It is often said that 95 percent of weight-loss measures don't work. Only, it's not true. Advances in behavioural treatments (such as cognitive behavioural therapy) for obesity and weight-loss drugs mean there are lots of approaches that help people lose weight.
In fact, weight loss is the easy part (relatively speaking). The problem is that when you come off a diet or stop taking a weight-loss drug, the weight will invariably creep back up.
To be clear, this does not mean that diets and other obesity treatments are useless. Far from it.
In a recent study, published in Lancet Public Health, researchers checked in on participants five years after they took part in a 12- or 52-week WW programme (formerly called Weight Watchers).
Although, on average, people's weight had crept back up, some weight loss – about 2 kilograms, on average – was sustained for up to five years.
Even this short time at a lower weight can substantially reduce a person's lifetime risk of developing diabetes, heart disease and other weight-related diseases. But for people with obesity, and their healthcare providers, weight regain can be demoralising.
The stigma surrounding obesity, which views a person's weight as their responsibility, means that this 'failure' of treatment is often felt as a personal failing. This is not true. So why does the weight come back on?
Your brain doesn't want you to lose weight
There are a few reasons why the weight creeps back on. First, our brain hates it when we lose weight. It considers this a reduction in our chances of survival, so it does everything in its power to drag your weight back up.
As you lose weight, your brain reduces your metabolic rate (the rate at which your body burns calories), making you subtly more efficient. The reality is, if there are two people of identical weight, one weight stable and the other having just lost weight, the latter will have to eat less food to remain the same weight.
It turns out that a hormone secreted from fat called leptin is largely responsible for this. One of leptin's key roles is to let the brain know how much fat you are carrying. The more fat you have, the more leptin is produced. So when you lose weight, your brain senses the corresponding drop in leptin.
What is exciting is that scientists have shown that if you administer just enough leptin to fool your brain into thinking you haven't lost any weight, then many of these weight-loss-related changes are mitigated. There is no treatment based on these findings yet – but watch this space.
As well as these biological causes, each person with obesity has their own combination of psychological, social, environmental and economic factors that have contributed to them gaining weight. Most of these will not resolve during a weight-loss treatment.
People with obesity who have lost weight still live in an environment where energy-dense, nutritionally poor food is widely available, heavily promoted, cheaper and more convenient. Social activities often centre around food. We celebrate with food, commiserate with food, and use food as both comfort and reward. Eating less requires continuous thought and considerable effort.
Behavioural treatments for obesity, such as commercial group programmes or cognitive behavioural therapy, teach us strategies that can help us to manage this, but they don't stop it from being difficult. They also can't make our lives easier.
Daily stressors and life events can disrupt the healthy habits and routines that people establish when trying to lose weight, while drugs that work to target biological drivers only work while they are being taken. Surgery also works to address biological drivers, but biology fights back.
It is unrealistic to expect that a one-off intervention will lead to permanent weight loss. If we take the example of high blood pressure medication, which is very effective, no one is countenancing stopping the treatment once your blood pressure has normalised. It would simply come back up again. The same is true for weight-loss treatment.
Obesity is perhaps best thought of as a chronic relapsing condition. People with obesity need lifelong access to treatment and support. Rather than dismissing effective treatment options because of weight regain, we should be honest with people about what treatments can achieve and the likelihood of needing ongoing support. After all, chronic conditions require chronic treatments.
The prevailing view of society is that obesity is a simple problem: simply eat less and move more. Thus, people with obesity just need to be "fat shamed" into becoming thin. However, people with obesity are not bad, lazy or morally bereft; they are fighting both their biology and their environment. Obesity is not a choice.
Amy Ahern, Principal Research Associate, MRC Epidemiology Unit, University of Cambridge and Giles Yeo, Professor of Molecular Neuroendocrinology, MRC Metabolic Diseases Unit, University of Cambridge, University of Cambridge