When it comes to losing weight, the fear of “ruining your metabolism” is widespread. Indeed, many people who have lost weight and then put it back on feel that every failed attempt leaves them worse off than before, with more fat, less muscle, greater hunger, lower energy, and an ever-diminishing ability to lose weight again.
For those looking to lose weight, the so-called “yo-yo effect” has become an almost constant threat. According to this view, losing and regaining weight is not only frustrating but also dangerous. It even leads some people to believe that they are better off not trying to lose weight at all.
However, a critical review published in The Lancet Diabetes & Endocrinology calls for a reevaluation of this idea. The authors review the available evidence on “weight cycling”- repeated cycles of weight loss and regain- and conclude that there is no solid evidence that this phenomenon, in itself, causes long-term clinical harm in people with obesity.
Nuance is important here. This does not mean that regaining weight is desirable, nor that every diet is a good idea. It highlights something more specific: current evidence does not support the claim that losing weight and then regaining it “breaks” the metabolism or necessarily leaves a person worse off than before.
This finding is important because the fear of the yo-yo effect can become a barrier to seeking help, making changes, or resuming healthy habits after regaining weight. And given that obesity is a chronic and recurrent condition, suggesting that every failed attempt causes irreversible damage can lead to feelings of guilt, despair and resignation.
What we know and don’t know about weight cycling
Part of the confusion stems from the way many observational studies have been interpreted. People who have been through multiple cycles of weight loss and regain tend to have greater difficulty maintaining their weight loss, as well as a higher amount of excess body fat and more years of exposure to obesity.
More metabolic abnormalities are observed in these groups, but it is not always easy to distinguish causes from effects.
To put it another way, the fact that a person with poor metabolic health has been on more diets does not prove that the diets caused that deterioration. The opposite may be true: greater excess body fat, a longer history of being overweight, or prior presence of risk factors could all be the reason for both a higher number of weight-loss attempts and poorer health outcomes.
Unjustified fear of muscle loss
One of the most widespread fears when starting a diet is the loss of muscle mass. When losing weight, the body does not just lose fat; it can also lose some lean body mass. The fear associated with the yo-yo effect stems from the fact that, when weight is regained, fat is regained rather than muscle, leading to an increasingly unfavourable body composition.
However, according to the recent Lancet review, the available data does not consistently show a disproportionate and permanent loss of lean body mass attributable to weight cycling in itself.
The outcome depends on many factors, including the final weight achieved, the amount of protein in a person’s diet, the type of intervention, the level of physical activity and, in particular, the presence (or absence) of strength training.
Something similar happens with energy expenditure. The common belief is that every diet slows down the metabolism, but metabolic rate is heavily influenced by body size and composition. If a person weighs less, they also need less energy to keep their body running, and if they put on weight, their energy expenditure adjusts accordingly. This adaptation does not necessarily equate to a permanent metabolic breakdown.
Keeping weight off
There is an important caveat here: debunking the myth of a “broken metabolism” does not mean we can trivialise weight regain. When a person loses weight, their blood pressure, blood sugar levels, lipid profile, mobility, sleep and quality of life can all improve.
If they regain the lost weight, some of those benefits may diminish or disappear, returning the person to their original metabolic state. But that does not prove that losing and then regaining the weight has caused any additional harm.
This is one of the article’s key points. The main problem is not so much having tried to lose weight, but the difficulty of maintaining sufficient and healthy weight loss over time.
This nuance is also important in the era of new obesity drugs, including GLP-1 receptor agonists like Ozempic and other similar treatments.
In many cases these medicines lead to significant weight loss, but coming off them can result in partial or complete weight regain. But it is an oversimplification to interpret this regain as proof that the treatment disrupts the metabolism- it more likely indicates that obesity requires long-term treatment strategies
No miracle diets
The conclusion should not be that yo-yo dieting is no big deal. It is often accompanied by frustration, guilt, a loss of self confidence, loss of healthy habits, and a deteriorating relationship with food.
It may also rely on poorly thought-out methods, such as extremely restrictive diets, unrealistic goals, lack of proper support, or an exclusive, blinkered focus on the number on the scales.
We also should never suggest that regaining weight means someone has failed irrevocably. Many people who manage to maintain significant weight loss in the long term only do so after multiple unsuccessful attempts. When it comes to making healthy choices, change is rarely linear.
Fighting despair
Regaining weight does not mean your metabolism is broken. Nor does it mean it is not worth trying again. It simply means that your previous approach was not enough, was unsustainable, or you lacked the right support.
The new review does not exonerate fad diets, nor does it portray the yo-yo effect as harmless. What it does is debunk the more specific and counterproductive notion that losing and regaining weight will inevitably damage the metabolism.
(The Conversation)
