Each week, MyHealthNewsDaily asks the experts to answer questions about your health.

This week, we asked mental health experts: How can you tell if someone has an eating disorder?

The experts noted that the diagnosis of any mental illness should be left to professionals. Still, there are some signs to look for. Here's what they said.

Sondra Kronberg, a nutrition therapist and spokesperson for the National Eating Disorders Association:

Eating disorders should be taken seriously. They are serious medical and mental health conditions that could potentially be fatal. 

Most eating disorders are triggered by someone deciding to go on a diet. It becomes no sugar, no fat, or whole food groups could be eliminated. It really depends on what you believe, what piece of information you take to an extreme: I'm not going to eat any bread, or I'm not going to eat anything with salt on it, for example.

Irregular appearance or disappearance of food in the household can indicate an eating disorder, as can a new anxiety around particular foods. Look for whether a person has changed their thinking around food: talking constantly about food, weight or calories if they never really talked about those subjects before. Or if a person who was once not picky becomes inflexible about the type or amount of food they eat.

Overexercising is one sign that gets overlooked in this culture. Rapid or extreme weight loss or gain is another sign of an eating disorder. As is when people eat beyond eating for huger or appetite but instead start eating because of emotions.

Changes in ability to focus, communicate or socialize are a sign. If you're starving your brain or undernourishing it, it doesn't perform well.

The other symptoms could be isolating yourself or disappearing before or after meals, or the inability to eat with other people.

An eating disorder is about something that's going on psychologically that gets played out in body image and food behaviors. In anorexia, in their minds people are thinking: 'I'm not good enough, I shouldn't have this, I don't deserve this.' So they play that out with food. It's not that the thought is 'I'm not hungry' it's that 'I shouldn't eat.'

Anorexia tends to happens in a rigid personality. However, bulimia tends to happen in a more impulsive personality, and they may have other impulsive behaviors that don't revolve around food.

Therapy can help. In anorexia, the goal is to start thinking 'I can take things in.' In bulimia, the thought is 'I can take things in and accept or keep them' and in binge eating it's the thought 'I can have enough.'

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Dr. Thomas Weigel, instructor in psychiatry at Harvard Medical School and the Associate Medical Director of the Klarman Eating Disorders Center at McLean Hospital

Looking at something like anorexia nervosa, which is associated with resistance to eating and weight loss, you are watching for rapid and severe weight loss because of diet, calorie counting and food restriction. People often develop a list of foods they cannot eat. They start becoming vegetarian, and subsequently vegan. It's difficult to recognize these signs, because people do these things to be health conscious, but we also see this in anorexia.

Extremes in exercise are also a sign. It's a difference between going for a run a few miles twice a week versus going for a run 10 miles twice a day. We've been in contact with some universities who have the gym staff report if people are spending too much time there, and ban them from the gym.

Some people start wearing baggy clothes, despite a lot of weight loss, because they feel like they have to hide their body. The other thing to notice is that people may feel down or depressed. Significant weight loss may mimic depression because of lack of energy, low mood and sleep difficulty, which are all associated with not getting enough nutrition.

In bulimia nervosa: where people have binge eating episodes, you look for fluctuating weight. You might also find evidence that they are using laxatives, diuretic use, or evidence of vomiting around the toilet. Sometimes families will find it in tupperware containers in closets. Other signs can be disappearing food from the kitchen and calluses on the hands, from self-induced vomiting.

With most things in life I think it's best to approach people directly and let them know that you have concerns. List the concerns and ask if they need help. If you're a parent of a minor, you have the option to then take them to the doctor, who can do weight checks and some labs to screen for anorexia including screens for low potassium levels, changes in heart rate and also to look at their weight in comparison to the past. If you are in the school system, such as a teacher, you can alert the administration or the parents.

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Laura Discipio, executive director of the National Association of Anorexia Nervosa and Associated Disorders:

People can have eating disorders and be of normal weight or overweight. So weight and body size are not the only predictors. Really, you want to look at behaviors and attitudes.

Are they now restricting the kinds of foods they are going to eat? Do they use the label of "good" and "bad" food? All food is good in moderation.

Sometimes they will spend a lot of time cutting up their food in little tiny pieces. They may be going to the bathroom immediately after they eat. It may be a sign of a disorder if large amounts of food are missing, if you find food hidden in the bedroom, or if they start to change the way that they dress. Sometimes if they're uncomfortable with their bodies they are going to wear bigger clothes to hide it.

Are they not seeing friends anymore? Are they avoiding going out with their friends on the weekend? Sometimes sadness is a sign, if they are withdrawing in the home or in their room.

They may being working out too much. Exercise is clearly important in a healthy lifestyle, it's when you get obsessive about it that it's a warning sign. If you are working out every day and you are working out whether or not you're still sick, you're exhausted, or you workout when you're in pain. It's also a sign if your workouts are dependent on the amount of food you eat.

Eating disorders have the highest mortality rate than any illness.

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Dr. Eugene Beresin, American Academy of Child & Adolescent Psychiatry, professor of psychiatry at Harvard Medical School:

There are all kinds of variations in eating disorders, especially in teens. Among teenage girls, anorexia nervosa is something to watch out for. Approximately 96 percent of anorexia nervosa happens at age 12 and at 18; there are two peaks. It's rare, but when it does occur, it's a very serious disorder, even deadly.

Parents or loved ones are not in the position to make a diagnosis. We should be very careful about making a diagnosis if you are not a trained individual. Pediatricians, or child and adolescent psychiatrists, can help diagnose an eating disorder.

In anorexia, one warning sign you could look for is weight loss. Weight loss typically occurs in anorexic girls in times of transition. Going away from home to camp, a new school, going away to college. Separation tends to be a trigger, but it's not a cause. If parents do notice that their daughters lose weight fairly dramatically, they should raise their concern.

Some of these things can look quite normal. Many of these girls will start exercise programs, they'll start eating more vegetables and vegetarian foods; they start eating less fats. In adolescents one of the most important things is image, so what might look like an effort to look fit and trim may be normal. Or it may be the warning signs of anorexia.

Many of these girls tend to be highly perfectionistic, obsessional, very driven, competitive and are very hard on themselves. Often, underneath, they have low self-esteem, but you would never notice. These are these girls who tend to be the class president; they get straight A's. They are extraordinarily sensitive to relationships; they can be caretakers in the family. Now there are many, many girls with these qualities who are normal.

Another thing to keep in mind is that 50 percent of girls with anorexia, and 70 percent of girls who become bulimic, will have depression. Also, eating disorders run in families, so note if there are other family members who have anorexia, bulimia or obesity.

The rule of thumb is these are traits that are associated with anorexia and bulimia, but they all can be normal. That's why it's hard to diagnose.