Tag Archives: Tufts University

Glycaemic Index

Definition:
The glycemic index or glycaemic index (GI) is a number associated with a particular type of food that indicates the food’s effect on a person’s blood glucose (also called blood sugar) level. The number typically ranges between 50 and 100, where 100 represents the standard, an equivalent amount of pure glucose.

The GI represents the total rise in a person’s blood sugar level following consumption of the food; it may or may not represent the rapidity of the rise in blood sugar. The steepness of the rise can be influenced by a number of other factors, such as the quantity of fat eaten with the food. The GI is useful for understanding how the body breaks down carbohydrates  and only takes into account the available carbohydrate (total carbohydrate minus fiber) in a food. Although the food may contain fats and other components that contribute to the total rise in blood sugar, these effects are not reflected in the GI.

The glycemic index is usually applied in the context of the quantity of the food and the amount of carbohydrate in the food that is actually consumed. A related measure, the glycemic load (GL), factors this in by multiplying the glycemic index of the food in question by the carbohydrate content of the actual serving. Watermelon has a high glycemic index, but a low glycemic load for the quantity typically consumed. Fructose, by contrast, has a low glycemic index, but can have a high glycemic load if a large quantity is consumed.

GI tables are available that list many types of foods and their GIs. Some tables also include the serving size and the glycemic load of the food per serving.

A practical limitation of the glycemic index is that it does not measure insulin production due to rises in blood sugar. As a result, two foods could have the same glycemic index, but produce different amounts of insulin. Likewise, two foods could have the same glycemic load, but cause different insulin responses. Furthermore, both the glycemic index and glycemic load measurements are defined by the carbohydrate content of food. For example when eating steak, which has no carbohydrate content but provides a high protein intake, up to 50% of that protein can be converted to glucose when there is little to no carbohydrate consumed with it.  But because it contains no carbohydrate itself, steak cannot have a glycemic index. For some food comparisons, the “insulin index” may be more useful.

CLICK & SEE
Glycemic index charts often give only one value per food, but variations are possible due to variety, ripeness (riper fruits contain more sugars increasing GI), cooking methods (the more cooked, or over cooked, a food the more its cellular structure is broken with a tendency for it to digest quickly and raise GI more), processing (e.g., flour has a higher GI than the whole grain from which it is ground as grinding breaks the grain’s protective layers) and the length of storage. Potatoes are a notable example, ranging from moderate to very high GI even within the same variety.

The glycemic response is different from one person to another, and also in the same person from day to day, depending on blood glucose levels, insulin resistance, and other factors.

Most of the values on the glycemic index do not show the impact on glucose levels after two hours. Some people with diabetes may have elevated levels after four hours.

Why  GI is so Important?
Over the past 15 years, low-GI diets have been associated with decreased risk of cardiovascular disease, type 2 diabetes, metabolic syndrome, stroke, depression, chronic kidney disease, formation of gall stones, neural tube defects, formation of uterine fibroids, and cancers of the breast, colon, prostate, and pancreas. Taking advantage of these potential health benefits can be as simple as sticking with whole, natural foods that are either low or very low in their GI value.

Determination of GI of a food:
Foods with carbohydrates that break down quickly during digestion and release glucose rapidly into the bloodstream tend to have a high GI; foods with carbohydrates that break down more slowly, releasing glucose more gradually into the bloodstream, tend to have a low GI. The concept was developed by Dr. David J. Jenkins and colleagues  in 1980–1981 at the University of Toronto in their research to find out which foods were best for people with diabetes. A lower glycemic index suggests slower rates of digestion and absorption of the foods’ carbohydrates and may also indicate greater extraction from the liver and periphery of the products of carbohydrate digestion. A lower glycemic response usually equates to a lower insulin demand but not always, and may improve long-term blood glucose control   and blood lipids. The insulin index is also useful for providing a direct measure of the insulin response to a food.

The glycemic index of a food is defined as the incremental area under the two-hour blood glucose response curve (AUC) following a 12-hour fast and ingestion of a food with a certain quantity of available carbohydrate (usually 50 g). The AUC of the test food is divided by the AUC of the standard (either glucose or white bread, giving two different definitions) and multiplied by 100. The average GI value is calculated from data collected in 10 human subjects. Both the standard and test food must contain an equal amount of available carbohydrate. The result gives a relative ranking for each tested food.

The current validated methods use glucose as the reference food, giving it a glycemic index value of 100 by definition. This has the advantages of being universal and producing maximum GI values of approximately 100. White bread can also be used as a reference food, giving a different set of GI values (if white bread = 100, then glucose ? 140). For people whose staple carbohydrate source is white bread, this has the advantage of conveying directly whether replacement of the dietary staple with a different food would result in faster or slower blood glucose response. A disadvantage with this system is that the reference food is not well-defined.

Classification:
GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:

Low GI…..(55 or less fructose;) …….Examples:beans (white, black, pink, kidney, lentil, soy, almond, peanut, walnut, chickpea); small seeds (sunflower, flax, pumpkin, poppy, sesame, hemp); most whole intact grains (durum/spelt/kamut wheat, millet, oat, rye, rice, barley); most vegetables, most sweet fruits (peaches, strawberries, mangos); tagatose; mushrooms; chilis.

Medium GI…..(56–69 Examples: white sugar or sucrose, not intact whole wheat or enriched wheat, pita bread, basmati rice, unpeeled boiled potato, grape juice, raisins, prunes, pumpernickel bread, cranberry juice,[10] regular ice cream, banana.

High GI….….(70 and above) Examples: glucose (dextrose, grape sugar), high fructose corn syrup, white bread (only wheat endosperm), most white rice (only rice endosperm), corn flakes, extruded breakfast cereals, maltose, maltodextrins, sweet potato , white potato , pretzels, bagels.

A low-GI food will release glucose more slowly and steadily, which leads to more suitable postprandial (after meal) blood glucose readings. A high-GI food causes a more rapid rise in blood glucose levels and is suitable for energy recovery after exercise or for a person experiencing hypoglycemia.

The glycemic effect of foods depends on a number of factors, such as the type of starch (amylose versus amylopectin), physical entrapment of the starch molecules within the food, fat and protein content of the food and organic acids or their salts in the meal — adding vinegar, for example, will lower the GI. The presence of fat or soluble dietary fiber can slow the gastric emptying rate, thus lowering the GI. In general, coarse, grainy breads with higher amounts of fiber have a lower GI value than white breads.  However, most breads made with 100% whole wheat or wholemeal flour have a GI not very different from endosperm only (white) bread.  Many brown breads are treated with enzymes to soften the crust, which makes the starch more accessible (high GI).

While adding fat or protein will lower the glycemic response to a meal, the relative differences remain. That is, with or without additions, there is still a higher blood glucose curve after a high-GI bread than after a low-GI bread such as pumpernickel.

Fruits and vegetables tend to have a low glycemic index. The glycemic index can be applied only to foods where the test relies on subjects consuming an amount of food containing 50 g of available carbohydrate.[citation needed] But many fruits and vegetables (not potatoes, sweet potatoes, corn) contain less than 50 g of available carbohydrate per typical serving. Carrots were originally and incorrectly reported as having a high GI.  Alcoholic beverages have been reported to have low GI values; however, beer was initially reported to have a moderate GI due to the presence of maltose. This has been refuted by brewing industry professionals, who say that all maltose sugar is consumed in the brewing process and that packaged beer has little to no maltose present. Recent studies have shown that the consumption of an alcoholic drink prior to a meal reduces the GI of the meal by approximately 15%.  Moderate alcohol consumption more than 12 hours prior to a test does not affect the GI.

Many modern diets rely on the glycemic index, including the South Beach Diet, Transitions by Market America and NutriSystem Nourish Diet. However, others have pointed out that foods generally considered to be unhealthy can have a low glycemic index, for instance, chocolate cake (GI 38), ice cream (37), or pure fructose (19), whereas foods like potatoes and rice have GIs around 100 but are commonly eaten in some countries with low rates of diabetes.

The GI Symbol Program is an independent worldwide GI certification program that helps consumers identify low-GI foods and drinks. The symbol is only on foods or beverages that have had their GI values tested according to standard and meet the GI Foundation’s certification criteria as a healthy choice within their food group, so they are also lower in kilojoules, fat and/or salt.

Weight control:
Recent animal research provides compelling evidence that high-GI carbohydrate is associated with increased risk of obesity. In one study,  male rats were split into high- and low-GI groups over 18 weeks while mean body weight was maintained. Rats fed the high-GI diet were 71% fatter and had 8% less lean body mass than the low-GI group. Postmeal glycemia and insulin levels were significantly higher, and plasma triglycerides were threefold greater in the high-GI-fed rats. Furthermore, pancreatic islet cells suffered “severely disorganized architecture and extensive fibrosis.” However, the GI of these diets was not experimentally determined. In a well controlled feeding study no improvement in weight loss was observed with a low glycemic index diet over calorie restriction.  Because high-amylose cornstarch (the major component of the assumed low-GI diet) contains large amounts of resistant starch, which is not digested and absorbed as glucose, the lower glycemic response and possibly the beneficial effects can be attributed to lower energy density and fermentation products of the resistant starch, rather than the GI.

In humans, a 2012 study shows that, after weight loss, the energy expenditure is higher on a low-glycemic index diet than on a low-fat diet (but lower than on the Atkins diet).

 Prevention of Diseases:
Several lines of recent [1999] scientific evidence have shown that individuals who followed a low-GI diet over many years were at a significantly lower risk for developing both type 2 diabetes, coronary heart disease, and age-related macular degeneration than others.  High blood glucose levels or repeated glycemic “spikes” following a meal may promote these diseases by increasing systemic glycative stress, other oxidative stress to the vasculature, and also by the direct increase in insulin levels.  The glycative stress sets up a vicious cycle of systemic protein glycation, compromised protein editing capacity involving the ubiquitin proteolytic pathway and autophagic pathways, leading to enhanced accumulation of glycated and other obsolete proteins.

In the past, postprandial hyperglycemia has been considered a risk factor associated mainly with diabetes. However, more recent evidence shows that it also presents an increased risk for atherosclerosis in the non-diabetic population   and that high GI diets,  high blood-sugar levels more generally,  and diabetes  are related to kidney disease as well.

Conversely, there are areas such as Peru and Asia where people eat high-glycemic index foods such as potatoes and high-GI rice without a high level of obesity or diabetes.  The high consumption of legumes in South America and fresh fruit and vegetables in Asia likely lowers the glycemic effect in these individuals. The mixing of high- and low-GI carbohydrates produces moderate GI values.

A study from the University of Sydney in Australia suggests that having a breakfast of white bread and sugar-rich cereals, over time, may make a person susceptible to diabetes, heart disease, and even cancer.

A study published in the American Journal of Clinical Nutrition found that age-related adult macular degeneration (AMD), which leads to blindness, is 42% higher among people with a high-GI diet, and concluded that eating a lower-GI diet would eliminate 20% of AMD cases.

The American Diabetes Association supports glycemic index but warns that the total amount of carbohydrate in the food is still the strongest and most important indicator, and that everyone should make their own custom method that works best for them.

The International Life Sciences Institute concluded in 2011 that because there are many different ways of lowering glycemic response, not all of which have the same effects on health, “It is becoming evident that modifying the glycemic response of the diet should not be seen as a stand-alone strategy but rather as an element of an overall balanced diet and lifestyle.”

A systematic review of few human trials examined the potential of low GI diet to improve pregnancy outcomes. Potential benefits were still seen despite no ground breaking findings in maternal glycemia or pregnancy outcomes. In this regard, more women under low GI diet achieved the target treatment goal for the postprandial glycemic level and reduced their need for insulin treatment. A low GI diet may also provide greater benefits to overweight and obese women. Interestingly, intervention at an early stage of pregnancy has shown a tendency to lower birth weight and birth centile in infants born to women with GDM.

Other factors:
The number of grams of carbohydrate can have a bigger impact than glycemic index on blood sugar levels, depending on quantities. Consuming fewer calories, losing weight, and carbohydrate counting can be better for lowering the blood sugar level. Carbohydrates impact glucose levels most profoundly,  and two foods with the same carbohydrate content are, in general, comparable in their effects on blood sugar.  A food with a low glycemic index may have a high carbohydrate content or vice versa; this can be accounted for with the glycemic load (GL). Consuming carbohydrates with a low glycemic index and calculating carbohydrate intake would produce the most stable blood sugar levels.

Criticism and alternatives:
The glycemic index does not take into account other factors besides glycemic response, such as insulin response, which is measured by the insulin index and can be more appropriate in representing the effects from some food contents other than carbohydrates. In particular, since it is based on the area under the curve of the glucose response over time from ingesting a subject food, the shape of the curve has no bearing on the corresponding GI value. The glucose response can rise to a high level and fall quickly, or rise less high but remain there for a longer time, and have the same area under the curve. For subjects with type 1 diabetes who do not have an insulin response, the rate of appearance of glucose after ingestion represents the absorption of the food itself. This glycemic response has been modeled, where the model parameters for the food enable prediction of the continuous effect of the food over time on glucose values, and not merely the ultimate effect that the GI represents.

Although the glycemic index provides some insights into the relative diabetic risk within specific food groups, it contains many counter-intuitive ratings. These include suggestions that bread generally has a higher glycemic ranking than sugar and that some potatoes are more glycemic than glucose. More significantly, studies such as that by Bazzano et al.  demonstrate a significant beneficial diabetic effect for fruit compared to a substantial detrimental impact for fruit juice despite these having similar “low GI” ratings.

From blood glucose curves presented by Brand-Miller et al.  the main distinguishing feature between average fruit and fruit juice blood glucose curves is the maximum slope of the leading edge of 4.38 mmol·L-1·h-1 for fruit and 6.71 mmol·L-1·h-1 for fruit juice. This raises the concept that the rate of increase in blood glucose may be a significant determinant particularly when comparing liquids to solids which release carbohydrates over time and therefore have an inherently greater area under the blood glucose curve.

If you were to restrict yourself to eating only low GI foods, your diet is likely to be unbalanced and may be high in fat and calories, leading to weight gain and increasing your risk of heart disease. It is important not to focus exclusively on GI and to think about the balance of your meals, which should be low in fat, salt and sugar and contain plenty of fruit and vegetables.

There are books that give a long list of GI values for many different foods. This kind of list does have its limitations. The GI value relates to the food eaten on its own and in practice we usually eat foods in combination as meals. Bread, for example is usually eaten with butter or margarine, and potatoes could be eaten with meat and vegetables.

An additional problem is that GI compares the glycaemic effect of an amount of food containing 50g of carbohydrate but in real life we eat different amounts of food containing different amounts of carbohydrate.

Note: The amount of carbohydrate you eat has a bigger effect on blood glucose levels than GI alone.

How to have lower GI?
*Choose basmati or easy cook rice, pasta or noodles.
*Switch baked or mashed potato for sweet potato or boiled new potatoes.
*Instead of white and wholemeal bread, choose granary, pumpernickel or rye bread.
*Swap frozen microwaveable French fries for pasta or noodles.
*Try porridge, natural muesli or wholegrain breakfast cereals.
*You can maximise the benefit of GI by switching to a low GI option food with each meal or snack

Resources:
http://en.wikipedia.org/wiki/Glycemic_index
https://www.diabetes.org.uk/Guide-to-diabetes/Managing-your-diabetes/Glycaemic-Index-GI/
http://www.whfoods.com/genpage.php?tname=faq&dbid=32

Advertisements

Green Tea May Help Reduce Risk of Certain Cancers

Researchers in Japan have said drinking green tea may be an important health resource to reduce the risk of developing certain types of cancer.

The study appearing in the American Journal of Epidemiology suggests drinking five or more cups of the antioxidant-rich beverage can reduce the risk of developing blood cancer by 42 percent. The same amount of green tea was also associated with a 48 percent lower risk of lymph system cancer, according to Reuters.

Researchers followed 19,749 men and 22,012 women with no previous history of cancer over a period of nine years for the study.

WebMD notes that previous research has linked the tea to fighting heart disease, lowering cholesterol and preventing diabetes and dementia.

“Taken altogether, the evidence certainly suggests that incorporating at least a few cups of green tea every day will positively affect your health. It’s not going to cure anything and it shouldn’t be consumed as a drug, but it can complement the rest of the diet,” Tufts University scientist Dr. Diane McKay tells WebMD.

Researchers involved with this study say further work is needed to confirm the health benefits of drinking green tea, and to determine whether daily consumption might prevent certain cancers.

Source:Better Health Research. Oct.20 ’09

Reblog this post [with Zemanta]

Tuna ‘Prevents Macular Degeneration’

Omega-3 fatty acids found in fatty fish such as tuna and salmon may help prevent age-related macular degeneration (AMD) progression,  depending upon the stage of the disease, suggest researchers.
C.LICK TO. SEE
AMD is a progressive disease that attacks central vision, resulting in a gradual loss of eyesight and, in some cases, blindness

During the study, the research team from Laboratory for Nutrition and Vision Research (LNVR) and Jean Mayer USDA Human Nutrition Research Center on Aging (HNRCA) at Tufts University calculated the intakes of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) among 2,924 patients aged 55 to 80 years.

The findings revealed that taking supplements of antioxidants plus zinc prevents progression of late-stage AMD.

“In our study, we observed participants with early stages of AMD in the placebo group benefited from higher intake of DHA, but it appears that the high-dose supplements of the antioxidants and/or the minerals somehow interfered with the benefits of DHA against early AMD progression,” said senior author Dr Allen Taylor, director of the LNVR at the USDA HNRCA.

The antioxidant supplements did not seem to interfere with the protective effects of DHA and EPA against progression to advanced stages of AMD.

The study also showed that participants who consumed higher amounts of DHA and EPA appeared to have lower risk of progression to both wet and dry forms of advanced AMD.

“Data from the present study also shows the supplements and omega-3 fatty acids collaborate with low-dietary glycemic index (dGI) diets against progression to advanced AMD,” said corresponding author Chung-Jung Chiu, DDS, PhD, a scientist in the LNVR and an assistant professor at TUSM.

“Our previous research suggests a low-GI diet may prevent AMD from progressing to the advanced stage,” Chiu added.

The researchers suggest that eating two to three servings of fatty fish such as salmon, tuna, mackerel, shellfish, and herring every week would achieve the recommended daily intake of DHA and EPA, however, further research is required to conclude dietary recommendations for people with AMD.

Source:The study appears in the British Journal of Ophthalmology.

Enhanced by Zemanta

Eating Fish ‘Prevents Eye Disease’

Want to keep your vision clear as the years go by? Put fatty fish on your menu, at least twice a week, says a new study.

….
Researchers have found that eating fish, like salmon and tuna at least twice a week can help prevent a devastating eye disease — the age-related muscular degeneration which is said to be the leading cause of blindness in the elderly
.

Over time the back part of the eye can degenerate, causing the disease, which can also be triggered by new blood vessels growing and bleeding in the region.

And, according to the study by Tufts University, the omega 3 fatty acids found in fish offers protection against the eye disease, the British media reported.

For their study, the researchers questioned 3,000 people about their general diet and then monitored development of the condition over eight years. Half of the volunteers were given some form of daily supplement, including antioxidants such as vitamins C
and E and beta-carotene.

The findings showed show that progression to both the dry and wet forms of advanced disease was 25 per cent less likely among those who ate a diet rich in omega 3 fatty acids.

And, those who took the antioxidants as well as zinc and beta-carotene were 50 per cent more likely to develop the advanced disease, according to the study published in the ‘British Journal of Ophthalmology’.

Source: The Times Of India

Reblog this post [with Zemanta]

Eat Indian Curry to Lose Weight

Eating lots of curry may help you lose weight, research suggests.

Click & see

Scientists believe that haldi, or turmeric, which is used in most Indian meals, has an active ingredient that can help fight obesity.

A meal that includes haldi will lead to less weight gain than one without the yellow powder.

This is because haldi contains a plant-based chemical called curcumin which suppresses the growth of fat tissue in mice and human cell cultures, according to a study by Tufts University in Boston, published in the Journal of Nutrition.

Curcumin is also easily absorbed by the body, the researchers said, after experiments on mice.

“Weight gain is the result of the growth and expansion of fat tissue, which cannot happen unless new blood vessels form, a process known as angiogenesis,” said senior study author Mohsen Meydani of the Jean Mayer U.S. Department of Agriculture Human Nutrition Research Center on Aging at Tufts.

“Based on our data, curcumin appears to suppress angiogenic activity in the fat tissue of mice fed high fat diets,” he said in a statement.

In particular, turmeric is effective when added to a high-fat meal, suggesting it could help fight obesity.

Researchers gave one set of mice high-fat diets and another set the same food with 500mg of curcumin added to each meal.

After 12 weeks, the mice which were fed curcumin weighed less than those which did not eat it.

The next step will be to perform clinical trials on humans, said the researchers.

Sources: The Times Of India

Enhanced by Zemanta