New research on the circadian rhythm tells us when to eat, sleep and train—and how this can help us race faster than ever.
The following story was published in the September/October, 2011 issue of Inside Triathlon magazine.
It is said that our bodies have clocks—body clocks. It might be truer to say our bodies are clocks. Recent advances in the understanding of the circadian rhythm, the 24-hour cycle of sleep and wakefulness and related processes, have revealed that the functioning of our bodies is affected far more extensively by circadian rhythm than was previously known. We now know that one out of every 10 genes in human DNA operates in 24-hour cycles.
In practical terms, what this new knowledge is telling us is that our bodies really want us to do certain things at certain times, namely sleep, wake, eat, be active and rest. When our behavior defies the programmed preferences of our body clocks, our bodies do not function as well as they should. If we sleep too little or too much, or if we eat when we shouldn’t or don’t eat when we should, our health is compromised. Our metabolic systems seem to be most affected when our lifestyle gets out of sync with our circadian rhythm. People who are chronically sleep deprived, for example, are more likely to become overweight or diabetic. And for athletes there are additional consequences.
“One of the problems that athletes have is that their lifestyle is fighting what their normal circadian rhythm is,” says Robert Portman, Ph.D., co-author of a new book, “Hardwired for Fitness,” which presents a diet and exercise program based on aligning behavior with circadian rhythm. “When that happens, you create metabolic inefficiencies.” For example, the athlete’s muscles might lose some of their ability to burn carbohydrates, which is critical to performance in workouts and races.
Circadian science suggests there is a right time for a triathlete to do everything. A triathlete who does everything at the right times over a 24-hour period has lived what we might call a perfect day. And a triathlete who lives a perfect day every day will realize his or her full potential in races. Of course, not enough is known to rigorously define a triathlete’s perfect day, and even if we knew everything, it would still be impossible for anyone to be perfect every day. Nevertheless, it’s a worthwhile exercise to define a perfect day in general terms.
When to Exercise
Some people—whether by choice or by necessity—are morning exercisers. Others are afternoon or evening exercisers. Of course, many triathletes are both. When is the best time to exercise?
Studies have shown that most people perform better and also feel more comfortable when they exercise in the afternoon. For example, in a 2009 study, French researchers recruited 16 competitive cyclists and had them perform a high-intensity exercise test at both 6 a.m. and 6 p.m. The test consisted of a maximal one-minute effort on a stationary bike against resistance. Researchers measured the cyclists’ peak power output, their mean power output for the first 30 seconds of the test, and their mean power output for the full minute. On average, the subjects performed roughly 8 percent better in each of these metrics in the afternoon than in the morning. But why?
“Our body temperature is lowest when we wake up in the morning,” says Portman. “Then it increases until about 2 or 3 in the afternoon. That’s the high point of the day. There’s been a fair amount of research done with endurance athletes and resistance athletes which shows that performance does improve when you exercise when your body temperature is peaking.”
That settles it. If you work out once a day, you should do it in the afternoon, when you can perform better and, by performing better, get a bigger fitness-boosting stimulus from the work. Right?
Not so fast. Other research has shown that exercise performance improves most at the specific time of day when workouts are habitually performed. So, if you always work out in the afternoon, your afternoon exercise performance will increase more than your morning workout performance. And if you always work out in the morning, your morning workout performance will improve more than your afternoon workout performance. For example, in a 1998 study, researchers at the University of North Texas put a group of college-age female non-athletes through a five-week high-intensity cycling interval training program. Half of the women did all of their workouts in the morning. The rest did theirs in the afternoon. At the end of five weeks, all of the subjects performed two separate high-intensity rides to exhaustion, one in the morning and one in the afternoon. The morning exercisers performed significantly better in the morning test, while the afternoon exercisers put up much better numbers in the afternoon test.
When do most triathlons take place? Early in the morning. Therefore, even if you are an afternoon exerciser by habit, you’ll want to consistently do some workouts in the early morning so that your race performances aren’t compromised by a lack of specific physiological adaptation to exercising at that time of day.
So, where does this leave us? If triathlon is one of the most important things in your life and you have the time, habitually exercising twice a day most days is your best bet. Not only will you become fitter than you would on a once-a-day training regimen by virtue of greater training volume, but you will enjoy the benefits of being able to work harder in your afternoon workouts and the specific improvements in morning exercise performance that come with training in the morning.
If you cannot or prefer not to exercise twice a day most days, then you’ll want to be sure to routinely do some of your workouts in the morning. If you’re normally a morning exerciser, go ahead and do all of them in the morning. If you’re normally an afternoon exerciser, breaking from that habit once or twice a week should be enough to avoid putting yourself at a disadvantage in morning races.
When to Eat
Our circadian hardwiring causes the same foods to be metabolized in different ways, depending on when they are eaten. You’ve heard a thousand times that breakfast is the most important meal of the day, and it is. Regular breakfast eaters tend to be leaner than breakfast skippers. This is the case even when eating breakfast causes a person to eat more total calories in a day, perhaps because eating breakfast increases energy expenditure.
If first thing in the morning is the best time to eat, late at night is the worst time to eat. Research suggests that exposure to artificial light at night disrupts natural circadian rhythms in ways that influence the timing of food intake, alter metabolism and promote weight gain. Mice housed in a constantly lit environment eat more at night and are significantly fatter than mice housed in an environment with a natural light/dark cycle, despite eating the same total number of calories and burning the same number of calories through activity.
You’re not a mouse, of course, and it is difficult to perform this kind of controlled experiment in humans to determine whether what’s true for mice in this case is true for us. But there is reason to believe it is because nightshift workers have been scientifically shown to carry more weight than dayshift workers. So try to restrict your eating after sundown.
What to Eat When
The body has different metabolic priorities at different times of the day. The main priority in the morning and mid-afternoon is energy provision because this is the most active part of the day. The main priority of the evening and nighttime is regeneration. These priorities are exaggerated for triathletes, who typically train after waking up and before mid-afternoon, and who need to recover from training in the evening and during the night.
Portman advises athletes to prioritize different nutrients in these two separate functional parts of the day. Specifically, carbohydrate, the great energy provider, should be prioritized between wake-up and mid-afternoon. Protein, the body’s main tool for regeneration, should be prioritized between mid-afternoon and bedtime.
At no time are carbs more important than first thing in the morning, especially for athletes who train then.
“When you get up in the morning, you are coming off the longest interval without eating in the entire 24-hour cycle,” Portman says. “Your liver glycogen stores are low at that time. You need to bring those up by eating carbohydrates before you start exercising, or you won’t perform as well.”
In addition, cortisol levels are high in the morning, and exercise brings them even higher. Cortisol is a “catabolic” hormone that breaks down fats, carbs and protein for energy. Without cortisol you couldn’t swim, bike or run very fast. But when cortisol levels get too high, a lot of muscle protein is broken down, compromising recovery. Consuming carbs before and during morning workouts lowers cortisol levels and helps recovery.
When your last workout of the day is behind you, your diet needs to change. While your breakfast and lunch should be packed with carbs (think old-fashioned oatmeal with fruit, and brown rice with stir-fried veggies), your dinner should be high in protein (for example, broiled fish with cooked, spiced lentils and amaranth).
Don’t stop there, though. “Prior to going to bed, take a protein drink,” Portman advises. “It will prevent large increases in cortisol during the night and it will drive some protein synthesis while you’re sleeping.”
Sleep anchors our circadian rhythms. Everything revolves around it. Our circadian circuitry makes us naturally sleepy at night, keeps us sleeping until we’ve gotten enough, and makes us wake up in the morning and feel wakeful throughout the day. Good thing, too, because we need sleep to live. Sleep deprivation compromises the function of every physiological system of the body. It messes up the nervous system, reducing cognitive function and fine motor coordination. It suppresses immune function, making us more susceptible to illness. And it distorts metabolic function, slowing recovery from recent exercise and promoting weight gain.
“Without adequate sleep, the biological machinery responsible for energy conversion doesn’t function as well,” says Portman. “For an athlete, that has huge implications because our performance is determined by our ability to efficiently convert carbohydrate into energy.”
Many triathletes with full-time jobs cut back on sleep during the week to create time for training. There are those who say this is a counterproductive tradeoff, and they cite studies demonstrating the performance-wrecking effects of sleep deprivation in endurance athletes. However, these studies don’t match what triathletes typically do in the real world: get by on less sleep during the workweek, catch up on weekends and sustain this routine long enough to adapt to it. It’s hard to imagine that someone like 2010 Ironman Canada winner Meredith Kessler, who keeps up this common routine, would race better if she slept five hours more and trained five hours less over the course of the week.
However, while Kessler’s routine might be optimal for athletes in certain situations, it’s not perfect. In a perfect day, you would get all the sleep you needed, which is 7.5 to eight hours for the average person, more for athletes in heavy training (which increases sleep needs), and ranges from as little as five hours to as much as 10 for individuals who are wired a little differently. And in a perfect world, you would be able to get as much sleep as you need every night without making any sacrifices in your training volume. You would be able to do what full-time triathletes such as TJ Tollakson do: sleep eight hours at night, nap two hours in the afternoon and train 30 hours a week.
In the reality you live in, you need to find the best balance you can. Avoid cutting back on sleep to train more if possible, but if you just can’t find enough time in the day to do the training you need, then reduce your sleep moderately on work nights and catch up when you can. Don’t go overboard and pay attention to your performance and how you feel. If you start to feel lousy and your performance stagnates, you’re probably trying to train too much on too little sleep and need to shift the balance back.
Expecting perfection is counterproductive. Because perfection is unattainable, expecting it causes frustration and disappointment. But aiming for perfection without ever expecting it is a recipe for success. To aim for perfection, we have to understand what it is. The triathlete’s perfect day has been generally defined. Now aim for it. Control what you can, don’t worry about what you can’t, and take satisfaction in knowing you are achieving the best days you can realistically achieve, even if they aren’t perfect.
Perfect Day 1a
Here’s a perfect workweek day for the triathlete who works full-time, trains once a day and prefers to work out in the morning.
6:15 High-carb snack (e.g., banana)
7:45 High-carb breakfast
12:30 High-carb lunch
6:00 High-protein dinner
9:45 High-protein snack
Perfect Day 1b
Here’s a perfect workweek day for the triathlete who works full-time, trains once a day and prefers to work out in the afternoon. If you follow this schedule, be sure to train in the morning at least once a week—perhaps on the weekends, if that’s most convenient—to adapt to morning exercise.
6:30 High-carb breakfast
12:00 High-carb lunch
6:00 High-protein dinner
9:45 High-protein snack
Perfect Day 2
Here’s a perfect workweek day for the triathlete who works full-time and trains twice a day.
5:45 High-carb snack (e.g., banana)
7:15 High-carb breakfast
12:30 High-carb lunch
6:00 High-protein dinner
9:15 High-protein snack
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