Exercise more, eat (and drink) fewer calories. It's a simple message, but hard to do. In fact, the more we learn about obesity, the more we realise how complex the problem is and why hammering home this message on its own doesn't get you very far, if you're trying to help people lose weight or prevent them becoming overweight in the first place. Two-thirds of English adults and one fifth of four to five-year-old children are obese or overweight. So what can we do, collectively, to tip the scales back towards a healthier number?
The first step is to understand the nature of the problem. Why are we, as a country, so much fatter than we used to be? We know that there are many environmental influences, which collectively, push us towards eating too much and being inactive. The result is people put on too much weight - "a normal response, by normal people, to an abnormal situation", as one paper puts it.
It matters how we characterise the obesity epidemic, because if it is characterised as, say, solely a failure of individual willpower, there may be a risk of exacerbating the problem. For example a recent paper found that women who thought they were overweight could end up consuming more calories if they felt stigmatised because of their weight.
Amid the welter of new insights into the influences that our social networks, our environment, our incomes and our level of education (among others) may have on our weight, it can seem difficult to know where to start.
What's clear is that there is no silver bullet solution. We need lots of changes in many areas of our lives, so it becomes easier for us to make the healthy choice rather than the unhealthy ones. We have to address the factors in our environment that promote excessive weight gain. And for that, actions need to be hard-wired into all our policies, not just health. We have to build this into how we plan our towns, our transport system, our workplaces, as well as taking personal responsibility for our health as individuals.
At Public Health England (PHE), our message is that the problem of obesity can best be tackled if there is leadership at many different levels. There is a role for all of us here. Individuals and families can commit to making lifestyle changes, and PHE gives concrete advice on how this can be done in our Change4Life campaign, with ideas for swapping food to take sugar and fat, and thus calories, out of diets.
But leadership is about more than an individual's food choices and what national government can do. Local authorities also have a crucial leadership role: through their many decisions on planning and transport - key levers in supporting a population approach to reducing obesity. Leadership also involves recognising that we can have a bigger impact on the obesity epidemic if we work together, with a range of stakeholders - including the voluntary sector and employers.
Indeed, the workplace could be a particularly fruitful place to embed key lifestyle changes. After all, work is where most adults spend a large part of their waking hours. And there's evidence that companies benefit from investing in the health and wellbeing of their employees - evidence that's growing beyond sickness absence to include impacts on productivity, brand allegiance and customer service.
How can employers help in the fight against obesity? There won't be one single template, but all employers will need visible leadership from the top.
Tackling obesity in the workplace is about enabling staff to make healthier choices, not demonising those with weight issues - and to find an approach that supports lasting change, rather than quick-fixes, which risk fizzling out when resources run out. It's about making sustainable changes to the environment that employees work in, so that the healthier diet and the more active travel choice become the norm rather than the exception.
What does this mean in practice? Healthy workplaces are ones that procure healthy food and provide healthy menus for their staff. They don't offer cheap fry-ups for breakfast or meal deals that include bags of crisps and sugary drinks! Vending machines should not be full of fatty and sugary snacks and drinks. And what about cutting out the biscuits during meetings? As for promoting physical activity, research suggests that signs, encouraging people to walk up the stairs rather than take the lifts, can be effective in a range of settings.
Obviously, employers will want to tailor their approaches. Staff wellbeing surveys and annual health checks provide information to develop workplace strategies and action plans, and monitor their progress. And the National Institute for Health and Care Excellence (NICE) has made recommendations on behaviour change policies and strategies, specifically for the workplace (including ones that relate to obesity and physical activity), which can also guide employers.
And increasingly, employers are also reporting on their efforts: for example, it's becoming more common for companies to publish data on executive commitment to staff wellbeing, as reflected in the Workwell Public Reporting Index. It's true that we still don't have a complete picture - measures for understanding productivity and resilience are less developed than those focused on sickness absence. The hope is this will evolve.
Employers could play a pivotal role in helping us to shift the culture around obesity. In fact, given how important the workplace is to many of us, it's an opportunity we can't afford to pass up.
My personal ambition, as national director for health and wellbeing at PHE, is that we are a role model for this vision: that our employees work in buildings that offer them only healthy food and access to schemes that increase physical activity; that we help staff to lose weight in the same that we help them to stop smoking. We all need workplaces that actively help us, as individuals, to become - and stay - healthy.