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The Ketogenic Diet and Your Gut Health

by previlli

How does this popular weight loss diet affect your gut bacteria and gut health?

If you follow diet trends — and even if you don’t — you’ve probably heard of the ketogenic diet (or keto diet).
The highly popular keto diet is a high-fat/low-carbohydrate diet. The idea is to reduce glucose in your diet to such low levels that your body is forced to use fat as its primary fuel source. Typically, people following keto strive to consume 75 percent of their calories from fat, 20 percent from protein, and no more than 5 percent from carbohydrates.[1]
The original purpose of the keto diet was to control epilepsy, and it has shown positive effects on this and other neurological disorders, such as autism and Alzheimer’s.[2] But now the keto diet is popular for a new purpose — weight loss.

Many people have found success losing weight with keto, but there may be a catch. Recent research indicates the keto diet may negatively affect gut bacteria and gut structure. And since we know that gut health is the gateway to overall health, that’s a pretty big catch.

What Keto’s Missing

Being carb-thrifty, the keto diet is low in carby things — not just sweets and treats, but also healthy carbs like whole grains, fruits, and vegetables. That’s a problem, because the good bacteria in your gut[3] like to feast on two things: fiber and polyphenols (a type of phytonutrient). Both of these prebiotics are found in whole grains and produce.
The lack of phytonutrients and fiber in the keto diet, as well as the presence of high levels of fat, can lead to a loss of microbial diversity and richness in the gut. In other words, you have fewer total gut bacteria (also called gut flora) and fewer species of gut bacteria. That’s no small consequence, because different species of gut bacteria improve your health in different ways. Just like developing a guest list for a party, you need a good mix. 
Another way the keto diet may impact gut health is by changing its structure.

Keto and Your Gut Structure

Your gut is a long, hollow, twisty tube that runs from your mouth to your anus. Whatever enters this pipeline is meant to be kept segregated from the rest of your body, except for the nutrients your digestive system carefully collects and delivers to your bloodstream to nourish you. 

If other things, like undigested food or bacteria, penetrate your gut barrier and roam through your body, they can cause all kinds of health issues — everything from cardiovascular to immune to respiratory problems. It’s like when a car strays into the wrong lane on a busy highway. The results can be devastating.
High-fat diets can increase the permeability of your gut barrier in several ways. First, they increase species of bacteria that disrupt the gut barrier, so there are more enemy soldiers trying to make their way through. Second, they dial up inflammation, which loosens the tight junctions that knit together the cells of your gut barrier. And third, they damage the mucus layer that lines the gut barrier, so it’s less effective at trapping germs and toxins.[4]

Not All Fats Are the Same

But it’s important to keep in mind that different kinds of fats have different effects on gut bacteria and gut structure. Let’s take a closer look at four kinds of fats:
Saturated Fats: 
These fats are found in red meat, dark poultry meat, lard, and full-fat dairy foods such as milk, butter, cheese, sour cream, and ice cream. They also occur in tropical oils, such as coconut oil, palm oil, and cocoa butter. Eating a diet high in saturated fats is linked to lower microbial diversity and richness.[5] Saturated fats are also linked to increases in gut permeability.[6]

Monounsaturated Fats:
Foods you’ve been told have healthy fats — nuts, avocado, canola oil, olive oil, peanut oil, and peanut butter — are all high in monounsaturated fats. The research on how these fats affect gut bacteria is a mixed bag. Some studies find they lower levels of beneficial bacteria, but others don’t.[7][8] While the jury is out on how monos affect the gut microbiota, there’s plenty of research showing they benefit cardiovascular health, so keep drizzling that olive oil!
Polyunsaturated Fats (Omegas): 
Salmon and other fatty fish, walnuts, flaxseed, chia seed, hemp seed, and seaweed are all good sources of omega-3 fatty acids. Omega-3s are good for your heart and your brain. If you’re on keto, there’s more good news — they get along pretty well with your gut bacteria.[9][10] Even better, animal research suggests omega-3s can help repair the damage to the gut barrier inflicted by a diet high in less healthy fats.[11]
Trans Fats:
If omega-3s are the superheroes in the world of fats, trans fats (found in shortening, margarine, vegetable oil, and fried foods) are the villains. These unhealthy fats cause runaway inflammation, which can lead to heart disease, diabetes, and other metabolic problems. So it’s no surprise preliminary research suggests that in addition to all this mischief, trans fats also increase harmful bacteria in the gut and decrease beneficial bugs.[12]

Why You Need Healthy Gut Bacteria

A healthy population of microbes is good for your gut and for your overall health.

Your gut bacteria support efficient and comfortable digestion and elimination. They harvest the nutrients from your food and even make some vitamins on their own. They produce short-chain fatty acids (SCFAs) that give you energy. And they make sure waste leaves your body at the right speed — not too quickly (diarrhea) or too slowly (constipation). 
If keeping your gastrointestinal tract in good working order was all gut bacteria did, they’d still be vital. (Anyone who’s experienced digestive difficulties can attest to that.) But they do a lot more.  
Good bacteria:
  • Support your immune system, by producing the chemical messengers it uses to facilitate communication among your white blood cells.
  • Keep inflammation from getting out of control, by helping balance the immune response.
  • Stop harmful bacteria from colonizing your gut, by crowding them out.
  • Help your gut and your brain “talk” to each other through the gut-brain axis. 
  • Enhance your cognition and boost your mood, by making neurotransmitters like serotonin, dopamine, and norepinephrine. 
  • Regulate bodily processes, by churning out hormones — including digestive hormones and sex hormones.

How to Keep Your Gut Bacteria Happy

Your gut bacteria do a lot for you — they want just a few things in return. These are good gut health tips for everyone, but they’re especially crucial if you’re following the keto diet.

  • Feast on Fermented Foods: Fermented foods contain beneficial bacteria, so eating them is a great way to repopulate your gut with the good guys. Most studies have been conducted on yogurt and other cultured dairy products, but sauerkraut, kimchi, pickles, tempeh, miso, and kombucha are also fermented.[13][14] Certain cheeses also contain probiotics, including cottage cheese, Gouda, some cheddars, and Parmesan. The friendly bacteria in Parmesan[15] have been shown to survive digestion and colonize the gut.[16]
  • Pass the Prebiotics: If you want beneficial bacteria in your gut, make sure to serve them snacks. Prebiotics are supplements of fiber and/or polyphenols that bacteria like to eat. (Everyone knows folks stay at a party longer if there are good eats.)
  • Pile Your Plate with Plant Protein: Trying to get more of your protein from plants may be a good way to protect your gut health. Several studies show that plant protein — like mung beans and peas — may improve the ratio of good guys to bad guys in your gut.[17][18] That could hold true for other types of plant protein, such as tofu, tempeh, lentils, chickpeas, and black beans.
  • Optimize Your Omega-3/6 Ratio: Most people eat too many omega-6s and not enough omega-3s. You can rebalance your omega-3 to omega-6 ratio by avoiding vegetable oils (and the processed foods that contain a lot of them); getting your omega-6s from healthful sources such as poultry, eggs, almonds, and whole grains; and eating omega-3-rich fatty fish or walnuts frequently.[19] Like plant protein, omega-3s seem to be gut bacteria-friendly.[20]
  • Avoid Artificial Sweeteners: There’s increasing evidence that artificial sweeteners, such as Ace-K and sucralose, are bad news for good bacteria.[21][22] Stevia, a more natural alternative, may be a safer choice; however, more research is needed to be sure.
  • The keto diet isn’t for everyone. A lot of people find it hard to stick to such a strict eating plan for the long term. But other folks swear by it. So if you’re intrigued and you want to give it a try, do it right by taking steps to care for your gut microbiota. If you keep them happy, they’ll return the favor.
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