Losing weight for good: what actually works

Faced with the multitude of methods and diets that promise quick results, it's useful to go back to what research actually confirms over the long term. It says two things. Losing weight is possible, and a modest loss is enough to improve health. But maintaining that loss is hard, for biological reasons that have nothing to do with a lack of willpower. Knowing this helps you set realistic goals and avoid getting discouraged.

A realistic goal rather than an ambitious one

You don't need to aim for a dramatic weight loss to get a benefit. A loss of 5 to 10% of initial body weight is already enough to markedly improve blood pressure, blood sugar, and blood fats. For someone weighing 90 kg (about 200 lb), that represents 4.5 to 9 kg (about 10 to 20 lb).

The American Diabetes Prevention Program study, published in 2002 in the New England Journal of Medicine, provided the best-known demonstration of this. In people at high risk of diabetes, a 7% weight loss combined with 150 minutes of physical activity a week reduced the risk of becoming diabetic by 58%.

The French National Authority for Health (HAS) recommends this 5 to 10% goal, over six to twelve months, followed by stabilizing the weight achieved. It also notes that not regaining weight is already a result, and that in some situations, the priority is to stabilize rather than lose more.

Why restrictive diets often fail in the long run

Very restrictive diets often produce rapid weight loss, followed by regaining it once the diet stops. This is the “yo-yo” effect. Follow-up studies show that most people regain much of the lost weight within a few years.

This isn't a matter of character. The body defends its weight. When intake decreases, several mechanisms kick in.

• Energy expenditure drops more than weight loss alone would explain. The body switches to economy mode.
• Appetite hormones change. Leptin, which signals fullness, decreases. Ghrelin, which stimulates hunger, increases. You end up hungrier while burning less, and these changes persist long after the diet ends.
• Some of the weight lost is muscle, especially if the diet is very restrictive and not combined with physical activity. And muscle burns energy.

In France, the national food safety agency (Anses) evaluated about fifteen popular weight-loss diets in 2010. It concluded that they exposed people to nutritional imbalances and muscle loss, and that they promoted weight regain. It advises against following them without medical supervision.

No diet is better than the others

Should you cut fat or cut sugar? A review of 48 trials, published in 2014 in JAMA (Johnston et al.), compared the major types of diets. Differences in weight loss at one year were minimal. What predicted the outcome was the ability to stick with it over time.

The best diet, then, is the one you can follow for years. The following guidelines are broadly agreed on:

• more vegetables, fruit, legumes, and whole grains, which are filling;
• less ultra-processed food, sugary drinks, and alcohol;
• appropriate portions, regular meals, eaten sitting down and without a screen;
• no food off-limits, so as not to fuel frustration and then overeating.

A Mediterranean-style diet also has a proven benefit for the heart, independent of weight: in the Spanish PREDIMED trial, it reduced cardiovascular event risk by about 30%.

What works over the long run

A sustainable way of eating, rather than a temporary diet, as described above.

Regular physical activity. On its own, it leads to little weight loss. But it plays a key role in maintaining weight lost, it preserves muscle, and it improves health even when the scale doesn't move. In the United States, the National Weight Control Registry has tracked more than 10,000 people since the 1990s who lost at least 13 kg (about 29 lb) and kept it off for more than a year. The large majority of them do about an hour of activity a day, most often walking. The What's my activity/sedentary level? tool can help you find your starting point.

Professional support. A primary care doctor, dietitian, psychologist, or adapted physical activity instructor: regular follow-up increases the chances of success. It's particularly useful when eating is used to soothe emotions, or in the case of eating disorders, which call for specific care.

Sleep and stress management. Too little sleep increases hunger and cravings for fatty, sugary foods. Chronic stress promotes snacking and abdominal fat storage. Both factors are often underestimated.

Self-monitoring. Weighing yourself regularly, without overdoing it, or logging meals for a few weeks, helps catch drift early and correct it without overreacting.

When more intensive medical care is warranted

For severe obesity, or obesity associated with complications, lifestyle changes aren't always enough. Other options exist. They are discussed with a doctor and add to, rather than replace, the measures above.

Medications. A new generation of treatments, GLP-1 analogs and related drugs, acts on the brain's appetite centers. In the STEP 1 trial, published in 2021 in the New England Journal of Medicine, semaglutide produced an average weight loss of 14.9% over 68 weeks, versus 2.4% with placebo. In the SURMOUNT-1 trial, published in 2022, tirzepatide produced an average loss of up to 20.9%. These medications are available in France on prescription, and in the United States with a doctor's prescription as well. They have side effects, mostly digestive, and weight tends to come back once treatment stops: they are therefore meant for the long term, with medical follow-up. Insurance coverage varies and should be checked with your doctor or pharmacist, as rules keep changing. Never obtain these medications outside the medical system.

Bariatric surgery. It is intended for people with a BMI of at least 40, or at least 35 with a complication such as diabetes or sleep apnea, after well-conducted medical management has failed for at least six months. The decision is made by a multidisciplinary team. It is the most effective long-term treatment: the Swedish SOS study showed weight loss maintained for more than twenty years, with reduced mortality. It requires lifelong follow-up, particularly to prevent vitamin deficiencies.

Pitfalls to avoid

“Fat-burning” supplements, “detox” teas, meal replacements used without supervision, and medications bought online have no proven effectiveness, and some are dangerous. A promise of fast, effortless weight loss should raise a red flag. Prolonged fasting and diets that eliminate an entire food group risk nutritional deficiencies.

What if the weight doesn't move?

Sometimes weight plateaus despite genuine effort. The health benefits, though, are already there: lower blood pressure, better blood sugar, better sleep, more stamina, less pain. Waist circumference sometimes decreases before weight does, as muscle replaces fat. These gains matter, and a doctor can help measure them.

What to remember

Lasting weight loss depends less on the intensity of a one-off effort than on changes you can maintain. A modest goal, kept up over time, delivers more than an ambitious one abandoned after a few months. And when lifestyle alone isn't enough, effective treatments exist: turning to them isn't a failure, it's treating a chronic disease.

To calculate your own BMI and waist circumference, take the “Am I overweight or obese?” test.