietary fiber and had improved markers for colon cancer within two weeks.

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This study, like previous research, found an association between increased dietary fiber intake (specifically from cereal and vegetable fiber) and a reduced risk of developing type 2 diabetes. However, they did not find this link with fruit fiber, and also if the person was obese. From Medical Xpress;

Study adds to evidence that increasing dietary fiber reduces the risk of developing diabetes

New research published today in Diabetologia (the journal of the European Association for the Study of Diabetes) indicates that consuming greater quantities of dietary fiber reduces the risk of developing type 2 diabetes. In this article the authors evaluated the associations between total fiber as well as fiber from cereal, fruit, and vegetable sources, and new-onset type 2 diabetes in a large European cohort across eight countries, in the EPIC-InterAct Study.

The authors divided the study participants into four equally sized groups from lowest to highest fiber intake, and assessed their risk of developing type 2 diabetes over an average of 11 years' follow-up.They found that participants with the highest total fiber intake (more than 26 g/day) had an 18% lower risk of developing diabetes compared to those with the lowest total fiber intake (less than 19 g/day), after adjusting for the effect of other lifestyle and dietary factors. When the results were adjusted for body mass index (BMI) as a marker of obesity, higher total fiber intake was found to be no longer associated with a lower risk of developing diabetes, suggesting that the beneficial association with fiber intake may be mediated at least in part by BMI.

When the authors evaluated the different fiber sources, they found that cereal fiber had the strongest inverse association: those with the highest levels of cereal and vegetable fiber consumption had a 19% and 16% lower risk of developing diabetes respectively, compared with those with the lowest consumption of these types of fiber. Again, these associations disappeared when the results were adjusted for BMI. By contrast, fruit fiber was not associated with a reduction in diabetes risk. Cereals accounted for 38% of the total fiber intake, and were the main source of fiber in all the countries involved in the study (with the exception of France where vegetables were the main source).

The authors also undertook a meta-analysis, where they pooled the data from this EPIC-InterAct study with those from 18 other independent studies (eight in the United States, four in Europe, three in Australia, and three in Asia). The meta-analysis included over 41,000 new-onset cases of type 2 diabetes and found that the risk of diabetes fell by 9% for each 10 g/day increase in total fiber intake, and by 25% for each 10 g/day increase in cereal fiber intake. They did not find a statistically significant relationship between increasing either fruit or vegetable fiber and reducing diabetes risk.

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How much fiber is there in the different foods we eat? And how much should we eat? Recent posts (Where Do I Get That Beneficial Gut Bacteria? and A Special Gut Microbe) stressed the importance of eating dietary fiber for various health benefits and to feed the beneficial bacteria (such as Faecalibacterium prausnitzii) in our gut. Are there different types of fiber and does it matter?

Currently the average American adult eats about 12 to 18 grams of dietary fiber daily. But the latest advice (from both National Academy of Sciences and Academy of Nutrition and Dietetics) is to eat over 20 grams of dietary fiber daily to about 35 grams daily, depending on weight. So a person eating a 2000 calorie daily diet should have about 25 grams of fiber daily. Their recommendation for children is that intake should equal age in years plus 5 g/day (e.g., a 4 year old should consume 9 g/day). 

Good fiber foods are: fruits, vegetables, whole grains, legumes (beans), nuts, and seeds. But people eating a typical westernized diet are instead eating a high fat, high meat, highly processed food diet which neglects plant-based foods. Go look at the ingredient labels of favorite American foods and see that many don't have fiber or are low in dietary fiber (e.g., hot dogs, salami, candy, cookies, potato chips).

Dietary fiber or roughage is the indigestible portion of food derived from plants. There are two types of fiber: soluble and insoluble, and both should be eaten for good health because they benefit health in a number of ways.

Insoluble fiber doesn't dissolve in water and passes through the intestines (it provides bulking), while soluble fiber dissolves in water, and becomes a gel. Plant foods contain both types of fiber in varying degrees, depending on the plant's characteristics. For example, plums and prunes have a thick skin covering a juicy pulp. The skin is a source of insoluble fiber, whereas soluble fiber is in the pulp.

One can also take fiber supplements, but actual real foods have many more health benefits to them, and also provide a variety of fiber sources. Eating a variety of whole plant-based foods is beneficial in many ways, including feeding the variety of bacteria species in your gut. Remember that different bacteria need different foods, and so eating a variety of foods is best.

To increase your daily dietary fiber intake, first take a look at the amount of fiber in different foods. And then eat lots of fruits, vegetables, whole grains, legumes (beans), seeds, and nuts.

The following tables give approximate fiber amounts in some high fiber foods (NOTE: different sources give slightly different numbers):

Fresh & Dried Fruit  Serving Size Fiber (g)
 Apples with skin  1 medium 5.0
 Apricot  3 medium 1.0
 Apricots, dried  4 pieces 2.9
 Banana  1 medium 3.9
 Blueberries  1 cup 4.2
 Cantaloupe, cubes  1 cup 1.3
 Figs, dried  2 medium 3.7
 Grapefruit  1/2 medium 3.1
 Orange, navel  1 medium 3.4
 Peach  1 medium 2.0
 Peaches, dried  3 pieces 3.2
 Pear  1 medium 5.1
 Plum  1 medium 1.1
 Raisins  1.5 oz box 1.6
 Raspberries  1 cup 8.0
 Strawberries  1 cup 4.4
Grains, Beans (Legumes), Nuts, Seeds  Serving Size Fiber (g)
 Almonds  1 oz 4.2
 Black beans, cooked  1 cup 13.9
 Bran cereal  1 cup 19.9
 Bread, whole wheat  1 slice 2.0
 Brown rice, dry  1 cup 7.9
 Cashews  1 oz 1.0
 Flax seeds  3 Tbsp. 6.9
 Garbanzo beans, cooked  1 cup 5.8
 Kidney beans, cooked  1 cup 11.6
 Lentils, red cooked  1 cup 13.6
 Lima beans, cooked  1 cup 8.6
 Oats, rolled dry  1 cup 12.0
 Quinoa (seeds) dry  1/4 cup 6.2
 Quinoa, cooked  1 cup 8.4
 Pasta, whole wheat  1 cup 6.3
 Peanuts  1 oz 2.3
 Pistachio nuts  1 oz 3.1
 Pumpkin seeds  1/4 cup 4.1
 Soybeans, cooked  1 cup 8.6
 Sunflower seeds  1/4 cup 3.0
 Walnuts  1 cup 5.0
 Vegetables  Serving Size Fiber (g)
 Avocado (fruit)  1 medium 11.8
 Beets, cooked  1 cup 2.8
 Beet greens  1 cup 4.2
 Bok choy, cooked  1 cup 2.8
 Broccoli, cooked  1 cup 4.5
 Brussels sprouts, cooked  1 cup 3.6
 Cabbage, cooked  1 cup 4.2
 Carrot  1 medium 2.6
 Carrot, cooked  1 cup 5.2
 Cauliflower, cooked  1 cup 3.4
 Cole slaw  1 cup 4.0
 Collard greens, cooked  1 cup 2.6
 Corn, sweet  1 cup 4.6
 Green beans  1 cup 4.0
 Celery  1 stalk 1.1
 Kale, cooked  1 cup 7.2
 Onions, raw  1 cup 2.9
 Peas, cooked  1 cup 8.8
 Peppers, sweet  1 cup 2.6
 Pop corn, air-popped  3 cups 3.6
 Potato, baked w/ skin  1 medium 4.8
 Spinach, cooked  1 cup 4.3
 Summer squash, cooked  1 cup 2.5
 Sweet potato, cooked  1 medium 4.9
 Swiss chard, cooked  1 cup 3.7
 Tomato  1 medium 1.5
 Winter squash, cooked  1 cup 6.2
 Zucchini, cooked  1 cup 2.6

The tables were from http://commonsensehealth.com/high-fiber-foods-list-for-a-high-fiber-diet/

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My last post A Special Gut Microbe was on the very essential and beneficial microbe Faecalibacterium prausnitzii. It is one of the most abundant  bacteria in the gut of healthy individuals, but low or depleted levels are associated with inflammation and found in a number of diseases, including intestinal bowel diseases such as Crohn's disease. It is a butyrate producing bacteria (beneficial).

F. prausnitzii is viewed as so essential that it has been called a "keystone species" in the gut. A question I've been asked is: how can one increase the numbers of this bacteria in the gut and where can one buy some to take as a probiotic? (Probiotics are live bacteria that are beneficial to health when consumed.)

The typical bacteria added to yogurts or sold as supplements are able to survive when exposed to air (oxygen). However, F. prausnitzii are "oxygen sensitive" and they die within minutes upon exposure to air. Researchers view this beneficial bacteria as a "probiotic of the future" and currently there is research going on to figure out ways it can be easily stored and be exposed to air a few hours and not die. Currently there is NO way to take a probiotic F. prausnitzii supplement. So what else can one do?

After reviewing the scientific literature, it seems that the current ways to get F. prausnitzii into the gut or increase its numbers are: fecal microbiota transplant or FMT (currently only done with desperately ill individuals), drastically restricting calories for one week by obese individuals increases beneficial bacteria, and making changes to the diet. For example, a high animal meat, high animal fat, high sugar, highly processed foods, and low fiber diet (the typical westernized diet) lowers F. prausnitzii numbers, while a high-fiber, low meat diet increases F. prausnitzii numbers.

Repeat: the number one thing a person can do to increase numbers of F. prausnitzii is to increase fiber in the diet. By the way, increasing dietary fiber increases butyrate, and butyrate is involved with colon health, is anti-inflammatory, and anti-cancer . See, it's all related.

High fiber is: whole grains, vegetables, fruits, nuts, seeds, and legumes. Eat a varied plant-based diet, which means lots of plant based foods. It seems that Michael Pollan's emphasis on "Eat real foods. Mostly plants. Not too much." is just right. And variety seems important - with different types of fiber feeding different bacteria.

While F. prausnitzii may be an important beneficial bacteria in the gut, it is not the only beneficial one. So a food labeled "with added fiber" may not be the right fiber for bacteria, This is even true for enteral formula supplementation, for example, one formula containing fiber used pea fiber and this did not feed the F. prausnitzii.

In the first paragraph I mentioned that research has consistently shown F. prausnitzii depletion in adults sick with IBDs such as Crohn's disease. So it was interesting to find that one recent study found that even people sick with Crohn's disease showed significant improvement and remission (92% remission at 2 years) on a semi-vegetarian diet, namely a lacto-ovo-vegetarian diet (daily 32.4 g of dietary fiber in 2000 calories). [High Amount of Dietary Fiber Not Harmful But Favorable for Crohn Disease ]This is totally opposite from the current prevailing medical view which currently encourages people with IBD to "rest the intestine" with a fiber-restricted diet.

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Improving gut bacteria is a good reason to eat apples. Take note that this study was done with mice, but the researchers think it also applies to humans. From Medical News Today:

Could an apple a day protect against obesity?

An apple a day may keep obesity away, particularly if it is of the Granny Smith variety, according to a new study from Washington State University.

Apples have many health benefits, according to previous research. Last year, Medical News Today reported on a study suggesting that eating an apple a day may be just as beneficial as daily statin use for preventing vascular mortality. A 2011 study also claimed that apples and pears may reduce the risk of stroke by more than 50%.

But according to the team involved in this latest research, very few studies have looked at how the bioactive compounds in apples that are not absorbed during digestion - such as polyphenols (a type of antioxidant) and dietary fiber - affect the friendly gut bacteria that boost immunity and aid weight maintenance.

With this in mind, Noratto and her team analyzed how the bioactive compounds of seven different varieties of apples - Granny Smith, Braeburn, Fuji, Gala, Golden Delicious, McIntosh and Red Delicious - affected the good gut bacteria of diet-induced obese mice. The researchers found that, compared with all other apple varieties, Granny Smiths appeared to have the most beneficial effect on good gut bacteria.

The balance of gut bacteria among obese people is usually impaired. But when comparing the feces of obese mice fed Granny Smiths with the feces of lean mice, the team found that the proportions of bacteria - specifically the presence of Firmicutes, Bacteroidetes, Enterococcus, Enterobacteriaceae, Escherichia coli and Bifidobacterium - were very similar.

The researchers explain that Granny Smiths are high in non-digestible dietary fiber and polyphenols, and low in carbohydrates. Even after chewing and exposure to stomach acid and digestive enzymes, the compounds are unscathed when they reach the colon. The bacteria present in the colon then ferment the compounds, producing butyric acid that spurs on the growth of friendly gut bacteria.

An imbalance of gut bacteria - determined by the food we eat - can cause chronic inflammation  that leads to diabetes. But the researchers say that re-establishing the balance of gut bacteria through consumption of Granny Smith apples may reduce such inflammation, as well as promote satiety.

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This research illustrates how little we currently know about gut bacteria.But it did show the importance of diet. From Science Daily:

Monitoring rise and fall of the microbiome

Trillions of bacteria live in each person's digestive tract. Scientists believe that some of these bacteria help digest food and stave off harmful infections, but their role in human health is not well understood.

To help shed light on the role of these bacteria, a team of researchers led by MIT associate professor Eric Alm recently tracked fluctuations in the bacterial populations of two research subjects over a full year. The findings, described in the July 25 issue of the journal Genome Biology, suggest that while these populations are fairly stable, they undergo daily fluctuations in response to changes in diet and other factors...."To a large extent, the main factor we found that explained a lot of that variance was the diet."

There are a few thousand strains of bacteria that can inhabit the human gut, but only a few hundred of those are found in any given individual, Alm says. For one year, the two subjects in the study collected daily stool samples so bacterial populations could be measured. They also used an iPhone app to track lifestyle factors such as diet, sleep, mood, and exercise, generating a huge amount of data.

Analysis of this data revealed that dietary changes could produce daily variations in the populations of different strains of bacteria. For example, an increase in fiber correlated with a boost in the populations of Bifidobacteria, Roseburia, and Eubacterium rectale. Four strains -- including Faecalibacterium prausnitzii, which has been implicated in protecting against inflammatory bowel disease -- were correlated with eating citrus.

During the study, each of the two subjects experienced an event that dramatically altered the gut microbiome. Subject B experienced food poisoning caused by Salmonella, and Subject A traveled to a developing nation, where he experienced diarrheal illness for two weeks.

During Subject B's infection, Salmonella leapt from 10 percent of the gut microbiome to nearly 30 percent. At the same time, populations of bacteria from the phylum Firmicutes, believed to be beneficial to human health, nearly disappeared. After the subject recovered, Firmicutes rebounded to about 40 percent of the total microbiome, but most of the strains were different from those originally present.

Subject A also exhibited severe disruptions to his microbiome during his trip, but once he returned to the United States, it returned to normal. Unlike Subject B's recovery from food poisoning, Subject A's populations returned to their original composition.