My patient lost 15 kg, did everything right. So why did he regain 8 kg?

Rajesh, a 43-year-old marketing executive, walked into my clinic looking defeated. “Doctor, I don’t understand what went wrong.” Eight months earlier, he had transformed his lifestyle. He stopped sugary drinks, cut down on takeaways, walked every morning, and lost nearly 15 kg. His blood pressure improved, his blood glucose returned to normal, and even his snoring disappeared. Friends admired his transformation, and colleagues wanted his diet plan. And then the weight came back.

A major project at work meant long office hours. Morning walks became occasional. Meals were eaten in a hurry. Sleep was cut short. One family holiday turned into several celebrations over the festive season. When Rajesh stepped onto the weighing scale again, he had regained almost eight kilograms. “I feel hungry all the time. It feels as though my body wants me to become overweight again,” he told me.

Surprisingly, he wasn’t entirely wrong. One of the biggest misconceptions about obesity is that losing weight is simply a matter of discipline, and maintaining it should be easy once the weight has come off. Modern science tells us something very different. In fact, maintaining weight loss is often harder.

Why keeping to weight is the toughest job

Our bodies are designed to resist weight loss. Research shows that the brain has something similar to a “weight thermostat.” Just as a home thermostat tries to keep the room at a fixed temperature, your brain attempts to defend a familiar body weight. Researchers call this the set-point theory. This helps explain why so many people regain weight despite their best efforts.

For thousands of years, human beings survived periods of famine, not food abundance. A body that resisted weight loss had a better chance of surviving starvation. Unfortunately, the same biological system that once protected us now works against us in today’s calorie-rich world. When you lose weight, your body does not congratulate you. Instead, it behaves as though it is facing a crisis. The stomach produces more of the hunger hormone, ghrelin. Hormones that help you feel full, including GLP-1, peptide YY and leptin, decline. Suddenly, the same meal that kept you satisfied a few months ago no longer feels enough. High-calorie foods appear more appealing, cravings become stronger, and resisting temptation requires far greater effort than before.

Metabolism slows with weight loss

At the same time, another invisible change occurs. Your metabolism slows. Part of this is expected because a lighter body naturally burns fewer calories. However, the body often goes a step further by becoming more energy efficient. Studies suggest that after losing around 10% of body weight, total calorie expenditure may fall by 20-25%, more than can be explained simply by weighing less. In other words, your body starts conserving energy while simultaneously making you feel hungrier.

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Imagine trying to drive uphill while someone is gently applying the brakes. That is what maintaining weight loss often feels like. This explains why obesity is increasingly recognised as a chronic disease rather than a problem caused simply by overeating or lack of motivation.

The mistake most make

The first mistake is believing that the diet used to lose weight can never change. Crash diets, detox plans and extremely restrictive eating patterns often produce impressive early results, but they are difficult to sustain. Once normal eating resumes, weight commonly returns because the underlying biology has not changed.

The second mistake is assuming that reaching the target weight means treatment is over. Many people stop monitoring their weight, become less active and slowly return to old eating habits. Weight maintenance deserves as much attention as weight loss itself.

Another common mistake is ignoring small gains. Most people avoid weighing themselves after a holiday or festival because they fear bad news. Unfortunately, by the time clothes begin feeling tight, several kilograms may already have returned. Correcting a two-kilogram gain is far easier than reversing a ten-kilogram regain.

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Sleep is another forgotten factor. People sleeping only five or six hours each night experience greater hunger, stronger cravings and poorer food choices the next day. Stress has a similar effect. Many people are not eating because they are physically hungry; they are eating because they are mentally exhausted.

Perhaps the biggest mistake is expecting perfection. One missed workout does not cause obesity. Neither does enjoying dessert at a wedding or eating festive sweets during Diwali. Problems begin when one indulgence turns into abandoning healthy habits altogether. Long-term success depends on consistency, not perfection.

GLP-1 is just one tool of weight loss

Modern GLP-1-based therapy such as semaglutide and tirzepatide work by reducing hunger, increasing fullness and making it easier for patients to sustain healthier eating habits. However, these medicines do not permanently erase the body’s biological drive to regain weight. When treatment is stopped, the hormonal signals promoting hunger gradually return. The body’s “weight thermostat” begins pushing weight upwards again.

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A recent review of 48 studies, found that after stopping GLP-1-based therapy, people regained weight in a predictable pattern. On average, nearly 60% of the weight lost during treatment returned within one year, with weight regain eventually reaching about three-quarters of the lost weight if no further intervention was undertaken. This should not be interpreted as “treatment failure”. Rather, it reinforces an important message: obesity behaves like other chronic diseases. Some people may need long-term medication, while others may successfully maintain weight loss through sustained lifestyle changes. The approach must always be individualised.

So instead of asking Rajesh to lose another 15 kg immediately, we focused on rebuilding simple habits. He restarted short evening walks, improved his sleep, planned his office lunches in advance and resumed regular follow-up. We also discussed whether long-term medical therapy would help him maintain his progress.

Three months later, the weight gain had stopped. Gradually, he started losing weight again. The lesson is simple. The goal of obesity treatment is not merely to lose weight. It is to maintain it.

(Dr Bhattacharya is an endocrinologist at Apollo Hospitals, Delhi)