The NHS was in the spotlight again last week after a report in the Lancet revealed that Britain has very high levels of premature deaths compared with other developed countries. Cue yet more chatter about where the health system is going wrong, our favourite national sport.

But what was most striking about the UK statistics was that three of the most important contributors to premature death – heart disease, lung cancer and stroke – are largely caused by preventable lifestyle factors. In short, too many of us smoke too much, drink too much and gorge on diets dominated by processed foods. This last was emphasised by another report last week which linked heavy consumption of processed meat with the risk of early death.

Most of us value our health but engage in behaviours that undermine it. It's all too easy to understand, tempted as we are by that extra pint at the pub or the brightly coloured chocolate bar at the checkout. But, viewed from inside the NHS, I think that as a nation we've also lost perspective about what healthcare and modern medicine can achieve. Don't worry if we let things slip, we think, we can always find a pill to fix things or secure a hospital makeover. (It's a belief, often encouraged, I have to admit, by a medical profession too ready to administer drugs.)

During a recent clinic consultation, I saw a slightly overweight man who happened to be a smoker. He had developed chest pains and an angiogram had confirmed narrowed coronary arteries but not so severe that he needed an operation. "Isn't there a special procedure to suck out and remove all the crud?" he asked.

I told him that, unfortunately, no such procedure existed and that the best thing he could do to improve his quality of life and longevity was to quit smoking – more effective in fact than all the medications we could chuck at him . But he seemed thrown, that the advice was so simple. He was expecting a magic bullet.

The truth is that while we doctors are well placed to educate and nudge our patients into adopting healthy behaviours, ultimately we have little direct control in shaping the environment that encourages bad habits. Neville Rigby of the International Association for the Study of Obesity told me that education will have limited impact when the food environment is working against you. "It's like telling a child who grows up in a sweetshop to not eat sweets." It doesn't help that hospitals continue to legitimise junk food with corridors littered with dispensers for cheap , nutritionally poor foods. What's more, 50% of the 1.4 million who work for the NHS are obese.

So, not only is it wise to keep yourself from needing a hospital in the first place; a campaign launched last week suggested the medical profession is guilty itself of perpetuating a quick-fix culture when we should be placing greater emphasis on prevention. The British Medical Journal's "Too Much Medicine" campaign is designed to combat over-diagnosis, and the harms and waste from unnecessary tests and treatments.

Richard Smith, director of UnitedHealth Group's chronic disease initiative, recently blogged that only 11% of the 3,000 health interventions out there have good evidence to support them, with four-fifths of new drugs copies of old ones. A few weeks ago, I discontinued an anti-hypertensive medication on a patient, after reading a review by the Cochrane collaboration (an internationally recognised benchmark for providing the highest quality information on healthcare). Forget pills when it comes to mild hypertension was the review's conclusion. Instead, exercise, don't smoke and eat a Mediterranean diet. Just because you've heard this before doesn't mean it's still not the best way.

Sadly, this has not translated through to clinical practice. The government's latest proposal for GPs is to call for an even lower threshold than the existing one for treating high blood pressure. A leading GP who doesn't want to be named said that not only would this harm patients by increasing the risk of side effects, but that GPs would be financially penalised if they didn't introduce medications. "The only beneficiaries will be the drug companies," he said. "We should be taking a step back from polypharmacy. "

If the health secretary, Jeremy Hunt, is serious about saving 30,000 early deaths from cancer, heart, stroke, respiratory and liver disease by 2020, he should implement cost-effective public health interventions. Curb the availability of junk food at schools and hospitals and severely restrict the advertising of products high in trans fats, sugar and salt to children.

Australia, which topped the health league, was the first country to impose plain packaging for cigarettes through legislation, a lead that the coalition has announced it will follow, with an announcement on legislation expected in May. Elsewhere, however, the government plans to increase private healthcare within the NHS. Private health companies profit through over-diagnosis, medicalising normal conditions and over-treatment. In the US, the most prescribed drugs are psychotropics. Mass advertising of anti-depressants to people with normal or healthy levels of stress has boosted demand.

Here in the UK, I am increasingly aware of health checks and total body scans being targeted at the ostensibly healthy by private providers. There is no evidence that this improves health outcomes, but it does increase the emotional and financial toll on an individual. It's time, instead, to take a step back and pay more attention to the environment and our own behaviour.

We can all learn from John, a taxi driver in his late 40s, who suffered from breathing problems and chest pains. He was overweight and his blood tests revealed borderline diabetes, a condition that brings with it the potentially devastating complications of heart disease, stroke, kidney failure and even amputation. Fortunately for him, his coronary arteries were not at a stage of severe narrowing.

Although he wished he could turn back the clock, I emphasised that some simple measures could turn his life around. There was no need for a lifetime's cocktail of medications. I advised him not to buy any food product advertised as "low fat", "heart healthy" or "cholesterol-lowering". They're usually heavily processed and loaded with sugar. By replacing sugary drinks with water, opting to eat a piece of fruit instead of the Mars bar and taking a daily 20-minute walk with his wife after dinner, John now feels like a "new man", he says. He's lost two stone and his blood glucose is within the normal range.

Sure, we're constantly having to grapple with environmental and commercial pressures that work against our ability to make healthy choices. But we still have the final say in what we choose to put into our bodies and in how we use them. Ultimately, it's up to us.