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。

剪掉贅肉和加強鍛煉可以將2型糖尿病患病風險降低58%。

多吃未經精制的食物（比如糙米和全麥）可以幫你防止血糖升高。

鍛煉可以通過提高胰島素感受性來改善血糖控制。

2型糖尿病患病率在全球范圍內都在不斷增長，專家說這主要歸責于我們自己。的確基因在控制風險方面扮演這一定角色，但是這種有損人的健康的疾病激增主要是由于不良飲食和缺乏體育鍛煉造成的。

權衡利弊，處方很簡單：如果你超重就減肥，并加強鍛煉。

簡單嗎？當然不。專家必須找出能幫助人們減肥的有效方法。防止或者降低糖尿病的飲食建議往往互相矛盾，讓人迷惑。美國糖尿病協會推行低脂肪高碳水化合物飲食來控制糖尿病近三十年了，這與此前數十年的高脂肪低碳水化合物的飲食方法正好相反，但是現在關于吃什么樣的碳水化合物和吃多少的問題仍爭論不休。

許多爭論的焦點集中于血糖生成指數。這是一種測量富含碳水化合物的食物如何影響血糖，以及這些影響在2型糖尿病的發生中起什么作用的方法。血糖生成指數高的食物，如含糖飲料、蛋糕和白米，食后可以使血糖水平急速升高。血糖生成指數低的食物，如西藍花、萵苣、糙米和全麥等需要較長的時間來消化的食物，可以保持血糖水平更平穩。

美國糖尿病協會指出，病人在選擇食物時不用考慮血糖生成指數。其政策聲明宣稱，盡管已證明碳水化合物可以影響血糖，但是數據并未顯示有明顯益處。

但這是錯的。波士頓兒童醫院內分泌學家、哈佛醫藥學校聯合教授大衛路德維格博士說，像精米等高糖食物可以使血糖水平比食用低血糖生成指數的食物高出2-3倍。他說，當血糖水平升高時，人體必需分泌胰島素來使葡萄糖與血液分離出來，進入細胞。在這里，葡萄糖將用作能量。

路德維格博士說，如果餐復一餐，日復一日的食用高糖食物，將會增加胰島素分泌系統的壓力。如果該系統已經因家族糖尿病史而受損，血糖的迅速波動可能導致兩個結果，一是保持健康，再就是轉成2型糖尿病。

路德維格用他做的一項研究作為引證。該研究中，白鼠被喂以高血糖生成指數的食物，逐漸失去了肌肉組織，變得肥胖，并喪失了控制血糖的能力。

路德維格博士說，高血糖白鼠體內的大量胰島素分泌細胞的組織結構被破壞、分解。他懷疑，同樣的事情也發生在人體內。

但是到目前為止，人體研究中獲得的證據已經被概括出來。在近期加拿大人的一項研究中，人們分成三組分別食用三種不同食物（分別是低碳水化合物食物、高碳水化合物低血糖生成指數食物、高糖食物）一年后，這162個志愿者的血糖控制并沒有什么差別。食用低糖食物的那一組的葡萄糖反倒升高了。葡萄糖被廣泛用于監測糖尿病風險。

另一項對1898個人的研究發現，不管人們吃的食物高血糖生成指數高還是低，2型糖尿病的患病風險是一樣的。

梅奧診所的糖尿病專家，約翰M.邁爾斯說，血糖生成指數給人直觀的感覺。許多人對此非常認可，但是這并沒有實證。

紐約St Luke’s-Roosevelt 醫院的糖尿病專家和內分泌學家Xavier Pi-Sunyer博士同意上述觀點。根據上面的發現，他在最近的一份關于該證據的評論中說，從這點來講，讓2型糖尿病人再去費力地去挑選高血糖生成指數食物和低血糖生成指數，是很不明智的。

但是主持了該項加拿大人實驗的多倫多大學研究員Thomas Wolever博士指出，食用低血糖生成指數食物的人飯后血糖控制有所改善。這可能是比禁食葡萄糖更好的葡萄糖控制方法。它們也能降低C反應蛋白的水平。C反應蛋白產生是發炎的表現，而發炎有往往與糖尿病的發生有關。

低血糖生成指數食物可能還有另一個重要的優勢。Wolever博士提示：它可以幫人減肥。他說，曾經有人跟我說，這是他們唯一可以減肥的方法。

由于沒有任何一種食物可以對所有人有效，減肥可能就是降低2型糖尿病患病風險的最有效的一種方法。相關證據來自于國家衛生研究院組織的一個大型實驗。該實驗中，對有糖尿病早期癥狀的志愿者由任意分組，并鼓勵他們減掉7%的體重，并每周進行150分鐘的適度體育鍛煉。

接下來的三年中，生活方式被調整的一組每年只有5%的人患糖尿病，而沒有調整的另一組則達到11%。實驗證明，減肥和體育鍛煉比任何先進的防治2型糖尿病的藥物都有效。

Wolever博士說，毫無疑問，如果我們能讓人們減掉5磅或者10磅，這將會對他們大有好處。現在的問題是如何使他們減肥。