Researchers followed 100 people on a weight loss program to understand why some people regain all their weight back while others keep it off. They discovered that people who regain weight the fastest actually started with better health markers and ate less food initially. However, their bodies didn’t respond normally to hunger hormones during the year after the program ended. This suggests that some people’s bodies may fight harder against weight loss, making it tougher for them to maintain results. Understanding these differences could help doctors create better, personalized weight loss plans.

The Quick Take

  • What they studied: Why do some people regain all their lost weight quickly after a diet program, while others keep the weight off? Researchers wanted to find early warning signs that predict who will struggle.
  • Who participated: 100 adults (56 women, 44 men) with an average age of 59.5 years who were overweight. They all completed a 3-week intensive program combining exercise and diet changes, then were tracked for one full year.
  • Key finding: People who regained all their weight back ate less food at the start and had healthier metabolic markers initially, but their hunger-control hormones didn’t respond normally during the follow-up year. This suggests their bodies may naturally resist weight loss more than others.
  • What it means for you: If you’re starting a weight loss program, knowing whether your body is an ‘adverse responder’ type could help you and your doctor plan better strategies. However, this is early research, and individual results vary greatly. Talk to your healthcare provider about your specific situation.

The Research Details

Researchers recruited 100 overweight adults and put them through an intensive 3-week program that combined supervised exercise and dietary changes. After the program ended, they tracked participants for one full year to see what happened with their weight. They divided people into three groups based on how much weight they regained: those who regained everything (group A), those who regained some (group B), and those who kept the weight off (group C).

Throughout the study, researchers measured multiple things: body composition (muscle vs. fat), what people ate, blood markers showing inflammation and metabolism, and special hormones that control hunger. They took these measurements at the start, during the 3-week program, and multiple times during the year-long follow-up.

This approach allowed researchers to compare the three groups and look for differences that might predict who would struggle to keep weight off long-term.

Most weight loss studies focus on what happens during the program itself. This research is valuable because it follows people for a full year afterward, which is when real-world challenges happen. By identifying early warning signs—like unusual hunger hormone responses—doctors could potentially help people at higher risk before they regain weight.

This study tracked real people over a meaningful time period (one year), which is stronger than short-term studies. The researchers measured multiple biological markers, not just weight. However, the sample size of 100 is moderate, and the study didn’t use a control group that didn’t do the program. The results need confirmation in larger studies before being considered definitive.

What the Results Show

The most striking finding was that people who regained all their weight (group A) actually started the program eating fewer calories per day (1,518 calories) compared to those who kept weight off (1,882 calories). This was unexpected because researchers typically assume people who struggle with weight eat more, not less.

Group A also had better metabolic health markers at the beginning of the study, meaning their blood sugar control and other health measures were actually better than the other groups. However, during the follow-up year, group A showed much lower compliance with the diet and exercise recommendations—only 38% adherence compared to 72% in the group that kept weight off.

Most importantly, the hunger-control hormones behaved differently in group A. In the successful groups (B and C), hormones that suppress appetite (like PYY) increased during follow-up, and hormones that trigger hunger (like ghrelin) decreased. This is the healthy pattern. But in group A, these hormones barely changed, suggesting their bodies weren’t responding normally to the weight loss.

The study found that group A’s blunted hormone response was consistent throughout the year, not just a temporary effect. This suggests it may be a stable characteristic of their physiology. Additionally, the lower initial calorie intake in group A might indicate they were already restricting food heavily before the program, which could have made it harder to sustain the diet long-term.

Previous research has shown that hunger hormones play a major role in weight regain, but this study provides new insight: some people’s hormones may not respond normally to weight loss at all. This aligns with emerging research suggesting that weight regulation is partly controlled by biological factors beyond simple willpower. The finding that better baseline health didn’t predict better outcomes contradicts some earlier assumptions.

The study is relatively small (100 people), so results may not apply to everyone. The participants were mostly older adults (average age 59.5), so findings may differ for younger people. The study didn’t include a control group that didn’t do the program, making it harder to know what would have happened naturally. Additionally, the 3-week intensive program is quite demanding and may not reflect typical weight loss approaches people use in real life.

The Bottom Line

If you’re considering a weight loss program, discuss with your doctor whether you might be an ‘adverse responder’ type based on your personal health history and hormone levels. If you are, you may benefit from: (1) longer-term support and monitoring, (2) strategies to improve adherence to diet and exercise beyond the initial program, and (3) potentially different dietary approaches. However, these are preliminary findings, so personalized medical advice is essential. Confidence level: Moderate—this is early research that needs confirmation.

This research is most relevant for people who have struggled to keep weight off in the past, older adults (the study focused on people averaging 59.5 years old), and healthcare providers designing weight loss programs. If you’ve successfully lost weight and kept it off, this may be less directly applicable to you. Anyone with hormonal conditions affecting appetite should definitely discuss this with their doctor.

Changes in hunger hormones and weight regain patterns typically develop over months, not weeks. Based on this study, you should expect to see whether you’re responding well to a program within 3-6 months, with clearer patterns emerging by one year. Don’t expect immediate results, and remember that the first few months are usually the easiest.

Want to Apply This Research?

  • Track weekly weight, daily diet adherence (percentage of days you followed your plan), and weekly exercise minutes. Also note hunger levels before and after meals on a 1-10 scale to monitor if your appetite-control hormones might be responding normally.
  • Set a specific adherence goal for diet and exercise (aim for at least 70% compliance based on the study findings). Use the app to log daily meals and workouts, and set reminders for exercise. If you notice your adherence dropping below 50%, flag this as a warning sign and reach out to your healthcare provider.
  • Monitor your weight weekly but focus on monthly trends rather than daily fluctuations. Track your hunger patterns and energy levels monthly. If you notice your hunger isn’t decreasing after 2-3 months of consistent effort, or if your adherence is dropping, discuss with your doctor whether you might need a different approach or additional support.

This research is preliminary and should not replace personalized medical advice from your healthcare provider. Weight loss outcomes vary greatly between individuals based on genetics, health conditions, medications, and lifestyle factors. Before starting any weight loss program or making significant dietary changes, consult with your doctor or a registered dietitian. If you have a history of eating disorders, hormonal conditions, or are taking medications that affect appetite, medical supervision is especially important. This study identifies patterns in a specific group and may not apply to your individual situation.