The Science of Weight Loss: What Actually Drives Change (and What Most People Get Wrong)

Melissa
Jan 26
6 min read

A NOTE: In my practice, weight loss is a neutral physiological outcome — not a moral goal or a prerequisite for worth, health, or performance. It’s also not a realistic outcome if someone is not, at the very least, meeting their daily nutrition requirements. Any reason someone pursues weight loss deserves clarity, not judgment. At the same time, I’ve seen how oversimplified, aggressive approaches to weight loss often create more harm than help, especially in active and high-performing bodies.

CONTENT NOTE: This post discusses weight and weight loss. If these topics feel triggering or unhelpful for you right now, I encourage you to skip this post and come back to it another time — or not at all. Take care of yourself first.

This post isn’t about prescribing a diet or telling you what you should want. It’s about explaining what the science actually says — and why so many well-intentioned efforts fail when physiology, adaptation, and sustainability are ignored.

Let's get started.

Weight loss is one of the most talked-about topics in health and fitness — and one of the most misunderstood.

It’s often framed as a test of discipline, motivation, or willpower. But biologically, weight loss is none of those things. It’s a physiological outcome, shaped by energy balance, metabolic adaptation, hormones, training stress, recovery, and sustainability.

Many people pursue weight loss for valid, non-problematic reasons: health markers, physical comfort, injury risk, performance goals, or medical guidance. The issue isn’t wanting weight loss. The issue is that most people are handed oversimplified, aggressive strategies that work briefly — then backfire.

This post resets the conversation by focusing on what actually drives weight loss from a scientific perspective, why so many “perfect” plans stall, and why active people often struggle despite doing everything they’re told to do.

Weight loss isn’t about willpower. It’s about physiology, energy balance, adaptation, and sustainability.

Energy Balance: Necessary, but Not Sufficient

At the most basic level, weight change requires a caloric deficit over time. This is a reflection of the First Law of Thermodynamics — energy in versus energy out.

But human bodies are not static calorie-burning machines.

Total daily energy expenditure (TDEE) is dynamic, not fixed. It changes in response to many factors, including but not limited to: food intake, training volume, stress, sleep, and weight loss itself. Two people can eat the same number of calories and experience very different outcomes — and the same person can experience different outcomes at different times.

When intake drops:

Non-exercise activity (NEAT) often decreases unconsciously
Resting metabolic rate declines
Energy efficiency improves

This means that a calorie deficit that initially produces weight loss may eventually maintain weight — without any change in effort.

Energy balance matters. But it does not operate in a vacuum.

Metabolic Adaptation: Why Weight Loss Slows Down

As body mass decreases, the body adapts in predictable ways:

Resting metabolic rate declines
Leptin decreases (satiety signaling drops)
Ghrelin increases (hunger rises)
Energy expenditure drops beyond what weight loss alone would predict

This is not “metabolic damage.”

It’s a normal survival response.

The body is designed to resist weight loss, especially when it happens quickly or aggressively. Long plateaus are not a failure — they’re often a sign that the body has adapted to a new intake and is conserving energy.

More extreme dieting accelerates this process, making continued fat loss harder and increasing the likelihood of rebound weight gain.

Macronutrients: It’s Not Just Calories

Calories matter — but what those calories are made of influences results, especially in active people.

Protein

Preserves lean mass during a deficit
Improves satiety
Has a higher thermic effect of food

It’s important to clarify that protein intake alone does not preserve muscle mass during weight loss. Protein provides the raw materials, but the body still needs a reason to use those amino acids for muscle maintenance. Resistance training provides that signal. Without a mechanical stimulus, amino acids are more likely to be oxidized for energy or used for other physiological processes rather than directed toward muscle tissue.

In other words, consuming an adequate amount of protein daily supports lean mass when it’s paired with strength training.

Carbohydrates

Support training quality and output
Help preserve metabolic rate
Reduce excessive cortisol responses

Fats

Necessary for hormone production
Increase meal satisfaction
Support absorption of fat-soluble nutrients

Very low-carb or very low-fat approaches may reduce calories quickly, but they often degrade training quality, recovery, and metabolic stability — which can stall progress long-term.

Poor fueling → poorer training → lower energy expenditure → worse outcomes.

Training Matters — Just Not the Way Most People Think

Exercise is important for body composition, but not because it “burns off” food.

Cardio can increase energy expenditure, but it also increases the likelihood of compensation — more hunger, less movement later in the day, or both.

Strength training plays a different role:

Preserves muscle mass
Helps maintain resting metabolic rate
Improves insulin sensitivity

More workouts are not always better.

Overtraining paired with underfueling is a common reason fat loss stalls — especially in high-volume athletes and performers.

Recovery is not optional; it’s a variable in the weight loss equation. At least one true rest day per week supports hormonal regulation, recovery, and long-term training quality — all of which influence weight loss outcomes.

Hormones, Sleep, and Stress: The Hidden Blockers

Weight loss does not happen in isolation from the rest of your physiology.

Sleep deprivation

Increases hunger hormones
Reduces satiety signaling
Impairs glucose tolerance

Chronic stress

Elevates cortisol
Encourages energy conservation
Increases cravings and fatigue

Low energy availability — whether intentional or accidental — disrupts endocrine function and can impair fat loss entirely.

If the body perceives ongoing threat, restriction, or exhaustion, weight loss becomes biologically undesirable.

Why Most Diets Fail Long-Term

Long-term data consistently shows that the majority of people regain weight after dieting.

Not because they’re weak.

But because most diets are:

Too aggressive
Ignorant of metabolic adaptation
Behaviorally unsustainable

Weight cycling can worsen metabolic efficiency over time, while psychological restriction increases binge risk and food preoccupation.

Long-term success is associated with:

Small, consistent deficits
Predictable routines
Flexible eating patterns

Sustainability is not a “mindset issue.” It’s a biological one.

Weight Loss Is Not a Moral Goal — It’s a Strategic One

Wanting weight loss does not mean you dislike your body.

But why you pursue it matters.

Performance vs punishment
Health vs fear
Function vs aesthetics

Weight loss driven by shame rarely lasts.

Weight loss pursued from a place of performance, vitality, and care is more likely to succeed — and feel better along the way.

You can work toward body composition change without hating your body or fighting it at every step.

Practical Takeaways for Active People

Small deficits outperform aggressive ones
Include protein at every meal (aim for The Dancer's Plate Framework)
Fuel training with carbohydrates
Lift weights 2–4x per week
Include at least one true rest day each week
Sleep 7–9 hours consistently
Manage stress like it’s part of your training plan
Expect plateaus — and don’t panic when they happen

Weight loss is not linear. Adaptation is normal.

A Final Note

For dancers, athletes, and high performers, weight loss is rarely the first problem to solve. Energy availability, recovery, consistency, and hormone health matter more — and weight changes may follow once those foundations are in place.

If you’re interested in exploring how these principles apply to your training, schedule, or goals, working together can help bring clarity and structure to the process — without hype, extremes, or unnecessary restriction.

References

Fothergill, E., Guo, J., Howard, L., Kerns, J. C., Knuth, N. D., Brychta, R., Chen, K. Y., & Hall, K. D. (2016). Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity, 24(8), 1612–1619. https://doi.org/10.1002/oby.21538

Hall, K. D., Heymsfield, S. B., Kemnitz, J. W., Klein, S., Schoeller, D. A., & Speakman, J. R. (2012). Energy balance and its components: Implications for body weight regulation. The American Journal of Clinical Nutrition, 95(4), 989–994. https://doi.org/10.3945/ajcn.112.036350

Helms, E. R., Aragon, A. A., & Fitschen, P. J. (2014). Evidence-based recommendations for natural bodybuilding contest preparation: Nutrition and supplementation. Journal of the International Society of Sports Nutrition, 11, 20. https://doi.org/10.1186/1550-2783-11-20

Longland, T. M., Oikawa, S. Y., Mitchell, C. J., Devries, M. C., & Phillips, S. M. (2016). Higher compared with lower dietary protein during an energy deficit combined with intense exercise promotes greater lean mass gain and fat mass loss. The American Journal of Clinical Nutrition, 103(3), 738–746. https://doi.org/10.3945/ajcn.115.119339

Loucks, A. B., Kiens, B., & Wright, H. H. (2011). Energy availability in athletes. Journal of Sports Sciences, 29(S1), S7–S15. https://doi.org/10.1080/02640414.2011.588958

Mann, T., Tomiyama, A. J., Westling, E., Lew, A. M., Samuels, B., & Chatman, J. (2007). Medicare’s search for effective obesity treatments: Diets are not the answer. American Psychologist, 62(3), 220–233. https://doi.org/10.1037/0003-066X.62.3.220

Mountjoy, M., Sundgot-Borgen, J., Burke, L., Ackerman, K. E., Blauwet, C., Constantini, N., et al. (2018). IOC consensus statement on relative energy deficiency in sport (RED-S): 2018 update. British Journal of Sports Medicine, 52(11), 687–697. https://doi.org/10.1136/bjsports-2018-099193

Rosenbaum, M., & Leibel, R. L. (2010). Adaptive thermogenesis in humans. International Journal of Obesity, 34(S1), S47–S55. https://doi.org/10.1038/ijo.2010.184