Sunday, January 31, 2010

the big bad brussel...and the science behind it (with recipe at end so if you hate science but love bacon, there's still hope)

MMM. Brussel sprouts. Who doesn't love them? In the doldrums of winter with very little greenery and little else to look forward to, when the cold darkness slowly eats at the core of every human soul, what else could brighten up my day more than a deliciously prepared emerald brussel sprout? Even if I adore them, brussel sprouts are the vegetable of disdain to many small (and large) children.

It would appear that this seemingly small offender, a tiny cabbage, wouldn't cause so much trouble. But, it seems that the hate of brussel sprouts, and also cabbage, broccoli, cauliflower, tea, coffee, and tobacco have a genetic basis. Although this is not new news, it certainly is to me. What could be better than the interface between food and science? A quick search on PubMed unveils a body of research as to why some children hate vegetables. With genetics to blame, parents are now completely off the hook for the nutritional deficiencies of their children with a diet of mac and cheese and chicken fingers.

Brussel sprouts contain large amounts of the chemical phenylthiocarbamide (PTC) and a related compound propylthiouracil (PROP). No need to worry about chemistry, just know that these compounds cause some foods to taste bitter. Scientists and anthropologists have known for a long time that different ethnic groups have different sensitivities and likes to bitter compounds and foods. Because many poisons and toxins are also bitter, this distaste could potentially have an evolutionary advantage, promoting the forager to pick a sweet berry vs. a poisonous mushroom. It was unknown, however, whether this variance in tastes was cultural, environmental, genetic, or a mixture.

Recently, and by recently I mean 7 years ago, with the advent of improved techniques for studying and isolating genetic material, a group of scientists discovered the gene and its mutations which accounts for the variations in taste of bitter food (1). Without getting too technical, the gene, TAS2R38 has three loci(regions) that have mutated to produce multiple variations of the gene. These mutations were found to account for the majority people's ability to taste or not taste bitter foods. (Of course, these genes do not account for 100% of the ability to taste bitter. Even if in freshman biology genetics seemed so short pea or tall pea, there are so many modifying factors for the expression of a trait that science is simply not that straight-forward.)

This fascinating genetic discovery was followed by many complex and rich studies to explain cultural and age related differences for the dislike of brussel sprouts. An excellent study published in Pediatrics in 2005 attempts to explain why children choose the foods they do (2). They discuss the influence of these choices from genetics, culture and their parents' likes and dislikes. After swabbing the mouths of 143 children to isolate the genetic variant of TAS2R38, looking only at the first of three mutations (A vs P) to stratify the group into homozygous AA, heterozygous AP and homozygous PP, the children were given water flavored with different amounts of PROP. The methodology section, unlike most journal articles, is the best part of the paper:
If the solution tasted like water, then they were told to give it to a stuffed toy of Big Bird (a likable, well-known television character puppet); but if it tasted “yucky” or bitter, then they should give it to Oscar the Grouch, “so that he can throw it in his trash can".

Like previous research, this paper showed variations in the ability to taste bitterness based on their genetic differences. Interestingly though, this project also compares children to their parents and their abilities to taste bitterness, and thus provides a possible explanation for why kids piss off their parents so much. The study shows that heterozygous children are more sensitive to PROP than genetically similar people of an older generation. Not only are children more sensitive to PROP when they carry the gene, but their decisions, unlike adults' decisions, "are less constrained by experiential and cognitive factors, and their taste preferences determine intake." This is why, even if we can taste bitterness, we still love beer, coffee, tea and other adult treats and overlook the potential threats of the toxins and poisons we are putting into our bodies (especially broccoli).

Thus, even if YOU are a carrier of a "taster" gene, as it is so lovingly called, you can make the adult decision to like brussel sprouts, and love the bitterly delicious flavors that waft over your taste receptors. Science shows that fewer people are tasters than before and approximately 20-40% of North American Caucasians are non-tasters (3). In Spain, they studied the El Sidron Neanderthal's TAS2R38, discovering that he was a taster (although with a sample size of one Neanderthal, it's hard to know whether his friends liked cauliflower or not) (4). Even if you are a taster, I am assuming we have evolved from Neanderthals. Thus I leave you with a recipe for these little gems topped with bacon, pine nuts, brown sugar, and lemon.

In this recipe, I like to slice up the sprouts very thinly so they cook quickly and evenly. If you prefer whole sprouts then blanch them in boiling water for 1 minute before sauteeing so that they cook inside without burning on the outside.

1lb brussel sprouts
2-3 slices thick cut bacon
1 shallot diced finely
1/4 cup pine nuts (other nuts such as almonds or walnuts would work too)
juice of one lemon
1 tbs dijon mustard
2 tsp brown sugar
salt and pepper to taste

1. Wash brussel sprouts thoroughly. Cut off bottom of sprout and discard top few leaves. Slice each sprout vertically and thinly.
2. Mix mustard, sugar and lemon together
3. Preheat large cast iron skillet or other skillet with a small amount of oil on medium-high heat. When hot, add bacon, and cook to your liking. Discard some of the fat (if you want) although not all because this is what you will cook the sprouts in.
4. When bacon is almost finished cooking add shallots and sautee for a couple minutes until translucent
5. Add pine nuts and saute briefly
6. Add brussel sprouts to pan. Salt and pepper to taste. Saute, stirring frequently for about 5 minutes until they are almost cooked (they will turn a bright green and look soft having lost some of their water when they are done)
7. When almost cooked, add lemon/mustard dressing to the mixture and cook out sugar for 1-2 minutes until veggies have slightly caramelized
8. Enjoy!


1. Kim, UK., et al. Positional cloning of the human quantitative trait locus underlying taste sensitivity to phenylthiocarbamide. Science. 299 (2003) 5610:1221-5

2. Mennella et al. Genetic and Environmental Determinants of Bitter Perception and Sweet Preferences. Pediatrics 115 (2): e216. (2005)

3. Guo, SW. and DR Reed. "The genetics of phenylthiocarbamide perception." Annals of Human Biology 28.2 (2001), 111-42.

4. Lalueza-Fox, C., et al. "Bitter taste perception in Neanderthals through the analysis of the TAS2R38 gene." Biology Letters 5.6 (2009), 809-11.

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