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Anti-obesity bias

Doctors show anti-obesity bias, claims study

There is strong implicit and explicit anti-fat bias among doctors

Medical doctors are as biased against obesity as the general public, according to a study published in the open access journal PLoS ONE.

The research carried out by Dr Janice Sabin from the University of Washington, Seattle, and colleagues from the University of Virginia, concluded that there is strong implicit and explicit anti-fat bias among doctors that should be addressed to prevent weight discrimination in healthcare and the quality of care delivered to overweight patients.

“We found that MDs' implicit and explicit attitudes about weight follow the same general pattern seen in the very large public samples that hold strong implicit and explicit anti-fat bias,” said Sabin. “It is important for physicians to be aware that this bias exists and to ensure that personal bias does not have a negative impact on the doctor-patient relationship.”

According to the authors, this is the first study to show that the strong anti-fat bias prevalent in the general public is also shared by many doctors.

“Strong negative implicit and explicit attitudes about weight among MDs may contribute to less-than-ideal clinical interactions and subsequent medical avoidance among overweight patients. Exploring the effects of physicians’ implicit and explicit weight bias on quality of care of overweight patients is an important area for future study,” the authors write.

Whether there is an association between these attitudes about weight and patient reports of weight discrimination in quality of health care, though, has yet to be studied.

"We do not yet know how MDs anti-fat attitudes affect clinical behaviour,” the authors concluded. “Nor do we know whether implicit weight bias is related to how overweight patients experience health care interactions.”

The study was supported by Project Implicit, an international collaborative network of researchers investigating implicit social cognition.


Between May 2006 and October 2010, a total of 359,261 volunteers accessed the Project Implicit website and opted to complete the Weight Implicit Association Test (IAT).  The results were reported as Cohen's d, the difference between two means divided by a standard deviation for the data

The volunteers reported their attitudes about weight by endorsing one answer from the list:

  1. I strongly prefer thin people to fat people.
  2. I moderately prefer thin people to fat people.
  3. I slightly prefer thin people to fat people.
  4. I prefer thin people and fat people equally.
  5. I slightly prefer fat people to thin people.
  6. I moderately prefer fat people to thin people.
  7. I strongly prefer fat people to thin people.

A sub-sample identified their highest level of education as MD (2,284). In this group, 55% were female, 78% reported their race as white, and 62% had a normal range BMI.

Implicit results

The study’s large sample of test-takers showed strong implicit anti-fat bias (Cohen’s d=1.0). MDs, on average, also showed strong implicit anti-fat bias (Cohen’s d=0.93). Implicit attitudes about weight among all test-takers were strong among both males and females.

Among all female test takers and female MDs’ implicit anti-fat bias was significantly weaker than for males (p<.01, and p<.01). Although there were differences by gender, implicit anti-fat bias was strong among both male and female MDs (Cohen’s d=1.02 for males and Cohen’s d=0.86 for females). These differences by gender remained significant after adjustments for multiple comparisons.

For the MD sub-sample, implicit anti-fat bias was strong among underweight, normal weight and overweight medical doctors. Among the 11% of MDs whose BMI classified them as obese, implicit anti-fat bias was moderate (Cohen’s d=0.60).

After adjustments for multiple comparisons, variations in implicit bias by MD weight remained significantly different between normal weight vs. obese MDS (p<.01) and overweight and obese MDs (p=0.01). This pattern of strong anti-fat bias among all weight groups except for obese individuals was similar among the complete sample of test-takers.

Strong implicit anti-fat bias was found among white (Cohen’s d = 1.0), and Hispanic (Cohen’s d = 0.93) MDs. After adjusting for multiple comparisons, there was a significant difference in implicit anti-fat bias between white and Asian MDs (p = .01). In the complete sample of test-takers all racial/ethnic groups showed strong implicit anti-fat bias. (not shown).

Explicit results

All test-takers reported a strong explicit preference for thin people over fat people on average (Cohen’s d=0.90). There was variation in self-reported anti-fat bias among all test takers by gender, however, the variation was within the range of strong bias (Cohen’s d=1.15 for males and Cohen’s d=0.84 for females).

The researchers found strong self-reported anti-fat attitudes among MDs by gender (Cohen’s d=1.44 for males and Cohen’s d=1.13 for females). These differences by gender for all tests takers and for MDs remained significant after adjustments were made for multiple comparisons.

For MDs who were underweight, normal weight and overweight they reported strong explicit anti-fat bias. Among the sub-sample of MDs who were obese, they found moderate explicit anti-fat attitudes (MD sample Cohen’s d=0.67), similar to all obese test-takers.

After adjusting for multiple comparisons, the researchers found a significant difference in strength of self-reported anti-fat attitudes between underweight vs. obese MDs (p<.001), normal vs. overweight MDs (p=0.05), normal vs. obese MDs (p<.001), and overweight vs. obese MDs (p<.001).

They also reported a significant difference in self-reported weight bias among white and African American MDs (p<.001), African American and Asian MDs (p=0.02), and African American and Hispanic MDs (p=0.02) although all groups showed strong anti-fat bias.


The authors acknowledge that an important limitation of this study is that the sample is
not a random, representative sample of MDs. Therefore, the sample means and distributions cannot be considered parameter estimates of MDs in general.

However, the analysis included more than 2,200 MDs and the note that this demonstrates that that implicit and explicit weight bias among medical doctors is “widespread”.

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