Why Eating Dinner Earlier May Help Protect Against Breast Cancer

Woman preparing dinner

Breast cancer is strongly linked to diet and lifestyle behaviors. Both obesity and diabetes are also connected to cancer because of the growth-promoting effects of insulin. So an intervention that would help keep blood glucose in a healthy range would likely help to not only prevent type 2 diabetes, but also breast cancer.

Disruption of normal circadian rhythms has also been linked to breast cancer.

Night shift workers have been found in multiple studies to have greater risk than those with a more conventional schedule, aligned with the light/dark cycle.

So, in addition to a healthy diet, one simple change—ending eating earlier in the evening—may improve both glucose metabolism and circadian clock alignment, leading to a reduction in breast cancer risk.

I have always recommended a long overnight fasting period—the time between dinner in the evening and breakfast the next morning—to maximize healing and repair. The catabolic phase begins when digestion is completed, and enhanced detoxification and repair occurs. Research has now accumulated suggesting that calories consumed late in the evening and duration of nightly fasting time (catabolic phase) affects breast cancer-related biomarkers.

Nightly Fasting Time, Inflammation, and Glycemic Control

Participants in a study using NHANES (National Health and Nutrition Examination Survey) data on 2,650 women found that those who ate a greater proportion of their daily calories in the evening (5:00pm – 12:00am) had higher levels of C-reactive protein (CRP), a marker of inflammation.

For every 10 percent increase in the proportion of calories eaten in the evening, there was a 3 percent increase in CRP. Women who had a longer overnight fasting time had lower CRP levels (an 8 percent decrease for each additional hour), but this was only true in women who were consuming less than 30 percent of their calories in the evening.

A longer interval in the catabolic phase and shifting eating to earlier in the day may help keep inflammation down.

Another study used NHANES data to relate overnight fasting time to biomarkers of glycemic control. Women who reported fasting longer overnight consumed fewer total calories, calories eaten after 10:00pm,  and a smaller number of total meals and snacks daily. An additional three hours of nightly fasting time was associated with a 4 percent decrease in postprandial (after meal) blood glucose, and a 19 percent lower likelihood of elevated HbA1c.

These studies did not address breast cancer directly. Instead they looked at biomarkers associated with risk. One more important study collected dietary data from women with breast cancer to determine whether there was a connection between nightly fasting time and recurrence of the disease.

Nightly Fasting Time in Women With Breast Cancer

In this study, dietary data was collected from 2413 women with breast cancer at baseline, one year, and 4 years.

The mean fasting time was 12.5 hours per night, and the participants were split into those fasting less than 13 hours or those fasting 13 hours or more. Fasting less than 13 hours was associated with a 36 percent increase in breast cancer recurrence over a follow-up of 7 years.

There were also reductions in HbA1c with longer overnight fasting; every 2-hour increase in fasting duration was associated with a 0.37 point lower HbA1c. Another interesting finding from this study is that the women who had a longer nightly fasting period slept a greater number of hours. Prolonging the nightly fasting period appears to be a lifestyle change with important protective effects against breast cancer.

More Time in the Catabolic Phase: The Body's Heal and Repair Mode

After a meal, there are two phases of metabolism: during the anabolic phase, blood glucose rises, and some is used for energy and some is stored as glycogen. Over time, blood glucose falls back to baseline; then, during the catabolic phase, the body breaks down stored glycogen for energy. When glycogen stores run low, the body starts using more fatty acids for energy.  During an extended catabolic phase (fasting period), the body engages in repair and removal of old and damaged cellular components, and the body builds stress resistance.

Prolonged fasting (several days) has been found to help reduce the activity of insulin and IGF-1 signaling pathways, reduce inflammation, reduce blood pressure, and improve insulin sensitivity. It seems likely that regular, long overnight fasts may also produce some of those same benefits.

Meal Timing and Circadian Rhythm 

The master clock in the hypothalamus sets the rhythm based on the light/dark cycle, and there are peripheral clocks in many organs. The peripheral clock in the liver, for example, is stimulated when we eat. The idea is that when we eat late at night, some peripheral clocks fall out of alignment with the master clock.  Finishing our food for the day earlier is eating more in sync with our circadian rhythms, leading to alignment of our circadian clocks and likely better sleep.

Insulin sensitivity has its own circadian rhythm; it is highest in the morning and lower in the evening, so it makes sense ending our eating window earlier rather than later would be beneficial for our health. This idea first with the research supports this, as CRP was higher in women who ate more calories in the evening.  How long should your overnight fast be? Based on the research, 13 hours is a good start, and longer is likely to be better.


Kamdar BB, Tergas AI, Mateen FJ, et al. Night-shift work and risk of breast cancer: a systematic review and meta-analysis. Breast Cancer Res Treat 2013, 138:291-301.

Wang F, Yeung KL, Chan WC, et al. A meta-analysis on dose-response relationship between night shift work and the risk of breast cancer. Ann Oncol 2013, 24:2724-2732.

Marinac CR, Sears DD, Natarajan L, et al. Frequency and Circadian Timing of Eating May Influence Biomarkers of Inflammation and Insulin Resistance Associated with Breast Cancer Risk. PLoS One 2015, 10:e0136240.

Marinac CR, Natarajan L, Sears DD, et al. Prolonged Nightly Fasting and Breast Cancer Risk: Findings from NHANES (2009-2010). Cancer Epidemiol Biomarkers Prev 2015, 24:783-789.

Marinac CR, Nelson SH, Breen CI, et al. Prolonged Nightly Fasting and Breast Cancer Prognosis. JAMA Oncol 2016.

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