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  • For healthy skin, you need a healthy gut. 

  • A healthy gut contains plenty of "good" microbes. Our gut actually contains trillions of microbes. In a healthy gut, the good guys ("good bacteria") far outnumber the bad guys ("harmful germs" or pathogens). 

  • These good microbes work hard to keep us healthy. They also produce substances that help fight inflammation.

  • To help these good microbes flourish in our gut, we have to feed them the right kinds of foods. Foods that encourage the growth of good microbes are called prebiotics.

  • Prebiotic foods include foods that are naturally rich in plant fibers, especially fruits, vegetables, and whole grains. Other phytonutrients found in fruits and vegetables (such as polyphenols), and even certain fats, can help promote the growth of good microbes.

Good bacteria and bad bacteria: why some germs are our friends and protectors

Your body is covered in germs. Don't be alarmed: that's normal. In fact, it's a good thing.

Your skin, mouth, nose, and other body parts are covered in germs. But the part of your body that contains the most germs is actually inside of you: your gut (in medical terms, the gastrointestinal tract). 

These germs, or microorganisms, have important roles to play in keeping us healthy. We now know that there actually trillions of these microbes on and inside your body. These microbes include bacteria, viruses, and other groups, and many of them act to help us. 


This entire community of microbes is known as the microbiota. These microorganisms and the genes (genetic material) that they contain are called the microbiome.

Trillions of microbes in the gut are needed for healthy skin

Your gut contains trillions of microorganisms. The "good" microbes help train the immune system, help digest our food, and fight off harmful bacteria. 

You may have heard of the microbiome in medical news. That's because research has found that the microbiome has many roles to play in keeping us healthy. In a healthy gut, there may be some pathogens (harmful bacteria), but they're far outnumbered by the good guys: the good microbes.


These microbes act as teachers, as policemen, and as factory workers. That's because they've been shown to help train our immune system, fight off the harmful germs that sometimes find their way into our digestive system, and even actively help to break down and digest our food.


In fact, we need these helpful microbes to digest many of our foods. The human body alone doesn't produce all of the enzymes needed to digest all types of foods. Different microbes contain different enzymes. These enzymes are critical in the digestion of certain foods, such as fiber-rich vegetables. They help break down these fibers and extract the nutrients. They help in another way, also: by taking that fiber and producing helpful substances. 

When your microbes are well fed, they really try to help you


When you feed your microbes fiber, they start digesting and fermenting that fiber. In the process, they produce some very helpful substances. These substances are called short chain fatty acids. There are different ones, including acetate, butyrate, and propionate.  Research has found that these short chain fatty acids (SCFAs) help us in a number of ways. SCFAs help fight inflammation. They also help protect the lining of our gut, which may help protect us from allergies and infections.

Good microbes are picky eaters, but they love fiber:

Why a diet rich in fruits, vegetables, and whole grains is so good for the health of our gut

When it comes to your health, it's always important to evaluate the research and then think about the actions that you can take. In this case, knowing that these good microbes are so important for our health, how can we make sure that they grow and flourish in our gut?


One major way is by feeding them the right kinds of foods. 

Foods that are naturally rich in fiber help us "grow" more of the good microbes in our gut. 

Research has shown that all of us have very distinct communities of microbes living on and inside of us. In other words, your germs are different than my germs.

Studies have shown that this is due to many different factors. Genetics plays a role, as does your age and other medical conditions. The medications you take play a role as well. For example, we know that while taking broad-spectrum antibiotics (such as that Z-Pak for your sinus infection) can eradicate harmful, infection-causing bacteria, they can also kill off some of the good microbes. 


But genetics, age, and medical conditions aren't the only factors. A major factor is your diet. 

Less foods that are processed and more foods that are naturally rich in fiber: why it's so important to fill up on whole foods


One of the most important ways that you can influence the health of your gut is through your diet. That's because the foods that you eat are the same foods that your gut microbes eat. 


Your microbes eat what you eat. 


And your gut microbes can be a picky lot. A diet high in added sugar and refined carbohydrates can cause some of your good microbes to die off. A diet rich in whole foods, on the other hand, helps them flourish. 


Let's start with the research. 


The foods that you eat are so important to the composition of your gut microbiome that you can see changes after just one day. In one study, researchers found that switching from a fiber-rich, plant-based diet to a more Westernized diet, high in sugar and high in fat, led to changes in the gut microbes after just ONE day. 

The changes go the other way, too. Researchers have found that if you start to eat more fiber, your gut starts to contain more of the good microbes. 

Good microbes love to eat fiber. And they're really good at it too.


You actually need the help of bacteria to digest certain types of fiber. Without these bacteria living in our gut, we just can't digest certain fibers. That can result in pain, along with constipation and/or diarrhea. In fact, it's believed that some cases of irritable bowel syndrome (IBS) may be due to changes in the gut microbiome resulting in a loss of the "good bacteria." 


The bottom line: To help grow more of the good bacteria in your gut, you have to keep feeding them fiber.  

And that's where prebiotics come in. 

Prebiotic foods: The importance of fruits, vegetables, and whole grains in growing more good gut microbes 

Prebiotics are defined as foods or substances that help encourage the growth of good gut microbes.


Researchers have identified lots of different foods that can be considered prebiotics. The largest category is fiber-rich fruits, vegetables, and whole grains. 

Prebiotic foods supply the fiber that our good microbes love to eat. Foods that are naturally rich in fiber and are great prebiotic foods include many fruits, vegetables, whole grains, and nuts and seeds

The list below is just a sampling of prebiotic foods. There are many, many other fruits, vegetables, and whole grains that contain prebiotic fibers. Some contain more, some contain less, but all are likely to be helpful. 


  • Vegetables: Artichokes, asparagus, leafy greens, onions, jicama, soybeans, legumes

  • Fruits: Bananas, berries

  • Grains: Whole wheat, oats, barley

  • Nuts and Seeds: Almonds, walnuts, flaxseeds

  • Other: Garlic 

Other foods and nutrients can help promote the growth of good bacteria 


The major category of prebiotic foods are foods that are naturally rich in fiber. But research has found that other nutrients found in whole foods may also act as prebiotics. For example, many fruits and vegetables contain polyphenols. These nutrients, such as the anthocyanins that are found in red grapes and red kidney beans, are powerful antioxidants. Research has found that these polyphenols also encourage the growth of good gut microbes. Other nutrients may also act as prebiotics, such as certain fats.

Processed foods labeled as "high fiber": why processed fiber may not be the same as the fiber consumed in vegetables


We've all heard of the benefits of fiber, of course. But that brings up an important question when you're actually in the supermarket staring at a shelf stuffed with "healthy" snack foods.


Is a "high fiber" granola bar good for you in the same way that a bowl of strawberries would be good for you?


They both contain fiber, but researchers have their suspicions about the fiber that's added to processed foods. 


While some granola bars may be naturally rich in fiber (due to ingredients such as lightly processed dates and nuts), other granola bars need factories to make their fiber.


Some manufacturers start with fibers, such as chicory root fiber and inulin, and then pulverize those fibers to create fiber additives. These additives are then added back to the bars. 


Here's the problem: we still don't know whether our gut microbes like these processed fiber additives as much as they like the fiber found in fruits and vegetables. 


Until we know that for sure, I wouldn't recommend that you rely solely on "high-fiber" processed foods to feed your gut microbes. While it's possible that they may be helpful, you'll still need lots and lots of fruits, vegetables, and whole grains. 

Why eating probiotic yogurt every day just isn't the same as eating a wide variety of prebiotic foods: you need a variety of different microbes (and lots of them) for a healthy gut


In a healthy G.I. system, there are many, many different types of microbes. That diversity of microbes is believed to help protect against chronic conditions (I say "believed" because research is ongoing).

However, if you just eat the same few foods day after day, you're not likely to end up with a wide variety of gut microbes. 


That's one of the reasons why experts always emphasize the importance of eating a wide variety of fruits, vegetables, and whole grains. 

Different plant fibers help encourage the growth of different microbes. And a diverse community of microbes is important for our health.

That's why it's so important to eat a wide variety of fruits, vegetables, and grains. 

These different fruits, vegetables, and whole grains each supply a different type of plant fiber. This means that you're feeding different types of gut microbes. And that means that you're growing different gut microbes.


All of which adds up to a more diverse community of microbes residing in your gut. 


The importance of gut diversity is also the reason why just eating a cup of probiotic yogurt every day just isn't enough, by itself, for a healthy gut. 


Many commercially available strains of yogurt contain 1 or 2, or maybe 10, different strains of bacteria. Your gut probably contains over a 1000 different species of bacteria alone. 

In other words, you can't just rely on a cup of probiotic yogurt every day. While that can help, it really is far more important to eat the rainbow: make sure you're consuming a wide variety of fruits and vegetables. 

Good gut microbes help keep your skin healthy

Research over the last decade has really highlighted one important point: our gut health and our skin health are closely intertwined.

For example, researchers have looked at the microbes in the GI tract of children with atopic dermatitis (eczema). 

That research has found that the gut microbes of children with eczema and other allergic diseases is different than that of healthy children. Children with eczema have higher levels of harmful bacteria in their gut, and they also have a less diverse community of microbes in their gut.


Researchers have also looked at other skin diseases. In some skin conditions, they've found a higher incidence of GI symptoms and GI disease. For example, a study  of close to 50,000 patients with rosacea found that these patients with rosacea were at a higher risk of several GI conditions, ranging from small intestinal bacterial overgrowth (SIBO) to inflammatory bowel disease.


For more on how our good gut microbes help our skin, see this page.

Bottom line: foods naturally rich in fiber are good. But how much fiber are we talking about? 

The USDA recommends that women should consume 25 g of dietary fiber a day, and men should consume 38 g of dietary fiber a day.


Between fruits, vegetables, and whole grains, you can get there. But it's not an amount that's easy to achieve if you eat the typical American diet. You may have to make a concerted effort to slowly increase your fiber intake. These recipes that feature chickpeas, red kidney beans, black beans, and lentils are easy ways to start. 

You also don't want to start eating that much fiber tomorrow. 

If your system isn't used to that much fiber, it's important to work your way up gradually. That gives your gut microbes time to get used to digesting that much fiber. It also gives your gut microbes more time to grow and multiply in response to this great new source of their favorite food. (And if you produce a lot of gas right now when you eat beans, it's good to know that eventually your system tends to get used to the fiber in those beans.) And with that increased fiber intake, make sure you're drinking plenty of water. 

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