An expert in obesity medicine explains the real reasons weight loss is so difficult and what you can do to work with your body rather than fight against it.
Weight loss is often framed as a simple equation of “eat less, move more,” but for many, the journey feels anything but simple. If you’ve ever struggled with slow progress, plateaus, or weight regain, you’re not alone, and it’s not your fault.
According to Dr. Jennah Siwak, a board-certified Family and Obesity Medicine physician (and known as @drjennahsiwak on social media), the reasons behind these challenges are deeply rooted in biology, genetics, environment, and even the design of our brains.
In this guide, Dr. Siwak shares evidence-based insights and compassionate advice to help people understand why weight loss is hard, and how to navigate it with more self-compassion and success.
“Much of our eating behavior occurs beneath our conscious awareness,” explains Dr. Siwak. “Nobody wakes up thinking ‘I want to overeat and harm my health.’” But our brains, particularly the hypothalamus, have evolved to regulate and defend body weight, especially against weight loss.
While this system isn’t fixed and can adapt over time, it tends to resist weight loss more strongly than weight gain, reflecting an evolutionary bias toward preventing starvation.
This “lipo-stat” system responds to fat loss by triggering hunger and cravings, often without us realizing it. Leptin, a hormone produced by fat cells, drops when we lose weight, signaling to the brain that we’re starving. As a result, the brain ramps up hunger and slows metabolism.
“This system was built for survival in an environment where food was scarce,” says Dr. Siwak. “Now it’s operating in a world of ultra-processed, calorie-dense foods. Our ancient brain circuits are overwhelmed.”
Book Recommendation
Dr. Siwak recommends reading The Hungry Brain by Dr. Stephan Guyenet for a deeper understanding of how brain biology drives eating behavior.
“Some people seem to eat whatever they want and not gain weight, while others have to be incredibly careful,” Dr. Siwak notes. That’s not just anecdotal. Genetic research backs it up as well.
Research suggests that
In other words, weight isn’t just a matter of willpower: it’s also biology.
One of the most frustrating aspects of weight loss is how it gets harder the longer you do it. That’s because
“When you lose weight, your body sees it as a threat,” says Dr. Siwak. “Hunger increases, metabolism slows, and you burn fewer calories, even at rest.”
This metabolic adaptation is your body’s way of protecting itself. For people with obesity, the body may defend a higher baseline weight, making long-term weight loss maintenance especially challenging.
Dr. Siwak uses the analogy of a thermostat: “Imagine your body is set to 80°F. You can open a window to cool it down, but the heating system kicks in to bring it back to 80. That’s what your brain is doing with fat stores.”
Stress and limited sleep don’t just affect your mood; they also directly impact hunger hormones, decision making, and self-control.
“Impulsivity increases when we’re sleep-deprived or stressed,” explains Dr. Siwak, meaning the brain’s logical control center is less able to override cravings and urges.
Chronic stress can trigger emotional eating, while poor sleep disrupts key appetite-regulating hormones like ghrelin and leptin.
That’s why Dr. Siwak emphasizes prioritizing sleep and stress management as essential strategies for supporting your weight goals.
Where you live, where you work, and what you have available can significantly impact your ability to lose weight. Dr. Siwak points out that people working long or irregular hours, like night shifts, often experience disrupted circadian rhythms that affect hunger and metabolism.
In food deserts, where healthy options are limited, people may rely on processed, high calorie foods. “If you don’t have a healthy lunch packed, you’re likely to grab what’s fast and convenient,” she says.
Certain medications can also contribute to weight gain. These include:
- Antidepressants (e.g., paroxetine, amitriptyline)
- Mood stabilizers (e.g., lithium, quetiapine)
- Diabetes medications (e.g., insulin)
- Steroids, antihistamines, and some birth control methods
“Sometimes these medications are necessary and their benefits outweigh the risks, but talk with your doctor before stopping any medication,” Dr. Siwak advises.
First, Dr. Siwak recommends confirming if it’s truly a plateau. “Weight loss isn’t linear,” she says. “Check your menstrual cycle, hydration, and digestion. Weight fluctuations are normal.”
If you’re not in a calorie deficit anymore (which becomes harder as your metabolism slows), weight loss will stall. This doesn’t mean you’re doing something wrong; it’s just how the body tries to maintain stability.
She suggests re-evaluating:
- food intake
- stress
- sleep
- physical activity
- medications
Metabolic adaptations and hormonal changes can also make you move less without noticing, a decrease in non-exercise activity thermogenesis (NEAT), which further slows progress.
Dr. Siwak says maintaining weight loss requires long-term strategy and consistency:
- Prioritize protein, fiber, and healthy fats to stay full.
- Avoid rapid, extreme diets, as they’re harder to sustain.
- Stay active with both cardio and strength training.
- Check in regularly with your habits and progress (e.g., weight, food logs, movement consistency).
- Build in recovery days and mix up the intensity of movement.
- Focus on sleep, stress management, and community support.
The goal isn’t perfection; it’s consistency.
The recommended rate of weight loss is
“You must be in a calorie deficit to lose weight,” Dr. Siwak says. “But how you create that deficit, whether it’s through intermittent fasting, low-carb, or portion control, is up to what works for you.”
The best diet is one that fits your lifestyle, preferences, and schedule, and one you can stick with for the long haul.
“Weight loss is extremely difficult,” Dr. Siwak emphasizes. “Your body is designed to defend its fat stores. Struggling isn’t a sign of weakness, it’s a sign that your biology is doing exactly what it was built to do.”
Her top message for anyone feeling discouraged: “You are stronger than you think. Understanding your body helps you work with it, not against it.”
That means recognizing how hunger hormones, metabolism, stress, sleep, and even medications influence your weight—not as excuses or blame, but as important factors to consider and manage with care.
If you’re struggling on your weight loss journey, you’re not alone, and there is nothing wrong with you. Biology, environment, and life circumstances all play a role, and knowing this can help you move forward with greater compassion and resilience.