Three studies published in the July 28 issue of Archives of Internal Medicine address diet and risk of type 2 diabetes. Researchers found no association between eating a low-fat diet and diabetes risk, but found that people who drink more sugar-sweetened beverages or eat fewer fruits and vegetables have an increased risk of the disease.

Public health experts expect that about 11.2% of US adults will have type 2 diabetes (also known as adult-onset diabetes) by 2030. In addition, rates of the condition are predicted to continue to increase quite rapidly in the developed world. One of the strongest risk factors for type 2 diabetes is obesity, and this is also one of the most modifiable as it can be partially controlled through diet and exercise. The set of papers published this week specifically focuses on how diet is related to type 2 diabetes risk.

One study was conducted by Julie R. Palmer, Sc.D. (Slone Epidemiology Center, Boston University) and colleagues. They analyzed 43,960 African American women who filled out a questionnaire (in 1995 and 2001) that asked about food and beverage consumption. The researchers sought to determine the link between type 2 diabetes, weight gain and sugar-sweetened soft drinks and fruit drinks. Of all the women, 17% consumed one sugar-sweetened soft drink each day, 32% consumed one sweetened fruit drink each day, and 22% consumed at least one glass of orange or grapefruit juice each day.

The researchers followed the women over a 10 year period and found that 2,713 developed type 2 diabetes. Diabetes development was predicted by the rate of soft drink and fruit drink consumption. Women who consumed greater amounts of regular soda, other fruit juices, fortified fruit drinks, and Kool-Aid – excluding diet soda, orange juice, and grapefruit juice – were more likely to develop type 2 diabetes than women who consumed smaller amounts of those sugary drinks.

More specifically, drinking two or more soft drinks each day was associated with a 24% increase in diabetes risk and drinking two or more fruit drinks each day was associated with a 31% increase in diabetes risk compared to women who had less than one soft drink or fruit drink per month, respectively. There was no association noted between type 2 diabetes risk and diet soft drinks, grapefruit juice, or orange juice.

The researchers statistically controlled for body mass index (BMI) and noted a decrease in the link between soft drinks and diabetes risk. This means that BMI partially explains some of the risk in type 2 diabetes that was attributed to soft drink consumption. “Our study suggests that the mechanism for the increase in diabetes risk associated with soft drink consumption is primarily through increased weight. Reducing consumption of soft drinks or switching from sugar-sweetened soft drinks to diet soft drinks is a concrete step that women may find easier to achieve than other approaches to weight loss,” the authors clarify.

“It should be noted that consumption of fruit drinks conveyed as high an increase in risk as did consumption of soft drinks. Fruit drinks typically contain as many or more calories compared with soft drinks and, like soft drinks, may not decrease satiety to the same extent as solid food.” The authors conclude that, “The public should be made aware that these drinks are not a healthy alternative to soft drinks with regard to risk of type 2 diabetes.”

A second study, conducted by Anne-Helen Harding, Ph.D. (Addenbrooke’s Hospital, Cambridge, England) and colleagues, looked at the relationship between type 2 diabetes, blood vitamin C levels, and fruit and vegetable consumption. The researchers analyzed 21,831 individuals who were about 58 years old and did not have diabetes upon entering the study between 1993 and 1997. The study participants filled out a food frequency questionnaire and provided blood samples. Since fruits and vegetables are the main source of vitamin C in the Western diet, the level of vitamin C found in the blood is expected to correlate highly with the number of fruits and vegetables that study participants claim to have consumed.

Participants were followed-up over a 12 year period, and 735 developed diabetes. The researchers found that higher blood levels of vitamin C were associated with a substantially lower risk of developing diabetes. They write: “Compared with men and women in the bottom quintile [fifth] of plasma vitamin C, the odds of developing diabetes was 62 percent lower for those in the top quintile of plasma vitamin C. A weaker inverse association between fruit and vegetable consumption and diabetes risk was observed.”

The authors suggest that the reduction in diabetes risk explained by the consumption of fruits and vegetables may operate through reducing or preventing obesity or by providing certain nutrients or antioxidants that make one less prone to diabetes. They conclude: “Because fruits and vegetables are the main sources of vitamin C, the findings suggest that eating even a small quantity of fruits and vegetables may be beneficial and that the protection against diabetes increases progressively with the quantity of fruit and vegetables consumed.”

A third article studying the relationship between diet and diabetes was written by Lesley F. Tinker, Ph.D. (Women’s Health Initiative, Fred Hutchison Cancer Research Center, Seattle) and colleagues. These researchers analyzed a sample of 48,835 post-menopausal women who, from 1993 to 2005, were randomly assigned into one of two groups. One group (29,294 women) was told to continue eating their usual diet and the second group (19,541 women) was instructed to consume a low-fat diet with high levels of fruits, vegetables, and whole grains.

The authors found that over an 8.1 year period, 1,303 women (7.1%) in the low-fat diet group and 2,039 women (7.4%) in the usual-diet group developed diabetes. Though there was no significant difference in diabetes development between the two groups, the researchers note that, “Trends toward reduced incidence were greater with greater decreases in total fat intake and weight loss.”

The study was not necessarily designed so that women in the low-fat diet group would lose weight, but they did lose an average of 1.9 kilograms or 4.2 pounds more weight during the study than women in the other group. “Weight loss, rather than macronutrient composition, may be the dominant predictor of reduced risk of diabetes,” conclude the authors.

Mark N. Feinglos, M.D., C.M., and Susan E. Totten, R.D. (Duke University Medical Center, Durham, N.C) write in an accompanying editorial that: “The relationship between food and the development of type 2 diabetes mellitus has been debated for many years.”

“So, what do we now know about the impact of diet on the development of type 2 diabetes mellitus, and what remains unknown?” ask the authors. “We know that, as a population, we eat too much for our level of activity, and we are growing fatter as a result. In association with this increasing weight, we are in the midst of a dramatic increase in the number of cases of type 2 diabetes mellitus, not only in the United States, but in countries like India and China, where the caloric intake has also increased.”

They add: “We do not know whether specific macronutrients put genetically predisposed people at increased risk of developing diabetes mellitus, or whether adding lots of fat or refined carbohydrate to the diet just makes it easier to take in excess calories.”

“Studies to isolate these effects will be difficult to perform, but, until we have more information, we have to assume that calories trump everything else, and that our number one goal for the reduction of new cases of type 2 diabetes mellitus should be to reduce the intake of high-energy, low-benefit foods, particularly in young members of the most vulnerable populations,” conclude the authors.

Sugar-Sweetened Beverages and Incidence of Type 2 Diabetes Mellitus in African American Women
Julie R. Palmer; Deborah A. Boggs; Supriya Krishnan; Frank B. Hu; Martha Singer; Lynn Rosenberg
Archives of Internal Medicine (2008). 168[14]: pp. 1487-1492.
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Plasma Vitamin C Level, Fruit and Vegetable Consumption, and the Risk of New-Onset Type 2 Diabetes Mellitus: The European Prospective Investigation of Cancer-Norfolk Prospective Study
Anne-Helen Harding; Nicholas J. Wareham; Sheila A. Bingham; KayTee Khaw; Robert Luben; Ailsa Welch; Nita G. Forouhi
Archives of Internal Medicine (2008). 168[14]: pp. 1493-1499.
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Low-Fat Dietary Pattern and Risk of Treated Diabetes Mellitus in Postmenopausal Women: The Women’s Health Initiative Randomized Controlled Dietary Modification Trial
Lesley F. Tinker; Denise E. Bonds; Karen L. Margolis; JoAnn E. Manson; Barbara V. Howard; Joseph Larson; Michael G. Perri; Shirley A. A. Beresford; Jennifer G. Robinson; Beatriz Rodríguez; Monika M. Safford; Nanette K. Wenger; Victor J. Stevens; Linda M. Parker
Archives of Internal Medicine (2008). 168[14]: pp. 1500-1511.
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Are You What You Eat, or How Much You Eat?: The Case of Type 2 Diabetes Mellitus
Mark N. Feinglos; Susan E. Totten
Archives of Internal Medicine (2008). 168[14]: pp. 1485-1486.
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Written by: Peter M Crosta