|
||||||
|
|
|
|
|||||||||||
|
|||||||||||||
| ||||||||||||||||||||||||||||||||||||
Recent evidence lends mounting support to the hypothesis that alow–glycemic-load diet may benefit patients with or at risk for diabetesand associated health conditions. But is existing evidence sufficient toinfluence nutritional-therapy guidelines?
EFFECT OF DIET ON DIABETES AND CARDIOVASCULAR DISEASE
When it comes to curbing obesity and preventing cardiovascular disease anddiabetes, a low–glycemic-load diet trumps a diet low in fat, suggestdata reported inJAMA.1
The glycemic index (GI) is a measure of the potential for a single food toraise the postprandial blood glucose level (DOC News, July 2004).Glycemic load (GL) is calculated by multiplying the GI of a food by itscarbohydrate content (in grams) and dividing by 100. A food with a lower GLwould be expected to raise blood glucose less than a food with a higherGL.
Researchers placed 39 overweight or obese adults on one of twoenergy-restricted diets, either low-GL or low-fat. Changes in resting energyexpenditure (REE), the rate at which energy is expended while at rest, wereused to measureoutcomes.1 Here'swhat investigators found.
The low-GL diet showed several advantages over the low-fat diet. Thefollowing markers for diabetes and cardiovascular disease, respectively,improved more for subjects on the low-GL diet than for those on the low-fatdiet: insulin resistance, serum triglycerides, C-reactive protein, and bloodpressure.
Plus, REE decreased less among the low-GL group than among those in thelow-fat group. This is noteworthy because, typically, REE decreases duringenergy-restricted diets, thereby slowing ongoing weight loss. Subjects in thelow-GL group achieved an approximate energy balance of –80 kcal/day.That's comparable to walking 1 mile/day or decreasing sugar-sweetenedsoft-drink consumption by 6 oz/day. The advantage wasn't enough to account forany significant, short-term change in body composition. Nor could researcherspredict if this change in REE would be maintained over the longterm.
GLYCEMIC INDEX (GI):
A ranking of carbohydrates based on their effect on blood glucose levelswithin 2 to 3 hours after a meal.
GLYCEMIC LOAD (GL):
Calculated by multiplying the GI by the amount of available carbohydratesin grams and dividing the total by 100.
RESTING ENERGY EXPENDITURE (REE):
The rate at which energy is expended while at rest.
But subjects in the low-GL group reported another potential weight-lossbenefit while on their diet: less hunger—a key component of dietadherence, says Allison B. Goldfine, MD, co-investigator of the study andresearcher at the Joslin Diabetes Center in Boston.
That the low-GL diet produced improvements in end points for diabetes andcardiovascular disease was perhaps the most notable finding. "What'sexciting is that there are measurable differences in insulin sensitivity,lipid, and inflammatory profiles between these two groups [low-GL andlow-fat]," Goldfine says.
RELATIONSHIP BETWEEN HIGH-GI DIET AND TYPE 2 DIABETES
The outcomes in another study, this one reported in Diabetes Care,suggest a correlation between type 2 diabetes risk and a high-GI diet.Investigators set out to examine an association between dietary fiber, GL, andGI and type 2 diabetes. The large-scale study drew data from 31,641 adultparticipants via a self-administered questionnaire. Results showed thatsubjects who consumed a diet rich in high-GI foods were at increased risk fortype 2 diabetes. White bread, which has a high GI, was the food found to bemost closely associated with development of type 2 diabetes. Researchersconcluded that a diet with a high carbohydrate content but a low GI mightcontribute to a reduced risk of type 2diabetes.2
CLINICAL APPLICATION
Should these and similar findings influence how we counsel patients onnutritional therapy? Not necessarily, say some critics. "The glycemicindex has a lot of problems," says Mary Austin, RD, CDE, president ofthe American Association of Diabetes Educators. For starters, while the GI maypredict the postprandial response of blood glucose to a single food, mostpeople typically consume in one meal a mixture of foods whose GIs vary.
Further, several factors can influence a food's effect on blood glucose.Some are intrinsic to the food: how it is prepared, degree of ripeness (infruits and vegetables), if and how it is processed, and so forth. Extrinsicvalues—such as a person's prior food intake, preprandial glucose level,and degree of insulin resistance—also play a role in how a foodultimately affects postprandial glucoselevels.3
SIGNIFICANCE OF MONITORING GLYCEMIC VALUES
While these studies provide some information about the role of glycemicvalues of foods, they also provoke further questions: For example, "Isit really the glycemic index or the magnesium?" Austin asks.
Austin doesn't entirely dismiss this recent research. "The glycemicindex is an interesting theory. [But] a lot more definitive studies need to bedone," she says.
While the U.S. medical community debates the glycemic theory, people inother parts of the world have embraced the concept.
Jennie Brand-Miller, PhD, professor of human nutrition at the University ofSydney, explains why, in Australia, research on the GI has translated intonutritional recommendations. "Our experience in Australia is that youneed the backing of a major credible organization like the ADA [AmericanDiabetes Association]. In Australia it was Diabetes Australia."
Currently, the ADA does not endorse a low-GL or low-GI diet to preventdiabetes, citing insufficient evidence. In its most recent statement on thetheory, the association noted the following: "Although some studies haveobserved an association between glycemic index or glycemic load and type 2diabetes, this relationship has been equivocal or absent inothers."3
So what can we do with the information we have thus far on dietary glycemicvalues? "We're all confused. What's very clear is that, currently,there's an epidemic in obesity," Goldfine remarks.
The medical community may not agree on the significance of monitoringglycemic values, but it does agree that obesity is the biggest risk factor forthe development of type 2 diabetes. It also recognizes the importance ofevaluating various methods that may help to curb these serious healthproblems. "There's an honest attempt to understand what should be thebest recommendations for nutritional therapy, what are the appropriateguidelines. I think this is something a lot of people are paying attentionto," Goldfine says. 
References
2. Hodge AM, O'Dea K, English DR, et al.: Glycemic index and dietaryfiber and the risk of type 2 diabetes. Diabetes Care 27: 2701–2706, 2004.
3. Sheard NF, Clark NG, Brand-Miller JC, et al.: Dietary carbohydrate(amount and type) in the prevention and management of diabetes: A statement bythe American Diabetes Association. Diabetes Care 27: 2266–2271, 2004.
CiteULike 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
| ||||||||||||||||||||||||||||||||||||
|
||||||
|
| DOC News | Diabetes | Diabetes Care | Clinical Diabetes | Diabetes Spectrum |
