Obesity myths: 7 common beliefs vs. the research

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Obesity myths: seven common beliefs vs. what the research shows

By Dr. Asnat Raziel, bariatric surgeon specializing in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal, Tel Aviv

Obesity myths: why it matters to debunk them

Obesity myths follow us everywhere: at home, at work and even in the doctor’s office. According to the World Health Organization, more than a billion people worldwide live with obesity. In Israel, according to the National Program for Quality Indicators in Community Healthcare, about 59% of adults aged 20 to 64 live with overweight, and about a quarter of all adults in this age group live with obesity. Even so, many people still see obesity as a matter of personal choice. In this article, we’ll look at seven common beliefs and see what the research actually says about them.

Obesity myths about causes and responsibility

Myth 1: “Obesity is a matter of willpower”

This may be the most widespread belief, and also the most harmful. In January 2025, an international commission of the journal Lancet Diabetes & Endocrinology published a new definition of obesity. Fifty-eight experts, including people living with obesity, defined clinical obesity as a chronic, systemic disease. The definition has been endorsed by 76 organizations worldwide. The commission also warned against health policies built on unproven assumptions that place the responsibility solely on the individual.

In December 2025, the World Health Organization followed suit. It defined obesity as a chronic, relapsing disease and, for the first time, issued a guideline on the use of GLP-1 medications to treat it. The environment plays an important role as well. In Israel, for example, the obesity rate among women of low socioeconomic status is 33.9%, compared with 18.1% among those of high socioeconomic status. A gap like that has nothing to do with willpower.

Genetics plays a central role too. A review of 88 heritability estimates from twin studies, covering more than 140,000 twins, put the heritability of body mass index at between 47% and 90%, with a median of 75%. In other words, our genes have a strong influence on our tendency to gain weight. I have written more about this in my article on obesity as a chronic disease.

Myth 2: “You just need to eat less and move more”

Diet and physical activity are very important; no one disputes that. But the body does not accept weight loss quietly. In a study published in NEJM, participants lost an average of 13.5 kg on a very-low-calorie diet. A full year later, most of their satiety hormones were still low, their levels of the hunger hormone ghrelin were still high, and their hunger remained strong.

Put simply, the body fights to regain the weight it has lost. That is one reason most people regain weight after dieting. It is not a personal failure; it is biology.

Obesity myths about diagnosis

Myth 3: “BMI tells you everything”

BMI, or body mass index, is a simple and convenient tool. But the Lancet commission concluded that it is suited mainly to assessing risk at the population level, not to diagnosing an individual. The commission therefore recommends confirming excess body fat with an additional measurement, such as waist circumference or waist-to-height ratio. Only above a BMI of 40 does the commission assume excess fat without further measurement.

Along the same lines, the new framework of the European Association for the Study of Obesity states that BMI alone is not enough for diagnosis. Under this framework, even a person with a BMI of 25 or more may be living with obesity if their waist circumference is high and their health is affected. Israel’s Prof. Dror Dicker co-authored the framework. I have also written about why a “normal” weight does not always mean good health.

Obesity myths about treatment

Myth 4: “Obesity medications are a cosmetic shortcut”

The data tell a different story. In the STEP 1 trial, patients who received Wegovy, whose active ingredient is semaglutide, lost an average of 14.9% of their body weight, compared with 2.4% for those on placebo. What’s more, half of the semaglutide patients lost at least 15% of their weight. At the same time, risk factors for heart disease and diabetes improved, and so did physical functioning.

But the real point is health. In the SELECT trial, which included 17,604 patients with cardiovascular disease and overweight or obesity, but without diabetes, Wegovy reduced the combined risk of heart attack, stroke or cardiovascular death by 20%. In other words, this is a medical treatment that reduces cardiovascular events, not cosmetics.

Myth 5: “A small amount of weight loss isn’t worth anything”

This is a particularly common mistake. In the US Diabetes Prevention Program, participants with prediabetes aimed to lose 7% of their weight and get 150 minutes of physical activity a week. The result: their risk of developing diabetes fell by 58%. By comparison, treatment with the drug metformin reduced the risk by 31%.

Similarly, in the Look AHEAD trial, among people with type 2 diabetes, losing 5% to 10% of body weight within a year improved blood sugar control, blood pressure, triglyceride levels and “good” HDL cholesterol. And the greater the weight loss, the greater the benefit. Every percentage point counts.

Myth 6: “If you stop the medication, it was all for nothing”

Here the picture gets interesting. In the STEP 1 extension, participants who stopped both the medication and the lifestyle program regained about two-thirds of the weight they had lost within a year. Even so, they still weighed 5.6% less than when they started.

So stopping doesn’t erase everything, but it does give up most of the benefit. Like blood pressure medications, obesity medications work for as long as you take them. That’s why it is important to plan treatment for the long term, as I explain in my guide to maintaining your results after stopping treatment.

Stigma: the most harmful myth of all

Myth 7: “A little social pressure will help people lose weight”

Research shows the opposite. An international consensus statement, endorsed by more than a hundred organizations, concluded that stigma against people with obesity harms their health. Between 19% and 42% of adults with obesity report discrimination because of their weight. What’s more, people who experience stigma are less likely to seek medical care.

The statement also addresses healthcare professionals. According to the statement, many of them hold biases against patients with obesity. The signatories pledged to stop describing people with obesity as lazy, gluttonous or lacking willpower. The language we use matters, and I have written more about respectful language in obesity care.

What this means for you

If you are living with obesity, it is important to know that this is not a personal failure. Obesity is a multifactorial disease with genetic, hormonal and environmental components. Today there are effective and safe treatments, from nutrition and physical activity to medication and surgery. The first step is to reach out to a professional team that can tailor treatment to you.

If you are a healthcare professional, it is worth examining our own approach as well. A respectful, blame-free conversation increases the chance that a patient will come back and stay with treatment. Diagnosis should also rely on measures beyond BMI and on an assessment of how a person’s functioning and health are affected.

Questions and answers about obesity myths

If obesity is a disease, does lifestyle no longer matter?

Lifestyle matters a great deal; it is the foundation of every treatment. The difference is in the approach: instead of blaming, we provide tools, support and appropriate treatment.

Do genes determine your destiny?

No. Genes influence your tendency, but environment, diet, sleep and treatment influence the outcome. People with a genetic predisposition can succeed, though they usually need a lot of support.

Does everyone with a high BMI need medication?

No. The decision is based on overall health, related conditions and the patient’s preferences. There are also different types of obesity, and each one calls for a different treatment.

Are obesity medications dangerous?

Like any medication, obesity medications have side effects. Most of the time these are mild, temporary digestive symptoms such as nausea or constipation. Serious side effects are rare, and it is important to recognize them early. That’s why treatment is always given under medical supervision. You can read more in my up-to-date guide to the side effects of weight-loss medications.

Is bariatric surgery “the easy way out”?

Not at all. Surgery is also a medical treatment for a chronic disease, and it requires a profound change in lifestyle and follow-up over many years.

The bottom line

Modern research debunks most obesity myths. Obesity is a chronic disease, not a character flaw. Modest weight loss improves health, and the newer treatments protect the heart rather than simply changing how you look. Ultimately, scientific understanding and respectful language are the first steps toward the right treatment.

The information in this article is general and does not replace personal medical advice.