The startling rise in diabetes is perfectly mirrored by our mounting consumption of refined carbohydrates, a new analysis reveals. The study adds to evidence that sugary foods should be eschewed and that public health advice to cut back on fat may have backfired.
Levels of obesity and late onset diabetes have risen slowly over the last century and accelerated in the last 40 years. While the problem is most acute in developed countries, there is evidence that rates are starting to increase in developing countries too. Most experts agree that worsening diets and increasingly inactive lifestyles are responsible, but the exact cause is hard to pin down.
Simin Liu of the Harvard School of Public Health, Boston, and his co-workers collected information on consumption and food composition for the period between 1909 and 1997. They compared this with data on disease incidence rates from the US Centers for Disease Control and Prevention.
The climb in diabetes goes hand in hand with the rise in total calorie intake, the team reports in the American Journal of Clinical Nutrition1. This fits the idea that obesity places people at risk of diabetes.
But when Liu broke down the figures into proteins, fats and carbohydrates, a different picture emerged. Neither fat consumption nor protein seem to be the root cause of the problem.
Instead, the diabetes rise best matches dropping fibre consumption and escalating consumption of corn syrup, a ubiquitous sweetener in today's processed foods. "It is quite striking," says nutritional scientist Cyril Kendall of the University of Toronto, Canada.
Foods high in refined carbohydrate, the argument goes, send blood sugar soaring, requiring the pancreas to pump out insulin. Over time, the body's tissues become resistant to the excess insulin and pancreatic cells wear out, resulting in diabetes.
Liuís analysis does not prove that corn syrup caused the increase in diabetes, experts are careful to point out. But the finding bolsters the idea that this and other highly refined carbohydrates such as white flour, white rice and sugar put people at risk of obesity and diabetes.
That refined carbs are the culprits might seem obvious, but the idea is at the centre of much controversy. In January this year, for example, the World Health Organization released a draft road map for tackling obesity, which among other targets pinpoints reductions in sugary foods. The US government attempted to undermine these recommendations, some claim, because of pressure from the food industry.
Studies by Liu and others now make it harder to deny that excess sugar is bad for our health. Epidemiological studies, which track people's health over time, have also shown that those who eat more refined carbohydrates are at greater risk of developing diabetes "Together they make a compelling case," says David Ludwig, a researcher also at the Harvard School of Public Health.
Liu's analysis also backs the argument that, since the 60s and 70s, advice to the public to cut back on fat has misfired. Some experts say such advice led food manufacturers simply to replace fats with carbohydrates, which ultimately fuelled obesity rather than combating it.
The study shows that the amount of corn syrup people ate started rocketing at roughly the time the low-fat health message was being broadcast. "Never before have people eaten so much highly refined carbohydrates and led such a sedentary lifestyle," says Ludwig.
Many nutritionists now advocate a diet that avoids refined carbohydrates in favour of wholegrain alternatives. They also promote the choice of healthy fats, such as vegetable oils rather than animal fats, as well as fruits, vegetables and frequent exercise.
But this message has yet to be accepted or incorporated into many public health guidelines, says nutritionist Kendall. On top of this, many people are confused by conflicting health messages, such as the Atkins diet's recommendation to spurn all carbohydrates. "We need to rethink our approach to diet," Kendall says.
Gross, L.S., Li, L., Ford, E.A. & Ford, S. American Journal of Clinical Nutrition, 79, 774 - 779, (2004). |Article|
source: http://www.nature.com/nsu/040510/040510-5.html 12may04