Chrononutrition is a relatively new specialty in the fields of nutrition and biology that attempts to understand how the timing of food ingestion affects health. The central idea here is that metabolic health, cardiovascular health and body composition are not just about What and How many we eat but also when we eat.
You know of course that our body works on a rhythm of about 24 hours governed 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 both in the central nervous system and in peripheral organs and tissues. Chrononutrition seeks to answer two broad and related questions:
- How do the body’s natural clocks affect food choices and metabolism?
- How does food timing affect circadian rhythmicity and therefore various markers of health?
The latter is especially relevant for people who, probably like you, are struggling to make food, movement, and lifestyle decisions to maximize their health and longevity. Although the topic of chrononutrition has only gained traction in the past decade, evidence increasingly suggests that we may be able to manipulate when we eat to improve our well-being.
Today I will briefly review the underlying premises of chrononutrition and return to a question that has come up many times in our community: should I eat or skip breakfast if my goal is healthy optimal now and for decades to come?
Here’s what you need to know to understand chrononutrition:
First, many biological functions are guided by central and peripheral clocks. I have already mentioned sleep-wake. Another example is body temperature. Body temperature peaks in the afternoon and decreases during the night, reaching its nadir in the early morning. More to the point of this post, many aspects of metabolism also operate on a circadian rhythm. These include
- Saliva production
- Gastric emptying and intestinal motility (movement of food through the digestive tract)
- The release of digestive enzymes
- Nutrient Absorption
- Beta cell function (insulin release from the pancreas)
- Glucose tolerance
Second, that elusive and enigmatic target we call “health” depends on proper alignment of the circadian rhythm – everything happens when it needs to. Research shows, for example, that circadian misalignment, as occurs with shift work and eating at the wrong time, leads to impaired immune function.
Third, we stay “on time” thanks in part to behaviors that tell the body’s clocks what time it is. These behaviors, such as sleeping at night and exposing themselves to the sun early in the morning, are called zeitgebers. Eating at the right time is another zeitgeber that keeps our circadian rhythms aligned, contributing to physiological homeostasis. Conversely, eating (or sleeping or exposure to light) at the wrong time causes misalignment and dysfunction.
The implication, then, is that we can use what we know about the body’s natural rhythms to determine the best and worst times to eat, and the consequences of error. This is chrononutrition.
So what are the good and bad times to eat?
There are few things that scientists agree on, but I bet you would be hard pressed to find a scientist who thinks eating at night is healthy or even neutral for your health. All evidence from shift workers, mice and human research subjects says eat during the day, do not eat at night (actually the reverse 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, is it better to eat 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? These are exactly the types of questions that chrononutrition researchers study.
Observational data from epidemiological and prospective studies suggest that eating earlier in the day (i.e. eating breakfast) is associated with better glycemic control and less type 2 diabetes, better cardiovascular health and less adiposity (lower body fat). Now, I know many of you practice time-restricted eating and frequently skip breakfast. Before you get too worried, let me qualify that statement with a few big caveats.
Let us first recall that observational studies cannot establish causation. These results tell us nothing about whether eating or skipping breakfast leads to better or worse health outcomes, just that they may be correlated. Only randomized controlled trials can point to causation, and that’s where those observations start to fall apart. RCTs looking at weight loss and cardiometabolic risk, for example, have shown conflicting results. And two recent meta-analyses of RCTs found no consistent relationship between eating or skipping breakfast and body composition.
Moreover, participants in these observational studies represent cross-sections of the population. Overall, they do not reflect the average health-conscious Primal individual who is suitable for fats and practice intermittent fasting to advantages. Rather the opposite. Take a new analysis from the large NHANES database that has linked skipping breakfast to an increased risk of cardiovascular disease mortality. In this sample, people who skipped meals were also more likely to smoke, drink excessively, have lower quality diets overall, and experience food insecurity, all of which are independently associated with cardiovascular disease. The authors even specify that “skipping meals, particularly breakfast, could also be a behavioral marker of unhealthy eating and lifestyle habits”.
In other words, people who skip breakfast – that is, people who simply do not eat breakfast, not people who intentionally practice time-restricted eating – have overall more risk factors than their breakfast-eating counterparts. To what extent can we say that skipping breakfast is to blame for their poor health outcomes?
What does it mean to skip breakfast?
Should you skip breakfast or not? At this point, it’s hard to say for sure. It’s still the beginnings of chrononutrition, much too early to top breakfast the most important meal of the day.
That said, the evidence is already pretty strong that humans are more sensitive to insulin in the morning. People with insulin resistance and type 2 diabetes may therefore have an easier time controlling their blood sugar if they load more of their carbs, and possibly more of their total calories, early in the day. Alternatively, if you plan to ingest more carbs in the afternoon, try timing them around exercise to take advantage. insulin-independent glucose uptake.
For everyone else I would say keep doing what feels good to you, but be open to experimentation. It doesn’t hurt to try changing your eating window if you’re currently skipping breakfast and still struggling with high fasting blood sugar, lack of energy during the day, or other issues. stubborn health.
I’m open to the possibility that as more human studies unfold, we may find that there are some benefits to an earlier feeding window for just about everyone. . Or we may find that it doesn’t really matter if you eat lunch as long as you don’t eat too late. If skipping breakfast means your eating window is pushed back, so you eat large meals shortly before bedtime, this may be the biggest problem.
In the end, the answer will probably not be simple. The best and worst times for a given individual to eat are almost certainly a function of genetic predisposition, lifestyle factors (which is most doable and least stressful), personal preferences, and current health. And, I expect meal timing and macronutrients to always be lower on the list of things to worry about than what and how much we eat.
Self-experimentation is always the best answer
If the epidemiological data makes you feel a little uncertain about your ways to skip breakfast, go ahead and see what happens if you start eating breakfast. Maybe you will notice a big difference. Or you won’t, and you can go back to skipping breakfast if you want.
The only caveat here is that research also suggests that regular meal times are important for circadian rhythm health. I wouldn’t recommend skipping breakfast one day, skipping dinner the next, then eating from 8am to 8pm on the third day. Choose a schedule and stick to it for, say, a month (a duration I chose somewhat arbitrarily). Then try the other feeding window for the same amount of time and compare.
See if you notice any differences and how you feel, look or perform in your workouts. Which is easier for you given your work and family obligations? Above all, is the quality of your sleep improved on one compared to the other? You might even want to check blood markers and see how lipids or insulin (HbA1c) are affected.
If you feel and perform better jumping or eating breakfast, this is your answer.
What is your n=1 data? Have any readers had good results after resuming breakfast after a period of skipping? How about the opposite?