At the University of Utah, a team led by Dr. Martha Slattery found that high intakes of vegetables, fruits and whole grains reduced the risk of rectal cancer by 28%, 27% and 31% respectively. A high-fiber diet (more than 34 grams of fiber per day) reduced rectal cancer by an impressive 66%, in this study of over 2000 people.
American Journal of Clinical Nutrition, February 2004; 79(2):274-281

Acculturation is the extent to which mainstream customs, beliefs, and practices are adopted by immigrants.  Researchers in Washington State recruited 1,689 adult Hispanic and non-Hispanic participants to investigate whether acculturation is a predictor of fruit, vegetable, and fat intake among Hispanics.  Using the National 5-A Day for Better Health program dietary assessment instruments, researchers determined that highly acculturated Hispanics in Washington State consume significantly fewer fruits and vegetables than less acculturated Hispanics. 
Journal of the American Dietetics Association, January 2004; 104:51-57 (Neuhouser M et al.) 

As part of the well-known Nurses’ Study, Simin Liu and fellow researchers at the Harvard School of Public Health followed over 74,000 women from 1984-1996, and concluded that women who consumed more whole grains consistently weighed less than women who consumed less whole grains.
American Journal of Clinical Nutrition, November 2003; vol 78(5):920-927

Researchers at the Royal Veterinary and Agricultural University, in Frederiksberg, Denmark, compared three different loaves: einkorn bread made with honey-salt leavening; naturally-leavened einkorn bread made with crushed whole grains; and commercial yeast bread made with modern wheat. The naturally-leavened einkorn loaves significantly reduced the gastrointestinal response of GIP (glucose-dependent insulinotrophic polypeptide), a hormone important in controlling insulin secretion.
European Journal of Clinical Nutrition, October 2003; 57(1):1254-61

While there are currently few data specifically connecting vegetarian diets and diabetes prevention or treatment, it is known that many of the specific foods that make up a vegetarian diet have advantages in the treatment of type 2 diabetes.  These foods include whole grains, legumes, nuts, seeds, soy proteins, and plant sterols.  This summary article from researchers at the University of Toronto details the benefits of different plant foods, and concludes that evidence documented in both cohort studies and intervention studies show that vegetarian diets “can help reduce the risk of developing type 2 diabetes and cardiovascular disease—a major complication of type 2 diabetes.”
American Journal of Clinical Nutrition. September 2003; 78(suppl):610S–6S. [Jenkins D et al.]

Researchers in Los Angeles examined whether the changing incidence of colorectal cancer in their city’s Mexican-American population was due to changes in dietary practices in this group.  Cancer incidence and dietary intake data were obtained for over 35,000 Latinos of Mexican national origin – the largest sample of Mexican-origin Latinos of any such study in the US.  The incidence of colorectal cancer saw the greatest increase between the first and second generations.  Nearly all dietary changes due to acculturation also occurred between the first and second generations.  These findings suggest an association between colorectal cancer risk and certain dietary components. Higher intakes of alcohol and refined carbohydrates were major risk factors, and lower consumption of vegetables was a protective factor.
Nutrition and Cancer 2003, Volume 45, Issue 2 (Monroe et al.)

In 2003, a study out of Madrid, Spain examined the high nutrient levels in buckwheat to determine whether it could behave as a prebiotic and be considered a healthy food. (Prebiotics are indigestible food ingredients that stimulate the helpful bacteria in our digestive systems.) Not only did the buckwheat-fed group emerge with a lower bodyweight when compared to the control, some of the best types of helpful bacteria were found, along with a decrease in some types of pathogenic bacteria.
Nutrition Research, June 2003; 23(6):803-14

Between first and second generation US immigrants, a striking increase in overweight and obesity occurs.  A study using data from the National Longitudinal Study of Adolescent Health set out to determine the underlying factors that cause this phenomenon.  More than 8,600 adolescents of varying ethnicity were assessed for overweight and several factors including diet.  Researchers concluded that immigrant adolescents are likely to be influenced by the “obesigenic” environment of the US, including sedentary lifestyles, large portion sizes, heavy advertising of high-fat, energy-dense foods, and mass media.  Lifestyle differences between foreign- and US-born Hispanic adolescent immigrants are likely to underlie the striking increase in overweight between first and subsequent generations of US residence.
Social Science & Medicine, April 2003; 57:2023–2034 (Gordon-Larsena P et al.)

In an effort to track the rise in chronic disease among people who move away from their traditional diets, scientists at Tufts University synthesized data about diets and health from many sources. They found a close association between dietary change (starting with the rich) and the health impacts of a more processed, energy-dense diet.
Cadernos de Saúde Pública. 2003; 19 suppl 1:S87-99. (Bermudez et al.)

University of Guelph researchers in Ontario, Canada found that amaranth can be a rich dietary source of phytosterols, which have cholesterol-lowering properties.  Of the four varieties tested, the top results came from Amaranthus K343, often called Plainsman, the most commonly cultivated amaranth in the United States.
Plant Foods for Human Nutrition, 2003; 58(3):207-11
 

Australian researches conducted a study focusing on Greeks who relocated to Melbourne but maintained their traditional Mediterranean diet.  During this study, the foods selected for nutrient evaluation – leafy green vegetables, figs in season, and various types of olive oil – were those commonly consumed by Greeks living in Melbourne, but not by native Australians.  Of all the commercial and wild leafy greens studied, amaranth leaves were found to contain some of the highest levels of beta-carotene and lutein, even higher than the commercially available chicory and endive.
European Journal of Clinical Nutrition, November 2002; 56(11):1149-54

Researchers from Oxford University studied a large cohort of British men and women in the context of diet, lifestyle, and disease risk. They found that hypertension (both systolic and diastolic) is significantly less prevalent among vegan men and women (5.8% and 7.7%, respectively) as compared to omnivorous men and women (15.0% and 12.1%, respectively). The researchers suspect that this is related to the vegan participants’ lower average Body Mass Index.
Public Health Nutrition. 2002 Oct 1;5(5):DOI 10.1079/PHN2002332. (Appleby et al.)