If you've hit a weight-loss plateau you may be wondering, what gives? There's plenty of reasons weight loss might stall out, but is your metabolism slowing down one of them?
Metabolism gets a lot of attention around weight loss. It also gets a lot of unnecessary credit and blame. Your metabolism is important when it comes to weight, but it's not the only factor at play. Here, we explain the biological changes that happen to your metabolism and your body during weight loss and what you can do about them.
What Is Metabolism?
Metabolism refers to the necessary chemical processes that happen in your body in order to maintain life.
Think about your body as a car. If you put gas in a car, it uses that fuel in order to move. In the same way, your body uses calories from food, or energy, in order for it to move, breathe and function. Metabolism is the process of your body utilizing the energy you put into it, or more simply, burning calories. You can also burn extra calories by adding activity, such as walking, dancing or exercising.
Your metabolism includes these functions that burn calories:
- Basal or Resting Metabolic Rate (BMR or RMR): BMR refers to how much energy (or how many calories) your body burns just to keep you alive. Even when you're asleep, your body still uses energy to pump blood and keep your heart beating.
- Thermic Effect of Food (TEF): Your body needs energy to process the food you eat. The thermic effect of food (TEF) includes the calories you burn digesting food. So, yes, eating burns calories—although the TEF is usually small and not enough to outweigh the calories you take in.
- Non-Exercise Activity Thermogenesis (NEAT): NEAT refers to the calories your body burns through daily activities such as fidgeting, walking to work, or going up the stairs.
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What's the Difference between a Fast Metabolism and a Slow Metabolism?
A fast metabolism is one that burns a lot of calories to support its metabolic functions. Your friends who can eat whatever they want without gaining weight likely have fast metabolisms. In contrast, a slow metabolism doesn't burn through as many calories to support the same metabolic functions.
You can blame genetics for this. "Many factors have an impact on metabolism including age, sex, genetics, body composition and weight," says Allison Knott, M.S., R.D.N., a registered dietitian based in Brooklyn, New York. While genetics largely determine how many calories you burn doing various activities, you do have some control over your metabolic rate.
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Can Losing Weight Slow Your Metabolism?
Yes, it can. If you eat fewer calories than you burn off through daily activities and exercise, you will lose weight. The hard part is maintaining that weight loss. More often than not, someone loses weight, keeps it off for a while and then gains it back. There are several factors at play during this process, and metabolism is just one of them.
"In general, losing weight leads to a lower resting metabolic rate and fewer calories burned, including during activity," says Sarah Gold Anzlovar, M.S., R.D.N., L.D.N., founder of Sarah Gold Nutrition. "Smaller bodies require less energy to function than a larger body—just like a small apartment requires less energy to heat than a larger house."
You don't need as many calories to function at 150 pounds as you did at 200 pounds. Your BMR falls, or slows, with weight loss.
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To add to the frustration, your brain also sends signals to your body that increase hunger and reduce the number of calories you burn. Evolutionarily, this was a protective mechanism to keep you from starving. Today it is a major cause of weight regain.
This may seem depressing, but you do have some control over the rate at which your metabolism falls. You can keep your metabolism from slowing too much by losing weight slowly versus through a crash diet.
"If you go at dieting very vigorously your metabolism falls, so it means you lose less weight than the calories you cut," says Susan B. Roberts, Ph.D., senior scientist at the USDA Human Nutrition Research Center at Tufts and founder of the online iDiet weight-loss program. "Slower dieting has a smaller effect. Once you have lost weight and stabilized, if you have been going at a moderate rate of one to two pounds per week, there does not seem to be a long-term impact. Your metabolism is lower because you are now a smaller person, but not disproportionately low."
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Other Reasons Your Metabolism Can Slow Down
Weight loss isn't the only culprit for a slower metabolism. If you eat too few calories or go too long between meals (more than three or four hours), your metabolism will slow down. This is known as "starvation mode" and is due to the same protective mechanism that happens when you lose weight. Your body slows down the rate at which it's burning calories in order to conserve energy, because it doesn't know when you are going to feed it again. This is a double whammy if you are severely restricting calories to lose weight.
The ratio of fat to muscle in the body also affects metabolic rate. Weight, or body composition, is made up of fat, muscle, bone and water. Muscle is more metabolically active than fat. In other words, it burns more calories. When you lose weight, you lose both fat and muscle, unless you are doing something to preserve the muscle mass. Losing calorie-burning lean muscle mass slows your metabolism.
"This is one reason why you see a change in metabolism over the lifespan," Knott says. "As you age, you naturally lose muscle mass, which results in a decreased metabolism. This can be influenced by maintaining muscle mass throughout the lifetime with weight-bearing physical activity."
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Can Your Metabolism Fall Below a "Normal" Level Because of Weight Loss?
There is no "normal" metabolism. What is normal for you is based on your genetics, age, sex, weight and activity level. But what you consider normal for yourself can change over time due to age, weight loss or muscle loss.
"Some newer research suggests that significant weight loss can lead to a lower metabolic rate than 'normal' for that weight and one that is consistently lower even after the weight is regained," Anzlovar says. "This means that if you started at 200 pounds and now weigh 150 pounds, you will burn fewer calories at rest and during exercise than someone who always weighed 150 pounds. What's even more frustrating for those that want to lose weight is that research has also shown that if the person who lost the 50 pounds regains that weight, his or her metabolism will be lower at 200 pounds than it was before he or she lost the weight." It is unclear if this always happens or why it happens, she added.
Can You Boost Your Metabolism?
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You might feel doomed to the metabolism you have, but you can do some things to keep your metabolism revved and prevent it from slowing down.
- Eat more high-quality foods. Stick to a diet with whole, unprocessed foods, and eat them often. "Eating a very low-calorie diet or excessively exercising and not eating enough often leads to a slower metabolism," Anzlovar says. Her clients are often surprised when she tells them they need to eat more. Eat every three to four hours to prevent the starvation mode that tells your body to conserve energy instead of burning it.
- Focus on protein and fiber. According to Roberts, research is ongoing on the topic of metabolism falling below a normal level. "Perhaps higher-protein diets help prevent the fall," she says. "Also, definitely higher-fiber diets will have a protective effect." She and her colleagues found that when people with stable weights replaced refined grains with whole grains, they were able to modestly increase their BMR (or RMR). That's why a high-fiber diet is the cornerstone of her weight-loss program. Other studies confirm that eating foods high in protein and fiber and lower on the glycemic index lead to less hunger and greater levels of fullness, which help combat the increased hunger caused after weight loss. Aim to eat at least 25 to 35 grams of fiber per day.
- Pick up the weights. "Physical activity is one of the few ways that metabolism can be significantly impacted, both because being active requires additional energy and because of the shift in body composition," Knott says. Instead of focusing only on cardio exercise, add weight-bearing activities too. Cardio may give you a higher total calorie burn, but that means you lose fat and muscle. Add two to three days of strength training per week to help lose fat but preserve muscle. "More muscle mass means a higher metabolism, so don't be afraid of weight training," Anzlovar says.
- Get moving. Research shows that people who are able to keep weight off long-term exercise close to an hour every day. The National Weight Control Registry, a database that follows people who successfully lose weight and keep it off, reports that 90 percent of their members exercise for an average of one hour per day. Studies also show that people who burn a lot of calories through daily exercise but eat enough to maintain their weight can raise their metabolic rate. Roberts adds, "Exercise has a transient effect. For a while after you exercise, your metabolism is increased. And then, long-term, the increase in muscle mass you get from weights has a small effect."
The Bottom Line
Unfortunately, losing weight slows your metabolism, but you do have some control. Nix the crash diets, and work on changing habits over time. You will burn fewer calories as you lose weight and will likely be hungrier, but you can offset some of this by eating foods high in protein and fiber, replacing refined grains with whole grains, and doing cardio and strength training exercises daily.
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