DEAR DR. ROACH: My daughter-in-law has stage 1 breast cancer and has just started her chemotherapy. I am concerned about her decision to fast for two days before and one day after each treatment. She weighs only 90 pounds, and fasting while you are trying to fight cancer does not sound like a good idea. What is your opinion of fasting during chemotherapy? — K.B.

ANSWER: In theory, fasting may make cancer cells more susceptible to chemotherapy, and there have been studies in mice suggesting this approach might have value. However, during chemotherapy, the whole body needs good-quality nutrition, and I could not recommend fasting for someone who weighs so little, nor could I recommend two full days of fasting before chemotherapy.

DR. ROACH WRITES: A recent column from a woman complaining of yawning after 10 minutes in her husband’s car generated a remarkable amount of mail. Most readers brought up one of two concerns: Could there be a carbon monoxide leak, and could her symptoms be due to a cabin air filter in need of cleaning or replacement?

Symptoms of carbon monoxide poisoning are varied, but the most common early symptoms are headache, nausea and vomiting. Yawning is listed in a few sources I’ve seen as a possible symptom of carbon monoxide poisoning.