You’ve probably heard at some point that it takes a roughly 3,500-calorie deficit between calories consumed and calories burned to produce a one-pound drop in body weight. This old chestnut is more than 60 years old and commonly cited in scientific literature. Problem is, it’s not exactly an accurate rule.
The 3,500-calorie rule dates back to 1958, when Max Washnofsky, M.D., wrote a paper in the American Journal of Clinical Nutrition concluding “that 3,500 calories is the caloric value of one pound of body weight lost.”
The number was simple, stark, and capable of being reduced to 500 calories per day multiplied by seven days a week to total 3,500 calories per week, or one pound of weight loss per week. That’s why you also hear that healthy weight loss for the average person is about four to five pounds per month.
This all seemed logical and even doable, so the 3,500-calorie rule stuck, and prospered. Today, many conventional weight-loss plans still tout the 500-calories-a-day approach. This isn’t wrong—when oversimplified, weight loss can boiled down to calories in need to be less than calories out. But this approach won’t work in the long term.
The 3,500-calories rule is actually largely accurate if you’re burning a pound of flesh in a chemistry lab. However, the human body isn’t a lab, where you can isolate and analyze one factor at a time and weight loss doesn’t exist in a vacuum. Rather, the body is an organic whole, and has many reactions to changes in calories, carbohydrates, fats, proteins, metabolism, exercise, hydration, and hormones.
When you’re making a lifestyle change through diet, almost all these interrelated events conspire to lower your daily metabolic rate through a process known as “metabolic adaptation.” As a result, a daily deficit of 500 calories produces slightly less effect on each subsequent day. The difference isn’t big at first, but grows substantially with longer periods of time, producing just 50 percent of the expected weight loss over 12 months.
“The biggest flaw with the 500-calorie-rule is that it assumes weight loss will continue in a linear fashion over time,” says weight-change mathematician Kevin Hall, Ph.D. “That’s not the way the body responds. The body is a very dynamic system, and a change in one part of the system always produces changes in other parts.”
That’s why physiologists, nutritionists, and researchers have since emphasized that the 3,500-calorie-rule is an estimation that doesn’t take into account the variety of factors that affect weight loss over time.
What’s realistic? According to Hall, in the first year of a new weight-loss program, most people will lose about half the weight that the 3,500-calories rule predicts. In other words, over 12 months, instead of losing around 48 pounds, the average person may lose around 24 pounds—if that. And even still, this estimation largely depends on the person, primarily assuming they have a significant amount of weight to lose.
Individual weight losses are highly variable. The most overweight people will lose the most weight in the first few months of a program; the leanest will lose the least. That’s also why the “last five pounds” is always the toughest. Once you get leaner, it’s more difficult to lose additional weight—this is our bodies’ natural survival mechanism.
Still, Hall believes it’s better to succeed with an evidence-based strategy than to fall short with the old, difficult-to-achieve model. And evidence suggests that the best weight loss plan is the one you can adhere to over the long term, which tends to be less restrictive.
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It’s important to remember that counting calories is not the be-all-to-end-all when it comes to weight loss. In fact, it can sometimes create an unhealthy relationship with food and exercise. Smartwatches, apps, and other calorie trackers are available if you need them, but when you run regularly and fill your plate with fresh, healthy options, you know you’re doing the right things to keep your body healthy—regardless of weight.
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