Refined Carbohydrate Consumption and Facial Attractiveness. Claire Berticat, Valérie Durand, Michel Raymond. Evolutionary Psychology, October 29, 2020. https://doi.org/10.1177/1474704920960440
Rolf Degen's take: https://twitter.com/DegenRolf/status/1321815394852753409
Abstract: Since the second half of the 20th century, a massive increase in the consumption of refined carbohydrates has occurred, generating well-described detrimental health effects such as obesity, insulin resistance, type II diabetes, cardiovascular diseases and dental caries. Certain physiological mechanisms involved, particularly through chronic hyperglycaemia and hyperinsulinaemia, suggest that a non-medical trait such as facial attractiveness could also be affected. To explore this possibility, variation in facial attractiveness was evaluated relative to refined carbohydrate consumption. Attractiveness was assessed from facial pictures as judged by raters of the opposite sex. Estimates of refined carbohydrate consumption were based on the glycaemic load of three mealtimes at-higher glycaemic risk (breakfast, afternoon snack and between-meal snack). In the presence of several control variables, facial pictures of women and men with higher between-meal glycaemic loads were preferred by opposite-sex raters. Structural equation modeling suggests that this result is possibly mediated by an increase in apparent age for men and an increase in femininity for women. The different physiological ecologies of the three meals at-higher glycaemic risk are discussed as well as the interpretation of the results in terms of adaptation or maladaptation to the modern and unique dietary environment.
Keywords: refined carbohydrates, sugars, evolutionary diet, dietary switch, facial attractiveness, social trait, glycaemic load
In this study, we investigated whether refined carbohydrate consumption is related to facial attractiveness in healthy women and men. We found that women and men with the highest between-meal glycaemic loads were preferred by opposite-sex raters, result in the opposite direction than the prediction based on known physiological effects for women. This preference was maintained when controlling for potential confounding effects such as age, age departure from actual age, BMI, scholarship level, smoking status, facial femininity/masculinity index, and for women, whether they took the contraceptive pill.
Attractiveness is not independent of the refined carbohydrate content of the food eaten estimated through glycaemic load, although this effect was evidenced from only one (between-meal snack) of the three mealtimes at-higher glycaemic risk considered. This meal is not the one with the higher mean GL, and is not particularly odd for its macronutrient content as well as carbohydrates, protein, fat and fiber (Table 3). A possible explanation is that these three types of meals could correspond to different ecological food habits that affect subjects differently with different physiological consequences. For example, the usual mid-afternoon eating occasion known in France as the “goûter” corresponds (for those who usually have one) to a real dietary need. This meal is associated with a pre-prandial decline in plasma glucose and insulin concentration and a high motivation to eat (Chapelot et al., 2004). In contrast, between-meal snacks are often not associated with physiological hunger and are rather motivated by social or other external stimuli, with few resulting effects on satiety and compensation mechanisms (Bellisle, 2014). Therefore, this meal category could better reflect chronic and acute refined carbohydrate consumption. Finally, it is worthy of note that consumers of the between-meal snack were at a frequency around 40%–50% (Table 2), allowing more statistical power to detect a difference between two groups, relative to the distribution of consumers for the two other meals (ca. 91% for breakfast, and 63%–70% for the afternoon snack).
How Chronic between-Meal Snacks Could Affect Attractiveness
Refined carbohydrate-rich food consumption generates hyperinsulinaemia as a consequence of hyperglycaemia, interfering with growth factors and sex hormones, which themselves modulate morphology and secondary sex characteristics (Cordain et al., 2003). This result occurs because hyperinsulinaemia stimulates androgen synthesis by the ovaries and testes, increasing the quantity of free (and thus active) androgens in the blood. Androgens are the precursors of male and female sex hormones such as testosterone and estrogen. Hyperinsulinaemia has been linked to diseases associated with significant perturbation of sex hormone levels, such as polycystic ovary syndrome and premature menarche (Cordain et al., 2003). If the influences of a refined carbohydrate-rich diet on other downstream consequences have been poorly studied to date, it is possible that these consequences include the development of secondary sexual traits, typically masculine or feminine facial features. In addition, it has been shown that sex hormones modulate facial femininity/masculinity, which in turn influences attractiveness, with men preferring more feminine faces and women preferring more masculine ones (for a review see Puts et al., 2012). To capture facial secondary sex characteristics, a femininity/masculinity morphological index was computed, for which the difference within each pair was used as a control variable. Structural equation modeling showed that for women, the effect of glycaemic load on attractiveness could be indirectly mediated through a direct effect of the femininity/masculinity index, leading to an increase of femininity. Sexual hormones are possible candidates to explain this effect (Cordain et al., 2003), although, as it is in the opposite direction than expected, further work is required for a better understanding.
Another physiological effect of refined carbohydrate-rich food consumption is hyperglycaemia, which has itself several physiological consequences. For example, hyperglycaemia accelerates glycation, a covalent bonding process that cross-links the amino acids present in the collagen and elastin that support the dermis. Cross-linked collagen fibers are incapable of repair through the usual process of remodeling, directly impacting youthful skin appearance, which relies on flexible and repairable collagen fibers (Danby, 2010). Thus chronic hyperglycaemia generated by chronic between-meal snacks could affect attractiveness because skin aging directly impacts age appearance (Nkengne et al., 2008), and age affects attractiveness (Samson et al., 2010). However, this possible effect was controlled for because apparent age was independently estimated, and the difference in age departure from the chronological age within each pair was used as a control variable. Structural equation modeling suggested that for men, the effect of glycaemic load on attractiveness could be indirectly mediated through a direct effect on age departure from actual age. Indeed, an increase in the age difference (chronological or apparent) within each pair increased attractiveness (Table 4), and thus any skin aging effect, which increases apparent age, also increases attractiveness. This increase in attractiveness with age is generally described for relatively young men in the range 20–50 years old and is classically explained by the correlation between age and characteristics that advertise adequate parental investment in terms of resource and social status (Buss, 1989; Jencks & And Others, 1979). For older ages, the correlation between age and attractiveness is reversed, perhaps due to somatic senescence compromising some type of paternal investment, fertility decline, or to higher chances of passing on genetic defects to offspring (Hellstrom et al., 2006; Kong et al., 2012). For women, the aging effect is the opposite: an increase in the difference in age departure from actual age within each pair decreased attractiveness, i.e. men preferred women that were perceived to be younger (or compared to women evaluated older) (Table 4). Indeed, age supplies a powerful cue related to female reproductive capacity, and men prefer younger women (Buss, 1989).
Ultimately, Why is an Increase in Refined Carbohydrate Consumption Associated with an Increased Attractiveness?
Traditional foods with a high level of sugar contents are energetically rewarding, although they are typically seasonal or scarce, such as ripened fruit and honey. Because sugar excess generated by hyperglycaemia is stored as fat, traditional foods that generate hyperglycaemia are sometimes used to intentionally increase fat storage, e.g. the case of the food intake of Japanese sumo wrestlers (Nishizawa et al., 1976) or the fattening sessions described in various ethnic groups before an expected general shortage period (Garine & Koppert, 1990; Garine & Koppert, 1991). Generally, traditional food, i.e. pre-industrial or non-refined, does not generate hyperglycaemia. This is the case for fresh fruits, legumes, traditionally prepared cereals, etc. although there are counter-examples such as honey. Globally, traditional foods that generate hyperglycaemia were not always readily available because they were scare or expensive. Thus, it is possible that intake of foods that generate hyperglycaemia represents an advantage in certain traditional environments, particularly when food shortages are not uncommon. In such an environment, detection and preference of facial cues that display an ability to find refined carbohydrates sources could constitute an evolutionary advantage for the choice of mating partner. This hypothesis could explain why an increased consumption of such food increases attractiveness. However, in the current industrial dietary environment, foods that generate hyperglycaemia are not limited, and their consumption is not a signal of quality anymore. Therefore, it is possible that the current increased attractiveness associated with the increased consumption of such food is better understood as a maladaptation.
How the Other Control Variables Could Affect Attractiveness
Several other variables potentially affecting attractiveness were controlled for, although only BMI has a significant effect in that a higher BMI decreased facial attractiveness for both men and women (Table 4). Indeed, body weight can be accurately judged from facial images alone (Coetzee et al., 2010), and cues of adiposity affect social judgements of female and male faces (Coetzee et al., 2009; Han et al., 2016; Re & Perrett, 2014).
Limitations
The effect of chronic between-meal snacks on attractiveness could be confounded by a variable not considered in this work. One possibility could be physical activity, which could have the effect of both increasing attractiveness (Faurie et al., 2004; Stephen et al., 2009) and increasing between-meal snacks (Kerver et al., 2006; Ovaskainen et al., 2006). Other diet factors not taken into account could affect facial attractiveness, such as fruit and vegetable known to increase skin yellowness (Appleton et al., 2018; Zuniga et al., 2017). Also, the main and more complex meals, i.e. lunch and dinner, were not included, precluding the computation of an overall diet quality index, which could have possibly captured other aspects of diet influencing attractiveness. However, diet quality indexes are correlated with low-GL food (higher values for an increase of low-GL food, see e.g. Azadbakht et al., 2016; Jones et al., 2016), and thus are partially described by GL measures. Finally, energy intake of each meal was not controlled for in our model due to the high correlation observed with glycaemic load, but gave qualitatively similar results when integrated alone (Table S1). As a consequence, it is unclear whether the associations observed are due to energy intake or to glycaemic load.
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