So What Are the Risks?

Being underweight can stop you from having periods and lead to fertility problems. It can be a factor in osteoporosis too. In a growing child being underweight can starve the brain and body for the neutrients needed to learn and grow. Not eating enough can cause kidney and liver problems by starving the organs. Long term extreme underweight can be deadly.

- Infertility
- type 1 diabetes
- osteoporosis
- immune deficiency
- anemia
- muscle loss (including heart muscle loss & smooth muscle loss; weak blood vessels, intestinal & peritineum, organ shifting/tearing/inability to push x through y)
- neural damage / nerve damage / brain loss
- vision loss
- etc

Those are just 'normal' underweight problems... jumping into chronic/severe/sudden underweight issues a whole host of others come into play... like multisystem organ failure. There's also a lot of nutritional illness/diseases that happen prior to, however (heart attack, stroke, seizures, kwashiokor, etc.) In *children* there are also a great deal more problems related to growth problems.. not just being "smaller" than they otherwise would be but that their organ systems don't develop properly (immature, deformed, etc) which leads to various issues.

ACTUALLY.... being underweight is FAR more devastating than being overweight, because one's organs get damaged from it (and faster) than being overweight. One can be obese for YEARS and even decades with minimal health problems. Being chronically underweight, however, is RARELY heard from (outside of those working in hospitals) because people tend to die fairly quickly from it. Check out ANY of the websites concerning anorexia or 3rd world / low to no food areas to find out the effects of being underweight. (It's one of the largest contributors to infant mortality, but it's also a HUGE problem for adults). Anorexia is an eating disorder, but the effects on the body are those of being severely underweight. It's also a problem found with people who are chronically ill or have digestive disorders (cancer + chemo, surgeries, etc.), or sensory disorders (autism, etc.) so dealing with the underweight community is most commonly found by health professionals/ parent caregivers/ etc.

Now... there is a VERY small portion of the population that are ectomorphs. They consume vast quantities of food, and their bodies have NO problem yanking the nutrition out of it that they need... and they have none of the underweight issues most people have. IT IS A VERY small percentage of the population. If you're not exercising and can eat 10,000 calories in a day every day for weeks and not gain an ounce... you're an ectomorph.

YES there is very definitely a "scale". Being 10lbs underweight, for example, is far less devastating than being 50lbs underweight. Also a timeline. 10lbs underweight for 5 years, vs 10lbs underweight for 6mo. ALSO, just like milestones, there is a fairly large "range" in healthy weights. For my height and bone structure my ideal weight is between 165 & 190. For my cousin (same height, different bone structure, it's between 150 & 175. BMIs also have a range, although it tends to be smaller.

BMI is a trendy, but not necessarily accurate, measurement. It strictly calculates weight in relation to height, but does not take in other factors such as bone density, muscle mass, etc. Someone might be tall and very muscular, with almost no fat at all, but be considered obese due to their height to weight ratio.

Likewise, being underweight doesn't account for people with a fast metabolism or small bones. If your dad has always been tall and thin, then having a BMI of 18 doesn't sound at all problematic. The important thing is that he eats a healthy, well rounded diet, with a sufficient amount of food. If his current "diet" is to manage his blood pressure, not his weight, I don't think there is anything to worry about.

You can be underweight and look healthy (like your dad), and you can be stick thin and sickly looking, and still technically be 'obese'. It's not just about your BMI, it has to do with cholesterol levels and plague in your arteries, stuff like that. I don't know much detail about it, but saw a very interesting medical show about 'skinny fat'.

My BMI has ALWAYS been in the "underweight" category. I am a very small person. I have always been very healthy with no vitamin deficiencies, hormone problems, period problems, fertility problems, thyroid problems, bone problems, or other ailments. I am small. My Dr. said I am one of the healthiest people she's come across. Do I think most woman my height should weigh what I do? No, probably not! However, I have a very slight frame...and I have always weighed little. No Dr. I have ever seen has seen it as a problem. IO used to play competitive soccer and have dealt with many nutritionists and specialists.

I think you run into health problems, when someone does not have a low BMI naturally. Meaning, they have deficiencies, are trying to keep themselves thin, or have something else going on.

BMI is not always the best indicator of healthy weight. Most male professional athletes, particularly football and basketball (minus the obviously huge linemen), are considered obese by BMI standards simply due to the fact that they have more lean body mass. The muscle weighs more which in turn makes their overall weight too high for their height, thus rendering them obese or even morbidly obese.

BMI should be used as a guide in conjunction with professional opinion and evaluation from a trained medical professional such as his primary care physician.

I would say change what he eats but not put him on a "diet" so to speak. Alter the types of food but increase his overall intake if possible.

Your father is barely underweight. A lot of the statistics that we have about being underweight come from people who are starving (anorexics, people from whom food has been withheld, etc), which is very very dangerous, of course. We need food to live. But there is a lot of research that suggests that people who are slightly underweight live longer than even people of healthy weight.

Leah-Maggie might have some evidence to back up her claim below, but my husband currently has cancer and I have never heard anything like this. He's a fine weight; he was just told to eat protein rich foods. In fact, he's going in for surgery for the cancer in 8 weeks and his surgeon told him to "lose weight like it was his job." When asked how much he said "as much as physically possible." Now, my husband is 6 feet tall and 200 pounds, so no waif, but also not even close to obese. The surgeon told him that the thinner you are the easier it is to do surgery. So there's some evidence to the contrary from below.

The long and short is, don't worry about your father's weight. If he's eating well and is otherwise healthy, that's what matters. Good luck.

Vitamin deficiencies, low or improper amount of fat casing to keep internal organs and muscles at a consistent temperature and barrier protection, osteoporosis, chances are higher of electrolyte imbalances (which includes sodium!), body M. start consuming muscle protein due to lack of stored fat reserves, etc.

The danger with obesity is that body fat surrounds vital organs. While we focus on the BMI calculation, the BMI measure that we use is not infalliable by any means and it is possible to appear thin, but have a high percentage of body fat from poor eating habits or lack of physical exercise. (just as it's possible to have a high BMI and low body fat.) Your dad is most likely on a low sodium diet for high BP. In addition to spicy, salty foods, a typical low sodium diet would not include a lot of baked goods (bread, cookies, cakes, etc) due to the high sodium content in baking powder. So if he is following his diet he is probably eating lean meat, fruit and veggies (assuming he likes fruits and veggies) with some whole wheat options (not necessarily bread unless you make it yourself, but whole wheat pasta, for example) - all of which are great to maintain low body fat. So the question would be how sedentary is his lifestyle? If he is getting moderate physical activity and following a heart friendly diet (and low sodium diets are generally also very heart-friendly), he should be fine.

It's interesting what you learn about nutrition when a loved one is ill. Kidney and some liver disease often necessitates low protein diets - because this takes pressure off the kidneys, low sodium is recommended for high BP, low gas diets are recommended for some gastric and pelvic conditions. I think all schools should be required to teach nutrition. We definitely grow up thinking fat is bad, thin is good and it's so much more complex than that!

A person who gets cancer and is underweight is sure to die. It takes 20 lbs to fight the disease. So that is the main danger. This is not true in young people but once you hit 35 it is over unless you have a bit of body fat. Once you have cancer you cannot put on the weight.
High blood pressure is frequently inherited.

BMI is not a reliable test of health. Did you know that body builders are considered obese on the BMI scale? It only takes into account height and weight, not body composition. Basing analysis solely on BMI is not the way to go when determining health. Body measurements, level of diet and exercise, levels of cholesterol and other blood related tests, genetics, overall feelings and general health are a much more reliable way to assess a person's longevity and health.

And to add something personal: I've been "underweight" on the BMI scale all my life. I'm pretty sure it has not negatively affected my health in any way, except that it makes it easier to hurt myself due to my bones being more exposed for injury. Being thin is only a problem if malnutrition or disease is present.

Monounsaturated fats are very caloric, but great for high blood pressure. They are found in oils - such as olive and canola, nuts and fish.