Yo-yo dieting: why diets fail and how to avoid it
Lose 5 kg, then put on 6: this pattern has a name, yo-yo dieting. It is common and well documented. According to Anses (the French food safety agency), weight regain affects 80% of people one year after a diet, and it rises over time. It is not a question of willpower: your body puts adaptations in place that push you to regain the weight you lost. The good news is that the factors that protect against regain are known. This guide explains the mechanisms, what the figures really say, and how to break the cycle.
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What the figures really say
One figure is everywhere: “95% of diets fail”. We have not found it in any official report. The 2010 Anses expert report on weight-loss diets, often cited in support, actually states that weight regain affects 80% of people after one year and increases over time. Follow-up studies paint a more nuanced picture than a blanket failure.
| Study or report | Population and duration | Main result |
|---|---|---|
| Anses, expert report (2010) | Literature review | Regain in 80% of people after one year, increasing over time |
| Wing and Phelan (2005) | Review, people with overweight | About 20% manage to lose at least 10% of their weight and keep it off for at least a year |
| Anderson et al. (2001) | 29 US studies, 4 to 5 years of follow-up | Average loss still present at 5 years: more than 3 kg; 2 kg (17% of the initial loss) after a balanced low-calorie diet |
| Sacks et al. (2009) | 811 adults, 2 years | Regain from month 12; 14 to 15% of participants kept a loss of at least 10% |
| Look AHEAD (2014) | 5,145 adults with diabetes, 8 years | With intensive support, 50.3% kept a loss of at least 5%, versus 35.7% without |
Keep two things in mind. First, regain is the rule rather than the exception, and the HAS (the French national health authority) acknowledges it: weight regain after weight loss is very common, and the idea is hard for patients and doctors alike to accept. Second, some people do maintain their loss, especially when they are supported over the long term.
Why the body regains: four mechanisms
1. Your energy expenditure drops, and not only because you weigh less
A lighter body burns less, which is logical. But the drop goes beyond that. In the study by Leibel et al. (1995), maintaining a weight at least 10% below usual weight lowered total energy expenditure by 6 to 8 kcal per kilo of lean mass per day, over and above what the change in weight explained. Anses sums it up: the main mechanism of regain is a fall in 24-hour energy expenditure, through a drop in thermogenesis and above all in basal metabolic rate. The practical consequence, as Anses points out: the intake needed to maintain the lost weight is lower than the intake that maintained your previous weight.
2. You have lost muscle
All weight-loss diets cause a loss of lean mass, around 15% of the weight lost according to Anses, and only physical activity done at the same time limits this loss. Yet lean mass sets the level of basal metabolic rate. Anses gives an order of magnitude: losing 3 kg of muscle lowers expenditure by around 60 kcal a day.
3. Hunger increases, and it lasts
After weight loss, levels of leptin, a hormone produced by fat tissue, fall, which sends the brain an “energy deficit” signal and increases the feeling of hunger, Anses explains. The study by Sumithran et al. (2011) measured this: in 50 people who had lost 13.5 kg on average, appetite hormones (leptin, ghrelin, peptide YY and others) and reported hunger had still not returned to their starting level a year later.
4. The weight regained is mostly fat
When eating returns to normal, the body recovers proportionally more fat than muscle. Anses cites the work of Weyer et al.: people who had lost 15% of their weight under moderate restriction over two years had returned to their starting weight six months after it ended, and the weight regained was almost entirely fat mass. So you can end up at the same number on the scales with less muscle than at the start.
The psychological side: cognitive restraint
Anses describes the most common complication of dieting: cognitive restraint. This is the intention to eat less in order to weigh less, letting rules and calculations take priority over feelings of hunger and fullness. It shows up as chronic under-eating, interrupted by episodes of eating a lot when control slips. Paradoxically, it can lead to eating more, and less well, than if you had never tried to control your intake. Anses regards it as a risk factor for triggering or worsening eating disorders.
The HAS (2023) also lists “repeated dieting” and “rapid weight gain or loss” among the warning signs to watch for, because they expose people to rebounds with an increase in BMI. If you recognise yourself in this cycle, our page on eating behaviour and the approach of mindful eating are good starting points.
When diets follow one another
Each cycle leaves its mark. Anses states that in a person who has gone through repeated diets and regains, the drop in basal metabolic rate can in some cases approach 800 kcal a day, and that regular physical activity then sometimes becomes the only reasonable way to raise expenditure. After 65, the succession of losses and regains leads to a loss of lean mass and a gain in fat mass.
The most spectacular case comes from the American TV show “The Biggest Loser”. Six years after the competition, 14 former contestants had regained an average of 41 kg out of 58 kg lost, and their resting metabolism remained around 700 kcal a day below their starting level (Fothergill et al., 2016). It is an extreme scenario, produced by very rapid and massive weight loss, which mostly illustrates what not to do.
Popular diets under the microscope
In 2010, Anses analysed the menus of around fifteen best-selling diets (Atkins, Dukan, Montignac, Weight Watchers, chrononutrition, cabbage soup, detox lemon and others). Their intakes ranged from 574 to 2,600 kcal a day, and several, including “detox lemon”, “cabbage soup”, “Mayo” and “Scarsdale”, fell below 800 kcal. The nutritional analysis shows many imbalances:
| Nutrient | Finding across the diet phases studied |
|---|---|
| Protein | Above the recommended intake in more than 80% of phases, sometimes two to three times higher |
| Fibre | Below the recommended intake in 74% of phases |
| Iron (women) | Average requirement not met in 61% of phases |
| Magnesium | Average requirement not met in half of the diets for women, and in 77% of phases for men |
| Vitamin D | Average requirement not met in 77% of phases |
| Calcium | Average requirement not met in 23% of phases |
| Sodium | Above the WHO limit (5 g of salt a day) in 58% of phases |
Anses concludes that following these diets is not a harmless act, and that the changes in metabolism and eating behaviour they cause are often at the origin of the vicious circle of regain, possibly a more severe one.
What really protects against regain
Physical activity, from the start
This is the strongest point. For Anses, physical activity is one of the factors, even the most powerful factor, in maintaining weight loss, with a high level of evidence. The main stabilising factor is to start physical activity at the beginning of the restriction and keep it up afterwards. In the study by Jakicic et al. (2008), women who had kept off a loss of at least 10% at two years did at least 300 minutes of activity a week. In Anderson’s meta-analysis (2001), six studies found better maintenance in those who moved the most. You will find practical ideas in our guide to everyday physical activity.
The habits of people who maintain
The US National Weight Control Registry follows people who lost an average of 33 kg and kept it off for more than five years. According to Wing and Phelan (2005), they report:
- a high level of physical activity, around an hour a day;
- a low-calorie, low-fat diet;
- eating breakfast regularly;
- regular monitoring of their weight;
- a consistent way of eating, on weekdays and at weekends alike.
And an encouraging message: after two to five years of maintenance, the chances of longer-term success increase markedly.
Support that lasts
In the Look AHEAD trial, eight years of intensive behavioural follow-up allowed half of the participants to keep off a loss of at least 5%. The HAS (2023) notes that with sustained therapeutic education, people regain weight when sessions stop, but less than without it. In POUNDS Lost, each group session attended was associated with 0.2 kg of extra weight loss.
A moderate loss and food you enjoy
Anses stresses that adapting the diet to the person’s tastes and habits is important for long-term adherence, and that a lasting change in habits, with a varied, balanced diet suited to needs, is a decisive factor in weight stability. Our guide to a balanced diet and our guide to a moderate calorie deficit detail the method. The principles of a slimming diet provide the framework.
Protein and muscle
A meta-analysis of 24 trials (Wycherley et al., 2012) shows that a diet slightly richer in protein, at equal calories, limits the loss of lean mass and the fall in resting metabolic rate. Combined with strength training, it is a way of limiting two of the mechanisms of regain.
Making the stabilisation phase work
The HAS insists: maintaining weight loss is essential and preventing relapse is crucial. For so-called non-complex overweight or obesity, it proposes three stages: stabilise your weight, then support a personalised goal towards a “comfortable weight”, the one at which you feel well physically and psychologically, and finally maintain that weight with good physical fitness and satisfactory muscle mass. In practice:
- Raise your intake gradually until your weight stabilises, without going back to your old portions: your needs have fallen.
- Keep your landmarks: vegetables at every meal, pulses at least twice a week, water as your main drink.
- Monitor your weight and waist measurement at regular intervals, and react as soon as the trend rises durably.
- Organise your week: batch cooking helps you keep meals balanced when time is short.
- Look after your sleep and stress: the HAS includes them among the lifestyle habits to assess. See our guide to food and stress.
Recipes to settle in for the long term
Go for balanced, satisfying dishes: salmon and edamame buddha bowl, chili sin carne, lentil, feta and tomato salad or chickpea and spinach curry. Browse our healthy recipes.
Myths about yo-yo dieting
“If I regain, it’s because I lack willpower”
The HAS reminds us that there are many factors of resistance to weight loss, physiological, genetic, environmental and psychological, and asks healthcare professionals to avoid any guilt-inducing language. The hormonal and metabolic adaptations described above do not depend on willpower.
“My metabolism is broken for good”
Drops in expenditure do exist, but their size depends heavily on the speed and scale of the loss. The “The Biggest Loser” example involves losses of nearly 60 kg in 30 weeks. Physical activity and keeping your muscle limit the phenomenon.
“It’s better never to try to lose weight”
This is not the authorities’ message. For a person with obesity, the HAS recommends a loss of 5 to 15% of body weight, and notes that a lasting loss of 3 to 5% already improves blood glucose and triglycerides. The problem is repeated restrictive diets, not the care process.
“A very fast diet means less time to crack”
Diets below 1,200 kcal a day expose you to a rebound after stopping, according to the benchmarks cited by the HAS. And the more massive the loss, the greater the loss of muscle, according to Anses.
Precautions
- If you go from one diet to the next, or if you have episodes where you eat a lot and lose control, talk to your doctor: the HAS recommends referral to a professional specialising in eating disorders.
- During pregnancy, no energy restriction should be undertaken, according to Anses.
- In teenagers, diets expose them to growth disorders: see our guide to teenage nutrition.
- After 65, the priority is to preserve muscle rather than to lose weight at all costs.
Frequently asked questions
Is it true that 95% of diets fail?
We have not found this figure in any official source. The Anses report (2010) states that regain affects 80% of people one year after a diet and increases over time.
How long after a diet are you at risk of regaining?
In the POUNDS Lost trial, regain began after 12 months. According to Wing and Phelan, the chances of maintenance increase markedly after two to five years of stability.
Can you avoid yo-yo dieting by losing weight slowly?
Losing weight moderately limits muscle loss and very restrictive diets. But Anses notes that regain increases in the following years whatever the speed of the previous weight loss: it is mainly physical activity and keeping up your habits that make the difference.
Why am I hungrier after a diet?
Because appetite hormones stay altered for at least a year after weight loss, with higher hunger (Sumithran et al., 2011).
Is exercise enough to avoid regain?
It is the best-established factor, according to Anses, but it is not always enough: even with restriction and exercise, studies observe partial regain. It works in combination with a sustainable diet and follow-up.
This article is for information only and does not replace the advice of your doctor or a dietitian.
Our sources
- Anses. Risk assessment of weight-loss dietary practices (in French). Collective expert report. November 2010.
- Haute Autorité de santé. Overweight and obesity in adults: first-line medical management (in French). Supporting report. September 2011.
- Haute Autorité de santé. Care pathway guide: overweight and obesity in adults (in French). January 2023, updated in February 2024.
- Wing RR, Phelan S. Long-term weight loss maintenance. Am J Clin Nutr. 2005. PMID 16002825.
- Anderson JW, Konz EC, Frederich RC, Wood CL. Long-term weight-loss maintenance: a meta-analysis of US studies. Am J Clin Nutr. 2001. PMID 11684524.
- Sacks FM, Bray GA, Carey VJ et al. Comparison of weight-loss diets with different compositions of fat, protein, and carbohydrates. N Engl J Med. 2009. PMID 19246357.
- Look AHEAD Research Group. Eight-year weight losses with an intensive lifestyle intervention: the Look AHEAD study. Obesity. 2014. PMID 24307184.
- Leibel RL, Rosenbaum M, Hirsch J. Changes in energy expenditure resulting from altered body weight. N Engl J Med. 1995. PMID 7632212.
- Sumithran P, Prendergast LA, Delbridge E et al. Long-term persistence of hormonal adaptations to weight loss. N Engl J Med. 2011. PMID 22029981.
- Fothergill E, Guo J, Howard L et al. Persistent metabolic adaptation 6 years after “The Biggest Loser” competition. Obesity. 2016. PMID 27136388.
- Wycherley TP, Moran LJ, Clifton PM, Noakes M, Brinkworth GD. Effects of energy-restricted high-protein, low-fat compared with standard-protein, low-fat diets: a meta-analysis of randomized controlled trials. Am J Clin Nutr. 2012. PMID 23097268.
