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Does Late-Night Snacking Increase Risk of Breast Cancer?

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Does Late-Night Snacking Increase Risk of Breast Cancer?

Oct 27, 2023

A recent study in The Journal of Nutrition challenges the notion that late-night snacking increases the risk of breast cancer, countering the findings of a previous extensive study that linked nocturnal eating with elevated breast cancer risk. Kirtly Parker Jones, MD, compares the methodologies of the two studies and shares her perspective on the initial research, which suggests a potential connection between late-night snacking and breast cancer risk.

Episode Transcript

Late-night snacking, does it increase your risk for breast cancer? Or maybe it doesn't and you can feel free to raid the fridge before bedtime.

Conflicting Studies: Late-Night Snacking and Breast Cancer Risk

I did a short podcast for the "7 Domains of Women's Health" that noted a study from Spain that suggested eating before bed increased the risk of breast cancer. But recently a study from a very big group suggested that snacks at night didn't make a difference. How can two groups of careful scientists look at the same issue and come to two different conclusions? Well, it happens all the time, but let's look at the studies and see if they really are looking at the same thing.

Limitations in Data Collection and Analysis

The recent study said that after-dinner snacks didn't increase the risk of breast cancer. It was published in "The Journal of Nutrition." It was an analysis of the famous nurses health study database. It looked at about 75,000 American nurses, ages 49 to 81, and that's a lot of nurses and a lot of data. They were asked at the beginning of the study if they had after-dinner snacks. Some did, some didn't. They didn't ask what the snacks were, or exactly when after dinner, or how close to bedtime the snacks were eaten. They didn't control for shift work, which is a common practice with nurses and is an independent risk factor for breast cancer.

So the report said, "Compared with the consumption of daily after-dinner snacks, avoidance of after-dinner snacks was not associated with invasive breast cancer." Actually, I think that's a little awkward. It suggests that avoiding snacks was not associated with breast cancer compared to eating a snack. Well, what they really said is that eating a snack or not eating a snack is the same. I might have said that eating snacks was not associated with an increased risk of breast cancer, but they should have said it's the same whether you eat snacks or not.

Different Approaches to Snacking and Sleep

Well, what about the Spanish study, the original study that looked like there was a risk? They looked at thousands of women and compared careful records of when they ate, when they went to sleep, and when they woke up. Their focus was on the chronobiology of the persons and how long they fasted each night. What they found was that women who ate shortly before they went to bed had shorter fasting periods, longer sleep times, and a small increase in breast cancer. So eating before bed wasn't good. It wasn't a big risk, maybe one extra breast cancer per 1,000 women per year. But this is fundamentally a different question about snacking than the report from the nurses health study.

So the women were Spanish, not American. Well, that doesn't probably make a difference. They weren't necessarily nurses. That probably doesn't make a difference, except nurses do a lot of shift work and that's an independent risk for breast cancer.

They specifically asked about the time of eating before sleeping and the time of fasting overnight. This makes a big difference in the two studies. There are many studies that show that late-night eating disrupts your biorhythms and your glucose tolerance. Disrupting biorhythms increases the risk of breast cancer as shown in studies on shift workers, even nurses. Disrupting the gut biorhythm by putting food in the gut, when it thinks it should be sleeping, disrupts the gut and the immune system, which can increase the risk of breast cancer. Increasing your insulin at night by eating, and increasing your glucose at night by eating increases your risk of diabetes, which is a risk for breast cancer.

Considering Biological Plausibility

Incidentally, another study in the "Journal of the American Medical Association," a very prestigious journal, found that breast cancer survivors who fast less than 13 hours or longer every night, meaning people have a short time between when they eat last and when they break their fast in the morning, people who have a fasting less than 13 hours have a 36% higher risk of recurrence of their breast cancer compared to women who avoid food for at least 13 hours. Now, that suggests, that if you're eating just before you go to sleep, unless you're sleeping for 14 hours, you're going to have a shorter sleep time and a shorter food abstaining time, and you're going to be at increased risk.

Lastly, another study from France looked at 41,000 women and men who were working days only, so they excluded shift workers. They asked the time of eating, of sleeping, how many snacks and what they ate. They found that eating right before bed, right before sleep increased the risk of breast cancer in women and prostate cancer in men. The risk was about a 50 percent increase in breast cancer in women and double the rate of prostate cancer in men.

The title of the paper was "Circadian Nutritional Behaviors and Cancer Risk." So what does that mean, circadian nutritional behaviors? It means when you eat compared to when your body wants to sleep. This large cohort study suggested that circadian perturbations, meaning messing up your biorhythms, resulting from late night time of last food may be involved in carcinogenesis at different locations. Translating, eating just before your sleep time can increase your risk of cancer.

Key Takeaways and Healthy Habits

So what's the takeaway? Suggestions that eating just before bed, which might be a slight risk for breast cancer, has biological plausibility. I love that term, "biological plausibility." That means that the biology of the issue and other studies looking at the problem shed light on the whole body's response to eating before sleeping.

The study suggesting that after-dinner snacks weren't a breast cancer risk really wasn't asking the same question. The studies that suggested that eating right before bed or, God forbid, getting up in the middle of the night to eat that leftover piece of cake, looked at the length of fasting and circadian disruption. The suggestion is that eating right before your bedtime biorhythm isn't good for you. It isn't good for your immune system, or for your sugar control, and it may increase your risk of cancer. It also increases your risk of gastroesophageal reflux disease or GERD. Acid reflux is bad for your esophagus, and you get heartburn.

So eat a modest dinner early in your biological evening, enough to keep you full and to decrease your motivation to stop by the fridge before getting to bed. Stick to your biorhythms. And thanks for joining us on The Scope.