I’ll be honest. Meal timing, nutrient timing, eating rhythm, whatever you want to call it is probably my least favorite topic to write about. I probably wouldn’t have attempted, but my husband insisted it would be a good subject that a lot of people are confused about, including himself.
And the confusion around this is well-founded, simply because even among experts, there isn’t agreement as to when the best times to eat are, or even whether it matters. What I will try to do is present some of the different sides, why they think that, and what I would recommend as a professional. Keep in mind that this article focuses mostly on weight loss and health, and not so much on eating for athletic performance, which may have some slight differences. Here goes!
Breakfast is the most important meal?
Let’s start with a view you’re probably familiar with, if not bought into already. Breakfast is the most important meal of the day. This is probably one of the most accepted views among nutrition experts, and there is some evidence to back it up.
For instance, many of the studies done linking up breakfast and positive things like healthy body weight, better concentration, and overall health have been what they call “observational” studies. This means researchers look at groups of people who do or don’t do a certain behavior, in this case eating breakfast, and then see what else they have going for them. These kinds of studies typically show that people who regularly eat breakfast have healthier body weight, overall health and eat overall fewer calories over the day. They also show that those who regularly skip breakfast have higher weight, more incidence of chronic disease and eat more over the day.
Sounds promising, but this type of research cannot prove that eating breakfast or not eating breakfast had anything to do with those other things like weight and health. It may be there’s something else about breakfast eaters that lead to healthy outcomes. There’s simply a correlation between eating breakfast and having a healthy weight, but nothing you can say definitively.
Eat more of your calories in the first half of the day?
There has been some experimental research looking at whether it matters for weight loss when you eat your biggest meal of the day. In these studies, people are given the same number of total calories a day. Some of them are given most of their calories at breakfast, and some are given most of their calories at dinner. Several of these studies show that when people eat more calories at breakfast, they lose more weight than the people who ate the majority of their calories at dinner. This supports the adage “eat breakfast like a king, lunch like a prince and dinner like a pauper.”
But not so fast! There have been other studies using the same set-up, but they found no difference in weight loss no matter what time the biggest meal was eaten. And even more confusing, some even found that those who ate most of their calories at the evening meal lost more weight! You’re starting to see why this subject is so confusing and frustrating.
If we go back to observational research again, where we simply look for trends and correlation, not cause and effect, we do get a picture that eating most of your calories later in the evening is linked with obesity and chronic diseases like diabetes and heart disease. But again, this doesn’t prove anything in the science world.
Perhaps the fascinating science of the circadian rhythm and our biological clock can give us some insight into metabolism’s natural flow. Your body, as well as every other living organism, has an internal rhythm to it. Light happens to be the biggest regulator of this internal clock, so it judges according to the time of day, or light, when to turn on and turn off certain biological functions. The “light switch” will turn up or down our body temperature, and based on that temperature, our metabolism and certain hormones are controlled.
While each person can vary a bit in their own rhythms, we typically start to increase the hormone cortisol around 4-6:30 am, when we start to come out of deep sleep. It sharply rises at 6:30, and increases until around 8:00 am, when it starts to gradually drop again over the day. Meanwhile, our alertness tends to have a cycle that continues to rise until about 11-noon. Between 1-3:30 pm there’s a dip (the afternoon slump!) and increase again around 4-8 pm. 8-10:30 pm gradually decreases, then there’s a sharp drop around 10:30 that continues past midnight. The lowest alertness and cortisol level is between 1-3:30 am, when sleep is deepest and body temperature is lowest.
So what does this mean for metabolism and weight loss? Well first, even this rhythm is more complicated than it sounds. For one thing, it would seem like our body temperature would track along this same cycle as our alertness, but of course that would be too simple! In fact, our highest core body temperature is around 6-7:00 pm, not when alertness peaks around noon, or when our cortisol peaks around 8:00 am. The body is very complex, and perhaps because it has so many of these different rhythms happening at different times, there’s no straightforward answer for when nutrient intake is best.
While there appear to be many different “answers” as to when we should eat during the day, there does at least seem to be compelling evidence that we should not be eating when we are supposed to be sleeping. Meaning in the middle of the night, especially when all the cycles tend to be depressed between 1-3:30 am.
Experimental research shows that even healthy people who eat meals late at night process that meal like a pre-diabetic! That means their blood sugar and insulin are higher as well as their triglycerides (fat in the blood) than that same meal eaten during the day. There is also a lot of observational evidence that links those working the night shift with much higher rates of obesity, diabetes and heart disease than those working regular hours.
What works long-term?
Of course a downfall of a lot of the research that’s done on meal timing is that they are only looking short-term. Even if people lose more weight eating more of their calories in the morning or the evening for a couple of weeks, these studies don’t follow these people long term. Just like anyone can lose weight on a weight loss diet, but 90-98% of them gain it back within two years.
Well a recent study came out, although observational again, that looked at a large group of people to see how their weight changed over time and their usual meal patterns. They found that those who ate breakfast regularly had lower BMI (body mass index). Interestingly, those who ate just 1-2 meals a day and no snacks lost weight over time, while those who ate the usual 3 meals plus snacks gained weight over time.
Agreeing with popular belief, those who ate the biggest meal at breakfast weighed less than those who had the biggest meal at dinner. Those who had the biggest meal at lunch were somewhere in between. Maybe the most interesting finding was that having a bigger fasting window, meaning a longer time between the last meal at night and the first meal in the morning was associated with lower BMI. This agrees with the increasingly popular intermittent fasting technique.
I won’t go into too much detail about intermittent fasting here, and there are several different ways to practice it. But one way of doing it is by increasing the time between the last meal of the day and first meal of the day, or prolonging the fast. In the short term, doing so can improve blood sugar and blood lipids like triglycerides, and may aid in weight loss. And the study I just described above shows it may be linked with longer term weight control.
The Bottom Line
All this just touches the surface of the research out there on this subject, and just shows you a taste of how contradictory and confusing it can get. What is the bottom line? Well, it depends. Chances are if you want to lose weight, looking in other places to make changes first, like how much, what and how you are eating may give you the most results. However, if you regularly skip breakfast, have a meager lunch then find yourself ravenous in the afternoon and evening, then yes, I would have you try something different.
I have worked with many people who eat so little protein and fat during the entire work day it’s no wonder they binge or overeat when they get home. Every time I have had them shift and eat more calories, protein and healthy fat earlier in the day, their ravenous eating later on stopped and they felt much more satisfied – without gaining weight!
I believe that because we are all so different, biologically and in our lifestyles, that science can only take us so far in this area, at least for now. It can give us some insights, like we are meant to eat during daylight hours. Beyond that, you need to become your own scientist. Experiment with different eating patterns and find one that works best for you. It should feel natural to you, and also be balanced with your daily routine so that you aren’t adding a ton of extra stress just to make sure you eat at certain times.
I knew someone who was sold on the belief of not eating after 8:00 pm. She typically worked late and had to speed home to make it before 7:30 and rush to throw anything she could find together and scarf it down before she turned into a pumpkin, or whatever happens after 8:00 pm. This is so not necessary, and actually probably added to belly fat due to all the extra stress hormones raging around in her body, on top of the fact that she was eating so fast. It would be far better to make a relaxed, healthy meal and eat and enjoy it slowly, even if it’s 9:00 pm.
If nothing else, the body is adaptable. Even people who work night shifts can adapt to have their body become more accepting of meal time after dark, as long as there’s a rhythm to it. It’s far better to focus on meal quality and eating in a slow, relaxed environment without distractions than to get all nit-picky with exact meal timing. And the best part is, you are free to experiment and find a pattern and rhythm that feels good and keeps you satisfied. Keep re-evaluating whenever something stops working.
Well, that’s it from me – time for my coffee!!
What is your eating rhythm like? How do you think it affects you? Let me know in the comments!
Hana Kahleova, Jan Irene Lloren, Andrew Mashchak, Martin Hill, Gary E Fraser. Meal Frequency and Timing Are Associated with Changes in Body Mass Index in Adventist Health Study 2. The Journal of Nutrition, 2017.
Mackowiak PA, Wasserman SS, Levine MM. A critical appraisal of 98.6 degrees F, the upper limit of the normal body temperature, and other legacies of Carl Reinhold August Wunderlich. JAMA 1992; 268(12):1578-80.
St. Pierre, Brian. Is Nutrient Timing Dead? And does when you eat really matter? http://www.precisionnutrition.com/nutrient-timing