Our taste buds contain a few types of specialized receptors, each tuned to a broad flavour category. Receptors for sweetness, saltiness, and delicious “umami” (a savoury quality linked to amino acids found in protein, especially glutamate) give us a sense of pleasure and encourage us to eat more of the simple sugars, important electrolytes, and nourishing protein that elicit these flavour experiences (5). There may be a receptor for fats as well (6), another important source of nutrition. Sour taste receptors have a more neutral role: if coupled with sweetness (think fruit), sourness can be pleasant. In other cases (think spoiled meat, or rancid fat), acidity feels wrong, and leads us to stop eating (7). But bitterness always acts as a deterrent: folks report that they just don’t like the flavour and tend to avoid bitter-tasting foods (8). This is obvious in children, who may have a higher concentration of bitter taste receptors compared to adults (9): even the small amounts of bitter compounds in vegetables like broccoli send them running. But if you look at the modern Western diet, you will find that we’ve systematically removed bitter ingredients from our food supply (10), and even altered our vegetables to contain fewer bitter constituents (compare the wild versions of carrots and lettuce to their domesticated, supermarket varieties) (11). Indeed Western culture seems to have a child-like palate.

The reason we turn away from the bitter flavour is the same reason children are more sensitive to bitterness: toxic, poisonous substances are often very bitter, and the receptors that detect their presence (known as T2R, or “taste type 2 receptors”) are there to protect us (12). This is important at any age, but even more so for the sensitive metabolisms of children. T2Rs on the tongue, like other taste receptors, are linked to the brain’s flavour perception centres via nerve fibres (13). There are more than 25 different types, sensitive to hundreds of different bitter compounds from the natural world (14). This broad spectrum includes simple polyphenols, such as the flavonoids in goldenrod herb (Solidago species); strongly bitter lactones found in roots from dandelion to gentian (Gentiana lutea L.); and alkaloids, from caffeine to atropine, which are rare, intensely bitter, and often deadly. While the protective effect of T2R stimulation makes sense for a poison like atropine (from Atropa belladonna L., the deadly nightshade), you might wonder why we need protection from the non-toxic dandelion root (or broccoli for that matter). In fact, we don’t – but whether goldenrod or dandelion, plants that are not toxic to humans may still be toxic to many insects, and a deterrent to browsing (15). Insects have primitive taste receptors that are thought to be the evolutionary precursors of T2Rs: similar in structure, they activate a primal, aversive response (16). The insect gets the message, and eats less.

This message alters behaviour in mammals, too. An interesting area of clinical research on the bitter taste involves appetite modulation. In an apparent paradox, bitters have been used to stimulate appetite in conditions like anorexia, or when appetite is suppressed during illness or convalescence (17). This gentle effect can help folks maintain or recover a healthy weight and may be related to the increase in digestive juice production and stomach muscle tone that accompanies a dose. But for those whose appetites are normal (or excessive), recent clinical research suggests that experiencing a bitter taste before or during a meal reduces overall consumption of food between 20% and 30% (18). The effect lasts throughout the day and can be valuable for those attempting to control their weight or reduce their intake of carbohydrate-rich foods (19). Bitters may affect our appetite much the same way bitter compounds affect insect browsing.