Dear Doctors: I am a vegan, and after a meal, I have uncomfortable and smelly intestinal gas. It has only ever eased when I took an antibiotic and after colonoscopy prep. I assume that’s because these killed my gut bacteria. Is there a fast way to reset the gut? Is this problem a health risk?

Dear Reader: The gut microbiome refers to the remarkable and complex ecosystem of trillions of bacteria, fungi, viruses and other microorganisms that make their home in our gut. While some are found in the small intestine, the vast majority live in the large intestine. Research continues to uncover new ways that the composition, diversity and health of these colonies of microorganisms affect our health. The microbes we host have a direct influence on diverse processes such as digestion, nutrient absorption, cardiovascular and neural health, immune response and even brain health and function.

You are correct that a primary cause of intestinal gas is the metabolic activity of bacteria in the gut. It has to do with dietary fiber, which is a complex carbohydrate. Unlike simple carbs, which get absorbed into the bloodstream in the small intestine, fiber passes undigested into the colon, or large intestine. There, the cellulose, pectin, lignin, hemicellulose, mucilage and other cell remnants that survived the digestive process become food for the resident bacteria.

First, enzymes produced by the bacteria dismantle the complex carbs. Then, through fermentation, the resulting simple sugars get processed into short-chain fatty acids the bacteria can absorb. One of the byproducts of that fermentation is -- you guessed it -- intestinal gas.

In your case, several considerations come to mind. As a plant-forward vegan, your diet contains a significant amount of plant-based fiber. Cruciferous vegetables such as broccoli, cabbage and cauliflower; foods that contain sulfur such as garlic and onions; and beans and legumes are associated with robust and sometimes smelly gas production. Some vegans who experience excessive gas find it useful to subtract, then gradually reintroduce, specific foods to help identify any that may be problematic. Some people then choose to limit or eliminate those foods.

It’s true that antibiotics and colonoscopy prep can significantly alter the balance of intestinal flora. Research shows that, when used only occasionally, antibiotics don’t cause lasting damage. Gut recovery can take anywhere from several weeks to a few months, so be patient. You can boost your gut recovery by eating dietary fiber from a wide range of sources. This can also temporarily increase intestinal gas.

Excessive gas production is not a health risk. It can sometimes be a symptom of an underlying disease or condition such as Crohn’s disease, irritable bowel syndrome (IBS), ulcerative colitis or small intestinal bowel overgrowth (SIBO). If changes to your diet don’t have a beneficial effect on gas production, check in with your health care provider for guidance.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Kansas City, MO 64106; 816-581-7500

Dear Doctors: I am 68 years old, and I am going to need a hip replacement. I’ve been reading about it, and some people say that you can prepare yourself physically so that you will do better after the surgery. Do you know if this works? If so, what do you need to do, and when?

Dear Reader: This approach to surgery is known as prehabilitation, or prehab. While rehabilitation (rehab) focuses on recovery after orthopedic surgery, prehab focuses on preparing before surgery. The idea is that increasing physical strength and stamina can lead to a better and faster post-surgical recovery.

In hip replacement surgery, the damaged portions of bone and cartilage in the hip joint are removed. The surgeon then replaces them with new implants made of a combination of metal, ceramics and polymers or plastics. After surgery, patients often deal with limited mobility and decreased muscle strength. This is particularly true in early recovery.

Research into prehab has shown it can help patients recover strength and range of motion more quickly than those who don’t prepare. This, in turn, gets them on their feet and mobile in a shorter time frame. Prehab has also been shown to reduce the need for follow-up inpatient care.

A prehab program for hip replacement often begins six to eight weeks before surgery. It should be done with a physical therapist, who will begin with an in-depth assessment. This is important because the pain and limited range of motion that trigger the need for a hip replacement often affect the biomechanics of how you walk, sit, stand and move. Exercises typically focus on strengthening the muscles of the back, legs and core, and include a cardio component to improve stamina. It can also be helpful for people to learn about the exercises they will perform following their surgery.

Some prehab programs include guidance on how to prepare your home for a safe recovery. This includes removing tripping or slipping hazards, such as area rugs, electrical cords or ground-level decor. Another important part of prehab is selecting and learning how to use the support and stability devices you will need in the early days of recovery. These may be crutches, a walker with or without wheels, or a walking cane. Not surprisingly, diet also plays a key role. You can boost your body’s ability to heal by getting plenty of lean protein, fatty fish, fresh vegetables, leafy greens and fruit; cooking with healthy oils; limiting alcohol; and avoiding ultra-processed foods and added sugars.

The data show that people who complete a prehab program can have a faster recovery with less pain, less downtime and less need for post-operative care. If you would like to prepare for your own surgery with a prehab program, ask your doctor to recommend a physical therapist with experience in prehab.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Kansas City, MO 64106; 816-581-7500

Dear Doctors: My ex-husband had a certain musty smell before he was diagnosed with Parkinson’s disease. Now my current husband has that same smell, and I’m worried he has Parkinson’s, too. Radon is a problem here in Tennessee, and I’ve heard it’s connected to Parkinson’s. Why isn’t this public knowledge?

Dear Reader: In recent columns, we have written about the health risks of exposure to radon gas, some unusual symptoms of Parkinson’s disease, and the biochemistry behind a distinct and musty scent that sometimes occurs in the skin of older adults. Your letter intrigued us with a discussion of all three.

Parkinson’s disease is a progressive neurodegenerative disorder. It changes the region of the brain associated with muscle movement and other functions. These result in a deficit of dopamine, a neurotransmitter crucial to smooth, sustained and deliberate movement. The steady decrease in dopamine production causes the primary symptoms of Parkinson’s. These include muscle rigidity, slowed movement, tremors, balance problems, difficulty swallowing and slurred speech.

Like many neurodegenerative conditions, there is no specific test for Parkinson’s disease, which often makes it difficult to diagnose. That’s why, when a woman in Scotland told researchers in 2009 that her husband’s scent changed several years before he was diagnosed with Parkinson’s and that she could recognize that scent in others with the disease, they were intrigued. A decade later, researchers had isolated four compounds specific to the skin secretions of people living with Parkinson’s. The hope is someday these can be used as biomarkers for early diagnosis of the disease.

In a recent column, we explored the age-related changes that can lead to a musty, dusty smell on the skin of older adults. Because the compound that causes the scent is not water-soluble, it can’t be washed off, so it can become quite noticeable. The compound is also easily aerosolized and can infiltrate an entire room. A significant portion of older adults emit this musty smell. By contrast, the number of adults over age 60 with Parkinson’s is far smaller -- about 10 out of every 1,000. A musty scent in older adults does not automatically indicate Parkinson’s disease.

That brings us to radon. A colorless, odorless and radioactive gas, it results from the decay of uranium and radium found in rocks and soil. Radon can seep into buildings through cracks and openings in foundations. Exposure poses health risks, primarily lung cancer. Some regions, including the area in Tennessee you are writing from, are radon hotspots. That makes it particularly important to use a reliable radon detector.

The results of some research have suggested a possible connection between radon gas exposure and neurodegenerative disease, including Parkinson’s. However, a definitive link has not been established. To ease your mind, discuss your concerns with your husband and his health care providers. At the very least, they can perform a baseline assessment to measure against for future neurological changes.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10960 Wilshire Blvd., Suite 1955, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)