Yahoo Lifestyle Experts Say Timing Your Meals Like This Might Help You Lose Weight And Gain Muscle
The reason you’re energized to get out of bed in the morning, but tired enough to crawl back under the sheets again at the end of the day? Your natural 24-hour body clock, also known as your circadian rhythm. But this internal cycle isn’t just responsible for waking up and winding down—it also has a major effect on a ton of your body’s other natural processes, from digestion to blood sugar regulation. In fact, aligning your eating habits to your circadian rhythm might be beneficial for improving your body composition.
For a lot of people, this practice can be effective through circadian rhythm fasting, says sports performance dietitian Umo Callins, RD, CPT. The goal is to consume a large chunk of your calories when your body is most metabolically efficient and your metabolism works at its fastest: when you wake up. On the contrary, at night, generally most people’s bodies (and metabolisms) are physically slowing down, says Jennifer McDaniel, RD, MS, a registered dietitian.
Meet the Experts: Umo Callins, RD, CPT, is a sports performance dietitian from Well Rooted Health and Nutrition in Oklahoma City. Jennifer McDaniel, RD, is a registered dietitian and the owner of McDaniel Nutrition Therapy.
Circadian rhythm fasting may boast a few benefits, like helping improve body composition, sleep, and more. But is it worth trying? Ahead, experts break down the main benefits and whether it’s right for your wellness goals.
Circadian Rhythm Fasting Vs. Intermittent Fasting
If you think circadian rhythm fasting sounds oddly similar to intermittent fasting (IF), you’re on the right track: CRF is a type of IF, Callins says. With any fasting method, the goal is to consume (or not consume) food during specified periods.
You can be flexible with the window in which you eat, and there are a lot of iterations of IF such as alternate day fasting, 5:2 fasting, and 16:8 fasting. With IF, you could eat between 10 a.m. and 6 p.m. (a 16-hour window) or between 9 a.m. and 7 p.m. (14 hours), for instance. So, you could be eating when it’s dark out, or fasting once the sun has come up. But with CRF, there’s only one eating window: wake-to-winddown.
With any type of fasting, the longer the fast is, the quicker you’ll lose weight, in theory. So, circadian rhythm fasting isn’t necessarily more effective than intermittent fasting in terms of weight loss results, Callins says.
If you’re deciding which type of fasting to try, CRF is more ideal for those who wake up around the same time as when the sun rises since your body will be more energized. But if you work long before or after sunrise, traditional IF—where you can adjust your eating windows to your liking—might be the better way to go.
The Benefits Of Circadian Rhythm Fasting
There’s not a ton of research on benefits specifically related to CRF, but there are a few potential pros that can come from eating within the period of when you wake up to when the sun is setting, McDaniel and Callins agree.
Improved Weight Management
While there aren’t any major studies to show how CRF directly impacts body composition, there *is* plenty of research to suggest that IF in general can help you lose pounds in some cases, according to a 2020 Canadian Family Physician study. “Eating within a specific timeframe can help avoid late-night snacking, which often contributes to an excess consumption of calories, which is a common cause of weight gain,” Collins says. Plus, when you eat more earlier in the day, you’re more likely to feel satiated for longer, Callins and McDaniel say.
Improved Blood Sugar
Eating a majority of your calories earlier in the day can also help with blood sugar control, which in turn helps with weight management. A 2023 study from Jama Network Open looking at people with type 2 diabetes found that individuals who followed a time-restricted eating plan and only ate between 12 p.m. and 8 p.m. for six months saw their blood sugar levels drop. Because CRF is a form of fasting, it likely has a similar benefit.
Easier Time Staying Sleep
If you’ve ever found yourself desperately scouring your medicine cabinet for Pepto-Bismol at 2 a.m. after a hearty late-night feast, you know that heavy eating in the evening can disrupt your snooze. In fact, eating less than an hour before bedtime can increase your likelihood of waking up in the middle of the night, per a 2021 study from the British Journal of Nutrition. Since circadian rhythm fasting requires you to eat a few hours before your likely bedtime, you’re digesting your food before you hit the hay. So, in theory, your sleep could improve from the diet, Callins says.
Better Hormonal Balance
“CRF is based on the idea of eating during daylight hours, when the body's metabolic processes are most efficient,” McDaniel says. When you first wake up, your body is surging with cortisol—the hormone is priming you to get moving and operate at full efficiency, according to 2021 research from the International Journal of Environmental Research and Public Health. Circadian rhythm fasting ensures that your eating habits don’t screw with this natural ebb and flow—you eat when your body is already naturally energized, not when it’s winding down, so your body will digest food more efficiently. This can also help balance your hormones, leading to a better mood and higher energy levels.
Circadian Rhythm Fasting For Weight Loss
While weight loss is complicated and involves factors like genetics and stress, at its simplest, it occurs when you consume fewer calories than you expend. CRF might be beneficial for weight loss because the bulk of your daily calories will be consumed within a few hours of waking. Then, in theory, if you’re avoiding eating past a certain time, you’re probably going to avoid consuming extra calories that can come from snacks and meals later in the day, Callins says. This makes it easier to reach weight loss and body composition goals.
But CRF may also contribute to weight loss for other reasons too, since your body is primed to take in fuel right when you wake up. It may “improve insulin sensitivity and fat oxidation, processes that tend to be more efficient in the morning,” McDaniel says. Plus, “by ‘front-loading’ your calorie intake earlier in the day, you may experience better blood sugar control, increased satiety, and improved lipid profiles, all of which can contribute to weight management,” she adds.
Circadian Rhythm Fasting For Muscle Gain
While there’s already an established connection between fasting diets, like CRF, and weight loss, muscle gain is a bit more murky, McDaniel says. “Some research suggests that eating in alignment with your circadian rhythm may support muscle protein synthesis,” she says. The thinking is that, because you’re feeding your muscles when they’re most primed to receive fuel, that would be most conducive and beneficial to muscle growth. However, more research is needed to better understand the full impact of circadian rhythm fasting on muscle growth, McDaniel says.
Diet chemistry aside, the key to muscle growth lies in a) consistent, heavy strength training, b) proper rest and recovery (including seven to nine hours of sleep!), genetics, and proper protein intake. So, if building muscle is your goal and you also want to try CRF, make sure to hit the gym in the morning or early evening, says Collins, so you’ll have enough fuel for your workout. Then, consume 25 to 30 grams of protein per meal during your fasting windows on CRF.
Risks Of Circadian Rhythm Fasting
The biggie? You might be hangry. (A lot.) “Transitioning to circadian rhythm fasting may result in low energy levels at first due to the time restriction of eating, but eventually most individuals will adapt,” Callins says.
Of course, restricting yourself food-wise (whether that’s calorically or in a fasting manner) comes with other cons. Intermittent fasting (and therefore circadian rhythm fasting) can potentially lead to disordered eating because it “involves restricting eating windows, which can trigger unhealthy eating patterns for some individuals,” McDaniel says.
A 2020 study from the Journal of Treatment and Prevention was done on intermittent fasters and their likelihood of engaging in eating disorder symptoms, like self-induced vomiting. The subjects took an assessment of eating disorder symptomatology and were asked about their IF use, and those who followed IF scored significantly higher than what’s considered normal, meaning, they portrayed eating disorder symptoms.
So, it’s important to fuel yourself properly during your non-fasting window. “Not consuming enough calories and nutrients during the eating window can lead to nutrient deficiencies, and undesired mood changes, such as irritability,” Callins says.
Another potential con? Restricting your eating window to eight hours might up a person’s risk of cardiovascular death, according to a 2024 study from the American Heart Association (although researchers aren’t entirely sure why). However, this study was pretty limited and didn’t take into account what the subjects were eating. What’s more, the full study has not been published or peer-reviewed, meaning the results may change, cardiologist Dr. Dariush Mozaffarian, MD, DrPH, previously told WH. He confirmed that what you eat, not the timing, has a bigger impact on your heart health, and that intermittent fasting in itself is safe.
The bottom line: Talk with a healthcare professional before you try circadian rhythm fasting, McDaniel says.
How To Start Circadian Rhythm Fasting
If you decide to give CRF a go, Callins and McDaniel say there are a few key considerations to keep in mind:
Mull over your lifestyle habits and relationship with food. An eating plan shouldn’t feel restrictive or stressful, McDaniel says. If you know that not having your nightly sweet treat at a certain time of night might make you crave 20 of them, or you have a history of disordered eating, CRF might not be right for you.
Start with a big eating window. “If you are planning to try circadian rhythm fasting, I recommend transitioning your eating window gradually,” Callins says. First, try a 12-hour eating window between, say, 7 a.m. and 7 p.m. (Or if you work later in the evening, or are generally a late riser, your window might start or end later.) Then, over time, shorten that window to between 7 a.m. and 5 p.m. later on to consume a bulk of your calories even earlier in the day.
Eat intentionally. “Ensure your meals are balanced with healthy fats, lean proteins, carbohydrates, and fiber to keep you satiated and ensure you are meeting your daily calorie and protein needs,” Callins says.
Guzzle H2O. “It is possible for the body to become dehydrated during circadian rhythm fasting if you don’t consume enough hydrating foods or drink enough fluid daily,” says Callins. So, stay hydrated throughout the day and during your fasted hours—that will ensure bodily processes like digestion and body temperature regulation are working properly, she adds.
Transition your workouts to the a.m. or early p.m. if you can. This scheduling detail will help ensure you have enough fuel stored to meet the demands of whatever activity you’re about to do, Collins says.
Although circadian rhythm fasting (and intermittent fasting) can be helpful for weight loss, they can be a slippery slope that can lead to unhealthy eating habits in some cases. So, it’s important to monitor both your mental and physical state as you progress in the eating plan—the second you start to feel restricted, or your energy or sleep levels seem out-of-whack, it might be a good time to throw in the towel.
Better yet, you can reframe the practice entirely and just focus on eating until you feel satiated: “Drop the word ‘fasting,’” McDaniel says. “Just focus on eating during the day and eating when your body needs it.”
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