Dear Doctor: Unless I’m cooking, my boyfriend eats only junk food and fast food. He says it’s no big deal because he’s not overweight and doesn’t have high cholesterol or high blood pressure. Is he right?

Dear Reader: There’s something important missing in your boyfriend’s theory regarding his less-than-stellar eating habits, and that’s the word “yet.” He isn’t overweight and he doesn’t have high cholesterol or high blood pressure -- yet. But decades of research point to the hard truth that a diet that regularly includes what we refer to as junk food is associated with a wide range of unhealthful and even dangerous consequences.

A survey of this research published a few years ago found that eating fast food more than twice a week increased the risk of high cholesterol and high blood pressure, which top the list of risk factors for cardiovascular disease, heart attack and stroke. It also paved the way for insulin resistance, diabetes, certain cancers, intestinal issues, an increased incidence of obesity and even depression.

Scientists in France recently looked at how a diet of junk food and fast food (the researchers refer to these as "ultraprocessed foods") may affect a person’s life span. The study, published in February in the journal JAMA Internal Medicine, examined eight years of dietary data collected from middle-aged volunteers in an ongoing nutritional study in France. Among the findings was a correlation between early death and regularly eating ultraprocessed foods. New information is also emerging about the negative effect of these foods on the gut microbiome, including reducing the numbers and diversity of beneficial bacteria.

So what are ultraprocessed foods? They’re premade and prepackaged foods whose original ingredients have been transformed with flavorings, additives and preservatives. Quite often, ultraprocessed foods achieve their final form via industrial methods like extrusion, molding and milling. The end result is that they’re flavor bombs that are high in salt, fat, sugar and calories, and low on fiber and nutrients. Not only are these foods inexpensive and readily available, the balance of salt, sugar, fat and added flavorings has been purposely engineered by food scientists to be irresistible. There’s even a term for it -- the "bliss point." Small wonder that the bag of cheese puffs or side of french fries is so easy to crave and so hard to put down.

Research shows that the potential ill effects of this type of eating reach the brain as well. Not only are the connections between the neurons in our brains adversely affected by unhealthy diets, so are several molecules related to learning and memory.

All of which brings us back to our original point. If your boyfriend doesn’t shift to healthier eating, it’s just a matter of time before his body begins to pay the price. But he doesn’t have to go cold turkey. When it comes to sweets and "treat" foods, we generally advise our patients to limit them to 20 percent of their total intake. For those with health issues such as hypertension or diabetes, we advise limiting splurges to 10 percent. Change can be hard. If he approaches healthy eating gradually but steadily, it will be easier to succeed.

(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: Those electric scooters that you can rent by the hour have come to our city, and our son, who is almost 18, wants to start riding one to school. My husband thinks it’s OK, but all I see are the different ways he can get hurt. Am I overreacting?

Dear Reader: It may seem like you’re asking a question about transportation, but the rapid spread of motorized scooters has been accompanied by a rising number of injuries to both riders and pedestrians. Here in Los Angeles, we’re at one of the epicenters of the electric scooter phenomenon. That means local emergency rooms and medical practices, ours included, are now seeing a spike in scooter-related injuries, many of them serious.

For anyone not familiar with the concept, several companies now offer electric scooters on a ride-share model. Since last spring, thousands of these rentable scooters have become available in an estimated 90 towns and cities across the country. They have a 15-to-37-mile range on a full charge and can go 15 to 30 mph. All it takes to get started is a credit card, a driver’s license and a smartphone to download the app. Although most companies require riders to be at least 18 years old and to wear a helmet, those rules are mostly self-enforced.

Doctors are now treating scooter-related injuries that are typically associated with vehicular collisions. These range from serious scrapes and cuts that require stitches, to broken wrists, ribs, collarbones, shoulders and noses. Riders who ignore the helmet rule risk head trauma that can leave lasting brain damage. Injuries to pedestrians are not uncommon. Several scooter-related deaths have been reported.

Electric scooters are so new that the tracking of accidents and injuries has not yet begun at either the state or federal level. Scooter companies, meanwhile, have declined to share their data. Emergency medicine departments in some cities, startled by the surge of injuries, have begun keeping their own statistics. An analysis by Consumer Reports found that at least 1,500 people nationwide have been injured in crashes related to electric scooters since late 2017, when the scooters first began to appear. Not all hospitals or law enforcement agencies track scooter accidents yet, so these numbers are certainly low.

Earlier this year, colleagues at UCLA conducted a study into the extent of electric scooter injuries. Among their findings: 80 percent of the injuries they tallied resulted from falls, 11 percent from collisions with objects and 9 percent from collisions with cars, bikes or other scooters. About 40 percent of riders who got hurt suffered head injuries, 32 percent had breaks or fractures, and the rest got away with just cuts, sprains or bruises. When the researchers spent seven hours watching riders at a busy intersection, they found that a stunning 94 percent of riders weren’t wearing helmets.

Because electric scooters are nimble, affordable and, let’s face it, fun, in many cases they’re being approached more as toys than as motor vehicles. If your son does decide to try electric scooter transportation, please make sure he understands the risks, becomes fully educated about best riding practices, and that he always -- and this is non-negotiable -- wears a helmet.

(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: My kids say you’re not supposed to admit it, but I hate to exercise. Running a mile once or twice a week is really the most I can manage. Should I even bother?

Dear Reader: In a word, yes. While it would be great if you enjoyed exercising enough to do more of it more often, intriguing new research suggests that when it comes to physical activity, every little bit helps. In fact, a study conducted on mice at the University of Texas Southwestern Medical Center in Dallas found that just one workout kept the nerve cells in the brain that play a role in metabolism activated for up to two days. The takeaway of that research, which was published in December, is that these neurons respond to even a small amount of activity.

The study focused on two types of neurons, which are part of a brain circuit found in humans as well as in mice. These two neuron types, when activated, have very different jobs. One plays a role in lowering glucose levels, muting appetite and revving up the metabolism. The other neuron type does pretty much the opposite -- it ramps up appetite and puts the brakes on metabolism.

Researchers found that a single vigorous workout amplified the activity of the first neuron type -- that’s the one that reduces appetite, lowers glucose and causes energy output to increase -- for up to two days. At the same time, it suppressed the effects of the second neuron type -- the one associated with an increase in hunger and a downshift in metabolic rate -- for the same amount of time. While this is good news for people like you who prefer a more modest exercise schedule, the study also contained an incentive to be even more active: It turns out that these changes to neural activity lasted even longer in people who exercised more often.

Speaking of frequency, would you be willing to take on just 10 to 15 minutes of exercise per day? Although exercise classes and gym sessions are typically measured in hours, emerging research is showing that short bouts of exercise -- as long as they are done daily -- can yield rewards. A study conducted at Pennington Biomedical Research Center in Louisiana found that sedentary women who walked briskly for just 72 minutes per week -- that’s about 10 minutes each day -- had similar improvement to heart strength and general fitness as did the group that walked almost twice as long.

Another study found that as long as it included at least 60 seconds of high-intensity exercise, a 10-minute workout yielded similar benefits to 45 minutes of steady jogging. And for those who take the long view, numerous studies have associated regular exercise with a lower risk of early death.

When it comes to building on your current level of activity, are there any sports or games you enjoyed in the past and would consider doing again? It doesn’t have to be the same thing every day. Even a 10-minute game of tag with your kids a few times a week will get you moving. Think creatively, and we’re sure you’ll land on a solution. And in the meantime, please do keep running.

(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.)