For decades, eating disorders were thought to afflict mostly, if not exclusively, women and girls. In fact, until 2013, the loss of menstruation had long been considered an official symptom of anorexia nervosa.

Over the last decade, however, health experts have increasingly recognized that boys and men also suffer from eating disorders, and they have gained a better understanding of how differently the illness presents in that group. A small but growing body of scientists and physicians have dedicated themselves to identifying the problem, assessing its scope and developing treatments.

Recently, two of these experts spoke to The New York Times about how the disease is affecting adolescent boys, what symptoms and behaviors parents should look for, and which treatments to consider. Dr. Jason Nagata is a pediatrician at the University of California, San Francisco, who specializes in eating disorders; he is senior editor of the Journal of Eating Disorders and editor of the book “Eating Disorders in Boys and Men.” Dr. Sarah Smith is a child and adolescent psychiatrist at the University of Toronto who specializes in eating disorders; she was the lead author on a study published in JAMA Open Network in December that showed sharp increases in the rates of hospitalizations for boys with eating disorders.

The conversation was condensed and edited for clarity.

The medical and scientific understanding of eating disorders is changing and expanding. What happened?

Dr. Smith: Historically, eating disorders have been conceptualized mostly as anorexia, which has been portrayed as an illness of adolescent females who want to lose weight for aesthetic reasons.

Dr. Nagata: There’s increasing recognition, particularly in the last decade or so, that some people with body image dissatisfaction are not trying to lose weight at all. Some men and boys are trying to become large and muscular. In fact, one-third of teenage boys across the United States report that they’re trying to bulk up and get more muscular. And a subset of those may develop eating disorders or muscle dysmorphia that can lead to significant psychological distress and physical health complications.

What is muscle dysmorphia?

Dr. Nagata: Also known as bigorexia or reverse anorexia, it’s a disorder where someone thinks that their body is puny or not muscular enough, even if objectively they would be considered fit or athletic by other people.

Dr. Smith: It might be because they want to be fitter for hockey, or because they want to be more muscular or “cut” from an appearance point of view. The motivation that might guide these behaviors might not align with being thinner, but we still see very similar behaviors. We see the obsessive exercise. We see eliminating certain types of food. We see marked dietary restraint. And then there are those who choke or vomit, become afraid of that, or have always been picky eaters and fall off their growth curve. And because kids and teenagers are growing and developing so quickly, those changes can lead to quite serious medical complications.

These complications can lead to a starvation state. What does that mean?

Dr. Smith: It is a mismatch between someone’s energy or nutrient needs and what they’re actually putting into their body.

Dr. Nagata: When your body is constantly exerting more energy than it is taking in, that can lead to a starvation state where your vital organs begin to shut down because they don’t have enough energy to sustain themselves. And I think it’s underrecognized that starvation can happen among people who exercise too much without getting enough nutrition.

So, is there an overlap here when it comes to boys and athletics?

Dr. Smith: Yeah, absolutely. I think boys who are athletes have a higher risk of eating disorders, because to some extent, some of these behaviors are normalized in competitive sports.

Dr. Smith: When it comes to the relationship between overexercise, undereating and physical consequences among athletes with eating disorders, we actually have a term called the “female athlete triad.”

What are the components of the female triad?

Dr. Smith: Weight loss, changes in bone density and amenorrhea, which is when females aren’t menstruating. It is another example of our gendered bias and how we approached this illness.

Dr. Smith, you’ve done some of the most up-to-date research on eating disorders, including the finding that eating disorders severely impact boys.

Dr. Smith: I looked at over 11,000 hospitalizations in Ontario for eating disorders of children and adolescents aged 5 to 17 from 2002 to 2019. What I found was that while rates of hospitalization increased overall by 139 percent, the largest relative increase was among males: Their rate of hospitalizations rose 416 percent. Common causes of hospitalization would include indications like very low heart rate, abnormal markers of minerals in their blood or suicidal ideation.

To what extent is your research in Canada suggestive of what’s happening in the United States?

Dr. Nagata: I would imagine our trends are pretty similar. We have a recent study that focused on boys who were hospitalized for eating disorders in the United States. We found that, compared to girls who are hospitalized, boys actually have more severe medical complications. Boys have longer hospital stays, greater heart-rate abnormalities, and higher rates of anemia than girls. That may partly reflect that boys are often identified or diagnosed later.

What do you think is responsible for the growing incidence of eating disorders and hospitalizations among boys?

Dr. Nagata: There is a genetic component, a biological component, and there are also social and environmental factors. Overall, one of the biggest changes has been the advent of social media, where not only are young people consuming body ideals from the media, but they feel pressure to produce content and display their own bodies on social media. And I think that has added a lot of pressure.

When you meet an adolescent male with an eating disorder, do they recognize their behavior as unhealthy?

Dr. Smith: Most of the time, eating disorders tend to be characterized by a lack of insight. Young people don’t appreciate the risks of the behaviors they’re engaging in. Often, they present for care because their parents or teachers or coaches or others become concerned first. I’ve had young people on cardiac monitors who argue with me and say they’re not that unwell, they’re not that skinny, and that we’re all overreacting around them.

As parents, we try to encourage healthy eating and fitness, and try to offset excessive screen time. How can we tell when fitness has gone too far?

Dr. Nagata: For people who develop eating disorders or muscle dysmorphia, exercise can be taken to the extreme and can cause more worry and preoccupation than enjoyment. So, to me, the red flags for parents are if their son starts to obsess or become preoccupied with the gym and fitness in a way that worsens their social life, school functioning and daily functioning. Those are instances when excessive exercise can tip over into the world of disorder.

What do you advise for parents who worry that their son might have an issue?

Dr. Smith: The challenge with eating disorders is that we know that the longer the issue is not treated, the worse the outcome. There’s a natural inclination to not be intrusive or to risk making things worse, but I think the earlier parents respond, the better. The risks of overreacting are small given the very real risks of eating disorders. I would recommend that parents reach out to their primary care provider. I also think that if parents want to learn more, there are good online resources.

Dr. Nagata: Primary care is often the best place to start, because they can do an initial screening and assessment, check vital signs and labs, and then provide appropriate treatment and referrals as needed. The most common reasons for referral that we get in our eating-disorders specialty clinic is from a primary care doctor seeing a teenager for their regular checkup and noticing a significant change in weight or unstable vital signs or labs.

What else would you add?

Dr. Nagata: We need to raise awareness of eating disorders and body image issues in boys because it’s been traditionally so underrecognized, underdiagnosed and undertreated. I think it’s also important to note that eating disorders can affect people of all genders, races, sexual orientations, ages and sizes.

Dr. Smith: On an optimistic note, with access to evidenced-based treatment — the earlier the better — people can recover. Although it’s a horrific illness, there is hope in this journey.