Dear Doctor: I’ve been doing paleo for a month, and I have lost 12 pounds. Now my mom is talking about a new study that says the diet is not good for your heart. Can you explain? Do you think it’s the same for keto?

Dear Reader: You’re referring to two popular approaches to weight loss that have captured the attention of many dieters. For those who may not be familiar with these eating plans, both entail limiting carbohydrate intake in some way. They also include a focus on proteins -- typically poultry, meat, fish and eggs -- as well as fats.

The paleo diet -- that’s short for Paleolithic -- relies on the nutrients that would have been available to our ancient ancestors through hunting and gathering during the Old Stone Age era. It eliminates foods obtained by farming and herding, such as legumes, grains and dairy products. The diet dates back to the 1970s, but it boomed in popularity beginning in 2002 after the publication of a paleo diet book. The paleo diet includes lean meats and fish, and limited amounts of certain fruits, vegetables, nuts and seeds.

The ketogenic diet, shortened to keto, was developed in the 1920s to manage some kinds of epilepsy. It recommends that fats account for 55% to 60% of daily nutrient intake, and that carbs make up no more than 10% of the daily diet. This leaves the remaining 30% to 35% of calories for protein.

Both diets trigger a metabolic process known as ketosis, which occurs in the absence of adequate carbohydrates, the body’s go-to energy source. It’s a lot more complex than we have time for in this column, but the bottom line is that when in ketosis, the body burns stored fat for energy.

Due to widespread interest in paleo and keto diets, and because each restricts various foods with essential nutrients, including vitamins, minerals, micronutrients and fiber, researchers are taking a closer look. Your mother is referring to a study published last summer in the European Journal of Nutrition. Scientists monitored the gut microbiomes of 45 people following the paleo diet, and compared them to a control group eating a balanced diet. After one year, the paleo group had significantly higher levels of a molecule known as TMAO (for fellow science nerds, that’s trimethylamine N-oxide), a marker associated with heart disease. The diversity of the gut microbiomes of the paleo group was also adversely affected.

Given the restrictive nature of these diets, as well as their high levels of meat and saturated fats, the results of the study are not surprising. This particular research didn’t look at the keto diet, but other studies have pointed to similar long-term health risks. In the short-term, however, we think low- and no-carb diets can be useful tools. We have seen this among our own patients, who use a low-carb approach to jump-start weight loss. We recommend that they minimize animal and saturated fats and instead focus on lean meats, seafood and plant-based fats, and then gradually transition to a well-rounded and sustainable diet.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Dear Doctor: Our family is worried; my 18-year-old grandson won’t give up vaping. How many people have gotten sick? We just read about something called popcorn lung. What is that?

Dear Reader: Ever since the first cases of vaping illness were made public last August, the outbreak has made front-page news. The Centers for Disease Control and Prevention, one of several federal agencies monitoring the outbreak, publishes regular updates about the number of cases of vaping illness, as well as the deaths it has caused. As of December, at least 2,400 hospitalizations due to lung injuries associated with vaping have been reported to the CDC from all 50 states, Puerto Rico and the U.S. Virgin Islands. At least 52 people in 26 states and the District of Columbia have died. Doctors and surgeons compare the lung injuries they’re seeing to the kinds of chemical burns usually associated with industrial accidents.

But statistics can be a hard sell, particularly for teenagers. Maybe the case of a 17-year-old boy in Detroit, who recently underwent a double lung transplant after falling ill from vaping, will help make the risks seem more real.

One of the striking things about the outbreak is the number of rare lung conditions doctors are now diagnosing. One of these is hard-metal pneumoconiosis, commonly referred to as “cobalt lung.” It’s a form of pneumonia usually seen in people with long-term exposure to the airborne particulates caused by metal grinding.

Another is bronchiolitis obliterans, or “popcorn lung,” which is the disease you’re asking about. The nickname arises because the disease is linked to a butter-flavored chemical called diacetyl, which was once used in the manufacture of microwave popcorn. This rare form of bronchitis causes the tiny airways within the lungs, known as bronchioles, to become inflamed. This results in tissue damage, including scarring, which thickens and blocks the airways.

Symptoms of popcorn lung include a persistent dry cough and shortness of breath, which become more pronounced during exertion. Additional symptoms can include fatigue and wheezing that are not associated with asthma or illness. Diagnosis often begins with tests to determine lung function. Since chest X-rays can often appear normal in the early stages of the disease, high-resolution imaging tests such as a chest CT scan are often used. There is no cure at this time, so treatment focuses on managing symptoms to slow the progression of the disease. Depending on the individual case, this can include medication to lessen the body’s immune response and to ease inflammation. Antibiotics, cough suppressants and supplemental oxygen may also be used. In extreme cases, a lung transplant may be necessary.

Fortunately, there is also good news. Statistics show that the pace of the vaping illness outbreak is slowing. In addition, research now points to black-market vape products as a source of many of the lung injuries. Still, very little is known about the long-term effects of any kind of vaping. Unless they’re using legitimate products in order to stop smoking, we recommend that our patients don’t vape. The risks of this as a recreational practice are just too great.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)

Hello, dear readers! We hope this new year is finding you happy and healthy, and that the expectations of the holiday season didn’t take their toll. Whether it’s a moment of meditation, a quiet cup of tea, or a romp with the family dog, always remember to take some time for yourselves. And now, onward to your letters.

-- In response to a column about an inflammatory condition known as polymyalgia rheumatica, or PMR, several of you wondered if changes to diet may be helpful. This condition causes pain and stiffness in the muscles and joints, most often in the neck and shoulders, but also the hips, thighs and lower back. Treatment includes corticosteroids, such as such as prednisone, and pain meds, such as ibuprofen and aspirin.

Research shows that lifestyle changes, including a diet to lower inflammation, can also help ease symptoms. One of the goals in this type of eating is to stabilize insulin levels. That translates to a diet low in added sugars and simple carbohydrates and rich in a variety of colorful, nonstarchy vegetables. Steer clear of alcohol, processed foods, fried foods and processed meats. Harness the anti-inflammatory properties of omega-3 fatty acids with fish such as mackerel, sardines and salmon, and flax seeds, chia seeds and leafy greens.

The good news is that this condition is usually temporary. Most people see relief in about a year, although in some cases, it can take longer to resolve.

-- We heard from several of you regarding the column about frozen shoulder. This is a condition in which pain and stiffness in the shoulder joint gradually makes movement difficult or even impossible.

One reader found relief after seeing a chiropractor. “I had one session, and it fixed my frozen shoulder for good,” she wrote. “That was eight years ago, and my shoulder is still fine. Really works!”

Another reader, whose doctor proposed a surgical fix, sought acupuncture instead. “After one treatment, I could lift (my arm) straight up as high as ever with no pain,” he wrote. “It would save a lot of people a lot of pain if everyone knew about acupuncture.”

-- A recent column in which we discussed the benefits of breathing through the nose rather than the mouth prompted this question from a reader: “What about people who sleep with their mouths wide open?” she asked. “They don’t have any control over how they are breathing.” Many people breathe through their mouths at night due to mild sinus blockage. Blowing one’s nose before bed, using a neti pot or saline nasal spray, adjusting sleep position, elevating the head, and using over-the-counter nasal or mouth strips can each be helpful. In some cases, mouth breathing can be a symptom of obstructive sleep apnea. This is a serious sleep disorder, and it requires medical care.

As always, thank you for your letters. We’re so glad you enjoy the column and find it useful. We love that you keep our mailboxes -- both snail mail and email -- full, and we look forward to hearing from you next month.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o UCLA Health Sciences Media Relations, 10880 Wilshire Blvd., Suite 1450, Los Angeles, CA, 90024. Owing to the volume of mail, personal replies cannot be provided.)