Up and Down the Ranks

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" HSI - Jenny Thompson " <hsiresearch

HSI e-Alert - Up and Down the Ranks

Wed, 08 Mar 2006 06:50:00 -0500

 

 

 

 

HSI e-Alert - Up and Down the Ranks

 

Health Sciences Institute e-Alert

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March 08, 2006

 

Dear Reader,

 

Elizabeth Mayer-Davis says the glycemic index is bunk.

 

As you may recall from previous e-Alerts, the glycemic index (GI) is a

scale that categorizes food items according to their effect on blood

sugar levels. Low GI foods (such as meat and most fruits and

vegetables) prompt a slow increase in blood sugar levels, while high

GI foods (such as foods with added sugar, processed baked goods and

starchy foods) produce a quick spike in blood sugar levels.

 

A steady intake of foods that rate high on the GI promotes a gradual

insensitivity to insulin - the precursor of type 2 diabetes. But some

nutritionists don't agree that the GI is a useful indicator. Enter Ms.

Mayer-Davis who recently led a study that found the GI to be an

ineffective measure. According to an Associated Press article about

the study, Mayer-Davis " says the use of the index should be ended

altogether. "

 

When you make a claim as bold as that, you'd better have bold data to

back it up.

 

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Sugar measured

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Ms. Mayer-Davis and her team studied the diets and blood sugar levels

for more than 1,250 adult subjects. The study lasted five years. Taken

at face value, those two details promise the possibility of an

exhaustive study. But in the end, it wasn't exhaustive at all.

 

As reported in the February 2006 issue of the British Journal of

Nutrition, the researchers asked subjects to fill out only two food

frequency questionnaires: at the beginning of the study and again at

the end. Blood sugar levels were also tested only at the beginning and

end. Along the way, more than 440 subjects dropped out of the study.

 

When the dietary information was analyzed for glycemic index rankings

and compared to the results of the blood sugar tests, researchers

found no association between glycemic index levels and blood sugar levels.

 

And that's it. Based on that, Ms. Mayer-Davis would advise us to

ignore the " flawed " (as she puts it) glycemic index.

 

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Pieces in a larger puzzle

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Let's take a quick look at another glycemic index study I told you

about last year. This one comes from the Children's Hospital in Boston.

 

Twenty-three obese subjects were divided into two groups. One group of

12 subjects followed a conventional low-fat, reduced calorie diet. The

other group of 11 subjects followed a low-GI diet, avoiding starchy

foods and consuming protein along with any carbohydrates they ate. In

addition, subjects in the low-GI group were unrestricted in their

calorie intake. Subjects in both groups were also urged to exercise

regularly.

 

One year later, the low-fat subjects had lost a little more than six

percent of their body weight on average, while low-GI diet subjects

lost an average of nearly eight percent of their body weight. That

difference may seem minor in whole numbers, but it's a change of 33

percent.

 

More importantly, markers for heart disease were significantly

improved by the low-GI diet. Low-fat dieters reduced their

triglyceride levels by less than 20 percent on average. Subjects on

the low-GI diet, however, reduced triglycerides by nearly 40 percent.

And concentrations of plasminogen activator inhibitor 1 (a coagulation

factor that increases blood clot risk) increased by more than 33

percent among the low-fat dieters, but DECREASED nearly 40 percent in

the GI-diet group.

 

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Which way is up?

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Neither the Children's Hospital study nor the Mayer-Davis study

provides the last word on the usefulness of the glycemic index. Both

have strengths and weaknesses, and both lay the ground word for future

research.

 

In other words, to isolate the Mayer-Davis study and insist that it

represents a final verdict is way off the mark.

 

In a press release posted by the University of South Carolina

(Mayer-Davis is a researcher in the university's Arnold School for

Public Health) Ms. Mayer-Davis states: " Several recent studies show

that dietary fiber is important to heart disease, diabetes and

obesity. Typically, foods high in fiber have a relatively low Glycemic

Index. "

 

The press release adds: " This means that, in some studies, the

Glycemic Index may have been related to good health because of dietary

fiber, not because of a unique characteristic of food called the

Glycemic Index, Mayer-Davis says. "

 

Is it just me, or does that sound like a pretty good argument in

SUPPORT of the glycemic index?

 

If you'd like to see what all the fuss is about, go to

glycemicindex.com, where you can access a large database that lists

foods and their GI rankings.

 

***************

 

Are you getting five-a-day?

 

In 1992 the National Cancer Institute started the campaign to

encourage everyone to eat five servings of fruits or vegetables each

day to promote good health.

 

So...have you succeeded in getting five-s-day? If so...do you think

you could step it up to maybe seven or nine?

 

Researchers at the University of London recently reviewed eight

dietary studies and concluded that three to five portions of fruit and

vegetables daily may cut stroke risk by 11 percent, while more than

five cuts risk by 26 percent. They credit the preventive effect to an

increased intake of antioxidants, folate, potassium and fiber.

 

One of the researchers - Dr. Feng He - told Net Doctor that increased

intake of fruits and vegetables was also shown to reduce the risk of

some cancers and cardiovascular disease.

 

The average fruit and vegetable intake in developed countries is three

servings per day.

 

To Your Good Health,

 

Jenny Thompson

 

 

Sources:

 

" Towards Understanding of Glycaemic Index and Glycaemic Load in

Habitual Diet: Associations with Measures of Glycaemia in the Insulin

Resistance Atherosclerosis Study " British Journal of Nutrition, Vol.

95, No. 2, February 2006, ingentaconnect.com

" Study Casts Doubt on Glycemic Index " John C. Drake, Associated Press,

3/1/06, ap.org

" Study Questions Glycemic Index as Diet Tool " University of South

Carolina press release, 2/28/06, newswise.com

" More than Five-a-Day 'Cuts Stroke Risk' " Net Doctor, 1/27/06,

netdoctor.co.uk