Researcher Nicholas Rule, Ph.D., said, “Women and men of average height need to gain or lose about three and a half and four kilograms, or about eight and nine pounds, respectively, for anyone to see it in their face. But they need to lose about twice as much for anyone to find them more attractive.”
The researchers suggest that weight in the face is a good predictor of body mass index (BMI), which is calculated by weight (kgs) divided by height (m). Dr. Rule added, “It is a robust indicator of one’s health. Increased facial adiposity is associated with a compromised immune system, poor cardiovascular function, frequent respiratory infections, and mortality. So, even a small decrease can improve one’s health.”
To achieve their findings, researchers digitally created facial images of men and women between 20 and 40 years of age. All images were neutral with hair pulled back and the researchers only changed the weight.
Participants were asked to compare randomly drawn images and choose the one that looked heavier. The researchers found that a change in BMI of 1.33 kg/m2 was noticeable.
Co-researcher, Daniel Re, said, “We calculated the weight change thresholds in terms of BMI rather than simple kilograms or pounds, so that people of all weights and heights can apply it to themselves according to their individual stature.”
The researchers also measured weight change in the face as it related to attractiveness. The researchers found an average weight loss of 2.38 kg/m2 in women and 2.59 kg/m2 in men translated to 6.3 and 8.2 kg for men and women of average height. Dr. Rule explained, “The difference between the groups suggests women’s facial attractiveness may be more sensitive to changes in weight. This just means women attempting to lose weight need to shed slightly fewer pounds than men for people to find them more attractive.”
Re concluded, “When it comes to incentives for weight loss, some people are more motivated to look attractive than to improve their health.”
The findings are published in Social Psychological and Personality Science.