Just because someone is thin doesn’t mean they’re healthy. And staying thin—especially through restriction, overexercise, or chronic stress—might not be protecting your health at all. In fact, research shows it may actually be doing harm.

Health isn’t about appearance. It’s about how you care for your body, not what size it is. Yet our culture often assumes that thinner automatically means better—which simply isn’t backed by evidence.

So what are the health risks of thinness? And is pursuing thinness actually good for your well-being, like we’ve been taught to believe?

Below is a short summary of research exploring the health impacts of thinness, with links if you want to dig deeper.

Thinness and Health: What the Science Tells Us

Being Underweight Puts People at Highest Risk of Dying - Underweight adults (BMI of 18.5 or less) have a 1.8 times higher risk of dying than those with a "normal" BMI of 18.5 to 24.9. This is HIGHER than for those who are "obese" and even for the severely "obese."

Being Underweight Is Associated with Increased Risk of Sudden Cardiac Death in People with Diabetes Mellitus - Being underweight is significantly associated with an increased risk of sudden cardiac death in those with diabetes in a study with over 2.5 million people. A steep rise in risk was seen as the BMI level dropped below 23. The underweight group was at higher risk that the “obese” group (BMI 30 and above). The lowest risk was seen in BMI of 27 to 28 group.

Deaths Associated With Underweight, Overweight, and Obesity - Those who are underweight (BMI less than 18.5) and those of average weight (BMI 18.5–24.9) had higher risk of dying even after adjusting for smoking, alcohol, etc. Believe it or not, overweight (BMI 25–29.9) was associated with reduced mortality. Many did not like this 2005 study. The data was reanalyzed and this report from 2018 found the same conclusions.

Losing Weight Results in Increased Risk of Death in Overweight People - Weight loss of 15% or more associated with increased risk of death among overweight. (You can see how the research is NOT as clear cut as the media and doctors report!)

Thinness and Weight Loss: Beneficial or Detrimental to Longevity? - This review examined the hypotheses that 1) low body mass index (BMI) is optimal for longevity and 2) weight loss reduces mortality rates. The evidence fails to support either of these ideas. Indeed, a number of studies show that thinness and weight loss (regardless of initial BMI) are associated with increased mortality rates.

Thinness is an Important Risk Factor for Low Bone Mass and Increased Bone Loss - Thinness was evaluated as a risk factor for low bone mineral density (BMD) or increased bone loss in study examining for prevention of osteoporosis in recently postmenopausal women with normal bone mass. 1999

Anorexia Nervosa and Health: What the Science Tells Us

Fear Doesn’t Work. But Here’s Why We’re Sharing These Articles.

Scare tactics don’t lead to recovery. In fact, for many people struggling with anorexia, hearing about the health risks just brings on more fear, guilt, and pressure—often making the urge to restrict even stronger. That’s why I don’t lead with fear, and I don’t recommend that you do either.

But I am including a few articles here about the medical impacts of anorexia. Why? Because many people keep their weight low enough to negatively impact their long-term health. We’ve worked with clients whose bodies met the criteria for anorexia, but they were told by doctors they “looked fine.” Just because this research is about anorexia doesn’t mean it won’t apply. If you’re in a smaller body and struggling, this information might still be relevant to you.

That said, if reading about health consequences feels overwhelming right now, skip it. You can come back to it later—if and when it supports your healing.

A note for parents and loved ones:
We know how scary it is to witness someone you care about struggling. You may feel the urge to share alarming facts in hopes of snapping them out of it. Please know: that rarely helps, and often makes things worse. Instead, try to offer calm presence, patience, and trust in the process. If you’re unsure how to support them, that’s okay—reach out. You don’t have to do this alone either.

Impact of Low Body Weight on Brain Structure - Underweight individuals with AN had significant deficits in brain volume compared to healthy controls. These deficits in grey matter volume improved with weight restoration. (Usually clients to not realize they are cognitively impaired until they get better and look back at their symptoms.)

Does Restrictive Anorexia Nervosa Impact Brain Aging? - Findings suggest that acute AN is linked to advanced brain aging during the acute stage, and that may partially normalize following weight recovery.

Low Body Weight and Bone Loss - Being thin puts a women at increased risk of developing osteoporosis (a condition which, believe it or not, often leads to death in older women). Amenorrhea virtually guarantees it. Those with anorexia can lose as much as 2% to 6% of their bone mass each year they have AN.

Estrogen Replacement is Not Effective at Reversing Bone Loss - Estrogen replacement seems to have little independent effect on correcting or preventing osteopenia in young women with AN. 2022

Oral Contraceptives Does Not Restore Bone Mineral Density - There is no evidence for benefits of hormone therapy in patients with anorexia. Their use can create false confidence that bones are protected against osteoporosis, delaying the most important intervention - increased nutrition. They conclude hormone and oral contraceptive therapy should not be prescribed for young women with amenorrhea who have eating disorders. 2013

Oral Contraceptive Pills and Adolescent Bone Health - Some contraceptives used by teenagers can impair bone formation in teenage girls, thereby compromising peak bone mass. This is true even if the teenager is normal weight and healthy. 2019

Exercise Is Actually Contraindicated - For those who are underweight, have anorexia nervosa, or irregular menstrual cycles due to undernutrition, exercise is a risk factor. Bone density in the spine and whole body in females with anorexia nervosa was found to be lower among those engaged in moderate levels of exercise (such as walking or pacing) compared to women who were not exercising. 2011