Dear Doctor: My gym has been closed for months, so I’ve been doing online workouts during the pandemic. A guy in our session keeps talking about something called “fasted cardio,” and how it’s helping him lose fat and gain muscle. What is it? Does it really work?

Dear Reader: The term fasted cardio refers to doing a heart-pumping workout after not eating for a stretch of time long enough to be considered a fast. Often, it’s overnight, which means anyone who has gone for a run or taken a dance class before grabbing breakfast can say they’ve done fasted cardio.

The logic behind the practice lies in the way that our bodies use stored energy. The body’s top choice when it needs energy is glycogen, a form of sugar that is stored in the muscles and the liver. It’s made up of multiple linked glucose molecules, the simple sugars in our blood that are derived from digestion. The body can burn either sugar or fat for energy, but using sugar is both faster and easier, so it uses that first. However, glycogen stores are finite, which is where fasted cardio comes in. The idea is that by the time you’ve gone 10 or 12 or more hours without eating, your body will have worked its way through a good portion of its existing glycogen stockpile. And, since those glycogen stores haven’t yet been replenished with a meal, the body will then be forced to turn to Plan B during your workout, which is to also burn stored fat.

The catch is that, despite the appealing and simple logic, the research into fasted cardio is scant, and the results have been mixed. A study from 2017, which analyzed research into the practice, didn’t find the promised changes to body composition. Another drawback is that, when in a fasted state, the body has another energy option besides fat to make up for the lack of glycogen. We’re talking about protein, with the source being your own muscle tissue. Losing muscle mass is the opposite of what you’re trying to achieve. And, while the big picture of how the body uses energy appears straightforward, it’s actually quite complex. At any given moment, processes such as hormone secretion, enzyme activity and gene activation -- to name just a few -- play a decisive role in fat metabolism. So does the type and duration of the exercise you’re engaging in.

All of which leads us back to our familiar refrain when it comes to diet and exercise. That is, moderation and consistency. Eat a healthy diet, steer clear of junk food and simple carbs, do a mix of aerobic exercise and strength training, and get enough sleep. These will serve you better than trying to game the system with a tricky diet or exercise routine.

For those of you who decide to give fasted cardio a try, be sure that you’re still drinking plenty of water. And don’t forget to eat a balanced breakfast after you’ve finished working out.

(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: A few years ago, you had a column about why it’s important to know CPR. My boyfriend took the Red Cross class, and he actually ended up helping someone once. But what about now, during the pandemic? Is it safe to give or get CPR?

Dear Reader: Considering that a main avenue of transmission of the coronavirus that causes COVID-19 is believed to be respiratory droplets from an infected person, your question about CPR is a timely one.

For anyone unfamiliar with CPR, which is short for cardiopulmonary resuscitation, it’s an emergency procedure performed when someone’s heart has stopped beating. This can occur for many reasons, including heart attack or cardiac arrest due to near-drowning, an extreme allergic reaction, asthma attack, smoke inhalation or poisoning. When initiated at the start of a medical emergency, CPR can double, or even triple, someone’s odds of survival.

The process is made up of three distinct components. First, call 911 and report the emergency. The other two elements of CPR are chest compressions, which are performed on the sternum in a specific rhythm, and mouth-to-mouth rescue breathing. The challenge during the pandemic is the proximity that is required to perform CPR. The rescuer is literally on top of, and just inches away from, the person they are helping. Even without the element of rescue breathing, an exchange of breath during the CPR process is likely. Regarding rescue breathing, only someone who is formally trained in CPR should attempt it. And during the pandemic, the Red Cross advises against performing rescue breathing when COVID-19 is either suspected or confirmed.

This leaves chest compressions, which still put people into far closer proximity than the 6-foot distance guidelines we’re all trying to adhere to. To keep both parties as safe as possible from the airborne respiratory droplets or aerosols, the Red Cross has outlined specific procedures. The person performing CPR should wear as much personal protective equipment as possible. This includes respiratory protection, eye protection, disposable gloves and a disposable gown or covering of some sort. Although N95 masks are optimal, they remain in very short supply. A properly fitted mask made of multiple layers of fabric is an acceptable substitute. The person receiving CPR should be outfitted with a mask as well. If only one mask is available, the Red Cross recommends using it on the victim.

Part of performing CPR is assessing whether or not the victim has begun to breathe on their own. At this time, the Red Cross is asking rescuers to do a visual assessment rather than listening or feeling for breath. Taking this precaution can decrease the risk of transmission of the virus. People trained in CPR have been taught that using rescue breathing when cardiac arrest follows a breathing problem, such as choking, a drug overdose or near-drowning, often leads to a better outcome. However, due to the risk of viral transmission, it is now recommended that compression-only CPR be administered until paramedics arrive in response to your 911 call.

(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: I saw on the news that if you work out for 11 minutes a day, you are protected from the bad stuff that happens from sitting too much. Is that really true? I’m stuck at my desk all day, and that’s not changing anytime soon.

Dear Reader: We think you’re referring to a recent study, published in the British Journal of Sports Medicine, which looked at the health outcomes of people whose lifestyles ranged from extremely sedentary to moderately active. According to the findings, even a small amount of daily exercise helped to mitigate the negative health effects of prolonged inactivity.

The conclusions outlined in the study caused quite a splash and have since popped up on TV, newspapers and magazines. And small wonder: Several years ago, research linked prolonged sitting -- that’s eight hours or more per day -- to an increased risk of premature death. With so many jobs, like your own, now tethering workers to their desks, people have become eager for information on how to lessen the ill effects.

This new research, which reexamines data collected in nine previous studies, focused on about 44,000 people who each wore an activity tracker to accurately monitor their daily movement. The participants, who were middle-aged and older, remained seated an average of 10 hours each day. When they did exercise, it consisted of short sessions -- eight to 35 minutes -- often simply walking at a moderate pace.

When the researchers looked at mortality rates in the years after the participants enrolled in the studies, they found the expected link between the people who exercised the least and an increased risk of premature death. The surprise came when quantifying just how much exercise it took to reverse the trend toward an earlier death. The answer was the 11 minutes of daily exercise that grabbed your attention in the news story you saw. It’s important to note that those 11 minutes of exercise did not, as you said in your question, completely erase the ill effects of prolonged sitting. However, the findings of the study do suggest that even a small amount of exercise appears to confer health benefits.

An important conclusion in the study, which headline writers didn’t get quite so excited about, is that the magic number when it comes to exercise appears to be 35. That is, the greatest benefit comes when someone engages in moderate exercise for at least 35 minutes per day. That’s actually in line with the current guidelines put forth by the Department of Health and Human Services. Specifically, at least 150 minutes of moderate aerobic activity, or 75 minutes of vigorous aerobic activity, spread out over the course of a week. Interestingly, several studies have suggested that those 35 minutes of exercise don’t have to happen all at once. Rather, they can be split up into several sessions throughout the day and still yield a similar benefit. That’s encouraging news for people who think they don’t have time to exercise. Let’s all celebrate by getting up out of our chairs right now and taking a brisk 10-minute walk.

(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.)