Large study in women strengthens the case for “prudent” diets versus diabetes
by Craig Weatherby
It seems intuitive to assume that diets high in fibrous, nutritious, antioxidant-rich vegetables, beans, and fruits should discourage diabetes.
After all, this is a disease associated with the standard American diet, with its lack of fiber and colorful plant foods and overabundance of sugar, refined foods, pro-inflammatory omega-6 fats, and empty calories.
- Prior epidemiological studies yielded mixed results for veggies versus diabetes risk.
- Large study in Chinese women finds strong link between vegetables or beans and reduced risk.
- Unlike soy protein or products, whole soy beans appear protective.
While most studies support this idea, a recently published review of epidemiological studies did not link diets rich in vegetables and fruits to reduced rates of diabetes:
“The consumption of three or more daily servings of fruit or vegetables was not associated with a substantial reduction in the risk of type 2 diabetes” (Hamer M, Chida Y 2007).
However, analyses of data from a huge study reinforce the hypothesis—supported by ample experimental research—that vegetable-rich diets should help discourage diabetes.
Sino-American population study finds vegetables protective
A joint team from the Shanghai Cancer Institute and the Diabetes Research and Training Center in Nashville, led by noted diabetes researchers Raquel Villegas, recruited 64,191 middle-aged Chinese women, aged between 40 and 70.
Using a diet questionnaire, the women’s food intakes were surveyed at the start of the study and again after 4.6 years (Villegas R, Shu XO et al. 2008).
Over the course of the study, Dr. Villegas and her co-workers documented 1,608 cases of adult diabetes.
The women who reported the highest vegetable intake—averaging just under one pound daily—were 28 percent less likely to have developed diabetes, compared to those who consumed the lowest average amount (just over ¼ pound of vegetables a day).
However, higher fruit intake was not linked to a reduced (or increased) risk of developing diabetes.
The failure of fruits to help deter diabetes is not surprising. While they offer some potentially protective factors—such as fiber and anti-inflammatory antioxidants—they contain much more sugar than most vegetables do. Accordingly, fruits tend to have higher glycemic indices, compared with most vegetables (other than sweet, starchy root vegetables).
(The glycemic index or GI is a measure of how high a food drives blood sugar levels: foods with little impact on sugar levels have a low GI.)
Based on the indications of prior studies, the authors proposed an explanation for the favorable effect of vegetables:
“The mechanism by which vegetables affect glucose tolerance [a key protective factor]… may be associated with the high content of antioxidants, fiber, and magnesium, or the low glycemic index in vegetables” (Villegas R, Shu XO et al. 2008).
While acknowledging the limitations inherent to epidemiological studies, this study adds weight to the small but growing body of evidence that link vegetable-rich diets to reduced risk of diabetes.
And the results are probably not unique to Chinese women, since the Tennessee group obtained very similar, veggie-favorable results from a study among Irish adults (Perry IJ et al. 2005).
Beans appear protective, too
When the China-Tennessee team analyzed the same group of women, they linked higher consumption of beans to reduced diabetes risk: “Consumption of legumes, soybeans in particular, was inversely associated with the risk of type 2 diabetes mellitus” (Villegas R, Gao YT et al. 2008).
This result was unsurprising, given the beneficial blood-sugar control and antioxidant, anti-inflammatory effects that beans exert.
Compared with those who ate the least amount of legumes, the risk of diabetes among those who ate the most legumes was 38 percent lower.
And the risk was even lower—47 percent less—among those who ate the most soybeans.
Interestingly, this benefit did not extend to soy products (other than soy milk) or soy protein: a result that supports the general superiority of whole foods versus processed fare.
- Hamer M, Chida Y. Intake of fruit, vegetables, and antioxidants and risk of type 2 diabetes: systematic review and meta-analysis. J Hypertens. 2007 Dec;25(12):2361-9. Review.
- Perry IJ, Villegas R, Salim A, Flynn A. Clustering of protective factors for glucose intolerance and insulin resistance: a cross-sectional study. Diabet Med. 2005 Aug;22(8):1091-7.
- Villegas R, Gao YT, Yang G, Li HL, Elasy TA, Zheng W, Shu XO. Legume and soy food intake and the incidence of type 2 diabetes in the Shanghai Women's Health Study. Am J Clin Nutr. 2008 Jan;87(1):162-7.
- Villegas R, Shu XO, Gao YT, Yang G, Elasy T, Li H, Zheng W. Vegetable but not fruit consumption reduces the risk of type 2 diabetes in Chinese women.J Nutr. 2008 Mar;138(3):574-80.