Why Weight Loss Is So Hard: A Physician Explains the Biology Behind Weight Loss Resistance
- Joshua Silva, MD
- 3 days ago
- 6 min read
Nearly 74% of U.S. adults are overweight or obese.¹ˌ¹¹ Millions struggle with weight loss despite dieting, exercising, and “doing everything right.”
The truth is simple:
Weight loss is not just about willpower — it’s about biology.
And modern research shows that your body is wired to resist weight loss and defend its highest weight.²–⁵
This article explains why weight loss is so difficult, why most diets fail long-term, and how medical weight-loss treatments — including GLP-1 and GIP medications like semaglutide and tirzepatide — can help shift biology back in your favor.
Transcript of the Video
Below is the full transcript of the physician-narrated video explaining why weight loss is biologically difficult and how GLP-1/GIP medications like semaglutide and tirzepatide help regulate hunger, cravings, and metabolism, particulary for people in Utah.
According to the CDC, nearly 74 percent of adults in the U.S. are overweight or obese. Let's understand why.
Our bodies are wired for survival, not modern life. We evolved to crave calorie-dense foods, over eat, and store extra energy as fat because food was once hard to find. Now-that food is everywhere, those same survival instincts work against us.
You might think, “But I hardly eat!”
Yet research shows most people underestimate calories eaten.In a New England Journal of Medicine study, participants who attributed their weight to slow metabolisms actually underreported calorie intake by 47%. Their metabolisms and hormone levels were shown to be normal — including thyroid and cortisol levels.
That’s where Potere Health MD can help.
Medications like semaglutide and tirzepatide mimic natural hormones that regulate appetite and digestion. They help you feel full sooner, reduce cravings, and quiet food noise — making it easier to maintain a calorie deficit.
Medications like semaglutide and tirzepatide mimic natural hormones that regulate appetite and digestion. They help you feel full sooner, reduce cravings, and quiet food noise — making it easier to maintain a calorie deficit.
Clinical trials show average weight loss of 15–21% of total body weight — beyond what lifestyle changes alone typically achieve.
Weight loss is challenging. It’s not fair that you can eat more in 60 seconds than you can burn in 60 minutes of strenuous exercise.
Let Potere Health MD help! We pair proven medications with real, physician-guided support to help you achieve your weight-loss-goals.
How Weight Loss Actually Works (and Why “Eat Less, Move More” Isn’t Enough)
Most people hear that weight loss is simply a matter of “calories in vs. calories out.”
While technically true, this model ignores the powerful metabolic and hormonal adaptations that occur when you restrict calories.¹²
Your body is not a calculator — it’s a survival machine.
Weight Loss Requires a Sustainable Calorie Deficit
To lose weight, you must consistently burn more calories than you consume. However, as soon as your body senses a calorie deficit, it begins triggering defenses to restore energy balance.²,³
This is a major reason why diets plateau and why weight loss often slows after the first few weeks.
Why Your Body Fights Weight Loss (The Science of Weight-Loss Resistance)
Humans evolved in environments where food was scarce — not in the modern world of fast food, constant snacking, and ultra-processed calories.¹⁵
Your physiology still behaves like famine is possible at any moment.
Evolution Hard-Wired Us to Crave High-Calorie Foods
For survival, the brain evolved to reward:
● Craving sugar, fat, and salt
Sugar – quick, immediate energy
Fat – highest energy density
Salt – essential electrolytes
● Overeating when food is present
● Storing extra energy as body fat
Today, these instincts make weight loss harder — and weight regain easier.
Your Body Defends Fat Stores During Weight Loss
When calories drop, your body activates survival mechanisms to conserve energy and fat stores:
● Hunger hormone (ghrelin) increases²
● Satiety (feeling full) hormones (leptin, PYY, CCK) decrease²
● Metabolism slows³
● Cravings intensify²
● The brain becomes hyper-focused on food²
These are not psychological weaknesses — they are normal physiology.
Even more importantly, these hormonal changes persist long after dieting stops, resulting in rebound weight gain.²
Why Most People Regain Weight (And Why Long-Term Weight Loss Is Rare)
The challenge isn’t just losing weight — it’s keeping it off.
Only About 20% Maintain Significant Weight Loss Long-Term
A major review found that only ~20% of people maintain a weight loss of at least 10% for one year or longer.⁵
This means 4 out of 5 people regain most of the weight, even with continued effort.
Over 50% of Lost Weight Is Regained Within 2 Years
Long-term follow-up studies show:³,⁴
● Most people regain half the weight within 2 years
● By 5 years, many regain most or all of the weight
● This happens even in structured programs with coaching and diets
This proves that obesity is a chronic, relapsing medical condition — not a lack of discipline.
Why We Underestimate Calories (and Why “I Hardly Eat” Feels True)
If you feel like you “barely eat,” but still can’t lose weight — you’re not imagining it.
H3: Research Shows We Underestimate Calorie Intake by ~47%
In a classic NEJM study, adults who reported eating <1,200 calories/day:⁶
● Underreported intake by 47%
Actual calories consumed 2,100/day
● Overestimated activity by 51%
● Had normal metabolism, coristol, and thyroid function
This is a common human bias we seem to share.
Modern Food Environments Confuse Portion Size and Appetite
Scientific studies show:¹³–¹⁵
● We consistently underestimate portion size
● Larger portions lead to automatic overeating
● Ultra-processed foods overstimulate reward pathways (dopamine) and weaken satiety
● Smoothies, bowls, and wraps often contain 600–1,200 calories
● Eating while distracted increases intake by 15–30%
The Bottom Line: Your biology and our modern environment make accurate calorie awareness nearly impossible.
How GLP-1 and GIP Medications Help With Weight Loss
This is where modern obesity medicine — including GLP-1 and GIP medications such as semaglutide and tirzepatide— changes the playing field.
What Semaglutide (GLP-1) and Tirzepatide (GIP) Do
These medications mimic natural satiety (fullness) hormones that regulate appetite and digestion.
GLP-1/GIP agonists:
● Increase fullness
● Reduce hunger and cravings
● Quiet food noise
● Slow gastric emptying (eat less, feel full longer)
● Improve insulin sensitivity and blood sugar
This makes it dramatically easier to maintain the calorie deficit required for meaningful weight loss without constant hunger and food noise.
Clinical Trials Show 15–21% Weight Loss With GLP-1/GIP Medications
Large randomized controlled clinical trials show:⁸–¹⁰
● Semaglutide 2.4 mg: ~15% average weight loss
● Tirzepatide: 15–21% average weight loss
These results are significantly greater than lifestyle alone — and offer new hope for long-term weight management.
Physician-Guided Medical Weight Loss at Potere Health MD
Weight loss is challenging — and it’s not fair that you can eat more in 60 seconds than you can burn in 60 minutes, or that one day of overeating can erase nearly a week of progress.
At Potere Health MD, our medical weight-loss program helps you work with your biology through:
● Evidence-based GLP-1/GIP medications
● Personalized physician dosing
● Monitoring to reduce side effects
● Muscle-preserving nutrition guidance
● Long-term support for weight maintenance
You don’t have to fight your biology alone.
Disclaimer:
This article is for educational purposes only and is not a substitute for medical advice.
About the Author
Dr. Joshua Silva, MD, is a licensed physician and Medical Director of Potere Health MD. He completed residency training in Occupational and Environmental Medicine from the University of Utah where he also earned a master's degree in Occupation Health. He now specializes in evidence-based weight management, including GLP-1/GIP therapies (semaglutide & tirzepatide). Dr. Silva provides in-person and virtual care for patients throughout Utah.
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Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity. NEJM. 2021.
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https://www.niddk.nih.gov/health-information/health-statistics/overweight-obesity
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