Your Good Health: Evidence on the Effectiveness of Mixed Intermittent Fasting


Dear Dr Roach: I’m interested in your take on intermittent fasting. I am part of a group of senior walkers (all 65 and over). Six of us went on this diet for six to eight weeks, and everyone consistently lost one pound per week. There is a lot of debate about how it works. We are on an eight hour meal window and a 16 hour fasting window. Our catering window is from 11:00 a.m. to 7:00 p.m.

Is it about insulin control? During the fast, one can have water and black coffee. Is it okay to have flavored coffee without sugar and without calories? How about a flavored sparkling water like LaCroix without sugar, calories and sodium?


Intermittent fasting is a strategy primarily used for weight loss in people without diabetes. Data on its effectiveness is mixed, with one trial showing weight loss of 5.2 kg (about 12 pounds) over a 12-week trial, which you and your group found. However, other trials have shown no benefit of intermittent fasting over calorie restriction or a control group that received no recommendation to change their diet.

Intermittent fasting can be done daily (“fast days” followed by “feast days”) or by time restriction, which your group did. The theory is that 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 my own patients has not been successful, but my weight management colleagues find it a useful tool for a subset of patients. Not everyone does well with intermittent fasting, regardless of the type.

From a weight management standpoint, black coffee and water, even flavored, is zero calorie and does not interfere with diet goals.

Dear Dr Roach: I visited my oncologist yesterday for follow-up after breast cancer treatment five years ago. My blood tests were normal, but I have lost 30 pounds in the past year. It was a goal: weight loss came by counting calories and exercising. My doctor is worried and wants me to have a CT scan of my chest, abdomen and pelvis. Is it really necessary? I feel perfectly healthy.


This is a situation that I have seen several times. I fervently hope that your hard work is paying off and your weight has been reduced thanks 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 return of cancer or a separate new problem, possibly related to cancer treatment.

Your oncologist is very careful and, in my opinion, is right to do so. The downside includes the cost, some radiation, and some dyes. These should not be ignored, but in the (hopefully) unlikely event that the cancer does return, knowing it as soon as possible will give you the best chance of successfully treating it.

I asked an oncology colleague about this situation, and he was reassuring, saying that losing weight is not the way breast cancer comes back, if it is. Personally, however, I think the scan is still worth it. I advise you to accept the recommendation of your oncologist.

Dr Roach regrets not being able to respond to individual letters, but will fit them into the column whenever possible. Readers can email their questions to [email protected]

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