Does it taste ‘calciumy’? (part 2)

funny-face-386070-mIn the study we described in our previous post (linking bitterness of vegetables to their calcium content), Dr. Michael Tordoff and his team of researchers also ran some additional tests in rodents. They found that lab mice which were previously known to prefer calcium ate collards (high calcium food) more than they ate cabbage (low calcium food). They also noticed that rats that were kept on a low-calcium diet ate collards more than rats kept on a standard diet. These results indicate that it is plausible that mice and rats can selectively choose to eat calcium-rich foods because they can ‘taste’ the calcium in these foods. In a subsequent study, Dr. Tordoff identified a calcium taste receptor in mice known as the T1R3 receptor, previously known to play a role in the detection of sweet and savoury (umami) tastes. (Here’s a neat picture from the journal Nature on taste receptor cells and where they reside on our tongues.)

Dr. Tordoff and his team then set out to discover whether humans have a calcium taste receptor as well and if T1R3 is the taste receptor in humans also. A key ingredient in their experiments was a substance known as lactisole. Lactisole interferes with our ability to taste sweetness. For this reason, it is used in jams and jellies to subdue the sweetness from the large amounts of sugar that are used in such products and to allow the flavour of the fruit to come through. At a molecular level, lactisole latches onto the T1R3 receptor and this prevents sugar molecules from reaching the receptor and triggering the sweet taste.

If T1R3 is also the taste receptor for calcium, then adding lactisole to a calcium-rich food should also suppress the calcium taste. To test this hypothesis, the researchers recruited 16 volunteers and trained them to recognize the taste of calcium by giving them several solutions to drink and taste, including a solution of calcium lactate. Calcium lactate is found in aged cheeses and is used medicinally as an antacid, and has also been used in animal studies of calcium taste. Once the volunteers in the study were able to recognize the calcium taste and differentiate it from the other solutions they tasted, four more solutions were added to their tasting experiments – a low concentration calcium lactate solution with and without lactisole, and a high concentration calcium lactate solution with and without lactisole. As expected, the volunteers recorded a decrease in the intensity of the calcium taste when lactisole was added – evidence that T1R3 was likely responsible for the calcium taste.

The results gathered from these experiments indicate that we have a taste receptor for calcium on our tongue – the T1R3 receptor. This means we can taste calcium as a distinct taste and be able to recognize and differentiate it from other tastes. If you want to try it out for yourself, eat some high-calcium vegetables such as collards and kale and see if you can pinpoint the common calcium taste that they have. Although dairy products are also high-calcium foods, it’s hard to taste the calcium in them as dairy also contains fat and proteins which can bind to the calcium and prevent it from being tasted. You can get around that however, by eating low-fat diary products such as low-fat yogurt, low-fat greek yogurt, or low-fat cheese, where there is less fat binding to the calcium. In fact, the slightly chalky, slighty bitter taste of calcium may be the reason that most people dislike eating low-fat dairy products. But despite the ‘calciumy’ taste, don’t forget that such foods are our best choices when it comes to cutting down on fat AND getting enough calcium.

Reference: Tordoff MG, Alarcón LK, Valmeki S, Jiang P. T1R3: a human calcium taste receptor. Scientific Reports 2012;2:496. PMID: 22773945

Does it taste ‘calciumy’? (part 1)

Collards (photo by Steven Jackson on Flickr)
Collards (photo by Steven Jackson on Flickr)

Some vegetables are hard to eat, no matter how health-conscious you might be. Hardly anyone professes kale or collards to be their favourite foods. Perhaps due to the bitterness of these and other vegetables, people generally do not eat enough vegetables. We also know that in general, many people do not get enough calcium in their diets.

A few years ago, researchers in Philadelphia came up with an interesting hypothesis: what if it is the calcium in them that gives vegetables a bitter taste?  To test their theory, they dug up data from a previous study that had asked participants to rank certain vegetables based on bitterness. They then looked up how much calcium each of these vegetables contained. Armed with both sets of information – vegetable bitterness score and vegetable calcium content – they ran some statistical tests to see if the two were related. 

They discovered that their hypothesis was true: there was a strong positive relationship between the amount of calcium contained in 24 vegetables and their bitterness rating. Vegetables such as collards and kale, which ranked high in bitterness, also had high amounts of calcium in them. But keep in mind, this information alone does not prove causation, i.e. the analysis only showed that vegetable bitterness and calcium content were related, but this did not mean that calcium caused the bitterness in the vegetables.

Nonetheless, these results raise an intriguing question: might there be a receptor on our tongue that actually ‘tastes’ calcium, similar to other receptors on our tongue that taste sweetness, sourness, salty, bitterness, and savoury (umami)? Turns out there is! Find out in our next post the experiments that led to the discovery of T1R3, the human calcium taste receptor.

Reference: Tordoff MG, Sandell MA. Vegetable bitterness is related to calcium content. Appetite 2009;52(2):498-504. PMID: 19260165