Chrononutrition is a relatively new specialty in nutrition and biology that seeks to understand how the timing of food intake affects health. The central idea here is that metabolic health, cardiovascular health and body composition depend not only on what and how much we eat, but also when we eat.
You know, of course, that our body works on a roughly 24-hour rhythm that is determined by circadian clocks. The sleep-wake cycle is the most obvious example. Many other aspects of human biology are also governed by 24-hour clocks operating in both the central nervous system and peripheral organs and tissues. Chrononutrition attempts to answer two broad and related questions:
How do the body’s natural clocks affect food choices and metabolism? How does meal timing affect circadian rhythms and consequently various markers of health?
The latter is especially relevant for people who, probably like you, are striving to make diet, exercise, and lifestyle choices to maximize their health and longevity. Although the issue of chrononutrition has only gained prominence in the last decade, increasing evidence suggests that we may be able to manipulate meal timing to improve well-being.
Today, I will briefly address the underlying premise of chrononutrition and return to a question that has often arisen in our community: Should I eat or skip breakfast when my goal is optimal health now and for decades to come?
Here’s what you need to know to understand Chrononutrition:
First, many biological functions are controlled by central and peripheral clocks. I already mentioned sleep-wake. Body temperature is another example. Body temperature peaks in the afternoon and drops overnight, eventually reaching its nadir in the early hours of the morning. To bring it to the point of this post, many aspects of metabolism also work according to a circadian rhythm. These include
Saliva production Gastric emptying and gut motility (the movement of food through the digestive tract) Release of digestive enzymes Nutrient absorption Beta cell function (release of insulin from the pancreas) Glucose tolerance Hunger
Second, that elusive and enigmatic goal we call “health” depends on proper alignment of the circadian rhythm—everything happens when it’s supposed to. For example, research shows that circadian misalignment, such as occurs with shift work and untimely eating, leads to impaired immune function.
Third, we stay “on time,” in part thanks to behaviors that tell our internal clock what time it is. These behaviors, like sleeping at night and sun exposure early in the morning, are called zeitgebers. Eating at the right time is another timing device that keeps our circadian rhythms in sync and contributes to physiological homeostasis. Conversely, eating (or sleeping, or exposure to light) at the wrong time causes misalignment and dysfunction.
So the implication is that we can use what we know about the body’s natural rhythms to figure out the best and worst times to eat and the consequences of eating wrong. This is chrono nutrition.
So what are the right and wrong times to eat?
There are few things that scientists agree on, but I bet you’ll have a hard time finding a scientist who agrees that late-night eating is healthy, or even non-healthy. All the evidence from shift workers, mice and human subjects says that they eat during the day, don’t eat at night (actually it’s the other way around for mice since they are nocturnal, but the point still stands).
That’s a pretty broad statement, though. We would like to know more precisely whether it is better to consume more of our calories in the morning, at noon or in the evening? Should we load carbs (or protein or fat) into our first meal of the day or closer to bedtime? The researchers at Chrononutrition are investigating precisely such questions.
Observational data from epidemiological and prospective studies suggest that eating earlier in the day (ie, breakfast) is associated with better glycemic control and less type 2 diabetes, better cardiovascular health, and less obesity (less body fat). Well, I know that many of you practice time-restricted eating and frequently skip breakfast. Before you worry too much, let me put that statement into perspective with some big caveats.
First, let’s remember that observational studies cannot establish causality. These results tell us nothing about whether eating or skipping breakfast leads to better or worse health outcomes, only that they may be correlated. Only randomized controlled trials can indicate causality, and this is where these observations begin to break down. RCTs looking at weight loss and cardiometabolic risk, for example, have produced conflicting results. And two recent meta-analyses of RCTs found no consistent association between eating versus skipping breakfast and body composition.
Also, the participants in these observational studies represent cross-sections of the population. On the whole, they don’t reflect the average health-conscious primal individual who is fat-adapted and practices intermittent fasting for the benefits. But on the contrary. Take a new analysis of the large NHANES database that links skipping breakfast to a higher risk of cardiovascular disease-related mortality. In this sample, people who skipped meals also smoked more, drank excessively, had poorer overall diet quality, and faced food insecurity—all independently linked to cardiovascular disease. The authors even note that “skipping meals, particularly skipping breakfast, may also be a behavioral marker of unhealthy diet and lifestyle choices.”
In other words, breakfast skippers—that is, people who simply don’t eat breakfast, not people who are intentionally on a time-limited diet—have more risk factors overall than their breakfast-loving counterparts. So how much can we say that skipping breakfast is to blame for their poor health outcomes?
What does this mean for skipping breakfast?
Should you skip breakfast or not? At this point, it’s hard to say for sure. It’s still the early days of chrono-nutrition, far too early to crown breakfast as the most important meal of the day.
However, the evidence is already pretty solid that people are more insulin sensitive in the morning. Therefore, people with insulin resistance and type 2 diabetes may have an easier time controlling blood sugar if they eat more carbohydrates, and perhaps more of their total calories, earlier in the day. Alternatively, if you want to consume more carbohydrates in the afternoon, try timing them out between your workouts to take advantage of non-insulin glucose uptake.
For everyone else, I would say go ahead with what feels right to you, but be open to experimentation. There’s no harm in changing your eating window if you’re currently skipping breakfast and still struggling with high fasting blood sugar, poor daytime energy, or other persistent health issues.
I’m open to the possibility that as we do more human studies, we’ll find that an earlier eating window has some benefit for almost everyone. Or we find that it doesn’t really matter if you eat breakfast as long as you don’t eat late. If skipping breakfast means pushing back your eating window so you eat big meals just before bed, that may be the bigger problem.
Ultimately, the answer probably won’t be easy. The best and worst times for a particular person to eat are almost certainly a function of genetics, lifestyle factors (which is most doable and least stressful), personal preference, and existing health. And I expect that meal timing and macronutrients will continue to be lower and lower on the list of things to worry about than what we’re eating and how much.
Self-experiment is still the best answer
If you’re feeling a little unsure about skipping breakfast based on the epidemiological data, you should definitely go ahead and see what happens when you start eating breakfast. You might notice a big difference. Or you won’t, and again you can skip breakfast if you wish.
The only caveat here is that research also suggests that consistent meal times are important for circadian rhythm health. I wouldn’t recommend skipping breakfast one day, skipping dinner the next day, and then eating from 8am to 8pm on the third day. Pick a schedule and stick to it for, say, a month (a length of time I’ve chosen somewhat arbitrarily). Then try the other eating window for the same amount of time and compare.
See if you notice any differences in how you feel, look or are performing in your workout. Given your work and family commitments, what do you find easier? Importantly, is your sleep quality improved compared to the other? You might even want to check blood markers and see how lipids or insulin (HbA1c) are affected.
If hopping or breakfast makes you feel and perform best, this is your answer.
What is your n=1 data? Have any readers had good results after going back to breakfast after a period of skipping? How about the opposite?
About the author
Mark Sisson is the founder of Mark’s Daily Apple, godfather of the primal food and lifestyle movement, and New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, in which he explains how he combines the keto diet with a primal lifestyle for optimal health and longevity. Mark is also the author of numerous other books, including The Primal Blueprint, which in 2009 is credited with accelerating the growth of the Primal/Paleo movement and maintaining optimal wellness, Mark founded Primal Kitchen, a real food company that sells Primal/ Paleo, Keto, and Whole30-friendly kitchen clips.
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