I did not intend to have a spa experience. The plan was to go for afternoon tea, but the spa next door was included in the price. And so arrived a “wellbeing” menu, where one could choose between seaweed wraps to purify and a meditative steam room with energising lights to destress. I thought massage was the least worst option, but after it was explained to me how it would detoxify and re-energise me, I felt a potent mixture of despair and rage.

“Wellbeing” as a modern concept causes me existential pain. “Holistically upgraded” hotels (including enemas and “medi-spas”) offer “wellbeing weekends”. Employers can buy corporate packages for “workplace wellness”, which will apparently increase productivity and reduce rates of sick leave. You can take spin classes in London that cost more than £20 a time (you could buy an actual bike for the same price as five of those) where you get offered wellness vitamin shots and earplugs as standard to help drown out the pounding music.

The modern iteration of “wellness” – defined, at least in part, by the need to purchase something to have it – piggybacks on the multibillion-dollar diet, supplement and fitness industry. A report from the Sports Think Tank claims that one in seven Brits are members of a gym, with the industry now worth more than £5bn. Some gyms take wellness to surreal levels – some offer cryotherapy, which involves standing in a space cooled to extremely low temperatures (to prevent signs of ageing and improve recovery, apparently), others have treadmills complete with oxygen vaporisers (to supposedly increase endurance.) Meanwhile, the diet book phenomenon has reached epic proportions.

Rather than wellbeing being straightforward (don’t smoke, don’t drink too much, do exercise you like, eat a variety of foods, with lots of vegetables and little processed stuff, see people and do things) the industry has created its own mythology. Wellbeing is presented as complicated, complex, difficult to achieve correctly and best when purchased – all while requiring gurus to access it. This entanglement of industries makes what should be straightforward – a healthy lifestyle – into a complicated consumerist mess.

This doesn’t mean that diet and exercise aren’t important. A global review published in the Lancet in 2017 found that more physical activity was associated with longer lives and fewer heart attacks and strokes. This included not just formal gym-going exercise but walking and housework. In other words, you don’t have to tie yourself to a treadmill to get fit.

A review published recently in the British Journal of Sports Medicine concluded: “Any amount of running, even just once a week, is better than no running, but higher doses of running may not necessarily be associated with greater mortality benefits.” Obsession isn’t necessary – some space, a pair of trainers and a bit of time may be all you need. If you are spending money you don’t have on kit, or neglecting your family or work because of the need to do it, that doesn’t sound like wellbeing.

The same goes for the diet industry. Weight loss is certainly a mainstay of treatment for some conditions, and the evidence points to wholegrains, fruit and vegetables, variety and olive oil as associated with better health. Yet the media onslaught of “experts” arguing for their diet over another is liable to make onlookers believe there is no broad agreement in food science about anything. Many dietitians are standing up for evidence-based advice, but much of the media concoct the illusion that a healthy diet is obtainable only via a particular belief system. Here, the very idea of pleasurable eating is immoral.

The worst thing about modern incarnations of wellbeing is that they devolve responsibility for health on to individuals via a commercial market. The environment we live in should be designed to maximise our health. Exercise should be joyful; at its best, we should hardly know that we are doing it. Street play used to be common – now in many areas it requires special schemes to give children priority over cars for short periods of time. We need to turn our understanding of wellbeing on its head: away from individuals and towards populations.

We need better infrastructure for walking and cycling so they become the primary method of urban transport. We should be able to cycle safely in everyday clothes, and it should be easier and faster than driving. It should be possible for children to walk to school without worrying about traffic. Our wellbeing should not be measured by how thin we are. Policies such as minimum alcohol pricing and mitigating the “food deserts” more than a million UK residents are estimated to live in – with limited access to affordable fresh fruit and vegetables – are far more likely to yield meaningful improvements in our collective health.

My preferred definition of wellness is not something offered by the contemporary wellness marketplace. It means not being sleepless with worry about a review of sickness benefits; it means not living in a damp house, and not working in a job with hours so variable and erratic that affordable childcare can’t be managed. It would be nice for wellness to mean that being poorer won’t impact on your lifespan, or your chances of being diagnosed with chronic diseases. Real, societal wellness is about fairness, public responsibility, science and evidence. It will certainly not come to us via an oxgyen-diffusing machine on a treadmill.

• Margaret McCartney is a GP in Glasgow who writes about evidence-based medicine