New results from the WHEL (Women’s Healthy Eating and Living) Study show that women who did not eat for at least 13 hours at night (6PM to 7AM) had a 36 percent lower risk of cancer recurrence (JAMA Oncology, published online March 31, 2016). In a seven-year follow up of 2,413 breast cancer patients, ages 24 to 70, who did not have diabetes, 390 developed a recurrence of their breast cancer. Among those cases, the women whose last meal of the day was no later than 6PM had lower blood levels of hemoglobin A1C (a measure of cell damage caused by high blood sugar levels that is used to measure blood sugar control in diabetics). Each two-hour increase in duration of the nighttime fast was associated with significantly lower hemoglobin A1c and longer sleep time. Lack of night-time sleep is also associated with increased risk for high blood sugar levels and weight gain (Appetite, 2012;59(1):9–16).
Eating Followed By Inactivity Is Associated with Higher Blood Sugar
Extensive recent research shows that all factors that raise blood sugar levels too high are associated with increased risk for breast and prostate cancers. Eating just before going to bed increases risk for high blood sugar levels because resting muscles draw almost no sugar from the bloodstream. Contracting muscles draw a lot of sugar from the bloodstream and do not need insulin to do so. When you eat late and then go to bed, your muscles are inactive and blood sugar levels rise much higher than when you move after eating. The safest time to eat is just before or just after you exercise so your contracting muscles can help control the rise in blood sugar.
How Nighttime Fasting May Help to Prevent Cancers
Mice fed a high-fat diet develop high blood sugar and insulin levels, an overactive immunity (called inflammation) and weight gain. All these factors are associated with diabetes, increased cancer risk and death. However, nighttime fasting prevented these mice from developing diabetes, inflammation, and weight gain (Cell Metab, 2012;15(6):848-860 and 2014;20(6):991-1005). Intermittent fasting appears to prevent these same factors in women (J Acad Nutr Diet, 2015;115(8):1203-1212) and reduces breast cancer risk (Cancer Epidemiol Biomarkers Prev, 2015;24(5):783-789). See my report on More Links Between Cancers and Sugar.
* Both human and animal data suggest that fasting reduces cancer risk (Cancer Metab. 2013;1(1):10)
* Intermittent fasting prevents breast cancers more effectively than just calorie restriction (Cancer Prev Res (Phila). 2009;2(8):712-719).
* People burn fewer calories of the food eaten in the evening than during the day (Int J Obes (Lond). April, 2013;37(4):604–611).
* Eating late in the evening is associated with decreased energy expenditure at rest, higher blood sugar levels and higher insulin levels (Int J Obes (Lond). 2015 May;39(5):828-33).
Using Intermittent Fasting for Weight Loss
This type of intermittent fasting (consuming all of your food within a window of 11 hours or less and then not eating at all for 13 or more hours each day) is being studied for various health benefits, but the WHEL participants did not lose weight. If you want to use intermittent fasting for weight loss, you need to include two days a week when you restrict the amount of food you eat.
The authors of this new study state that "Randomized trials are needed to adequately test whether prolonging the nightly fasting interval can reduce the risk of chronic disease" (in this case, breast cancer recurrence). We already have convincing data that not eating at night may reduce breast cancer risk in women and prostate cancer risk in men. The data shows only association, not cause, but this dietary change is so simple and painless that I think it is worth following while we await further studies. I recommend eating breakfast in the morning and an early main meal (finishing by 6PM, but 2PM-4PM would be even better), with any snacking also ending by about 6PM. Make exceptions for social events, but try to make this pattern your regular habit.
I also recommend trying to eat just before or after you exercise, when your body will burn more of the calories from the food that you eat.