Pawelec is investigating how much information about a person’s physical appearance can be inferred from their voice and whether a description of a crime perpetrator could be prepared from a recording.

“This is a fascinating area we still know too little about,” he said.

The study, published in Scientific Reports, examined how body composition—specifically the ratio of fat to fat-free mass, including muscle, bone, and water—affects voice. Body composition was measured using bioimpedance, a method that passes a low-intensity current through the body.

Fat conducts electricity less efficiently than hydrated tissues, allowing researchers to calculate its proportion.

Earlier studies linking body mass to voice relied mainly on body mass index (BMI), which does not distinguish between muscle and fat.

The study found that body fat affects male and female voices differently. Men with more muscular arms had lower voices, which may be linked to testosterone’s effect on the vocal tract. Men with higher body fat had a higher value of the first formant in their voice.

“Formants are parameters that shape the timbre of a voice. The lower they are and the smaller their spread (so-called formant dispersion), the more the tone is perceived as masculine (‘deep/dark’). A higher formant in overweight men suggests a ‘brighter’ tone, closer to a feminine one,” Pawelec said.

He added that adipose tissue is hormonally active, producing the enzyme aromatase, which converts androgens, including testosterone, into estrogens. “These sex hormones determine voice tone: high testosterone levels promote a low tone, while a predominance of estrogens shifts it toward a feminine tone,” he said.

Among women, higher abdominal fat was associated with greater vocal intensity. Pawelec suggested this may be caused by higher subglottic pressure. “Visceral fat (located between internal organs in the abdominal cavity) exerts pressure on the space below the larynx, which translates into greater vocal power,” he said.

Greater lean body mass in women was linked to longer maximum phonation time, reflecting the ability to sustain a continuous sound during exhalation. Pawelec said this indicates more efficient respiratory muscles, including the diaphragm.

Asked whether voice alone can reliably indicate overweight, Pawelec urged caution. “In my studies, so-called competent judges were able to identify individuals with higher body fat based on recordings, but the results were only slightly above the chance level,” he said.

Machine learning algorithms are being developed to classify voices by BMI with increasing accuracy. However, Pawelec said correlations between voice and appearance are still too weak to reconstruct a person’s figure from recordings. “I hope that in the future this will allow investigators to at least narrow down the suspect pool to individuals with a specific body type,” he said.

Whether voice changes caused by weight gain are reversible requires further study. Pawelec noted that voices change naturally throughout life. “In women, the phases of the cycle and pregnancy influence this, and in both sexes, differences may even depend on the time of day, which is related to hormonal levels. Initial studies of patients after bariatric surgery suggest that after drastic weight loss, the voice may become quieter or higher-pitched,” he said.

Voices also change with age. “We are observing a process called gender unification. With age, the average frequency of women's voice often decreases, while in the case of men it increases. This is due to changes in hormonal profiles, including dropping testosterone levels in men and postmenopausal changes in women. Although the structure of the larynx and vocal tract, which develops until the age of 21, retains sexual dimorphism, the influence of hormones on the vocal folds in old age blurs these differences,” Pawelec said.

“The voice is not just a communication tool, but a complex biological message. Understanding the connections between body structure and voice may in the future benefit not only forensic specialists but also be used in remote diagnostics by dietitians and physicians,” he concluded.

PAP - Science in Poland, Ludwika Tomala

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