New study suggests carbohydrates are worse than fats. Do we need to panic?

by Jennifer Bowden / 22 September, 2017

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The average Kiwi already eats a low-carb diet, so no, not really.

QUESTION: A recent nutrition column was helpful to anyone trying to understand the difference between healthy and less-healthy carbs. But I’ve just read about a new study that shows a high-carb diet is bad for our health. Does this mean all types of carbs are bad if we eat too much of them?

ANSWER: “People don’t eat nutrients, they eat food,” was my nutrition lecturer’s sage advice. Nobody goes to the supermarket to buy a bottle of calcium to pour onto their carbohydrates for breakfast. No, we pour milk on to our oat-based muesli or top our white toast with jam. Both of those breakfasts contain carbs and calcium, but one is healthier than the other.

The Prospective Urban Rural Epidemiology (Pure) study findings made the news recently. “Too many carbs worse than fat, study finds”, and “High carb – not fat – intake linked to greater early death risk” were among the internet headlines after the Lancet published the findings.

The study investigated the associations of dietary fat and carbohydrate with cardiovascular disease and total mortality. The dietary-intake and health outcomes of more than 135,000 participants from 18 low-, medium- and high-income countries were assessed over about seven years. Analysis led the research team to conclude that removing restrictions on dietary-fat intake but limiting carbohydrate intake (if it was high) may improve our health.

So, what were their findings? That a higher carbohydrate intake was linked to increased total mortality, but not with the risk of cardiovascular disease or cardiovascular-disease mortality.

On paper, this looks bad for carbs, but not all carbs are the same. And this is a key limitation of the Pure study, according to University of Otago professor of human nutrition and medicine Jim Mann.

“[The study makes] no distinction between carbohydrates that have been repeatedly shown to be detrimental to health – for example, free sugars such as table sugar and refined grains – and those that have been clearly shown to have health benefits, such as fibre-rich wholegrains, legumes, vegetables and fruits.”

For example, in 2016, the British Medical Journal published a detailed meta-analysis and systematic review that found whole-grain intake was associated with “a reduced risk of coronary heart disease, cardiovascular disease and total cancer, and mortality from all causes, respiratory diseases, infectious diseases, diabetes and all non-cardiovascular, non-cancer causes”. There was little evidence, on the other hand, of such an association with refined grains, white rice, total rice or total grains.

In other words, the type of carb-containing food has a significant effect on health.

“Other large-cohort studies have shown there are health benefits when saturated fat is replaced either by polyunsaturated fat or wholegrains, but not when replaced by sugars or refined grains,” says Mann. That reaffirms that the food source significantly affects our health.

So, not all carbs are bad for us. But any macronutrient or food consumed to excess can damage our health, whether it’s water, alcohol, carrots or doughnuts.

Although the Pure study showed a 28% higher risk of death from high-carb diets versus those that are low in carbs, New Zealanders can rest easy. That’s because those in the Pure study with the lowest carb intake, and therefore the lowest risk of death, were consuming about 46% of their energy from carbohydrates. And yes, the average New Zealand man and woman consume 46% and 47% respectively of their energy from carbs, according to the most recent national nutrition survey.

Says Mann: “Current guidelines, which we endorse, recommend that people continue to eat a diet that is rich in vegetables and fruit, legumes, pulses, nuts, wholegrains and vegetable oils. Importantly, people should limit the amount of free sugars, salt and highly processed food. A range of dietary patterns, including Mediterranean, Asian-style and other traditional patterns can be consistent with this approach.”

Because one size doesn’t fit all, diets included.

This article was first published in the September 23, 2017 issue of the New Zealand Listener.

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