Niki Bezzant: You can't run off a bad diet

Last week's column on the sugary drinks tax provoked some expected responses.

"For the odd time I buy a bottle of fizzy, why should I pay extra just because others have serious nutrition and over-consumption problems?" was fairly typical of the opinions against taxation.

Others asserted that obesity was not just down to diet but also lack of exercise.

Health Minister Jonathan Coleman is apparently of the same view. He said last week taxes don't work and that the answer lies in education and exercise.

I agree that education and exercise are critically important in the fight against obesity. But both should be part of an overarching strategy that includes regulation in key areas, including a sugary drinks tax and the removal of GST on vegetables and fruit.

But if we try to solve the obesity crisis by prioritising exercise programmes over strategies to change the way we're eating, we will get nowhere.

And that goes for us personally, too, if we think we can lose weight just by working out or going for a few runs. You can't outrun a bad diet.

Many of us have a warped idea of how much exercise contributes towards weight loss. It's not surprising; watch a show like The Biggest Loser and all you'll see is people working out to the point of exhaustion.

It appears they are literally working their butts off. Very little airtime is given to what must also be major dietary changes.

But it's the diet, not the exercise, that probably contributes most to huge weight losses.

Nutritionists hate having to make hard and fast rules about eating. Everyone is different, they rightly point out, and when it comes to weight loss that's especially true.

But when pushed to describe the relative effects of diet and exercise, most will tell you that for those who need to lose a significant amount of weight, it's very, very difficult to do it through exercise alone.

There are many reasons for this.

We often don't realise how much energy is in the food we eat - or how much exercise we need to "work it off" (language I hate using about food, by the way).

That extra helping of dinner or the biscuits at morning tea might seem insignificant, but if the only exercise we're getting is a half-hour walk each day, our weight is unlikely to change.

It's quite common to overcompensate for exercise with treats. We think: "I've worked out today, I deserve that piece of chocolate."

Couple that with the fact that exercise can make us more hungry, and we're risking making no headway with weight loss.

Post-workout drinks and snacks can also be traps. If we're not exercising intensely or for a long time, we're unlikely to need a sports drink. A snack can be a good idea, but take care it's not just adding extra energy. And don't forget that as we lose weight, our energy needs decrease, too - as we get smaller, we need to eat less. People often strike a weight-loss plateau when that balance changes.

Exercise is still really important for our overall health, and has lots of benefits. Regular physical activity reduces the risk of developing cardiovascular disease, type 2 diabetes, dementia and some cancers. It has big benefits in terms of mental health and stress relief.

And when we're trying to lose weight, exercise - especially resistance training - helps maintain and build muscle mass, which in turn helps us maintain weight loss.

So as with our national strategy, our personal strategy needs to include changes to diet and exercise.

• Niki Bezzant is editor-in-chief of Healthy Food Guide magazine.