NZ study reveals link between smell and obesity

New Zealand scientists have revealed a link between obesity and scent, finding that the better a person can smell, the more likely they are to be slim.

Lead-author of the study, Dr Mei Peng, from the University of Otago's Department of Food Science, says the link between smell and people's body-shape was previously a relatively unknown area of scientific study and knowledge.

"After compiling our evidence we found there is in fact a strong link between a person's body weight and their smell ability," Peng said.

Of the five senses, Peng considered smell to be the least understood, but at the same time noted it was perhaps the most important sense for influencing eating behaviour through detecting and discriminating between different flavours.

"We found obese people's ability to detect and discriminate smell was not as efficient as slim people," she said.

"This can result in obese people having a higher chance of making poor food choices because they will need other forms of stimulation to enjoy food.

"For example they might choose, or be more attracted to, saltier and tastier foods such as bacon and maple syrup instead of blander foods such as low-fat cereal with less sugar."

Of note was that body weight had to pass a certain benchmark for the link to become obvious – so the reduction in ability to detect and discriminate between different smells was greater among people who were closer to being obese.

The researchers hypothesised that once a person was obese, their metabolism altered several peptides and hormones which had an impact on the gut-brain signalling pathway.

This leads to another area of consideration about two surgical obesity treatments; stomach removal, and gastric bypass.

The research found stomach removal could actually improve smell ability, whereas other obesity surgeries do not have the same effect on people's smell ability.

"Cutting the stomach could change nerves in the stomach that affect the gut-brain pathway, so smell changes could be the key to the difference between the two surgeries – essentially the smaller size of the stomach might not be the factor that leads to weight loss, it is more likely due to the gut-brain pathway being reset."

The study, conducted this year, involved a systematic review and drew on data of 1432 individuals from empirical and clinical worldwide studies.

The research was supported by a Royal Society of New Zealand Marsden Fast-Start grant.
Peng hoped the research would increase awareness around the link between human's eating behaviour and our senses.

She hoped to continue the line of research to investigate the reward-factor smell had in various body-shape groups.