Type 2 Diabetes

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The prevalence of type 2 diabetes has reached epidemic proportions with over 150 million cases diagnosed worldwide; this number is expected to double by 2025. The concurrent rise in obesity has been directly linked to insulin resistance and compensatory hyperinsulinemia and eventual type 2 diabetes, with over 80% of diagnosed type 2 diabetes being the result of excess body fat. Public health recommendations to reduce fat intake, especially saturated fat, have led to a rise in the proportion of carbohydrates (particularly refined carbohydrates) in the diet with consequences for postprandial glucose and insulin metabolism. The source of carbohydrate is also important. Whole-grain foods commonly have a low glycemic index because whole-grain foods with an intact bran and germ layer have a much smaller impact on blood glucose than refined carbohydrate foods because of their larger particle size, slowing the rate of enzymic attack. The level of soluble fiber within whole grains has also been identified as a possible protector and the higher amylose content is also thought to be beneficial. Slower rates of digestion are observed when foods have more compact granules, contain high levels of viscous soluble fiber, and have a higher amylose to amylopectin ratio.

The relationship between whole grains and diabetes has been studied in five large cohorts as highlighted in Table 3. All of the studies have found an inverse relationship between consumption of whole grains or cereal fiber and disease reduction despite slight variations in methodology.

As a proxy measure of whole-grain consumption, the relationship between the intake of total and specific sources of dietary fiber, dietary glycemic index, and glycemic load in the Nurses' Health Study and the Health Professional's Study was examined. Among the 65 173 women who participated during 1986-1992, women in the highest quintile of cereal fiber intake had a 28% lower risk of diabetes than those in the lowest quintile of intake (RR 0.72; 95% CI 0.58, 0.90; P = 0.001), a significant reduction that was not observed with fruit or vegetable fiber intakes. In men there was an inverse relationship between cereal fiber intake and risk of type 2 diabetes: a reduction in risk of 30% following adjustment for confounders. Again, no significant relationship of fruit or vegetable fiber to diabetes risk was observed.

The fiber content of whole grains has been suggested as a possible explanation for the inverse relationship between total and whole-grain intakes and risk of type 2 diabetes observed in a 10-year follow-up of Finnish men (n = 2286) and women (n = 2030). When the highest and lowest quartiles of whole-grain consumption were compared there was an over 30% reduction in risk following adjustment for age, sex, geographic area, and energy intake. Cereal fiber, but not that from fruits and vegetables, was inversely related to risk of type 2 diabetes even after adjustment for a number of

Table 3 Summary of the evidence relating a reduced risk of type 2 diabetes to increased whole grain consumption, including studies where cereal or dietary fiber intake is taken as a surrogate marker for whole-grain intakes

Evidence for a reduced risk of:

Cohort

Reported Association

Reference

Epidemiological

Type 2 diabetes Nurse's Health Study

Type 2 diabetes

Type 2 diabetes

Type 2 diabetes

Type 2 diabetes

Risk factors for type 2 diabetes and CVD

Intervention

Insulin sensitivity

Health Professionals Follow-up Study Finnish Mobile Clinic Health

Examination Survey Health Professionals Follow-up Study Nurse's Health Study

Framingham Offspring Study

11 hyperinsulinemic overweight patients

Lower RR with increased dietary fiber

Lower RR with increased dietary fiber

Lower RR with increased whole grains

Lower RR with increased whole grains

Lower RR with increased whole grains

Reduction in fasting insulin with increasing whole-grain intake

Reduction in fasting insulin following diet rich in whole grains

Salmeron et al. (1997a) Dietary fiber, glycemic load, and risk of non-insulin-dependent diabetes mellitus in women. JAMA 277: 472-477.

Salmeron et al. (1997b) Dietary fiber, glycemic load, and risk of NIDDM in men. Diabetes Care 20: 545-550.

Montonen et al. (2003) Whole-grain and fiber intake and the incidence of type 2 diabetes American Journal of Clinical Nutrition 77: 622-629.

Fung etal. (2003) Whole-grain intake and the risk of type 2 diabetes: a prospective study in men. American Journal of Clinical Nutrition 76: 535-540.

Liu et al. (2000) A prospective study of whole-grain intake and risk of type 2 diabetes mellitus in US women. American Journal of Public Health 90: 1409-1415.

McKeown et al. (2002) Whole grain intake is favourably associated with metabolic risk factors for type 2 diabetes and cardiovascular disease in the Framingham Offspring Study. American Journal of Clinical Nutrition 76: 390-398.

Pereira et al. (2002) Effect of whole grains on insulin sensitivity in overweight hyperinsulinaemic adults. American Journal of Clinical Nutrition 75: 848-855.

confounders. Adjustment for cereal fiber considerably weakened the association between whole-grain consumption and risk of type 2 diabetes, suggesting that this may be a significant component of the whole-grain package.

The effect of whole-grain consumption specifically, rather than fiber intakes, on incidence of type 2 diabetes was examined in the Health Professional's Follow-up Study. Over a 12-year follow-up period, intakes of whole and refined grains were analyzed using a validated semiquantitative FFQ. Despite no baseline history of diabetes or CVD, 1197 cases of incident type 2 diabetes were identified in this male cohort. Following adjustment for dietary and life style confounders including age, smoking, physical activity, and fruit and vegetable intake, there was a reduced risk of type 2 diabetes of almost 40% in those with the highest quintile compared with the lowest quintile of whole-grain intakes. The results were attenuated after adjustment for BMI, although the relationship remained significant. In those with a BMI >30kgm—2 the association between whole grain and type 2 diabetes was weak, whereas in those men with a BMI <30kgm—2 a 50% risk reduction was observed in those who consumed the most whole grains. However, after adjusting for components of the whole-

grain package such as cereal fiber, magnesium, and glycemic load, the statistical significance was lost (Figure 4).

These findings in men were similar to those observed by Liu et al. (2000) when they looked specifically at whole and refined grain intakes in the women participating in the Nurses' Health

Relative risks of cumulative average whole and refined grain intakes on risk of type 2 diabetes in men by quintiles of grain intake

Relative risks of cumulative average whole and refined grain intakes on risk of type 2 diabetes in men by quintiles of grain intake

Quintiles of intake

Figure 4 O adjusted for age, period, physical activity, energy intake, missing FFQ data, smoking, family history of diabetes, alcohol intake, fruit intake and vegetable intake. * additionally adjusted for BMI <30kg/m2 and >30kg/m2.

Study. During the 10-year follow-up, 1879 cases of incident type 2 diabetes were confirmed. Although the women with the highest intake of whole grain had other beneficial dietary and lifestyle factors, whole-grain intake was inversely related to risk. There was a significant inverse association between the highest and lowest quintiles of whole-grain intake after adjustment for age and energy intake. Although attenuated after adjustment for BMI and other lifestyle factors, the relationship remained significant. Again BMI appeared to be the strongest confounding factor. Women in the lowest quintile of intake ratio (those with low whole grain or large refined grain intakes) had a 57% greater risk of type 2 diabetes than women in the highest quintile.

In a cross-sectional assessment of 2941 subjects in the Framingham Offspring Study the effect of whole-grain intake on metabolic risk factors for type 2 diabetes and CVD was examined. Dietary intake was assessed using a semiquantitative FFQ in the participants who were free from diabetes or high cholesterol. Breakfast cereal type was used to quantify whole-grain intakes based on a whole-grain content of over 25%. Other foods identified as whole grain were dark breads, popcorn, and oatmeal. Whole-grain intakes were similar between men and women (mean 8.3 and 8.8 servings per week, respectively) but refined grain intakes were much higher (22.0 and 18.5 servings per week, respectively). Similar to other studies, those in the highest quintile of whole-grain intakes (20.5 servings per week) had lower BMI, were less likely to smoke or drink, and dietary habits were better. Following adjustment for a host of confounding factors, whole-grain consumption in the highest quintile was associated with a significant reduction in fasting insulin in comparison to those in the lowest quintile of intake. Even after further adjustment for BMI and dietary factors such as vegetable and fat intakes, this relationship remained significant, but was no longer significant after further adjustment for magnesium, and insoluble and soluble fibers. The association between whole grain and fasting insulin was most striking in those with a BMI >30kgm-2 with the highest fasting insulin levels being observed in those with the highest BMI and the lowest intake of whole-grain foods.

Prospective epidemiological studies are generally stronger than cross-sectional associations. In the CARDIA study by Pereira and coworkers, a significant inverse relationship was observed between whole-grain foods and fasting insulin levels among over 3500 black and white young Americans aged 18-30 years. A dietary history was collected at baseline and 7 years later, while insulin measurements were collected at 10 years follow-up. After adjustment for a number of dietary and lifestyle factors an inverse and graded response was observed between whole-grain intake at 7 years and the insulin measurements collected at 10 years follow-up, although the relationship was not significant in black women.

There is only one small intervention study that examines the impact of increasing wholegrain consumption. In this study, it was found that after 6 weeks there was a 10% reduction in fasting insulin compared to results observed following the refined grain diet (141 ± 3.9pmoll-1 versus 156 ± 3.9 pmol l-1; P < 0.01). This relationship remained even after adjustment for body weight changes (nonsignificant change of -0.7kg on whole-grain diet) and physical activity.

As for other diseases the mechanism of the effect of wholegrain on insulin sensitivity is not entirely clear and may in part be mediated through effects on body weight. Cereal fiber and possibly certain micronutrients such as magnesium may also be important since the wholegrain effect is attenuated after adjustment for these variables.

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Diabetes 2

Diabetes 2

Diabetes is a disease that affects the way your body uses food. Normally, your body converts sugars, starches and other foods into a form of sugar called glucose. Your body uses glucose for fuel. The cells receive the glucose through the bloodstream. They then use insulin a hormone made by the pancreas to absorb the glucose, convert it into energy, and either use it or store it for later use. Learn more...

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