Maybe you've heard that noshing at night will derail your diet because your metabolism is "off the clock." When evening hunger pangs hit, you might wonder if there's any truth to the claim that your metabolism slows down at night.
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Well, the truth is that there's no specific time period in which your metabolism isn't working. While it's commonly believed that the metabolism sleeps when you do, this isn't actually the case, Mir Ali, MD, a bariatric surgeon and medical director of Memorial Care Surgical Weight Loss Center, tells LIVESTRONG.com.
While your baseline metabolic rate will stay the same throughout the day and night, you will burn fewer calories at night, which can have an effect on your weight-loss efforts. Other factors, including sleep and stress, can also affect your metabolism at night.
Here's what you need to know about how your metabolism changes at night, and what you can do to manage your weight-loss efforts.
What Is Metabolism?
First things first: Metabolism is the general term for the process of converting the food we eat into energy that can be used for day-to-day processes in the body, Dr. Ali says. The metabolic rate is how fast the energy that is generated by the food is used as fuel.
The metabolism is composed of two key parts: Your baseline metabolism level, which fuels the body's daily functions, and the additional process of energy burning that occurs through exercise and physical activity, Kelly A. Waters, MD, a sleep medicine neurologist with Spectrum Health Medical Group, tells LIVESTRONG.com.
Because most of us aren't completely sedentary, our bodies require additional energy to perform activities outside of their standard duties. These activities may include exercising, regulating body temperature, fighting off illnesses and addressing stress. Many of these activities happen when we're awake — so it's true that the metabolism works to burn more calories during the day.
What Happens to Your Metabolism at Night?
While it's commonly thought that metabolism slows down at night or when you sleep, that's not actually what happens. Your baseline metabolism will not change at night — it remains the same, no matter what hour of the day or night it is, Dr. Ali says.
What does change? Most of us tend to be much less active at night, so our organs become less active as well. Because of this, the body doesn't require as much energy as it does throughout the day.
The body's natural circadian rhythm at night plays a role in the metabolism, Dr. Waters says. "Your body also takes cues from your environment and daily activities in order to keep your body chemistry on schedule," she says Because eating is what she calls a "wakeful activity," any meals or snacking you do will cue the wakeful portion of your circadian rhythm.
On the flip side, slowing down your food intake at the end of the day, along with other cues, such as dimming lights and screens, sitting and physically resting and turning down background noise and stimulus cues a shift toward the sleep portion of your circadian rhythm.
In order to best support your body's circadian rhythm and sleep schedule, Dr. Waters recommends finishing your last meal about two hours before bedtime, and avoiding midnight snacking (barring any other health considerations, of course, such as diabetes, which might require maintaining consistent blood sugars).
Although your baseline metabolic rate may not change at night, both doctors say that you can best support your metabolism through managing stress levels, keeping a consistent sleep schedule and reducing calories as appropriate for your age and activity levels in order to lose weight.
Ultimately, it may take some experimentation before you find the best eating cycle that works for you and your weight-management efforts.
"Not everyone responds the same to every diet," Dr. Ali says. "It can be trial and error on which type of eating cycle is best for a particular person to lose weight. Not one thing works for every person."
6 Others Factors That Can Affect Metabolism
Some metabolism factors are pre-set, but others are modifiable through lifestyle choices, Dr. Waters says.
1. Weight Training
Weight training will increase your lean body mass and your baseline metabolism, Dr. Waters says. Strength training is associated with increased metabolic health markers, per a February 2019 study in Frontiers in Physiology.
In contrast, aerobic exercise will impact how much daily energy you will need, but it won't necessarily change that baseline metabolism.
2. Activity Levels
The more active you are, the more calories your body will burn throughout the day. Still, your baseline metabolic rate will not necessarily be altered.
3. Body Temperature
If you need to increase your body temperature — whether you are cold or are ill and running a fever — the need for more baseline energy will also increase.
Providing your body with appropriate nutrients keeps your metabolism running smoothly, Dr. Waters says. Like a sedentary lifestyle, a poor diet will slow your metabolism.
Sleep plays a big role in metabolism. Without adequate sleep, your brain and body are missing sufficient processing and recovery time, Dr. Waters says. And when sleep is interrupted long-term — like for new parents or from a condition like sleep apnea — the body's stress response can also be triggered.
When you're having difficulty sleeping or not sleeping well, you trigger your sympathetic nervous system (the "fight or flight" system) on a smaller scale instead of the primarily parasympathetic activities it should be operating under, Dr. Waters says.
When this happens, your body turns to "survival" mode and releases stress chemicals that ultimately affect energy storage and utilization. For instance, interrupted sleep can lead both to the release of ghrelin, which increases your appetite, and leptin, which suppresses satiety hormones, and will make you feel hungrier even when eating the same amount of food.
A June 2008 study in Sleep Medicine Reviews found that while sleep deprivation's direct effect on metabolism can't be precisely measured, interrupted sleep is linked to an increased risk for obesity and diabetes as a result of changes to how the body regulates glucose, insulin resistance and the hormones that control food intake and hunger.
"As you can imagine, keeping your brain and body well-tuned, both during wake and sleep, works to tune your metabolism," Dr. Waters says.
Like sleep, stress can change your body's hormone levels, which might have you feeling hungrier while slowing down your metabolism, Dr. Ali says. Chronic stress can lead to overeating, increased visceral (belly) fat and ultimately, weight gain, per a June 2016 article in Behavioral Sciences.
- ACE Fitness: "Resting Metabolic Rate: Best Ways to Measure It—And Raise It, Too"
- Frontiers in Physiology: "Strength Training Improves Metabolic Health Markers in Older Individual Regardless of Training Frequency"
- Sleep Medicine Reviews: 'The Metabolic Consequences of Sleep Deprivation"
- Behavioral Sciences: “Impact of Stress on Metabolism and Energy Balance”