AACR 2015

Extended overnight fasting may lead to reduced breast cancer risk

Dr Catherine Marinac - University of California, San Diego, USA

There is some really interesting work that’s done in mice that has shown that decreasing the amount of time we spend eating during the day and increasing the amount of time we spend fasting overnight may influence several metabolic parameters that are high relevant to breast cancer. There’s a wealth of evidence showing that timing of feeding schedules may influence metabolism and we worked to look at how this exciting work in rodents translated into humans.

Can you put some of those links together for me? What is it about the duration of eating and the duration of fasting that would influence metabolic factors, theoretically first of all?

One of the hypotheses here, specifically with these long overnight fasting periods, is that overnight fasting may influence circadian rhythm parameters. In particular eating late at night may influence circadian rhythms in our peripheral tissues which could have downstream effects on cancer risk. For example, we know that nightshift workers have higher rates of chronic disease and breast cancer than people who don’t work at night and we think that that has some sort of regulation on these circadian rhythm factors.

We used a national survey dataset of over 2,000 women participating in a national health and nutrition examination survey. We used 24 hour time-stamped dietary records to approximate the length of the nightly fasting duration and looked at associations between this nightly fasting duration and biomarkers of glycaemic control. In particular we looked at haemoglobin A1c and two hour post-prandial glucose. This is cross-sectional data, it’s publically available, it’s a national dataset. What we did is we looked at these patterns of associations and we found that women who fasted for longer nightly intervals had lower concentrations of haemoglobin A1c and two hour glucose, so they seemed to have better glucose control. What’s really interesting is this was independent of how much they ate.

How did that translate to breast cancer risks?

It’s hypothesised that high levels of glucose can fuel tumour growth and progression so we’re using this proxy biomarker of cancer risk.

Let me get this right, then. It’s looking as if having a meal late at night is going to be a risk factor for breast cancer.

It looks as though it has negative impacts on metabolic health and downstream effects on cancer risk.

Obviously it’s early days but these are extremely interesting data. What would you say to doctors generally, people generally, and particularly cancer doctors about this?

If these findings are reproduced in other studies and if these are confirmed by experimental trials it would mean that a long overnight fasting duration could be a new strategy to prevent cancer. This is a simple and understandable dietary guideline that we believe most women can understand and adopt and may have a big public health impact.