One in four people born today are expected to develop Type 2 diabetes during their lifetimes.

Shedding excess weight and exercising more can cut Type 2 diabetes risk by 58 percent.

Favoring foods in their unrefined state -- brown rice and whole grains, for instance -- can help keep blood sugar levels from spiking.

Exercise improves blood sugar control by increasing insulin sensitivity.

As rates of Type 2 diabetes continue to rise around the world, experts say we mostly have ourselves to blame. Genes certainly play a role in determining risk. But the surge of new cases of this debilitating disease is caused mostly by poor diets and lack of physical activity.

By all rights, the prescription should be simple: lose weight if you are overweight, and get more exercise.

Easy? Of course not. Experts have yet to come up with anything close to a surefire approach to help people shed pounds. And dietary recommendations to prevent or slow diabetes have often been contradictory and confusing. Nearly 30 years after the American Diabetes Association recommended a low-fat, high-carbohydrate diet to control diabetes, overturning the high-fat, low-carbohydrate approach of earlier decades, controversy still swirls around the amount and types of carbohydrates to eat.

Much of the debate focuses on the glycemic index, a measure of how carbohydrate-rich foods affect blood sugar, and whether these effects play a significant role in the progression of Type 2 diabetes. Foods high on the glycemic index, like sugared beverages, cake and white rice, are known to send blood sugar levels up sharply after a meal. Foods low on the index, like broccoli, lettuce, brown rice and whole grains, on the other hand, take longer to digest and hence keep blood sugar levels on a more even keel.

The American Diabetes Association has decided that patients should not be counseled to take the glycemic index into account when choosing foods. “Although it is clear that carbohydrates do have differing glycemic responses,” its policy statement declares, “the data reveal no clear trend in outcome benefits.”

That’s a mistake, says Dr. David Ludwig, an endocrinologist at Children’s Hospital in Boston and an associate professor at Harvard Medical School. “High-glycemic foods like refined grains raise blood sugar levels two to three times higher than unprocessed foods with a low glycemic index,” he said. When blood sugar levels spike, the body must churn out insulin to move glucose out of the bloodstream and into cells, where it is used for energy.

“If you’re eating high-glycemic foods meal after meal, snack after snack, day after day, that’s going to put a lot of stress on the system that produces insulin,” Dr. Ludwig said. “If the system is already compromised due to a family history of diabetes, those rapid swings of blood sugar could make a difference between remaining healthy or decompensating into Type 2 diabetes.”

Dr. Ludwig cites a study he conducted in which rats fed foods high on the glycemic index lost lean muscle mass, gained body fat and began to lose their ability to control blood sugar.

“A high percentage of insulin-producing cells in the high-glycemic rats were undergoing a process of destruction, disruptions in their architecture and scarring,” Dr. Ludwig said. The same thing, he suspects, happens in people.

But so far, evidence from human studies has been sketchy. In one recent Canadian study, there were no differences in blood sugar control among 162 volunteers assigned to one of three very different diets for a year: a low-carbohydrate regimen; a high-carbohydrate, low-glycemic-index diet; or foods high on the glycemic scale. Fasting glucose, a test widely used to monitor diabetes risk, actually rose in the group eating the low-glycemic foods.

A second study of 1,898 people found that risk of Type 2 diabetes was the same whether people reported eating foods high or low on the glycemic index.

“The notion that glycemic index matters makes intuitive sense,” said Dr. John M. Miles, a diabetes expert at the Mayo Clinic. “A lot of people have strong feelings on the subject. But the evidence just isn’t there.”

Dr. Xavier Pi-Sunyer, an endocrinologist and diabetes expert at St Luke’s-Roosevelt Hospital in New York, agreed. Given the new findings, “It seems unwise at this point to burden Type 2 diabetes patients with trying to pick and choose among different high- and low-glycemic-index foods,” he wrote in a recent review of the evidence.

But Dr. Thomas Wolever, a University of Toronto researcher who led the Canadian trial, noted that those who ate low-glycemic-index foods showed improvements in blood sugar control after meals, which may be a more important measure of glucose control than the fasting glucose test. They also had reductions in levels of C-reactive protein, a marker for inflammation that also appears to be linked to diabetes risk.

Low-glycemic diets may have another crucial advantage, Dr. Wolever suggested: they help some people shed pounds. “I’ve had people tell me it’s the only way they’ve been able to lose weight,” he said.

While no single diet works for everyone, losing weight may be the single most effective way to lower Type 2 diabetes risk. Evidence for that comes from a major trial sponsored by the National Institutes of Health, in which a randomly assigned group of overweight volunteers with early signs of diabetes were encouraged to lose about 7 percent of their body weight and engage in 150 minutes of moderate exercise weekly.

Over the next three years, only 5 percent of the lifestyle intervention group went on to develop diabetes each year, compared with 11 percent of volunteers in a control group. Weight loss and exercise proved more effective than a leading diabetes medication in preventing Type 2 diabetes.

“There’s no question that if we can get people to lose 5 or 10 pounds, we’ll be doing them a world of good,” Dr. Wolever said. The confounding question remains how.

今天出生的人口的四分之一，有可能在其一生中得2型糖尿病。

剪掉赘肉和加强锻炼可以将2型糖尿病患病风险降低58%。

多吃未经精制的食物（比如糙米和全麦）可以帮你防止血糖升高。

锻炼可以通过提高胰岛素感受性来改善血糖控制。

2型糖尿病患病率在全球范围内都在不断增长，专家说这主要归责于我们自己。的确基因在控制风险方面扮演这一定角色，但是这种有损人的健康的疾病激增主要是由于不良饮食和缺乏体育锻炼造成的。

权衡利弊，处方很简单：如果你超重就减肥，并加强锻炼。

简单吗？当然不。专家必须找出能帮助人们减肥的有效方法。防止或者降低糖尿病的饮食建议往往互相矛盾，让人迷惑。美国糖尿病协会推行低脂肪高碳水化合物饮食来控制糖尿病近三十年了，这与此前数十年的高脂肪低碳水化合物的饮食方法正好相反，但是现在关于吃什么样的碳水化合物和吃多少的问题仍争论不休。

许多争论的焦点集中于血糖生成指数。这是一种测量富含碳水化合物的食物如何影响血糖，以及这些影响在2型糖尿病的发生中起什么作用的方法。血糖生成指数高的食物，如含糖饮料、蛋糕和白米，食后可以使血糖水平急速升高。血糖生成指数低的食物，如西蓝花、莴苣、糙米和全麦等需要较长的时间来消化的食物，可以保持血糖水平更平稳。

美国糖尿病协会指出，病人在选择食物时不用考虑血糖生成指数。其政策声明宣称，尽管已证明碳水化合物可以影响血糖，但是数据并未显示有明显益处。

但这是错的。波士顿儿童医院内分泌学家、哈佛医药学校联合教授大卫路德维格博士说，像精米等高糖食物可以使血糖水平比食用低血糖生成指数的食物高出2-3倍。他说，当血糖水平升高时，人体必需分泌胰岛素来使葡萄糖与血液分离出来，进入细胞。在这里，葡萄糖将用作能量。

路德维格博士说，如果餐复一餐，日复一日的食用高糖食物，将会增加胰岛素分泌系统的压力。如果该系统已经因家族糖尿病史而受损，血糖的迅速波动可能导致两个结果，一是保持健康，再就是转成2型糖尿病。

路德维格用他做的一项研究作为引证。该研究中，白鼠被喂以高血糖生成指数的食物，逐渐失去了肌肉组织，变得肥胖，并丧失了控制血糖的能力。

路德维格博士说，高血糖白鼠体内的大量胰岛素分泌细胞的组织结构被破坏、分解。他怀疑，同样的事情也发生在人体内。

但是到目前为止，人体研究中获得的证据已经被概括出来。在近期加拿大人的一项研究中，人们分成三组分别食用三种不同食物（分别是低碳水化合物食物、高碳水化合物低血糖生成指数食物、高糖食物）一年后，这162个志愿者的血糖控制并没有什么差别。食用低糖食物的那一组的葡萄糖反倒升高了。葡萄糖被广泛用于监测糖尿病风险。

另一项对1898个人的研究发现，不管人们吃的食物高血糖生成指数高还是低，2型糖尿病的患病风险是一样的。

梅奥诊所的糖尿病专家，约翰M.迈尔斯说，血糖生成指数给人直观的感觉。许多人对此非常认可，但是这并没有实证。

纽约St Luke’s-Roosevelt 医院的糖尿病专家和内分泌学家Xavier Pi-Sunyer博士同意上述观点。根据上面的发现，他在最近的一份关于该证据的评论中说，从这点来讲，让2型糖尿病人再去费力地去挑选高血糖生成指数食物和低血糖生成指数，是很不明智的。

但是主持了该项加拿大人实验的多伦多大学研究员Thomas Wolever博士指出，食用低血糖生成指数食物的人饭后血糖控制有所改善。这可能是比禁食葡萄糖更好的葡萄糖控制方法。它们也能降低C反应蛋白的水平。C反应蛋白产生是发炎的表现，而发炎有往往与糖尿病的发生有关。

低血糖生成指数食物可能还有另一个重要的优势。Wolever博士提示：它可以帮人减肥。他说，曾经有人跟我说，这是他们唯一可以减肥的方法。

由于没有任何一种食物可以对所有人有效，减肥可能就是降低2型糖尿病患病风险的最有效的一种方法。相关证据来自于国家卫生研究院组织的一个大型实验。该实验中，对有糖尿病早期症状的志愿者由任意分组，并鼓励他们减掉7%的体重，并每周进行150分钟的适度体育锻炼。

接下来的三年中，生活方式被调整的一组每年只有5%的人患糖尿病，而没有调整的另一组则达到11%。实验证明，减肥和体育锻炼比任何先进的防治2型糖尿病的药物都有效。

Wolever博士说，毫无疑问，如果我们能让人们减掉5磅或者10磅，这将会对他们大有好处。现在的问题是如何使他们减肥。