The Rebound Effect: Why You Regain Weight and How to Really Avoid It

How many people regain the weight: what the data say

People often repeat that “95% of diets fail”, but that figure has no solid study behind it. The good data paint a less extreme picture, though just as serious. A meta-analysis of 29 studies of structured weight-loss programmes in the United States (Anderson, 2001) found that, after 4–5 years, participants had kept off a little over 3 kg of their loss on average. Put the other way round, as Hall and Kahan summarise in their 2018 review: more than half of the weight is regained within 2 years and more than 80% by 5 years.

The 4 causes of rebound

• Hunger rises and does not go away: after weight loss, appetite hormones push you to eat more for at least a year
• Expenditure drops: a smaller body burns less, you may have lost muscle, and an extra adaptation appears on top (adaptive thermogenesis)
• Rigid rules: banning foods turns any slip into a “what the hell” that ends in a binge
• Diets with an end date: they do not teach habits, so when they finish you go back to your old ways with a body that now burns less

The hunger that does not go away: what the NEJM study measured

In the study by Sumithran and colleagues (New England Journal of Medicine, 2011), 50 people with overweight or obesity followed a very-low-calorie diet for 10 weeks and lost 13.5 kg on average. One year after the weight loss, their appetite hormones had not returned to where they started: leptin, which curbs hunger, was still lower; ghrelin, which triggers it, higher; and satiety hormones such as peptide YY and cholecystokinin, lower. Most importantly, they reported being hungrier than before they began. According to the estimates gathered by Hall and Kahan, for every kilo lost, expenditure falls by about 20–30 kcal a day, while appetite rises by about 100 kcal a day. That is why rebound is explained more by eating a little more without noticing than by a “broken” metabolism. To dig deeper into these signals, read how to control appetite and hunger hormones.

What really happened in the Minnesota experiment

It is the study most often quoted to explain why restrictive diets fail, and it is usually told with embellishments. The facts: during the Second World War, Ancel Keys and his team at the University of Minnesota put 36 healthy young men, volunteer conscientious objectors, through 24 weeks of semi-starvation followed by 20 weeks of refeeding. Most lost more than 25% of their body weight, and many suffered anaemia, fatigue, apathy, extreme weakness, irritability, neurological problems and swelling of the legs. When they were finally allowed to eat freely, they ate well above what they had eaten before the experiment, and later analyses of their data show that they regained fat faster than muscle; some ended up with more fat than at the start, especially those who began leaner. What it was not: a moderate weight-loss diet. It was prolonged hunger in normal-weight men. It shows the direction of the body’s response (more hunger, energy saving, priority on regaining fat), not how much of it will happen to you on a reasonable deficit.

Does losing weight fast make you rebound more?

The best trial to test it says no. In the study by Purcell and colleagues (The Lancet Diabetes & Endocrinology, 2014), 200 adults with obesity were randomly assigned to a rapid 12-week programme or a gradual 36-week one, both aiming at a 15% weight loss. And at 144 weeks (almost 3 years), both groups had regained practically the same: around 71% of what they lost. Speed on its own does not decide the rebound; what happens afterwards does. Even so, a moderate deficit makes sense for other reasons: it is easier to sustain without supervision, it leaves room to eat enough protein and to train, and it makes you build from day one the habits you will need to maintain. Very-low-calorie diets, if done at all, are best done under professional supervision.

Rigid restriction: why a slip turns into a binge

Restriction does not only change your physiology; it also changes how you think about food. As early as 1985, psychologists Janet Polivy and Peter Herman proposed that dieting can be a cause of binge eating, not just its consequence. The mechanism is familiar: if the rule is “never anything sweet”, a slice of cake at a dinner feels like having “broken the diet”, and the “what the hell, I will start again on Monday” kicks in. The data support distinguishing two styles of control. In an analysis of more than 54,000 participants in a weight-loss programme and a sample of 1,838 people from the German population, rigid control (all-or-nothing, forbidden foods) was associated with a higher body mass index and with more frequent and more severe binge episodes; flexible control (watching amounts and compensating without drama) was associated with lower weight, fewer binges and a higher chance of losing weight successfully in the one-year programme (Westenhoefer, 1999).

• No forbidden foods: what you enjoy fits into the day if you count it and adjust the rest
• After a slip, the next meal is normal: no punishment and no compensatory fasting
• Targets as ranges, not exact numbers that “break” with any unexpected event
• If you notice frequent binges or a feeling of loss of control, talk to a healthcare professional

What people who keep the weight off actually do

The National Weight Control Registry studies people who have managed to keep off a substantial weight loss. According to the review by Wing and Phelan (2005), its members had lost 33 kg on average and had kept it off for more than 5 years. What they report doing: a lot of physical activity (around one hour a day), a low-calorie, low-fat diet, eating breakfast regularly, checking their weight often and eating in a similar way on weekdays and weekends. Maintenance also seems to get easier over time: after 2–5 years, the chance of continuing to maintain rises sharply. Keep in mind what it is: a registry of volunteers who have already succeeded, so it describes what they do but does not prove that each habit is the cause.

Two caveats. The breaks in the MATADOR study were done with food prepared by the research team, and most trials of other intermittent schemes have found no advantage: it is a reasonable option if it helps you stick with the plan, not an obligation. To know how much to eat once you reach your goal, recalculate your expenditure with your current weight in the total daily energy expenditure (TDEE) calculator: that will be your starting point for maintenance.

How to avoid the rebound (the plan)

The key: stop thinking in terms of diets

As long as you see weight loss as a phase with a beginning and an end, the rebound will be waiting for you at the finish line. The decisive mental shift is understanding that you are not “on a diet”: you are building a way of eating and moving for life. When habits replace willpower, keeping the weight off stops being a daily fight.

Maintaining your weight is as important as losing it. Keep logging your meals with Renzy from time to time, even in maintenance: it is the best way to catch a drift early and correct it before a full rebound.