Yo-yo dieting - why does weight come back after a diet, and what can you do differently?

The yo-yo effect (yo-yo dieting, or weight cycling) is weight regain after losing weight, often back to your pre-diet weight and sometimes above it. To a large extent, it is caused by the way the body responds to weight loss: after you lose weight, your appetite increases and your energy expenditure falls. In a model based on a study of 153 people with type 2 diabetes, each kilogram lost was matched by an increase in estimated energy intake of about 100 kcal a day. This figure does not apply to everyone after every diet (1). In studies of weight-loss programmes, more than half of the weight lost came back within two years, and more than 80% within five years (3). The Polish Society for the Treatment of Obesity (PTLO) describes obesity as a chronic disease that does not go away on its own and tends to recur. If your weight keeps coming back after each new diet and your BMI is at least 30, or at least 27 with a condition related to excess weight, it is better to see a doctor about it.

In brief

• Appetite increases after weight loss. In a model based on a study of people with type 2 diabetes, estimated energy intake rose by about 100 kcal a day for each kilogram lost, while energy expenditure falls by 20-30 kcal a day per kilogram after weight loss. That is why weight stops going down after a few months, even though you may feel you are eating the same as at the start of the diet.
• A year after a diet, levels of the hormones that control hunger and fullness are still different from before the weight loss. In a study of a 1,000 kcal a day diet, metabolism slowed straight after the diet by about 90 kcal a day more than the lower body weight would explain, and after a year this difference was no longer found.
• A 1,000 kcal diet provides less energy than PTLO usually recommends, and losing more than 1.5 kg a week on a diet of less than 800 kcal increases the risk of gallstones. PTLO recommends losing weight more slowly, partly so that the result is easier to maintain. In one study, however, a similar proportion of the weight lost came back after both rapid and slow weight loss, on average more than 70%.
• If your BMI is at least 30, or at least 27 with a condition related to excess weight, and previous comprehensive treatment without medication (diet combined with physical activity and psychological support) has not worked, PTLO says the doctor may suggest medication without waiting 3-6 months to see the effect of another lifestyle change.

What is the yo-yo effect, and how soon does the weight come back?

The yo-yo effect is a repeated cycle of losing weight and putting it back on. After you start a diet, your weight usually falls for several months, then stops falling and then slowly rises. This pattern has been described with almost every weight-loss method, although the number of kilograms differs.

In an example weight-loss programme analysed by Polidori and colleagues, weight stopped falling after 6-8 months (1). In a meta-analysis of 29 long-term studies, more than half of the weight lost came back within 2 years, and more than 80% within 5 years (3). In this meta-analysis, people who completed a weight-loss programme weighed on average more than 3 kg less after 5 years than before they started. There is also no set time after which the yo-yo effect wears off. According to calculations by Polidori and colleagues, the increased appetite persists for as long as your weight remains lower than before the diet.

Why do some people end up heavier than before the diet?

Not everyone ends up weighing more than before the diet, but in a Finnish study of 4,129 twins followed from age 16 to age 25, those who had dieted later gained weight faster than the others (8). People who had intentionally lost more than 5 kg at least once were more likely to be overweight at age 25. This was most evident in women who had lost weight in this way two or more times.

The authors concluded that frequent dieting mainly reflects a tendency to gain weight. However, a comparison of identical twin pairs in which only one twin had dieted suggests that dieting itself may lead to a small weight gain. At age 25, the twin who had dieted had a BMI on average 0.4 higher than the other twin. For someone 170 cm tall, this corresponds to just over 1 kg.

Why does weight come back after a diet?

After weight loss, changes take place in the body that make it harder to maintain a lower weight. The most important of these is an increase in appetite (1). According to PTLO, appetite regulation is disrupted in people with obesity, so when choosing food they have to consciously resist what their appetite is telling them. That is why a diet alone often does not produce a lasting result (4).

How much does appetite increase after weight loss?

Polidori and colleagues estimated the increase in appetite using a one-year study of 153 people with type 2 diabetes who were taking a medicine that increases the amount of glucose passed in the urine (1). The patients could not directly feel this loss of calories in their urine, so they had no reason to consciously eat differently. Using a mathematical model, the researchers calculated that as their weight fell, the participants ate more and more, until they were eating about 350 kcal a day more than before treatment. At that point, their weight stopped falling.

For each kilogram lost, appetite rose by about 100 kcal a day, more than three times the fall in energy expenditure. This is a group average calculated from a model, and the participants lost only a few kilograms. The authors note that it is not known whether the same relationship applies to larger weight losses.

You do not have to feel obviously hungry after a diet for this to happen. Hall and Kahan, the authors of a review of research on weight maintenance, explain that the brain regulates appetite without conscious awareness and that the amount of food a person eats varies by 20-30% from day to day. Portions can therefore grow gradually and unnoticed, while you remain convinced that you are still sticking to your diet (2). So if your weight stops going down after a few months, this does not necessarily mean you have stopped trying.

Do hunger hormones return to normal after a diet?

A year after weight loss, levels of the hormones that control hunger and fullness are still different from before the diet. A study in Melbourne included 50 people with overweight or obesity but without diabetes, who followed a very low-calorie diet for 10 weeks. They lost an average of 13.5 kg. After the diet, levels of leptin, peptide YY and cholecystokinin, which suppress appetite, fell, while levels of ghrelin, which stimulates hunger, rose. The participants were also hungrier, and a year after the diet ended, the hormonal changes and stronger hunger were still present (5).

Does your metabolism slow down permanently after a diet?

After weight loss, energy expenditure falls by about 20-30 kcal a day for each kilogram lost (2). Part of this fall is because a smaller body needs less energy. If metabolism slows down more than the new body weight and body composition would explain, researchers call this metabolic adaptation.

In a Norwegian study, 71 people with obesity followed a 1,000 kcal a day diet for 8 weeks and lost an average of 14 kg. Straight after the diet, their resting metabolic rate was about 90 kcal a day lower than predicted from their body weight and composition. After 4 weeks of weight stabilisation, this difference had roughly halved, and after a year it was no longer found in the 45 people with complete measurements. How much a person's metabolism had slowed was not related to how much weight they regained over the year (6). So when weight loss stalls and the weight comes back, increased appetite probably matters more than a slower metabolism.

Does a 1,000-calorie diet lead to yo-yo dieting?

Weight usually comes back after a 1,000 kcal diet, just as it does after other ways of losing weight. This diet also provides less energy than PTLO usually recommends for obesity treatment. However, faster weight loss in itself did not make the yo-yo effect bigger in a study that compared rapid and slow weight loss: a similar proportion of the weight lost came back in both groups.

In an Australian study, 200 people with obesity were randomly assigned either to rapid weight loss over 12 weeks on a very low-calorie diet or to slow weight loss over 36 weeks, and in both groups the goal was a 15% reduction in body weight. More people in the rapid weight-loss group lost at least 12.5% of their weight (81% vs 50%), but one person in this group developed gallbladder inflammation that required surgery. Those who lost at least 12.5% then followed a maintenance diet for almost 3 years. By the end of that time, the people who completed the study had regained about 71% of the weight they had lost in both groups (7).

The weight-loss diet recommended by PTLO usually provides about 1,200-1,500 kcal a day for women and 1,500-1,800 kcal for men, and its calorie content is set individually. A diet must not provide less energy than the body uses at rest, because this risks nutrient deficiencies. PTLO does not recommend diets with excessive calorie restriction, such as the Copenhagen diet (a popular very low-calorie diet) or fasting, because in the long term they are probably ineffective and sometimes harmful. Losing more than 1.5 kg a week on a diet of less than 800 kcal a day also increases the risk of gallstones (4).

PTLO recommends losing about 1 kg in the first week and about 0.5 kg a week after that. According to the guidelines, a slower pace is better for your health and also increases the chance of maintaining the result (4). The authors of the Australian study say that their result does not support the belief that weight comes back faster after rapid weight loss (7). In this study, however, rapid weight loss required a very low-calorie diet, and such a diet carries the risk described above.

When should you consider obesity medication if your weight keeps coming back?

It is best to see a doctor about the yo-yo effect if your weight comes back after repeated attempts to lose it and your BMI is at least 30, or at least 27 with a condition related to excess weight, such as high blood pressure, prediabetes, diabetes or lipid disorders. In that case, PTLO recommends discussing medication with the patient if their weight has not fallen by at least 5% after 3-6 months of lifestyle changes (4).

According to the guidelines, people with obesity who change only their habits usually lose no more than 3-5% of their body weight. The doctor may suggest medication earlier if your medical history shows that previous comprehensive treatment without medication (diet combined with physical activity and psychological support) has not worked, or if your obesity comes with conditions that significantly increase the risk of heart and vascular disease. With a BMI of 40 or more, the doctor suggests medication from the start and considers bariatric surgery (4). In our article on eligibility for obesity medication, we explain who a doctor will prescribe medication for and why they may refuse.

Before your appointment, it helps to write down:

• Your lowest and highest weight as an adult
• Each attempt to lose weight: the method, how many kilograms you lost and how long it took for them to come back
• Medicines you take regularly, because some of them promote weight gain
• Episodes of binge eating or emotional eating, if you have them

We write more about the first appointment in our article on where to start obesity treatment.

When is weight gain not the yo-yo effect?

If your weight is going up even though you are eating and moving the same as before, the cause may be a medicine you take or an illness. If the doctor suspects secondary obesity, meaning obesity caused by another disease such as Cushing's syndrome or hypogonadism, they will refer you to an endocrinology outpatient clinic. Medicines you take long-term should not be stopped on your own; any change to them is decided by the doctor who prescribed them. We write about medicines that cause weight gain in our article on weight gain caused by medicines. What to check when your weight does not go down despite your efforts is covered in our article on why you can't lose weight despite diet and exercise.

What can a doctor offer after several unsuccessful diets?

If you meet the PTLO criteria, the doctor may suggest an obesity medicine that reduces appetite and makes you feel full sooner. It is the increased appetite that does most to drive weight gain after a diet. While taking the medicine, you still change how you eat, move more and work with a psychologist. PTLO considers treatment with medication lasting at least 12 months to be optimal, and the medicine is taken for as long as it is needed, works and is well tolerated. Stopping treatment too early may make it harder to keep your weight down (4). Weight usually comes back after the medicine is stopped. When stopping makes sense and how to plan it is covered in our article on what happens after you stop obesity medication.

In the obesity treatment programme at Nasz Gabinet, the doctor first diagnoses obesity based on your BMI and waist circumference, assesses your blood test results and checks whether you are eligible for medication under the PTLO criteria. During the 6-month programme, you have video consultations with a doctor and with a psychologist, and every month the doctor checks how your treatment is going, based on the weekly weigh-ins and monthly body measurements you record in the app. If medication is indicated, the doctor issues an e-prescription after each medical review, and you buy the medicine at a pharmacy.

How can you plan weight loss so that you keep the weight off afterwards?

When you try to lose weight again, the choice of diet matters less than having a plan for after the weight loss and care that continues after the diet ends (2).

PTLO recommends initially losing 5-10% of your starting weight over 3-6 months, which means 5-10 kg for someone weighing 100 kg. Even a loss of this size, if maintained, brings clear health benefits (4).

It is best to agree on a weight maintenance plan while you are still losing weight. After the diet ends, regular contact with a doctor, a dietitian or a support group helps you keep your weight down. The Look AHEAD study included 5,145 adults who were overweight or had obesity and also had type 2 diabetes, who were randomly divided into two groups. In the group that received regular lifestyle support for 8 years, one in two people weighed at least 5% less than at the start by the end of that time, compared with 36% in the group that had only occasional educational sessions (10).

Weighing yourself regularly lets you act before a lot of weight comes back. Hall and Kahan recommend agreeing with your doctor on a weight above which you should seek help again (2). People in an American registry who have kept their weight down for an average of more than 5 years report that they weigh themselves regularly, are physically active for about an hour a day and eat in a similar way on weekdays and at weekends (11).

Physical activity makes it easier to maintain your weight. PTLO recommends 150-300 minutes of moderate exercise a week and at least 2 strength training sessions a week, because strength training protects against muscle loss while you are losing weight. With a BMI above 35, it is better to choose exercise that does not put too much strain on the joints, such as exercising in water or on an exercise bike (4).

Strict rules, such as cutting out carbohydrates completely, are hard to stick to for years. Hall and Kahan advise deciding in advance what you will do when you slip up, so that you do not abandon the whole treatment (2).

If you eat to cope with stress or sadness, obesity treatment should include help from a psychologist. According to PTLO, psychological support also includes analysing setbacks and preventing a return to old habits, and psychotherapy is indicated, for example, for depression and eating disorders. How to tell emotional eating apart from an eating disorder is explained in our article on binge eating.

Frequently asked questions

Does the yo-yo effect happen to everyone who loses weight?

No, the yo-yo effect does not happen to everyone. According to a review of studies, roughly one in five people who are overweight manage to lose at least 10% of their body weight and keep it off for at least a year (11). It is easier to keep your weight down when your care does not end at the same time as your diet.

Is the yo-yo effect bad for your health?

In observational studies, people whose weight fluctuated were more likely to have heart and vascular disease and high blood pressure, and more likely to die during the follow-up period (12). However, such studies do not prove that the weight fluctuations themselves are harmful. In a meta-analysis of 124 studies of weight-loss programmes, the authors calculated that 5 years after the programme ended, participants still had lower glycated haemoglobin (average blood sugar over recent months) and a more favourable ratio of total cholesterol to HDL than people in the comparison groups, even though they had regained some of the weight. The more weight they regained, the smaller these benefits were. However, only a few studies followed participants for this long (13).

Is there a yo-yo effect after stopping obesity medication too?

After you stop obesity medication, your weight usually comes back. In a one-year follow-up after the STEP 1 trial, participants who stopped taking semaglutide and stopped receiving diet and physical activity counselling regained about two-thirds of the weight they had lost. Over the same period, most of the measures assessed, including blood pressure and metabolic test results, moved back towards their pre-treatment values (9). That is why it is best to decide about stopping the medicine together with your doctor and to have a plan for after treatment.

Sources

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