Colours in food: should we colour-coordinate our plates?

Article written for Visionen 2015/5.


 

It is intuitively clear that we prefer vivid colours in our food, rather than bland brownish/beige colours. Indeed, we as a species have colour preferences that affect many aspects of our life: from buying a car (bicycle?), to selecting an outfit for a date, or choosing the colour pattern to decorate our rooms. A recent study explored this affinity, and found that we tend to like more those colours that are associated with things we like; the blues of the sea are preferred over the browns of the soil [1]. Of course, brown is not always unappetizing in food: think about a wonderful beef stew, caramel at 180 C, or cinnamon-flavoured apple strudel. Still, our eye tends to be drawn towards the multicoloured dishes, and I would like to explore here some reasons why.

the connection of colour and physiology

Robust research on the relationship of colour perception and physiological functioning in humans is surprisingly new [1]. True, already Johann Wolfgang von Goethe (1749-1832), in his work “Theory of colours” separated colours into “plus colors”—yellow, red-yellow, and yellow-red—thought to induce positive feelings and “minus colours”—blue, red-blue, and blue-red—thought to induce negative feelings. Goethe’s idea was extended in the works of his successors. The overarching thought was that color produces direct physical reactions in the body, and the explanations for the mechanisms differed. For example, it was thought that pink and orange light have an endocrine-based weakening effect on muscle function [2]. Unfortunately, many experiments, some conducted as recently as 1994, suffered from methodological flaws—e.g., ignoring the three attributes of colour, hue, lightness, and chroma—and therefore led to few conclusive findings.

Applying a more robust theoretical framework led to the research of colour in contexts such as affiliation or attraction. For example, Elliot and Niesta found that men find women more attractive when they are in a red context, for example in red clothing [3]. Surprisingly—for me, at least—was that the “red effect” is present also in the opposite direction: women rated men wearing red shirts more favourably [4].

The effect of colour extends to food/beverage consumption [1] and references therein. Think about the following findings when you select dishes for your next (dinner) party: popcorn taken from a red bowl is perceived to be sweeter; people eat fewer snacks from a red plate; hot chocolate was found to be more chocolatey when served in orange or dark-cream coloured cups; and red wine was rated better when served in blue glasses.

Nutritional quality indicated by the colour

One often stated hypothesis for the existence of colour preference in food is that variation in colour indicates variation in nutrients and this in turn indicates a healthier meal. Indeed, many cultures put emphasis on the variation of colour on the plate.

Pigments in food

In many cases, the variety in colour in fruits and vegetables stems from several classes of phytochemicals. Just like macronutrients (i.e., carbohydrates, proteins, and fats) and micronutrients (i.e., vitamins and minerals), phytochemicals are naturally occurring molecules that absorb light of specific wavelengths; when the absorption is in the visible range for humans (390 to 765 nm), we perceive the respective produce as coloured.

Phytochemicals are produced for the benefit of the plant, not for our benefit. Still, they can influence our health. For example, it was shown that consuming whole foods can provide health benefits through the associated phytochemicals such as carotenoids and flavonoids. There are three major classes of phytochemicals: carotenoids, chlorophylls, and anthocyanins. And it is these phytochemicals that we turn to next.

Carotenoids

Carotenoids are a type of phytochemicals that give yellow, orange, and red colour to foods. For example, the carotenoid that gives orange colour to carrots, ß-carotene, is converted to vitamin A in our body; since we cannot produce vitamin A ourselves, it is crucial that we consume it in our food.

Foods that contain carotenoids were found to be beneficial for our health [5]; however, we do not get the beneficial effect if we merely supplement our food with carotenoids [6]. The best thing to do: make a nice pumpkin soup or a pumpkin risotto and get the carotenoids from source where they are plentiful: hokkaido pumpkin [7].

Chlorophylls

Chlorophylls are responsible for the green colour of many fruits and vegetables. As you have surely noticed, they are not particularly stable: cooking and high acidity can affect chlorophyll and make the bright green appear dull. Additionally, a plant hormone ethylene destroys chlorophylls; in food industry, this process is sometimes artificially induced with ethylene to turn picked unripe tomatoes red.

I will refrain from commenting on the health benefits of chlorophylls, as I do not particularly trust the sources I found that praize chlorophyll. Nevertheless, I find the bright colour appealing, and there are two green dishes that are particular favorites of mine, tabbouleh and “blitva,” the latter being a mix of crushed floury potatoes, Swiss chard, salt, pepper, and copious amounts of olive oil. You can find a (kind of) recipe for blitva on my blog.

Anthocyanins

Anthocyanins are a large group of phytochemicals responsible for the blue, purple, violet, magenta, and most of the red hues of plant parts. Two exceptions are worth noting: the red colour of tomatoes stems from lycopene and the purple colour of the beet stems from betanin, neither of the pigments belonging to the anthocyanins group.

Molecules in this group were found to have anti-inflammatory effect. Additionally, population-based investigations associate anthocyanins intake with reduced incidences of cardiovascular disease, diabetes mellitus, and cancer [8].

It is not like one needs an excuse to eat a cheesecake, but here is one nonetheless: when sour cherries are added to the cheesecake, we enrich it in berry antioxidants [9]. Let us not nitpick about the calories, ok? The recipe is here.

Can we see what is good for us?

There is indeed much evidence that different-coloured food is good for us, and I hope that the recipes I linked managed to convince you—if any convincing is needed—that it is also tasty. However, I will just briefly reflect on the “invisible” goodness in our food. We cannot always see what is good for us. For example, vitamin C, a vitamin necessary for our growth and development, does not absorb light in the wavelength range humans can see. It will appear white (e.g., when it is sold as powder), and other plant pigments might mask its presence. We therefore cannot estimate the vitamin C content from the appearance only [10].

Therefore, one should not ignore white vegetables. For example, the American groundnut is a tuber similar to potato, used abundantly in the diet of Native Americans. It is rich in protein, but also has the highest concentration of a phytochemical that does not contribute any of the vivid colours,  a type of isoflavone.

Another more accessible food hero is cauliflower. Even though the brightly coloured varieties have higher levels of carotenoids, the humble white cauliflower is rich in non-colored phytochemicals associated with health benefits, e.g., sulforaphane, produced during cooking or chewing, and indole-3-carbinol. In model organisms, both of these compounds have shown anticancer properties [11].

Have a look here for a very modern—low carb— take on “rice.”

Parting words

I am not sure if I have done much more than provoked a strong hunger and a sense of curiosity in you with this article. Still, based on the literature I read, I recommend to keep an eye out for different coloured vegetables next time you go grocery shopping. In addition to the various phytochemicals, perhaps try adding something that wasn’t featured on your menu in a long time?

References

  1. Elliot AJ, Maier MA. Color psychology: effects of perceiving color on psychological functioning in humans. Annu Rev Psychol. 2014;65: 95–120.
  2. Ott J. The Eyes’ Dual Function. A Physician’s Handbook on Orthomolecular Medicine. Elsevier; 1977. pp. 173–180.
  3. Elliot AJ, Niesta D. Romantic red: red enhances men’s attraction to women. J Pers Soc Psychol. 2008;95: 1150–1164.
  4. Roberts SC, Owen RC, Havlicek J. Distinguishing between perceiver and wearer effects in clothing color-associated attributions. Evol Psychol. 2010;8: 350–364.
  5. Donaldson MS. A carotenoid health index based on plasma carotenoids and health outcomes. Nutrients. 2011;3: 1003–1022.
  6. Jeon Y-J, Myung S-K, Lee E-H, Kim Y, Chang YJ, Ju W, et al. Effects of beta-carotene supplements on cancer prevention: meta-analysis of randomized controlled trials. Nutr Cancer. 2011;63: 1196–1207.
  7. Kreck M, Kürbel P, Ludwig M, Paschold PJ, Dietrich H. Identification and quantification of carotenoids in pumpkin cultivars ( Cucurbita maxima L.) and their juices by liquid chromatography with ultraviolet-diode array detection. J Appl Bot Food Qual. 2012;80: 93–99.
  8. Fang J. Classification of fruits based on anthocyanin types and relevance to their health effects. Nutrition. 2015; doi:10.1016/j.nut.2015.04.015
  9. Blando F, Gerardi C, Nicoletti I. Sour Cherry (Prunus cerasus L) Anthocyanins as Ingredients for Functional Foods. J Biomed Biotechnol. 2004;2004: 253–258.
  10. Barnes S, Prasain J, Kim H. In nutrition, can we “see” what is good for us? Adv Nutr. 2013;4: 327S–34S.
  11. Bradlow HL. Review. Indole-3-carbinol as a chemoprotective agent in breast and prostate cancer. In Vivo. 2008;22: 441–445.