Something (or Someone) Smells Fishy: Diet and Body Odor

A rather extreme protection against objectionable body odor. Tamara Polajnar/Flickr

These past few days I have been struck down with a deadly winter cold.

By “struck down” I mean I didn’t really want to get out of bed yesterday. And by “deadly” I mean my nose was blocked. So, hardly a reason to request an air ambulance land on my roof and evacuate me to the nearest intensive care unit.

Losing your sense of smell for a week is more of an inconvenience than a debilitating health-risk. But new research released in the past month suggests that olfaction is a more important sense than we previously thought, especially when it comes to attraction.

Diet and body odor

As the saying goes, we are what we eat. But do we also smell of what we eat? Andrea Zuniga and her colleagues at Sydney’s Macquarie University decided to find out. They had 43 men wear a plain cotton t-shirt under their usual clothing for 24 hours, during which they were instructed to avoid spicy foods and scented products and to undergo at least one hour of exercise. The t-shirts were then frozen to preserve their unique aromas.

The men also completed a detailed dietary questionnaire, reporting how frequently they had eaten 242 food items within the past year. The foods were split into groups: fruits, vegetables, meat, legumes, seafood, eggs and tofu, dairy, oils and fats, and carbohydrates.

Later, the t-shirts were defrosted and nine women volunteered to give them a sniff. The women rated how attractive, strong, and healthy the t-shirts smelled.

They also rated how much each shirt smelled like each of a list of 21 descriptors. The researchers found that many of these descriptor clustered together. For example, men who smelled floral also smelled fruity, sweet, and medicinal, but did not smell meaty, animal, or oily. The researchers called this the animal/floral factor. Another cluster — the fishy factor — was based on odors of fish, egg, garlic, yeast, sourness, and tobacco: men who smelled of one tended to smell of the others. The final cluster was the chemical factor: men who smelled of chemicals also smelled burnt.

Does a diet rich in fruit and vegetables make a man’s sweat smell like a bouquet of flowers? Derek Hatfield/Flickr

Results showed that the body odor of men who ate more eggs and tofu, and more oils and fats, were rated more favorably than that of men who ate more seafood or carbohydrates. Diet explained 20% of the differences between men’s odor, meaning that diet has an important affect on body odor but is clearly not the only factor.

Men who ate more fruit and oils and fats tended to rank highly on the animal/floral factor (they smelled of flowers but not of meat). Eating more seafood and carbohydrates had the opposite effects: these men smelled less of flowers and more of meat. Eating fruit and vegetables was associated with high scores on the chemical factor, but eating legumes, meat, and eggs and tofu made a man smell less of chemicals and burning. No food types were associated with a fishy smell, which suggests that this type of odor is not linked to diet.

In an extra twist, the researchers used a spectrophotometer to measure the skin color of their male volunteers’ hands. Previous research has shown that eating fruits and vegetables rich in pigments called carotenoids makes our skin appear more yellow. This skin color is rated more attractive and healthy, which makes sense because carotenoids are essential for a healthy immune system. So, if diet is related to odor and to skin color, do men with yellower skin smell more attractive?

The answer is yes: men whose skin is more yellow — and whose diet is presumably rich in foods such as pumpkins, kale, and tomatoes — smell more attractive and healthy.

This suggests that eating a healthy diet isn’t only great for your health, but also for how you look and how you smell.

Fertility and Body Odor

As Zuniga’s research shows, diet has important effects on how we smell, but food isn’t the only factor.

Research has suggested that women smell more attractive to men when they are in the fertile phase of their menstrual cycles (when they are most likely to conceive).

Women have a better sense of smell than men, so Kelly Gildersleeve of Chapman University, along with her colleagues at UCLA, decided to test whether women can also detect cycle-related differences in the odor of other women.

They had 33 women “donate” body odor samples, using a similar procedure to that used by Zuniga and colleagues. Women wore cotton pads in their armpits for 24 hours. Normally cycling women wore pads twice: once each during the high and low fertility phases of their cycles. Women who used the oral contraceptive pill provided only one sample, as previous research has shown that the pill cancels out any effects of cycling hormones on appearance, odor, and behavior.

The researchers then recruited another 100 female volunteers from a local gay pride event. These volunteers gave each of the sweaty patches what the researchers call “ a hearty sniff”, then rated them for attractiveness, pleasantness, sexiness, and intensity.

This is one way of doing it, I guess. Not exactly a “double blind” study though, is it? Pretty Poo Eater/Flickr

Odor samples collected at high fertility were chosen as more attractive than low fertility samples from the same woman 60% of the time: women didn’t smell phenomenally more attractive when fertile, but there was a detectable difference. High fertility samples were also rated as more pleasant, sexier, and less intense than low fertility samples.

The samples of normally cycling women and women using the pill did not differ on any measure. Taking the pill does not make a woman smell any less attractive, sexy, pleasant, or intense than she otherwise would. This is, perhaps, surprising given what we know about the effects of the pill from other research.

Are body odor changes across the cycle likely to be meaningful? Given that approximately 25% of the variance in women’s odor ratings were explained by cycle phase, it seems so. This is 5% more than the difference in men’s smell explained by diet in Zuniga’s study. However, as Gildersleeve and colleagues point out, their research was conducted in a laboratory and:

“It is possible that in a more naturalistic setting, day-to-day variation in women’s diet and activities, the weather, ambient odors, and so on would introduce so much ‘noise’ as to render subtle changes in women’s scent attractiveness linked to their fertility undetectable.”

One things’s for sure: until my sinuses unblock, every scent is going to be undetectable to me…

Gildersleeve, K., Fales, M. R., & Haselton, M. G. (in press). Women’s evaluations of other women’s natural body odor depend on targets’ fertility status. Evolution and Human Behavior. View summary

Zuniga, A., Stevenson, R. J., Mahmut, M. K., & Stephen, I. D. (2017). Diet quality and the attractiveness of male body odor. Evolution and Human Behavior, 38(1), 139–143. View summary

For an audio version of this story, see the 17 January 2017 episode of The Psychology of Attractiveness Podcast.

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