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Should I Stop Eating After 7 PM?

If I had a dollar for every time someone asked me whether they should stop eating after a certain time in the day, I probably wouldn’t need to be a dietitian anymore!

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My answer to this popular question has always been that it doesn’t really matter what time of day you eat when it comes to how much you “burn”, but our food choices tend to be worse later on in the day – you’re more likely to eat chips or ice cream while sitting in front of the TV at night versus for breakfast first thing in the morning!

However, I recently attended a webinar hosted by Dr. Courtney M. Peterson of the Pennington Biomedical Research Centre on the role of circadian rhythms in weight management that threatened to turn my answer on its head.

Dr. Peterson’s presentation was very fast-paced and covered a lot of ground, including whether eating more frequently helps with weight loss (no), whether skipping breakfast impacts weight loss/gain (no) and whether intermittent fasting helps with weight loss (potentially)

Key Learnings on The Role of Circadian Rhythms in Weight Management

We Have Multiple Circadian Clocks

While most people know about our central circadian clock, which is responsive to light (that’s why it’s recommended to limit screen time before bed), we have peripheral circadian clocks that respond to other stimuli, including meal timing. The theory is that when these internal clocks are out of sync, this could lead to issues in metabolism.

Normally, our hunger should peak in the evening (around 8 PM). It is thought that this is to prevent us from becoming hungry while we’re asleep. However, one study of Muslims observing Ramadan (a holy month where practicing Muslims fast between sunrise and sunset, and eat during the overnight hours) found that even by the second week, levels of leptin, an appetite-regulating hormone, dip in the nighttime, where normally it would peak. In other words, instead of suppressing hunger overnight, the dip in leptin encourages appetite and eating in response to the night time eating that happens during Ramadan. Interestingly, the same study found that there was no effect on ghrelin, another appetite-regulating hormone.

The Time of Day Can Affect Your Metabolism

To test the effect of the time of day on metabolism, another study put subjects through three days of a mock night shift. On the first day, as they transitioned from normal daytime activities to their first night shift, the subjects had increased energy expenditure. The authors attributed this to the subjects spending more hours awake, as they were only allowed an afternoon nap. (We burn more calories when we’re awake than when we’re asleep, obviously.) On the second and third days of the night shift, however, the subjects burned fewer calories than they did at baseline. The difference was only about 50-60 calories per day, so while it’s statistically significant, it’s only about the same amount of calories as a small apple.

One study found that diet-induced thermogenesis (i.e. the calories that you burn as a result of metabolizing food) is 44-50% higher after a morning (8 AM) meal versus an evening (8 PM) meal, regardless of whether you are on a day shift or a night shift.

It's not as simple as calories in, calories out. When you eat/are awake can affect how much you burn. Click To Tweet

Intermittent Fasting is an Emerging Area of Research Showing Promise

While it’s tempting to believe that intermittent fasting (IF) only exists in the world of fitness and dude-bros (Fitness Bros?), it’s an area of research that’s gaining a lot of interest.

The most common definition of IF is that you have certain days of the week where you don’t eat, or undergo a modified fast where you only eat a small amount (most studies provide 500 calories), then eat normally on non-fasting days. Variations of this include alternate day fasting, or the 5:2 Diet (eat five days a week, fast two non-consecutive days a week).

Another version of IF is time-restricted feeding, where you restrict eating to a certain number of hours a day, then fast for the rest of the time. Dr. Peterson is currently conducting two studies where subjects eat three meals within 6 hours per day (8 AM – 2 PM), compared to a more “normal” pattern of eating that stretches over 12 hours per day.

Most of the IF studies available have been done on rodents, but the few human studies available have been promising, showing that IF generally produces similar weight loss to “daily dieting” (i.e. slight calorie restriction every day), but there may be more fat loss and less lean body mass loss in IF. Some studies have also shown improved cholesterol levels and less insulin resistance, but this has been inconsistent.

You Might Not Have to Go as Extreme as Fasting to See Benefit

Another interesting area of study is whether just the timing of our meals can effect weight management. A study of 420 Spanish people trying to lose weight, found that those who had their biggest meal earlier in the day tended to lose more weight than those who had their biggest meal later, despite the subjects reporting similar energy intakes.

Similarly, a study of 93 women that were split into large breakfast/small dinner vs. small breakfast/large dinner groups (lunch for both groups was the same size, and all the women received the same number of total calories per day) found that the group that was given the larger breakfast lost more weight (19 lbs vs 8 lbs), had better cholesterol levels, and lower blood sugar levels after 12 weeks.

What Does This All Mean?

The question of whether when we eat has an effect on our weight and health is relatively new. Most of the studies done so far have been in animal models, and only a few small studies have been performed in humans. Most of the studies that Dr. Peterson cited in her webinar had less than 15 participants.

At this stage in the research, I think we have more questions than we do answers, like,

“If we time our meals according to daylight, does that mean I should eat supper at 10 PM in the summer, and 4 PM in the winter?”

“We know that light exposure can affect sleep; does it affect hunger, metabolism and weight loss?”

“Intermittent fasting might look good in the lab, where food is provided, but what happens when people just do IF on their own? Won’t they just gorge on food on the feeding days?” 

Even when I asked Dr. Peterson whether she thinks people should stop eating after a certain time of day, she said it was too early in the research to give a definitive answer – we don’t know whether our circadian rhythms are affected more by cutting off eating after a certain time, or by eating more earlier in the day.

I would say my answer to “Should you stop eating after 7 PM?” hasn’t really changed – it’s true your metabolism does slow down in the evening, but based on what we know, the change in the amount of calories you burn isn’t huge. If you do choose to eat in the evening, what and how much you eat is still going to make the bigger difference. Making sure that you’re eating enough during the day might help decrease the amount that you eat at night.

Would I recommend intermittent fasting to everyone? Not yet – there’s still so much we don’t know. But, if it’s something that resonates with you, and you’d like to give it shot, let’s make it happen.

Should you stop eating after 7 PM? The answer is not as simple as you think! Click To Tweet
Are you a night time snacker or an intermittent faster? Do you think learning about this research is going to change the way you eat? Share your insights in the comments below.

4 Comments

  • Emma Train on Jun 09, 2016 Reply

    Pretty interesting, looking forward to hearing more from her in the future!

    • Vincci Tsui on Jun 09, 2016 Reply

      Me too!

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