Why You're Gaining Weight Back - The Hidden Science Behind

YI ZHANG, MS, RDN 2025/3/29

Congratulations! I believe you have put a lot of effort into your weight loss journey, and you’ve already experienced success. However, new challenges may have arisen. Many people find themselves stuck at some point - whether for a week, a month, or even longer. Some may regain the weight they worked so hard to lose. This can be frustrating, but understanding the science behind our amazing human body can help you stay positive and motivated. Let me guide you through it and support you in staying on track.

You may have heard Thermodynamics.

“The first law of thermodynamics states that energy can neither be created nor destroyed, only transferred”. This is also applied with weight management - the body must spend more energy than it takes in to lose weight or take in more than it needs to gain weight.

That is why weight loss involves creating a calorie deficit fundamentally through:

1. Decreasing energy intakes

2. Increasing energy needs

Thus, the body can “be forced” to use stored energy fat for fuel. Now you had succeeded to create the calorie deficit and lost weight. There is another term you may haven’t heard about much: Adaptive Thermogenesis (AT). In short, after the initial shock of lower calorie intakes then weight is lost, the body no longer thinks you need that much calorie to survive, and it automatically adapted to the new weight and decided to slow metabolic during caloric restriction. The time of AT occurs varying, some people may experience as early as the first week with caloric restriction, and metabolic adaptation occurs with weight changes over time. AT is believed commonly one of the reason people regaining weight back fast after weight loss. Some thermogenic modification may also occur with weight loss and contributes to lower energy needs for weight with a “new weight” after weight loss, including hormonal modifications, mitochondrial adaptation, non-exercise activity thermogenesis (NEAT), and body composition shifts in favor of a higher ratio of fat mass to lean tissue.

Now, you know why - our body is smart and aligns with decreased “needs” when detecting “weight loss”. How to prevent the regain or maintain the new weight is the question we want to discuss.

1. Preventatively refuse rapid weight loss through restricted diet.

• Overly restrictive diets can lead to mental fatigue, increased cravings, and binge eating behaviors. Aim for gradual, long-term diet changes.

2. Prioritize Protein & Strength Training

• To preserve muscle mass and keep a good metabolism.

3. Manage Stress and Sleep well

High stress and poor sleep increase hunger hormones and cravings. Your hunger/fullness are controlled by three key hormones: cortisol, Ghrelin, Leptin.

Cortisol Increase: Chronic stress raises cortisol levels, which promotes fat storage (especially around the abdomen) and increases cravings for high-calorie, carb-rich foods.

Ghrelin & Leptin Disruption: Poor sleep increases Ghrelin (hunger hormone) and decreases Leptin (satiety hormone), leading to overeating.

4. Self-detect body’s signals:

• Learn to listen to your body and identify the physical and emotional hunger before meals and snacks, sometimes are you hunger, or thirsty?

5. Set realistic expectations and allow for setbacks.

• Work closely with your Dietitian to set the goals.