Is It Really Okay To Be Overweight? New Danish BMI

A new study presented at the 2025 European Association for the Study of Diabetes (EASD) grabbed headlines when it reported that people in the “overweight” range of body mass index (BMI) did not have a higher mortality risk over five years compared to people in the normal range.

At first glance, this sounds like permission to relax about excess weight. Headlines in ScienceDaily and EurekAlert! even went so far as to suggest that being too thin could be deadlier than being overweight.

However, as we’ll see later in this article, even the study’s own authors and outside experts highlighted important limitations—including a short follow-up period, missing body composition data, and potential bias in the study’s participants. Those caveats change how we should interpret the results.

What the Study Found

Researchers examined 85,761 adults in Denmark (81% women, median age 66) who were followed for about five years. During that time, ~7,555 participants (8%) died.

Compared to people with a BMI of 22.5–24.9 kg/m² (upper “normal” range):

Underweight (<18.5) → 2.7 times higher risk of death
BMI 18.5–20.0 → ~2 times higher risk
BMI 20.0–22.5 → 27% higher risk
Overweight (25–29.9) → no significant increase
Moderate obesity (30–34.9) → no significant increase
BMI 35–39.9 → ~23% higher risk
Severe obesity (≥40) → ~2.1 times higher risk

In short, risk was elevated at both ends of the BMI spectrum—low BMI and severe obesity.

Too low or high BMI increases the mortality risk

What Exactly Is BMI?

BMI = weight (kg) ÷ height² (m²)

What it measures: total body weight relative to height.
What it does not measure:
- Muscle vs. fat
- Visceral fat (around organs) vs. subcutaneous fat (under skin)
- Fat distribution across the body

This makes BMI a blunt tool—helpful for populations, but misleading for individuals.

The Role of Muscle Mass

People in the lower normal BMI group who had higher mortality may not just have been “thin”—they may have had too little muscle.

Low muscle mass (sarcopenia) increases the risk of frailty, falls, infections, and earlier death.
Muscle is not only a tissue; it’s an indirect marker of how much physical activity and exercise a person does. Active people tend to maintain more muscle, while those who are sedentary often lose it.
Without measuring muscle, the study cannot determine whether the deaths in the lower BMI group were due to being lean and healthy or frail and under-muscled.

The TOFI Problem

BMI also fails to detect TOFI (“thin outside, fat inside”).

Some people with “normal” BMI carry large amounts of visceral fat around their organs.
Visceral fat contributes to inflammation, insulin resistance, fatty liver disease, and cardiovascular disease.
A TOFI person may have a BMI of 22 but be far less healthy than an overweight person with strong muscles and less visceral fat.

The Limits of This Study

Even with its large size, this study has critical blind spots:

No body composition data

The study used BMI only—a person’s weight divided by their height squared. While easy to calculate, BMI ignores the details of what that weight is made of. This is a major limitation because:

Muscle vs. fat: A 70-kg athlete with strong muscles and a 70-kg sedentary older adult with low muscle and high fat can have the same BMI but very different health risks.
Visceral vs. subcutaneous fat: Visceral fat (around the liver, pancreas, and intestines) drives inflammation, insulin resistance, and a higher risk of diabetes and heart disease. Subcutaneous fat (under the skin) is generally less harmful. BMI can’t tell the difference.
TOFI individuals (“thin outside, fat inside”): Some people with a normal BMI may still have high levels of visceral fat, making them metabolically unhealthy even though they look slim.
Sarcopenia (low muscle mass): Especially in older adults, low muscle mass can coexist with normal or even low BMI. Sarcopenia is a strong predictor of disability, frailty, and mortality.

Because the study didn’t measure lean body mass, fat mass, or fat distribution using tools such as DXA scans, CT, or MRI, it cannot answer the critical question: Were the deaths in the low-BMI group driven by a lack of muscle, excess visceral fat, or underlying illness?

Experts commenting on the study have pointed out that the data actually came from people who underwent DXA scans, which are capable of measuring muscle and fat:

“The data come from ‘persons with Dual-Energy X-Ray Absorptiometry (DXA)-scans’, it is not clear how representative this is of the general population. If people in poorer health or overweight are more likely to attend these scans, it could then distort the association.” (Science Media Centre)

This makes the absence of data on muscle and fat distribution even more striking. DXA can provide detailed information about body composition, yet none of that was reported in the summaries.

This gap makes the conclusion incomplete—and highlights why future studies must move beyond BMI to encompass whole-body composition.

Reverse Causation

The authors themselves acknowledge this issue:

“One possible reason for the results is reverse causation: some people may lose weight because of an underlying illness. In those cases, it is the illness, not the low weight itself, that increases the risk of death, which can make it look like having a higher BMI is protective.” — Sigrid Bjerge Gribsholt (ScienceDaily)

This means illness may have caused both low weight and early death, making low BMI look more dangerous than it really is.

The study reports that people with a lower BMI—especially those under 22.5—had a higher risk of dying. At first glance, this might look like being lean is dangerous. But it may be due to reverse causation.

What it means: Instead of low BMI causing early death, an underlying illness may have caused both weight loss and higher mortality.
For example, someone with cancer, COPD, heart failure, or chronic infection may unintentionally lose weight. That weight loss moves them into the “low BMI” group. When they die sooner, the statistics show “low BMI = higher mortality”—but in reality, the illness came first.
This effect can make thinness look riskier than it really is. Without excluding people with pre-existing illness or accounting for unintentional weight loss, it’s impossible to know how much of the mortality in the low BMI group was due to their body size versus hidden disease.
In older populations, especially (median age in this study was 66), weight loss often signals frailty or muscle loss, which can precede death regardless of BMI.

Reverse causation is a well-known problem in observational studies, and it means the association between BMI and mortality must be interpreted with caution.

Short Follow-Up

The study followed participants for only about five years. That is a very brief window when looking at conditions like diabetes, heart disease, cancer, and obesity-related complications, which often take decades to develop.

Someone who is overweight at 66 may not show increased mortality within 5 years, but the risks of stroke, cancer, or heart failure may appear over 10–20 years.
In Denmark, life expectancy is 82.9 years for women and 79.5 years for men (WHO). Since the median age of the participants was approximately 66, most were expected to live well beyond the study’s follow-up period. Five years captures only a fraction of their likely lifespan.
This means the study might underestimate the long-term dangers of excess fat, particularly visceral fat and obesity.

A longer study period would give a more accurate picture of how BMI and body composition affect lifetime risk, not just short-term survival.

Selection Bias

Another limitation is the inclusion criteria for the study. All participants had undergone health scans in Denmark. This introduces what researchers call selection bias.

Individuals who undergo medical scans are not representative of the general population.
They may already have medical conditions (diabetes, osteoporosis, cancer, or chronic pain) that prompted the scan.
They might also be more health-conscious, since some scans are done for preventive reasons.
Either way, this group may not represent the average person walking around in the community.

Due to this, the study results may not be applicable to everyone. If many participants already had illnesses, that could explain why those in the lower BMI range had higher mortality (illness leads to weight loss, then early death).

On the other hand, if the group was unusually health-conscious, the risks of overweight and obesity might be underestimated compared to the broader population.

As the authors put it:

“Since our data came from people who were having scans for health reasons, we cannot completely rule this out.” (ScienceDaily)

Unmeasured Protective Traits

The researchers also suggested that some heavier participants who lived longer may have had unique advantages:

“It is also possible that people with higher BMI who live longer — most of the people we studied were elderly — may have certain protective traits that influence the results.” (ScienceDaily)

These could include greater muscle mass, favorable fat distribution, or genetic resilience.

The BMI Mortality study should be interpreted carefully

The Real Takeaway

This study does not prove that being overweight is safe. Instead, it shows that:

Low BMI can also be risky, likely due to muscle loss, frailty, or illness.
Mortality risk climbs again with obesity, especially BMI ≥35.
What matters most is body composition: building muscle, minimizing visceral fat, and staying active.

A Note on Headlines and Health Decisions

The EurekAlert! article about this study ran with the headline:

“Overweight and obesity don’t always increase the risk of an early death, Danish study finds.”

Meanwhile, ScienceDaily titled its piece:

“Being too thin can be deadlier than being overweight, Danish study reveals.”

Both headlines contain a grain of truth, but both can be seriously misleading when taken alone.

EurekAlert! makes it sound like extra weight is harmless, when in fact the study found higher risks at BMI ≥35.
ScienceDaily implies that thinness is more dangerous than obesity, but the actual results showed risk at both extremes—low BMI and severe obesity.

The real problem is that many people never read past a headline. Some may make life-changing decisions—like not trying to lose excess fat, or dismissing the importance of exercise—based on a half-truth.

What the study actually shows is much more nuanced:

BMI alone is incomplete. It doesn’t reveal muscle mass or fat distribution.
Short follow-up. At only five years, the study cannot capture the long-term risks of obesity.
Both low BMI and high BMI carry danger. The safest zone appeared to be at the upper normal BMI range.

Headlines strip out these critical caveats. That’s why it’s essential to go beyond the summary, understand the methods, and put results into context before drawing conclusions.

✅ Final Bottom Line:

The way this study has been summarized in the media may leave the impression that “extra weight is fine” or even that being overweight protects you. That is not what the data truly show.

The real message is that both extremes are dangerous: too little weight often signals frailty or illness, while too much—especially severe obesity—raises mortality risk.

Headlines that downplay obesity’s long-term dangers can be harmful. People may relax about weight gain or neglect exercise and muscle maintenance because they believe the risk is exaggerated.

In truth, excess visceral fat and loss of muscle mass remain major health threats. A healthy lifestyle—not a single BMI number—is what determines resilience and longevity.

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References:

European Association for the Study of Diabetes. Body Mass Index and Mortality: Results from a Danish Cohort. Presented at the 61st Annual Meeting of the European Association for the Study of Diabetes (EASD), Vienna, 15–19 Sept. 2025. Conference abstract.
Bosy-Westphal, Anja, et al. “Classification of weight status and body fatness in children and adolescents: validation of BMI cut-offs by dual-energy X-ray absorptiometry.” European Journal of Clinical Nutrition, vol. 68, no. 6, 2014, pp. 658–664. https://doi.org/10.1038/ejcn.2014.26.
Cruz-Jentoft, Alfonso J., et al. “Sarcopenia: revised European consensus on definition and diagnosis.” Age and Ageing, vol. 48, no. 1, 2019, pp. 16–31. https://doi.org/10.1093/ageing/afy169.
De Lorenzo, Antonio, et al. “Sarcopenic obesity: clinical implications of a new emerging condition.” Nutrition, Metabolism and Cardiovascular Diseases, vol. 23, no. 12, 2013, pp. 1051–1060. https://doi.org/10.1016/j.numecd.2013.09.007.
Romero-Corral, Abel, et al. “Normal weight obesity: a risk factor for cardiometabolic dysregulation and cardiovascular mortality.” European Heart Journal, vol. 31, no. 6, 2010, pp. 737–746. https://doi.org/10.1093/eurheartj/ehp487.
“Being too thin can be deadlier than being overweight, Danish study reveals.” ScienceDaily, 14 Sept. 2025, https://www.sciencedaily.com/releases/2025/09/250914205759.htm.
“Overweight and obesity don’t always increase the risk of an early death, Danish study finds.” EurekAlert!, 14 Sept. 2025, https://www.eurekalert.org/news-releases/1098063.
World Health Organization. “Denmark.” WHO Data Portal, https://data.who.int/countries/208.
Zamboni, Marco, et al. “Health consequences of obesity in the elderly: a review of four unresolved questions.” International Journal of Obesity, vol. 29, no. 9, 2005, pp. 1011–1029. https://doi.org/10.1038/sj.ijo.0803005.

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Is It Really Okay to Be Overweight? New Danish BMI–Mortality Study Explained

Introduction

What the Study Found

What Exactly Is BMI?

The Role of Muscle Mass

The TOFI Problem

The Limits of This Study

No body composition data

Reverse Causation

Short Follow-Up

Selection Bias

Unmeasured Protective Traits

The Real Takeaway

A Note on Headlines and Health Decisions

✅ Final Bottom Line:

Related:

References:

Like this:

Discover more from Don't Get Sick!

Introduction

What the Study Found

What Exactly Is BMI?

The Role of Muscle Mass

The TOFI Problem

The Limits of This Study

No body composition data

Reverse Causation

Short Follow-Up

Selection Bias

Unmeasured Protective Traits

The Real Takeaway

A Note on Headlines and Health Decisions

✅ Final Bottom Line:

Related:

References:

Share this:

Like this:

Discover more from Don't Get Sick!

Discover more from Don't Get Sick!