Why does chemotherapy make food taste terrible?

People who go through chemotherapy say one of the most frustrating side effects is that even their favourite foods taste awful. Pasta tastes like cardboard, meat tastes metallic. Patients have no desire to eat and end up getting fewer calories and less nutrition when they need it most—to battle the cancer as well as the ravages of the therapy. Why?

Why does chemotherapy ruin food’s appeal? Does radiation therapy, often involved, make matters worse? Scientific American asked Beverly Cowart, director of clinical research at the Monell Chemical Senses Center in Philadelphia, to explain the mechanisms as well as strategies patients can use to make food more desirable.

Chemotherapy is supposed to work by killing cancer cells. How might that affect taste?
Cancer cells proliferate rapidly, and most chemotherapies target rapidly growing cells. Taste cells turn over rapidly, too; stem cells in the base of a taste bud regularly replenish the taste cells. So the chemicals attack the taste cells as well. They either attach to a cell or enter it, then destroy it. As many cells die, taste disappears.

What about bad tastes, such as metallic or bitter sensations, instead of a lack of taste?
Like most medications the chemicals enter the bloodstream and they get into saliva that way. The saliva brings them to the taste cells and the cells send messages of “metallic” or “bitter” to neurons that lead to the brain. It’s strange to think of it this way but we can “taste” things in the bloodstream. For example, researchers in Japan injected saccharin into people’s bloodstreams and the people quickly tasted it.

Patients often complain of nausea. That also makes food less appetizing.
Right. Your body is programmed to tie nausea to something you ate. If you eat a specific food and get sick, you will find it hard to eat that food again. Cancer patients who feel nauseous become conditioned to avoid all kinds of foods they may be eating.

What about radiation?
If radiation is being used near the mouth area, such as for oral cancer, it can have an effect. Radiation elsewhere in the body does not. In these cases, even though the radiation is highly targeted, it’s still impossible to avoid hitting salivary glands. The glands get knocked out, and the patient gets chronic dry mouth.

For us to taste something, it has to go into solution so it can enter a taste bud’s taste pore; saliva is there to dissolve food into solution. Without saliva, it is hard to taste anything.

Does chemotherapy also affect smell, which is central to taste?
The smell system’s receptors also interact with chemicals in the bloodstream, but the cells turn over more slowly than taste cells, so the chemicals might not attack them as much. They regenerate from stem cells, too, but that takes longer and it’s more complicated, because smell cells are actually the ends of neurons, signalling the brain directly. When they regrow they have to mature and they also have to connect to the brain. Overall, smell cells get involved but they seem to be less affected than taste cells.

What are common, good tactics patients can use to help make food more appealing?
Because nausea makes you associate sickness with specific foods, don’t eat the things you regularly eat before a chemotherapy treatment. Eat so-called scapegoat foods—unusual or unusually flavored foods you wouldn’t be likely to eat otherwise. You may end up hating them, but it won’t matter for your other meals.

If the problem is diminished taste, rely on liquid nutrients to create solution that penetrates the taste pores—especially if you have dry mouth.

In general, eat slowly and chew a lot, to give food more of a chance to enter the few healthy taste buds that are there. Sour flavors tend to come through more readily, so things like lemon can be used to enhance flavor. To enhance smell, jack up the volatile compounds—herbal ingredients and liquid spices.

Does taste return to patients after treatment is done?
With chemotherapy, once the drugs clear from the body the taste system usually returns over time. Recovery from radiation can take longer, even a few months, but there can also be some permanent damage to the salivary glands. Patients sometimes use artificial salivas to help themselves.

Source: Scientific American