Fitness: Exercise can’t outrun a bad diet

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We’ve all justified a deep dive into a big bag of chips or a pint of ice cream after a workout by telling ourselves we earned it. But did we really?

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The idea that spending a few extra minutes on the treadmill protects you from the consequences of dietary vices is a tempting one. Yet there’s little proof that an unhealthy diet can be mitigated by regular exercise — a theory recently tested by a group of researchers from Australia, the U.S., Italy and Norway. Using a large sample of British adults, the multinational team reviewed the impact of exercise and diet, independently and jointly, on all-cause mortality, cardiovascular disease and several types of cancer.

Armed with the health history and self-reported diet and exercise habits of 346,627 study subjects age 40 to 69, the researchers cross-referenced the data against local death records over the course of a decade. The idea was to link the cause of death to baseline health records gathered 10 to 11 years earlier and gauge the impact of diet, exercise or a combination of both on mortality.

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The researchers were motivated by the sparsity of studies examining the long-term outcomes of diet and exercise on health, but were also eager to add another layer of complexity, looking at whether vigorous exercise offered any additional protection against the risk of early death when compared to more moderate exercise intensity.

“We hypothesize that physical activity and diet quality are independently associated with lower mortality risk, and that high levels of physical activity, either in total moderate-to-vigorous physical activity or vigorous physical activity, cannot offset detrimental effects of poor-quality diet,” said the researchers.

The study subjects looked to be a fair reflection of western society, with 40.8 per cent doing no vigorous exercise during the week, 26.5 per cent doing less than 75 minutes of high-intensity workouts a week and the rest devoting over 75 minutes a week to vigorous exercise. As for diet, 22 per cent had a poor ranking, 53.4 per cent rated medium and 24.5 per cent qualified for the healthiest diet category.

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The good news is that when reviewed separately, high levels of physical activity — 211 to 450 minutes of moderate to vigorous exercise a week — and a high-quality diet both have a positive influence on longevity. And for those who can boast about excelling at both, congrats — you’ve got an even lower mortality risk.

But for those who hope that surpassing expectations in one healthy habit can make up for failing in another, the results are eye-opening.

“Overall, there is no evidence for high levels of physical activity, measured as moderate-to-vigorous or vigorous physical activity, fully offsetting low diet quality in any of the analyses; neither was there evidence for a higher diet quality index fully offsetting a lack of physical activity,” said the researchers.

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Still, some additional findings proved interesting. Vigorous physical activity provided slightly more protection against cardiovascular disease than moderate-intensity exercise — but only for those accumulating 10 to 150 minutes a week of vigorous exercise. Those who logged over 150 minutes a week didn’t realize the same boost in benefits.

Also worth noting is that those with the healthiest diets had a 14 per cent lower risk of cancer mortality — a benefit that didn’t extend to those with a low- or medium-quality diet. Before you swear off ice cream or potato chips forever, rest assured that the occasional indulgence isn’t going to have a negative impact on your long-term health and wellness. But what is clear is that a love of exercise can’t mitigate the negative effects of a love of fast food.

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If you want to lower the risk of chronic disease and an early death, your best bet is to pay equal attention to exercising and eating well. If you want an extra boost to your health, adding some — but not too many — vigorous workouts to your routine is a good idea. Just keep in mind that there are no shortcuts to being the healthiest you can be. Improving your diet and putting in the exercise minutes pays off, in the short and long term.

“Sensationalized headlines and misleading advertisement for exercise regimes to lure consumers into the idea of ‘working out to eat whatever they want’ have fuelled the circulation of the myth about ‘exercise outrunning a bad diet,’ ” said the researchers. “Our study provided important evidence for health professionals that exercise does not fully compensate for a poor diet and that we should recommend and advocate for both an active lifestyle and a healthy diet.”

Words to live by if you’ve got into the habit of rewarding yourself with a trip to the Tim Hortons drive-thru after every tough workout. Better to head straight home for a healthy dose of fruits and veggies.