Most people think losing weight and keeping it off are the same challenge. According to Israa Ali, MD, an endocrinologist at The University of Texas Medical Branch (UTMB Health), they are two distinct biological processes. Understanding that difference helps explain why weight loss is difficult — and why maintaining that loss can be even harder.
“Your weight is not a straightforward balance of what you eat and how much you exercise,” Ali said. “The equation also includes genetics, stress, social factors, the time available to shop for and prepare food, and your basal metabolic rate, or energy expenditure.”
Ali, medical director of the UTMB Health Victory Lakes Town Center subspecialty clinics and co-director of the Medical Weight Management Clinic, said excess weight is often the result of chronic metabolic disease rather than a lack of willpower.
“Struggling with weight is often driven by a chronic metabolic condition, just as hypertension, or high blood pressure, is a chronic condition,” Ali said. “More than 42% of adults in the United States have obesity, and that number is projected to reach 50% by 2030.”
Patients often focus on the number on the scale, she said, but that number only tells part of the story and does not reflect the complex biological processes taking place inside the body.
Weight loss begins with an energy deficit
Weight loss begins with creating a calorie deficit, meaning the body uses more energy than it takes in. Once weight is lost, however, the body activates separate processes designed to restore those lost pounds.
“When we want to lose weight, we have to create a calorie deficit, which means we must consume fewer calories than we expend,” Ali said. “But once weight loss occurs, maintaining that lower body weight activates another mechanism called adaptive thermogenesis.”
Adaptive thermogenesis is the body’s natural response to weight loss. It slows metabolism to conserve energy, making it more difficult to maintain a lower body weight.
“The body senses that you are in a calorie deficit and interprets it as a form of stress,” she said. “One of the ways it responds is by slowing energy expenditure, or the number of calories the body burns each day.”
Basal metabolic rate accounts for about 60% to 70% of the body’s daily energy expenditure.
“If you lose 10% of your body weight, your energy expenditure may decrease by about 15%, which is significant,” Ali said. “In other words, your metabolism slows.”
The body works to restore lost weight
Hormones also shift during weight loss. Hunger signals increase while feelings of fullness decline, making it more difficult to control appetite.
“During weight loss, there’s a shift that increases the hormones that promote hunger and decreases the satiety signals that go to the brain,” Ali said. “Your appetite increases while you are trying to maintain weight loss because the body activates biological mechanisms designed to restore lost weight. The body is attempting to defend its previous weight.”
One of the key hormones involved is leptin, which is produced by fat cells and helps regulate long-term appetite. As body fat decreases, leptin levels fall, signaling the brain to increase hunger and reduce energy expenditure.
“This is a complex biological process,” Ali said. “Losing weight requires creating an energy deficit. Maintaining that weight loss means overcoming the body’s natural defense mechanisms, which increase hunger and slow metabolism.”
Those biological adaptations help explain why maintaining weight loss is often more difficult than losing it. Research shows that many people regain much of the weight they lose over time.
“It’s better to lose weight gradually — no more than 5% of your body weight over three months — to give the body time to adapt,” Ali said. “That may decrease the likelihood of regaining the weight.”
Nourishing the body supports long-term weight management
Ali said she often hears patients say they eat only one meal a day and still gain weight.
“That places stress on the body,” she said. “Instead, focus on nourishing your body with lean protein, healthy carbohydrates, and regular physical activity. Giving your body the nutrition it needs helps support long-term balance.”
Weight loss and management can be a frustrating, lifelong challenge for many people. Ali hopes to help patients understand that the body is responding exactly as biology intended and educate them about why maintenance is so difficult.
“It has nothing to do with a lack of willpower,” she emphasized.
“The body is designed to protect against weight loss, and when patients understand what their body is doing and why, it helps explain why maintaining weight loss can be just as challenging as losing it in the first place,” she said. “I strongly recommend working with a healthcare team to develop strategies that support long-term success.”
To establish care with a primary care physician, learn more about UTMB Health services.