DEAR DR. ROACH: I am interested in your perspective on intermittent fasting. I am in a walking group of seniors (all 65+ years). Six of us have been on this diet for six to eight weeks, and everyone has consistently lost a pound a week. There is a lot of debate about how it works. We are on an eight-hour eating window and 16 hours of fasting. Our eat window is 11:00 am to 7:00 pm.

Is it about insulin control? During fasting, we can have water and black coffee. Is it OK to have flavored coffee, like coffee that has no sugar and no calories? How about flavored carbonated water like LaCroix without sugar, no calories and no sodium? — L.S.

ANSWER: Intermittent fasting is a strategy mostly used for weight loss in people without diabetes. The data on its effectiveness is mixed, with one trial showing weight loss of 5.2 kg (about 12 pounds) in a 12-week trial, which is what you and your group have found. However, other trials have shown no benefit in intermittent fasting compared with calorie restriction or a control group that received no recommendations for changing diet.

Dr. Keith Roach

Intermittent fasting may be done on a daily basis (“fast days” followed by “feast days”) or by time restriction, which is what your group has done. The theory is that the fasting works with the body’s circadian rhythm to improve insulin sensitivity; however, the mechanism by which it works (when it does) is not well understood.

My experience with it in my own patients has not been wildly successful, but my colleagues in weight management feel it is a useful tool for a subset of patients. Not everyone does well with intermittent fasting, no matter what type.

From the standpoint of weight management, black coffee and water, even if flavored, are zero calories and do not interfere with the goals of the diet.

DEAR DR. ROACH: I visited my oncologist yesterday for a follow-up after breast cancer treatment five years ago. My bloodwork was normal, but I have lost 30 pounds over the past year. This was an on purpose: Weight loss came via counting calories and exercising. My doctor is concerned and wants me do have a scan of the chest, abdomen and pelvis. Is this really necessary? I feel perfectly healthy. — D.S.

ANSWER: This is a situation I have seen many times. I fervently hope that it’s your hard work paying off, and that your weight is down due to your healthy lifestyle. But I have seen, and I’m sure your oncologist has seen, many people whose weight loss is due in part to the cancer coming back, or to a new, separate problem, possible related to the cancer treatment.

Your oncologist is being extra cautious, and in my opinion, is right to do so. The downside includes cost, some radiation and some dye. These are not to be ignored, but in the (hopefully) unlikely case that the cancer has returned, knowing about it as soon as possible will give you the best chance to get it successfully treated.

I did ask a colleague in oncology about this situation, and he was reassuring, saying that weight loss is not how breast cancer shows back up, if it does. Personally, however, I think the scan is still worth the downside. I’d advise you to accept your oncologist’s recommendation.

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Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.