One thing I've learned for certain after counseling hundreds of clients over the years is that there is no way to accurately predict how long it will take to lose weight. But it's helpful to understand the factors that can affect weight loss and why. This knowledge can explain what to expect, and help you hang in there if you feel frustrated with the rate at which you're losing weight. Here are some insights about how weight loss works, and why ditching restrictive diets is one of the best ways to see results.
Slow, steady weight loss is generally better
You may have heard that a healthy rate of weight loss is one to two pounds per week. According to the Centers for Disease Control and Prevention (CDC), people who shed pounds at this rate are more successful at keeping weight off (the ultimate goal). And while many people would like to lose weight faster, even modest weight loss has been shown to result in health benefits, such as improvements in blood pressure, blood cholesterol, and blood sugars.
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Why some people lose weight faster
One to two pounds per week is also a rate that's reasonable for many, in that it shouldn't require extreme eating or exercise habits. That said, there are several factors that affect the speed of weight loss. One is simply how much weight you have to lose.
In a nutshell, people who are more overweight generally lose weight faster, which is partly calorie-driven. For example, if you've been eating enough calories to maintain a weight of 170 pounds, and you reduce your calories to a level that will only maintain 130 pounds, you've created a calorie deficit. The greater the deficit, the faster the weight loss, which is why people who have 40 pounds to lose typically lose weight faster than those who only have 15 pounds to lose. But as you lose weight, the deficit shrinks, which is why the rate of weight loss tapers the closer you get to your weight goal, regardless of where you started.
While calories matter, the concept that weight loss is purely driven by "calories in versus calories out" is outdated. It's also a poor predictor of how fast you'll shed pounds. That's because the quality, balance, and timing of the calories you take in also play key roles in how weight is lost. For example, simply slashing your caloric intake while still consuming a lot of processed foods, or eating a big chunk of your calories in the evening, may not result in losing weight as quickly.
For example, A 2017 study, published in the American Journal of Clinical Nutrition, found that replacing refined grains with whole grains for six weeks resulted in higher resting metabolic rates (greater calorie burning), among both men and post-menopausal women. A Washington University in St. Louis study found that in post-menopausal women, those who ate the recommended amount of protein experienced the greatest benefits in metabolism and insulin sensitivity, even compared to those who followed a high protein diet.
And a 2020 study, published in the Journal of Clinical Endocrinology & Metabolism, found that eating a late dinner worsened blood sugar tolerance and reduced the amount of fat burned. So no, a simple math equation isn't the ultimate determinant of how much weight you'll lose, or how quickly.
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Too few calories can stall weight loss
If you're tempted to eat as few calories as possible, please don't. Cutting calories too low can negatively impact weight loss—because your body can kick into survival mode, conserve calories, and resist weight loss. This is especially true when you eat fewer calories than it takes to support a healthy weight.
For example, if it takes 1,600 calories to support your ideal weight and you cut your intake to 1,200, or even below 1,600, your are likely to either resist weight loss, or lose too much lean muscle mass as part of your weight loss. The latter can weaken immune function, increase injury risk, and reduce the chances of keeping the weight off. Basically, it's a myth that you need to undereat in order to lose weight. You just have to stop eating more than it takes to maintain a healthy weight goal.
The calorie equation is complicated
Metabolism, which is basically how your body burns calories, is an important factor in the weight loss puzzle, and it's complex. Appetite-regulating hormones also play a role in weight loss. Both can be affected by factors like poor sleep, stress, and the makeup of your gut microbiome, the collection of microbes that reside in the digestive system.
Research shows that gut microbiota can actually influence both sides of the calorie balance equation; meaning it impacts how we utilize calories from the foods we eat, and how we burn or store them. For this reason, as well as genetic factors, weight loss—and how quickly you may drop pounds—isn't so straightforward.
Weight fluctuations are normal
It's also important to know that weight loss isn't always linear. It's normal for your weight to shift from day to day, even hour to hour. When you step on a scale, you're measuring everything that has weight — not just your muscle, bone, and body fat, but also water volume (which can change quickly and wildly), undigested food (even if it will all later be burned off), and waste in your GI tract that your body hasn't eliminated yet. If you're retaining water, due to PMS or an extra salty meal, your weight on the scale will be higher, even if you've simultaneously lost body fat.
What's important is your personal patterns. Don't worry about temporary or predictable fluctuations. On the other hand, if you see a steady increase in your weight, rather than an up-and-down pattern, or if your clothes are consistently getting tighter, take an objective look at your habits. Have you been ordering takeout more often (which can mean extra hidden calories), or snacking frequently because of stress? If so, you can address those issues and then continue to see results.
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Be patient, not discouraged
Hopefully I've driven home the point that weight loss is complex, and nobody can realistically forecast exactly how much weight you'll lose within a given time frame. The truth is that focusing on healthy, balanced habits you can stick with is far more important. I've seen countless people lose weight with quick fixes that resulted in gaining back all (or more) of the weight they lost. That kind of yo-yoing isn't good for your health, and it's just not worth the mental agony.
If you're on a weight loss journey, the best thing you can do is to focus on the bigger picture, be consistent with healthy habits (which does not mean being perfect), and remain patient. You'll know if you're moving in the right direction. And even if it takes longer to get there, you're far more likely to keep the weight off for good, and feel a whole lot happier along the way.
Cynthia Sass, MPH, RD, is Health's contributing nutrition editor, a New York Times best-selling author, and a private practice performance nutritionist who has consulted for five professional sports teams.
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