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An F may mean failure in school, but the letter earns high marks in your diet. The two biggest dietary Fs — fiber and fermented foods — are top priorities to help maintain healthy digestion, and they potentially offer much more. How can you fit these nutrients into meals? Can this help your overall health as well as gut health?

Fiber, fermented foods, and the gut microbiome

The gut microbiome is a composed of bacteria, viruses, fungi, and other microorganisms living in the colon (large intestine). What you eat, the air you breathe, where you live, and many other factors affect the makeup of the gut microbiome. Some experts think of it as a hidden organ because it has a role in many important functions of the body — for example, helping the immune system function optimally, reducing chronic inflammation, keeping intestinal cells healthy, and providing some essential micronutrients that may not be included in a regular diet.

Your gut communicates with your brain through pathways in the gut-brain axis. Changes in the gut microbiome have been linked with mood and mental health disorders, such as depression and anxiety. However, it’s not yet clear that these changes directly cause these types of problems.

We do know that a healthy diet low in processed foods is key to a healthy gut microbiome. And increasing evidence suggests that fiber and fermented foods can play important parts here.

Fiber 101

Fiber’s main job is to make digestion smoother by softening and adding bulk to stool, making it pass quickly through the intestines.

But fiber has other benefits for your microbiome and overall health. A high-fiber diet helps keep body weight under control and lowers LDL (bad) cholesterol levels. Research has found that eating enough fiber reduces the risk of heart disease, type 2 diabetes, and some cancers.

What to know about fiber

There are two types of fiber: insoluble (which helps you feel full and encourages regular bowel movements) and soluble (which helps lower cholesterol and blood sugar). However, recent research suggests people should focus on the total amount of fiber in their diet, rather than type of fiber.

If you’re trying to add more foods with fiber to your diet, make sure you ease into new fiber-rich habits and drink plenty of water. Your digestive system must adapt slowly to avoid gas, bloating, diarrhea, and stomach cramps caused by eating too much too soon. Your body will gradually adjust to increasing fiber after a week or so.

How much fiber do you need?

The fiber formula is 14 grams for every 1,000 calories consumed. Your specific calorie intake can vary depending on your activity levels.

“But instead of tracking daily fiber, focus on adding more servings of fiber-rich foods to your diet,” says Eric Rimm, professor of epidemiology and nutrition at Harvard’s T.H. Chan School of Public Health.

Which foods are high in fiber?

Fruits, vegetables, legumes, nuts, seeds, and whole grains are all high in fiber. The Dietary Guidelines for Americans has a comprehensive list of fiber-rich foods and their calorie counts.

What about over-the-counter fiber supplements that come in capsules, powders that you mix with water, and chewable tablets? “If you have trouble eating enough fiber-rich foods, then these occasionally can be used, and there is no evidence they are harmful,” says Rimm. “But they should not serve as your primary source of dietary fiber.”

Fermented foods 101

Fermented foods contain both prebiotics — ingredients that create healthy changes in the microbiome — and beneficial live bacteria called probiotics. Both prebiotics and probiotics help maintain a healthy gut microbiome.

What to know about fermented foods

Besides helping with digestion and absorbing vital nutrients from food, a healthy gut supports your immune system to help fight infections and protect against inflammation. Some research suggests that certain probiotics help relieve symptoms of gut-related conditions like inflammatory bowel disease and irritable bowel syndrome, though not all experts agree with this.

Many foods that are fermented undergo lacto-fermentation, in which natural bacteria feed on the sugar and starch in the food, creating lactic acid. Not only does this process remove simple sugars, it creates various species of good bacteria, such as Lactobacillus or Bifidobacterium. (Keep in mind that some foods undergo steps that remove probiotics and other healthful microbes, as with beer or wine, or make them inactive, like baking and canning.)

The exact amounts and specific strains of bacteria in fermented foods vary depending on how they are made. In addition to probiotics, fermented foods may contain other valuable nutrients like enzymes, B vitamins, and omega-3 fatty acids.

How often should you eat fermented foods?

There is no recommended daily allowance for prebiotics or probiotics, so it is impossible to know precisely which fermented foods or quantities are best. The general guideline is to add more to your daily diet.

Which fermented foods should you choose?

Fermented foods have a range of tastes and textures because of the particular bacteria they produce during fermentation or that are added to foods. Yogurt is one of the most popular fermented foods (look for the words “live and active cultures” on the label). Still, many options are available if you are not a yogurt fan or want to expand your fermented choices. Kimchi, sauerkraut, kombucha, and pickles are a few examples.

As with fiber, probiotics are also marketed as over-the-counter supplements. However, like all dietary supplements, they do not require FDA approval, so there is no guarantee that the types of bacteria listed on a label can provide the promised benefits — or are even in the bottle. “Therefore, it is best to get your probiotics from fermented foods,” says Rimm.

To learn more about the value of fiber, fermented foods, and a healthy gut microbiome, listen to this episode of the Food, We Need to Talk podcast, “Understanding the Microbiome.”

About the Author

Matthew Solan, Executive Editor, Harvard Men's Health Watch

Matthew Solan is the executive editor of Harvard Men’s Health Watch. He previously served as executive editor for UCLA Health’s Healthy Years and as a contributor to Duke Medicine’s Health News and Weill Cornell Medical College’s … See Full Bio View all posts by Matthew Solan

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

In parts of the United States and Canada, warming temperatures driven by climate change may be contributing to a rise in tick-borne illnesses. Ticks are now thriving in a wider geographic range, and appearing earlier and sticking around later in the shoulder seasons of spring and fall. That means we need to stay vigilant about protecting ourselves against ticks that cause Lyme disease and other illnesses — even during winter months in many warmer states and provinces.

Here’s a timely reminder about why preventing Lyme disease is important, and a refresher on steps you can take to avoid tick bites.

What are the symptoms of Lyme disease?

Lyme disease is best known for its classic symptom, a bull’s-eye red rash that appears after a bite from an infected tick (scroll down to see photos of classic and non-classic rashes). However, 20% to 30% of people do not develop a rash. And a rash can be easy to miss because ticks tend to bite in dark body folds such as the groin, armpit, behind the ears, or on the scalp. Some people have flulike symptoms such as a headache, fever, chills, fatigue, and aching joints. So if you notice a rash or have these symptoms, call your doctor for advice. At this stage, prompt antibiotic treatment can wipe out the bacterial infection.

When people don’t receive treatment because they didn’t see the rash or didn’t have other early symptoms, the bacteria can spread to different parts of the body. Not only can the bacteria itself cause problems, but the body’s immune system can over-respond to the infection. Either process, or sometimes both, may harm joints, the heart, and/or the nervous system. And some people treated for any stage of Lyme disease develop post-Lyme disease syndrome, which can cause a range of debilitating symptoms that include fatigue, brain fog, and depression.

How to avoid getting Lyme disease

Preventing tick bites is the best way to avoid Lyme disease and other tick-borne illnesses. Blacklegged ticks (also called deer ticks) may be infected with the bacteria that causes Lyme disease. If you live in one of the areas where the incidence of Lyme disease is high, these steps can help.

Know where ticks are likely lurking. Ticks usually crawl up from leaves or blades of grass on the ground to the legs. So be extra careful when walking through fields or meadows and on hikes where you may brush up against bushes, leaves, or trees. Try to walk on well-cleared paths.

Wear protective clothing. Long pants tucked into socks is the best way to keep ticks from crawling up under the pant leg. Lighter-colored clothing can make ticks easier to see.

Use repellents. You can buy clothing that’s pretreated with the insecticide permethrin (which repels ticks). Or you can spray your own clothes and shoes; just be sure to follow the directions carefully. On all exposed skin, use a product that contains DEET, picaridin, oil of lemon eucalyptus (OLE), IR3535, para-menthane-diol (PMD), or 2-undecanone. This search tool from the EPA can help you find a product best suited for your needs. Pay attention to the concentration of active ingredients: for example, at least 20% but not more than 50% with DEET; between 5% to 20% with picaridin; and 10% to 30% with oil of lemon eucalyptus. Many products come in pump spray bottles or as sticks or wipes, which may make them easier to apply where needed.

Get a tick check. After spending time in tick-infested areas, ask a partner to check you for ticks in areas on your body that you can’t see very well. The common bite areas are the back of the knee, the groin, under the arms, under the breasts in women, behind the ears, and at the back of the neck. The tick species that transmits Lyme disease is about the size of a sesame seed. Note that a tick has to be attached to your skin for 24 to 36 hours for it to transmit enough bacteria to give you the disease.

For more information about preventing Lyme disease or living with it, visit the Harvard Health Publishing Lyme Wellness Initiative.

About the Author

Julie Corliss, Executive Editor, Harvard Heart Letter

Julie Corliss is the executive editor of the Harvard Heart Letter. Before working at Harvard, she was a medical writer and editor at HealthNews, a consumer newsletter affiliated with The New England Journal of Medicine. She … See Full Bio View all posts by Julie Corliss

About the Reviewer

Howard E. LeWine, MD, Chief Medical Editor, Harvard Health Publishing

Dr. Howard LeWine is a practicing internist at Brigham and Women’s Hospital in Boston, Chief Medical Editor at Harvard Health Publishing, and editor in chief of Harvard Men’s Health Watch. See Full Bio View all posts by Howard E. LeWine, MD

You probably know that you have a thyroid gland. Perhaps you or someone you know has had thyroid tests or a thyroid disorder such as hypothyroidism.

But did you know you also have a parathyroid gland? It’s true — in fact, most people have four of them, even though one would suffice.

Where are the parathyroid glands?

From the name, you might assume the role of the parathyroid glands is related to that of the thyroid gland. Well, you’d be wrong. The name comes solely from their location: they sit just behind the thyroid gland: two on the right side, two on the left.

The parathyroid glands are small (the size of peas), and can weigh less than a thousandth of an ounce each. Although it’s normal to have four parathyroid glands, about 13% of people have fewer and 5% have more. And some people have parathyroid glands in other locations, such as alongside the esophagus or in the chest. This variation rarely matters, unless surgery is necessary to remove one or more of them.

What do the parathyroid glands do?

Logically enough, parathyroid glands make parathyroid hormone (PTH). And what does PTH do? It has several functions, including:

• Regulating calcium: Calcium is a mineral with many essential roles throughout the body, such as maintaining bone strength, allowing nerves and muscles to function normally, and making sure blood clots as it should. Higher levels of PTH lead to higher calcium levels in the blood through actions on the kidneys and bones.
• Regulating phosphorus: Among other roles, this mineral is a key component of our DNA, bones, and teeth. Phosphorus activates essential enzymes throughout the body, including enzymes necessary for cell reproduction and survival. It also helps with nerve and muscle function.
• Regulating vitamin D: This vitamin is actually a hormone that helps maintain normal levels of calcium throughout the body, by controlling how much gets absorbed from food in the intestinal tract and how much is lost by the kidneys in your urine. Remember PTH? Well, PTH regulates production of the enzyme that converts inactive vitamin D to an active form that helps your gut absorb calcium and reduces the loss of calcium in urine.

PTH released by the parathyroid glands helps keep each of these nutrients in balance. For example, if your blood calcium level falls, your parathyroid glands make more PTH. Higher amounts of PTH prompt bones to release stored calcium into the bloodstream, and also signal the kidneys to pull back on the amount of calcium lost through urine.

What if your blood calcium level rises? Then the parathyroid glands make less PTH, which helps to correct the blood calcium level.

Which diseases involve the parathyroid glands?

The most common are:

• Hyperparathyroidism: This is a condition in which the parathyroid glands make more than the normal amount of PTH. This can be due to a benign or cancerous tumor on a single gland, or due to multiple glands becoming overactive. Or it may be due to some other trigger, such as a low level of calcium in the blood, inadequate vitamin D levels, or kidney failure. When there’s too much PTH, blood calcium levels can become dangerously high and phosphorus levels fall. Surgery may be recommended to remove the overactive gland or glands.
• Hypoparathyroidism: This rare condition is diagnosed when less than the normal amount of PTH is produced. The most common causes are prior neck surgery or radiation, autoimmune disease, or low magnesium levels.
• Parathyroid cancer: Risk factors for parathyroid cancer include certain genetic diseases and prior radiation to the neck.

Why do we rarely hear about the parathyroid glands?

The reason is that most of the time they do their job without fuss or fanfare. Although disorders of the parathyroid glands are not rare, they are just uncommon enough that most people will never hear about them. I think of the parathyroid glands as one of many parts of our bodies that play a huge role in our health, but go unappreciated because they are so good at what they do.

Many other quiet heroes, including the thymus gland, serve as testaments to the remarkable design and function of the human body. Then again, I can think of a few body parts that could be considered expendable.

The bottom line

I hope it’s comforting to know that your amazing parathyroid glands are keeping tabs on your calcium levels and helping your bones, nerves, muscles, and other organs to function normally.

Ounce for ounce, the parathyroid glands may be the most important glands you’d never heard of. Until now.

About the Author

Robert H. Shmerling, MD, Senior Faculty Editor, Harvard Health Publishing; Editorial Advisory Board Member, Harvard Health Publishing

Dr. Robert H. Shmerling is the former clinical chief of the division of rheumatology at Beth Israel Deaconess Medical Center (BIDMC), and is a current member of the corresponding faculty in medicine at Harvard Medical School. … See Full Bio View all posts by Robert H. Shmerling, MD