Does your chronotype affect your ability to lose weight?

Are you a morning person or an evening person? And could that affect your ability to lose weight?

In this episode, Lara looks at chronotype, which is your individual disposition to be awake or asleep at certain times. And how that might affect your overall health and metabolism.

Transcript

Are you a morning person or an evening person? And could that affect your ability to lose weight? In today’s episode, we’re going to look at chronotype, which is your individual disposition to be awake or asleep at certain times. And how that might affect your overall health and metabolism.

Welcome back to the podcast. I’m your host Lara Briden, a naturopathic doctor and author of the books Period Repair Manual and Hormone Repair Manual. It’s November, so late spring in New Zealand, and I’m settling in to enjoy the long, warm days and do some deep thinking about topics I’ve been interested in for a while. One of those topics is circadian rhythm and how it relates to health and to metabolism, which is a big part of health. In simplest terms, circadian rhythm is your body clock, and it’s very important.

As humans, we are, of course, diurnal, which means we’re evolved to be active during the day. That’s in stark contrast, by the way, to mice, who are the main animals we study to try to learn about human physiology and metabolism. Mice are nocturnal, but we often make the mistake of studying them during the day, and scientists are starting to point out that could render much of what we’ve learned from mice completely irrelevant.

According to one scientist, “if you test a mouse during the middle of its active period, which is during the dark, you can translate that data to a diurnal creature like humans. That’s fine.” But if you test a mouse during the light, anything you learn about metabolism is far less helpful. It would be like testing a person’s response to food and exercise at three in the morning.

And yes, intuitively, you probably understand that it’s a bad idea to eat or exercise at three in the morning. You’re supposed to be asleep then. And your body is expecting to be in rest and repair mode. Which is much easier to do in a fasting state, which is why the simple strategy of fasting overnight can dramatically improve health, metabolic rate, and the ability to lose weight. But what about during the day? Is there a better time to eat or exercise? And does it depend on whether you’re a morning or evening person?

When I started researching this question, I thought there’d be a lot more science than there actually is. Which happens sometimes and makes me sometimes wish I’d pursued my original career as a biologist so I could try to work some of this out directly. But, given the science we have, here is what we know so far:

First, humans are fairly evenly distributed between being morning types, who are most active and alert in the morning, and evening types, who are most active and alert in the evening. There’s really only a normal variation of two to three hours, meaning that healthy morning types have a sleep cycle that’s two to three hours earlier than healthy evening types. Most of us are somewhere in the middle, and anything more extreme is classified as a circadian rhythm sleep disorder.

Next, we know that chronotype is affected by genetics, age, sex, and lifestyle. Everyone has a baseline genetic chronotype, but then, as children, we’re generally all morning types, only to swing to evening types in our teens and then slowly drift back to morning types by middle age. To a greater or lesser degree, depending on genetics. Women, on average, are more likely to be morning types compared to men. And, of course, your timing of sleep and activity can be changed by your job schedule, your alarm clock, and light, which entrains — or instructs — your central body clock, called the suprachiasmatic nucleus, located in your hypothalamus.

As an aside, you also have peripheral clocks in each and every cell and tissue, including your microbiome, which we’ll come to. Peripheral clocks work somewhat independently but also communicate and align with your central clock. So, “misalignment of body clock” can mean misalignment with natural light-dark cycles and/or misalignment between the central and peripheral body clocks.

The best estimate of your natural genetic chronotype is probably to observe your preferred sleep pattern on days when you don’t have to follow a rigid schedule and preferably on days when you’re exposed to natural light and dark, such as when you’re camping.

Finally, we know that chronotype correlates quite strongly with metabolism and health. Specifically, evening types are more likely to have insulin resistance, metabolic syndrome, and weight gain—which is the bad news I was not expecting to find when I started looking into all of this. Now, at this stage, it’s just a correlation, and the mechanism is not clear. For example, it could be that at least some evening types are actually more morning type than they realize but have a misaligned body clock as a result of late-night eating and/or late exposure to blue light. As one scientist said, “Insults to the body clock are insults to metabolism.” Or it could be that evening types just can’t adapt well to the way that society is structured. For example, it could be that evening types are better suited to late afternoon exercise but have trouble fitting that into a common schedule. Or it could be that evening types are not hungry at standard meal times, so are then more likely to snack in the evening on junk food. Which the research has observed that they do. And that suggests that the problem could be junk food rather than meal timing per se.

I’d love to see research on people who are genuinely genetic evening types but who get enough exercise and don’t eat junk food. And see what that means for metabolic outcomes. Unfortunately, that research does not yet exist.

By the way, if you’re an evening type and feeling a little depressed at this point, I can also tell you that evening chronotypes generally rank higher in creativity and intelligence, which is interesting. And evening types also tend to have more muscle than morning types, although it’s muscle that is less metabolically active.

So, what does this all mean? Well, first, we need a lot more science and should probably be careful about how we study mice.

Second, it feels like most fitness advice is designed for morning types and may be leaving evening types in a bit of a lurch. For example, morning exercise is a common recommendation, and that’s fine if you’re a morning type. However, if you’re an evening type — either genetically or because your circadian rhythm has drifted later— you should probably not wipe yourself out with vigorous exercise too early in the morning but instead try to make time later in the afternoon. You should, however, go outside for a gentle morning walk to soak up the morning light you need to shift your circadian rhythm a little earlier.

A big breakfast is another recommendation that’s easier for morning people. But, if you’re an evening type, a big breakfast may be a challenge. And yet, according to all the research, you really do need to try to get all your food in during the day. Because you’re human and therefore diurnal. At the same time, you don’t need to force a super-early breakfast, especially not a high-carb breakfast, because that accomplishes nothing.

What you need is morning protein when you’re ready for it. The advantages of morning protein are:
a) it will help you feel full and less likely to overeat later, and
b) it will help to entrain your circadian rhythm and shift it earlier.

That’s why when you’re jet-lagged, you should try to get protein plus outdoor light in the morning of your new location. To align with the new time zone.

Importantly, morning protein does not have to mean eggs at 7am. Instead, it could be meat, cheese, or protein powder by 10am. Ten am is still morning, and by 9 or 10, your digestion has hopefully come online, including appetite hormones, stomach acid, motility, and most importantly, your microbiome!

Because your gut microbiome has its own 24-hour circadian rhythm, which is weird given that individual bacteria live for only a couple of hours. But it turns out that populations of different species of gut bacteria rise and fall over the course of 24 hours, kind of like a miniature rise and fall of bacterial empires in your gut. And those populations of bacteria release hormones and signalling molecules that affect appetite, metabolic rate, and many other aspects of health. We can measure that by observing which gut microbe genes are active at different times. For example, in humans, during the day, the gut microbe genes that are active include genes responsible for energy metabolism and protein production. While at night, the microbe genes that are active are genes that help with detoxification and repair.

Now, in one direction, the current circadian rhythm of your gut microbiome affects your appetite, digestion, and metabolism. In the other direction, when you eat, when you exercise, and when you’re exposed to light all affect the circadian rhythm of your gut microbiome. It’s another example of the cross-talk between the central and peripheral body clocks.

So, supporting a healthy gut microbiome clock is one reason to eat only during the day. Other reasons include aligning with and supporting the circadian rhythm of insulin sensitivity, liver function, satiety hormones and something called diet-induced thermogenesis, which means “heat production” and is the tendency to burn off excess calories as heat rather than storing them as fat. Some people have a lot more diet-induced thermogenesis than others, and yes, those are the people who stay skinny no matter what they eat. Science is looking into ways to enhance diet-induced thermogenesis, but one simple way is to eat only during the day because it’s recently been discovered that diet-induced thermogenesis, like everything else, is aligned with light-dark cycles.

So, in summary, yes. Your chronotype can affect your metabolism and ability to lose weight. It probably affects when you should exercise and when you should eat. But in general, because you’re diurnal, you should eat only during the day and as early in the day as feels good, even if you’re an evening chronotype. Plus, you’ll probably find that you naturally become more of a morning person as you get older. That is, as long as your circadian rhythm is healthy and not impaired.

As always, there’s a section in my forum at LaraBriden.com to discuss this episode. You can chime in there with your knowledge, experience, and questions.

I hope that’s been helpful, and thanks so much for listening. Please share and leave a review. And I’ll see you next time when I’ll discuss how common medications, including hormonal birth control, can affect metabolism and weight gain.