Beyond the great debate about how many carbs we should be eating, there is another question you might be wondering about: When is the best time of day to eat carbs?
Today we’re going to dig into the data and see if we can get some answers. Before we do, though, I want to make something clear. The types and amounts of food you are eating are much more important than nutrient timing when it comes to health, body composition, and even athletic performance.
Before worrying about nutrient timing, you should:
- Eliminate the “big three”—grains, excess sugars, and offensive vegetable and seed oils
- Consume an appropriate amount of food for your goals and activity level—neither too much nor too little
- Ensure that you are getting enough micronutrients via diverse, nutrient-dense foods, plus supplementation when necessary
I’d also say that macronutrients—the relative amounts of carbs, protein, and fat you’re eating—comes before nutrient timing in the hierarchy of “likely to matter.” A Keto Reset is probably going to impact your health and body composition more than changing the timing of your carb intake.
Still, I know many of you are self-experimenters and optimizers. You like to explore ways to squeeze a little more “edge” out of your diet and lifestyle. For some of you, nutrient timing might be the key to resolving a nagging issue that hasn’t been fixed by diet and lifestyle changes. If this is something you’re curious about, read on.
The growing field of “chrononutrition” investigates how food timing affects overall health. I’m sure you know that many bodily systems operate according to biological clocks. Sleep, immune system activity, and body temperature are all governed by circadian (~24-hour) clocks, for example. Disruption to our normal biological clocks negatively impacts health.
Metabolism operates according to circadian rhythms, too. On a basic level, we are meant to sleep when it’s dark, move and eat when it’s light. Insulin sensitivity and beta cell activity (the cells in the pancreas that produce insulin) are highest in the morning. Research shows that glucose tolerance—the body’s ability to clear glucose from the bloodstream after a meal—goes down if your sleep is poor or under conditions of circadian misalignment. There also seems to be a link between eating later at night, weight gain, impaired fat oxidation, and other negative health outcomes.
Taken together, this has led some researchers to suggest that we should eat most of our food earlier in the day to entrain, or align, our circadian rhythms. Doing so, they argue, could improve glycemic control (glucose regulation) and insulin sensitivity. It might also regulate appetite hormones and cortisol, and have downstream effects on body composition.
Carb Timing for Glycemic Control and Insulin Sensitivity
A number of studies seem to suggest that eating later is associated with impaired glucose tolerance and/or insulin sensitivity. On the other hand, both may be improved with early time restricted feeding (eTRF). This is where you eat in a compressed window, say 8 or 10 hours, and that window is shifted toward the morning. A typical eTRF schedule might entail eating all one’s food between 8 a.m. and 4 p.m.
Most of these studies focus on food timing generally, not nutrient timing per se. For example, in this study, men with type 2 diabetes ate all their calories in a 9-hour window. In one phase, they ate from 8 a.m. to 5 p.m. (eTRF). In the other, they ate from 12 p.m. to 9 p.m. Both schedules improved glucose tolerance, but only eTRF decreased fasting glucose.
A handful of studies do specifically look at carb timing:
- Healthy volunteers kept three-day food diaries. Those who ate relatively more of their food, and more carbs specifically, in the morning were also more insulin sensitive than late eaters. (Eating more fat in the evening was also correlated with poorer insulin sensitivity. It’s not clear how much these effects were driven by total caloric intake.)
- In another interesting study, researchers assigned men to eat two different diets for four weeks. They either ate most of their carbs before 1:30 p.m. and most of their fat after, or vice versa, in a cross-over design. For men who started out normal glucose control, carb timing didn’t matter. However, among men with high fasting glucose or impaired glucose tolerance, eating carbs at night led to unfavorable changes on several makers of glucose tolerance.
- In contrast, in this study, men followed a hypocaloric diet for eight weeks. Participants who were assigned to eat most of their carbs at lunch instead of dinner ended up with higher fasting glucose and insulin, and poorer insulin resistance.
Does type of carb matter?
Maybe. Researchers compared low-GI (glycemic index) and high-GI meals with most of the calories loaded into either the morning or the evening. Participants had the highest postprandial glucose (glucose after a meal) and insulin in the high-GI + evening eating condition. It didn’t matter when participants ate low-GI carbs. (Participants also consumed 302 grams of carbohydrate per day. Diets consisted of bran cereal, low-fat fruit yogurt, “fruit loaf,” and a Mars bar, among other things. It’s not clear exactly how these findings apply to Primal eaters.)
Conclusion: More research is needed in this area, but the available evidence points to morning carb consumption being favorable for glycemic control, perhaps especially among people who already struggle in this area.
Carb timing for athletes
As you know, I’m a big fan of athletes using fat for fuel. It’s an efficient, cleaner burning, more abundant source of energy. Once you become fat-adapted, it’s amazing what you can do as a fat-burner. As I detail in Primal Endurance, low-carb and keto diets work tremendously well for endurance athletes and even for hard-core strength athletes.
That said, there is no denying the ergogenic effect of carbs – carbs’ effect on stamina, physical performance and recovery. When you’re fat-adapted and running mainly on fat (and maybe ketones), adding some carbs to the mix can be like rocket fuel. I’m a fan of the “train low, race high” strategy for endurance athletes. Conduct most of your training using a low-carb approach, but add carbs strategically for your highest-intensity training sessions and races. You don’t need a lot, maybe 60-100 grams per hour.
Targeted Carbs: Should You Eat Carbs Before a Workout?
One strategy I’ve talked about before is targeting your carb intake around workouts. There are two rationales here. One is the aforementioned ergogenic effect — giving your workouts a boost. The second is that when you exercise, a glucose transporter in muscle cells called GLUT4 moves to the surface of the cell. This facilitates the transport of glucose into the cells without insulin.
Intense exercise also depletes glycogen, so there is a window after exercise in which ingested carbs are more likely to go to replenish glycogen. This is what I mean when I talk about the “glycogen suitcases being open” after exercise.
Thus, it makes sense to time your carb intake around exercise, especially hard and/or long bouts. In the keto world, this strategy is called “targeted keto.” The same principle applies for low-carb-but-not-keto folks. It’s not because you need the carbs for workouts—most of us do just fine without any special carb loading—but that’s when the body is most ready to use or store them.
Does Eating Carbs in the Evening Help You Build Muscle?
In the world of muscle gains, there are a handful of approaches that involve backloading carbs into the evening following a workout. Bill Lagakos does an excellent job unpacking them in a two part blog series here and here. Briefly, the logic behind carb backloading is that you don’t want to eat carbs when you’re more insulin sensitive in the morning because they’ll get stored as fat (oversimplifying here). Instead, wait until later in the day when insulin sensitivity decreases, then use exercise to push carbs into muscle instead of fat.
There’s no real evidence that this works, beyond anecdotal evidence from people who enjoy eating carbs at night. If you have body fat to lose, I think the evidence favors shifting calories and carbs toward the morning.
For the average person looking to gain strength and functional fitness, carb timing is not a great concern. For fitness competitors or people trying to push their physical limits, it might start to matter.
If you’re looking to gain lean muscle, you might find that ingesting a small amount of carbohydrate—25 to 30 grams—before hitting the gym can be beneficial. Contrary to popular belief, however, post-workout carbs do not seem to enhance muscle synthesis or recovery to a meaningful degree, especially not when protein needs are covered.
Bottom line: Carb timing isn’t important for muscle building except maybe for elite competitors and high-performers.
Timing Carbs for Weight Loss: What Does the Science Say?
In recent years, some people have claimed that eating carbs at night actually supports weight loss. In fact, this is one of the rationales offered for the aforementioned carb backloading. However, the studies they typically cite as evidence for this assertion have methodological problems that I can’t overlook.
Those studies are also at odds with a larger number of studies linking weight loss to eating more of your calories earlier in the day. Mechanistically, eating late delays the onset of the overnight fast, interfering with fat-burning and potentially with switching on ketosis. Eating later can also be associated with eating more, period.
Unfortunately for the purposes of this post, studies that look at meal timing and weight loss don’t examine nutrient timing, with one exception. In this study, researchers compared two diets, one prioritizing carbs at lunch and protein at dinner, and the other vice versa. Participants lost equal amounts of fat on each, but the group who ate most of their carbs at dinner also lost more lean tissue—not what you want! (This was also the study that showed poorer glycemic control with lunchtime carbs, in contrast to most other studies.)
Bottom line: When it comes to weight loss, there’s not enough data to convince me that carb timing seems very important.
Carbs Before Bed and Sleep Quality
Theoretically, carb intake at night could positively affect sleep by increasing tryptophan production, which is a precursor of serotonin, which in turn promotes sleep. It makes sense. No empirical research directly supports this hypothesis, though. Still, experts recommend you try adding some carbs at night if you’re struggling with sleep, especially on a low-carb diet.
There are plenty of studies looking at the relationship between macronutrients and sleep. However, they look at dietary composition as a whole, not nutrient timing. A single small study found that eating a high-GI meal four hours before bed improved sleep onset, compared to a lower-GI meal, and also compared to eating that same high-GI meal eaten one hour before bed. That’s all we have data-wise, besides anecdotes.
Conclusion: Anecdotal evidence aside, there’s no proof that timing carbs at night help your sleep. It probably doesn’t hurt to try.
Well first, it leaves us asking for more studies that systematically investigate carb timing. I specifically want to see more studies looking at carb timing in a low-carb population. As usual, the studies I cited here involved a standard high-carb paradigm. If you read the reports and see what researchers are feeding their participants… well, let’s just say you Primal folks wouldn’t volunteer for these studies.
This always leaves me wondering how well any of these findings apply to us fat-adapted folks. We can’t know for sure.
Let’s summarize the findings we have, though. First, for entraining your circadian rhythm, improving glycemic control, and losing weight, the available data altogether point to the benefits of eating more of your carbs earlier in the day.
You might wonder how this fits with intermittent fasting. First of all, I.F., doesn’t have to mean skipping breakfast. Many people skip breakfast largely out of convenience. If it works for you, great. Nothing I’ve said suggests that it’s bad for you. That said, if you’re still struggling with glucose tolerance, or you have a few stubborn pounds of body fat you’d like to lose, loading more of your calories and carbs earlier in the day seems to be a worthwhile experiment, as I’ve said before.
It makes sense to target carbs around exercise, but it’s generally not necessary for athletic performance. Most weekend warriors can get by just fine without any special carb timing strategy. People looking to gain muscle may want to ingest a small amount of pre-workout carbs, and endurance athletes should be open to using carbs around heavy training and races. I still think becoming fat-adapted should be every athlete’s first priority.
Finally, maybe experiment with some extra nighttime carbs if you’re a low-carb eater whose sleep is suffering.
But Don’t Sweat It
Nothing I’ve seen suggests that carb timing is more important than the amount and quality of food you eat. Once you dial in those higher-priority goals, by all means go ahead and try being more intentional about your carb timing if you want.
It might make a difference if you’re at the top of your performance game looking to squeeze out a few more drops, or if you have lingering health issues. Otherwise, I’d consider it just another variable you can experiment with if you want, but don’t sweat it if you have bigger things to worry about.
More related posts from Mark’s Daily Apple
Dear Mark: Glycogen
Should You Sleep-Low to Boost Performance?
Additional references
Challet, E. (2019). The circadian regulation of food intake. Nature Reviews Endocrinology, 15(7), 393–405.
Oda, H. (2015). Chrononutrition. Journal of Nutritional Science and Vitaminology, 61 Suppl, S92-94.
Oike, H., Oishi, K., & Kobori, M. (2014). Nutrients, Clock Genes, and Chrononutrition. Current Nutrition Reports, 3(3), 204–212.
Qian, J., Dalla Man, C., Morris, C. J., Cobelli, C., & Scheer, F. A. J. L. (2018). Differential effects of the circadian system and circadian misalignment on insulin sensitivity and insulin secretion in humans. Diabetes, Obesity and Metabolism, 20(10), 2481–2485.
Wefers, J., van Moorsel, D., Hansen, J., Connell, N. J., Havekes, B., Hoeks, J., van Marken Lichtenbelt, W. D., Duez, H., Phielix, E., Kalsbeek, A., Boekschoten, M. V., Hooiveld, G. J., Hesselink, M. K. C., Kersten, S., Staels, B., Scheer, F. A. J. L., & Schrauwen, P. (2018). Circadian misalignment induces fatty acid metabolism gene profiles and compromises insulin sensitivity in human skeletal muscle. Proceedings of the National Academy of Sciences of the United States of America, 115(30), 7789–7794.
Zilberter, T., & Zilberter, E. Y. (2014). Breakfast: To Skip or Not to Skip? Frontiers in Public Health, 2. Retrieved from https://www.frontiersin.org/articles/10.3389/fpubh.2014.00059/full.
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