If you’ve set out to lose weight for personal or health reasons, it’s reasonable to ask yourself: How long does it realistically take to lose weight? Diet culture and its obsession with before-and-after photos set the expectation to see transformations overnight, but that’s simply not how it works. Below, registered dietitians share how weight loss occurs and how long it takes to lose weight—which, spoiler alert, is not a universal timeline.
How weight loss occurs
The magical secret to losing weight seems to change with whatever fad diet is trending, but in reality, physiologically, there’s one way to do it. (That’s not to say other factors can’t impede, but we’ll get to those later.)
“Weight loss occurs when there is a sustained calorie deficit, leading the body to utilize stored fat for energy,” explains Crystal Scott, R.D., a registered dietician with Top Nutrition Coaching. “This typically happens through a combination of reduced calorie intake and increased physical activity.”
In other words, weight loss happens when you eat fewer calories than you burn, and the body turns to fat stores for fuel. The more you work out, the more burning takes place, and the more likely weight loss becomes.
Weight loss contributing factors
Although the scientific formula for weight loss is simple, we, as individual humans, are not. Lots of factors play a huge role in the process, like:
“Each person’s genetic makeup can influence how their body responds to diet and exercise, impacting weight loss,” says Scott. This phenomenon is widely studied—research shows genetics and a person’s susceptibility to weight gain are linked.
The higher your initial weight, the more likely you are to drop weight, faster. “Basically, the more you weigh, the more energy your body needs to function,” explains Megan Hilbert, R.D., registered dietitian with Top Nutrition Coaching, so the energy expenditure (caloric burn) is going to be higher to start out. However, “as weight loss progresses, the rate of loss tends to slow down for everyone,” Scott adds.
“Hormonal imbalances or conditions such as thyroid disorders can affect weight loss progress,” explains Scott. Other conditions including polycystic ovarian syndrome, Cushing’s disease, menopause, and low testosterone may cause fluctuations in weight, according to the National Library of Medicine.
Research shows that adults over 70 can have 20 to 25% lower resting metabolic rates (the number of calories the body burns at rest), making it more difficult to lose weight with age.
Overall health and lifestyle
Scott explains that medical conditions and physical ability can affect a person’s weight loss, as can sleep hygiene and general physical activity.
Risks of losing weight too quickly
Dropping too far into calorie restriction can cause a slew of health issues, including nutrient deficiencies, irritability, fatigue, and constipation, says Hilbert. “It’s important to meet your body’s minimum daily requirements for this reason,” she adds. (The general daily recommended calorie intake is anywhere between 1,600 and 2,400 calories, depending on age and activity level, per the United States Department of Agriculture. But a registered dietitian can help you find your sweet spot.)
Other side effects of rapid weight loss, according to Scott, include:
- Muscle loss: Rapid weight loss can lead to muscle loss, which may negatively impact metabolism and body composition.
- Gallstones: Rapid weight loss can prevent the gallbladder from emptying properly, increasing the risk of developing gallstones.
- Electrolyte imbalances: This can cause adverse effects on the body.
- Psychological impacts: Extremely restrictive diets can lead to feelings of deprivation, disordered eating patterns, and a negative relationship with food.
So, how long does it take to lose weight?
If you follow a calorie deficit, Scott says you can generally expect to see initial weight loss within a few weeks. Hilbert adds that some may see changes in as little as a week.
“Aiming to lose weight at a rate of 0.5 to 1 lb per week is generally considered a safe and sustainable goal,” says Scott. “Gradual weight loss allows for better preservation of muscle mass, adherence to healthy habits, and long-term success.”
It’s important to note, however, that weight fluctuations are normal.“Progress is often not totally linear, so keep in mind some weeks you may lose more, other weeks you may be in a plateau, and this is all part of the process,” says Hilbert. “Weight loss is a long term game.”
For ideal, healthy results, alongside an appropriate exercise regimen, Scott recommends consulting a registered dietitian to develop an individualized weight loss plan.
Kayla Blanton is a freelance writer who reports on all things health and nutrition for Men’s Health, Women’s Health, and Prevention. Her hobbies include perpetual coffee sipping and pretending to be a Chopped contestant while cooking.