Sunday, September 18, 2016

Glycemic Index of foods- its relevance and reliability under a cloud

Diabetes is by now considered a debilitating disease which many viewing it as a silent killer. While educated people with some basic knowledge about the etiology of this affliction understand how the food we eat affects the blood glucose level and the adverse effect high glucose levels can have on different health parameters. It is sad to see millions of people suffering from diabetes, not very much aware of the consequences of eating high carbohydrate foods, that too based on highly refined ones, on the dynamics of glucose generation within the body and fall prey to serious ailments affecting eyes, heart, kidneys, limbs etc destroying the quality of their life. According to available reports there are more than 422 million people suffering from this disorder which is fast becoming a top killer among all the diseases. In India itself number of people afflicted by diabetes is placed around 62 million and if experts are to be believed, India may become the world capital of diabetes soon, if not checked effectively. Once diabetes is diagnosed appropriate diet and disciplined eating habits can provide substantial benefits along with correct drugs in right dosage. Inability of the body to assimilate sugar at a rate that will prevent undue build up in the blood, due to insulin insufficiency or insulin insensitivity has to be recognized and such build up can be "managed" only by a diet predominant in whole grains with particular emphasis on pulses, vegetables, meat, fish and nuts with low rate glucose release when consumed.

It is not that information is lacking regarding the type of foods that can be eaten moderately and the quantity that can be safe but often the logistical difficulties in adhering to a strict diet regimen besides often conflicting nature of such information, make it impractical to follow the guidelines of the physicians. Against such a situation the evolution of the concepts of Glycemic Index (GI) and glycemic load (GL) during early eighties provided a reasonably reliable guide to the ability of different foods consumed regularly to generate glucose in the body. Thus high GI, medium GI and low GI foods were developed or conceptualized that will safeguard against undue glucose spikes in the blood after consumption. But if recent reports by a group of scientists from the US are to be believed, GI is not as reliable as it was thought to be pushing millions of diabetics as well as the food industry developing products with low GI into a new era of uncertainty. What are the implications of the results of this study? 

Traditionally blood glucose levels, estimated after a 12 hour fasting  and 2 hours after ingesting a normal breakfast provided a reasonable clue as whether a person is diabetic or not. While a glucose level of 100 mg per 100 ml after fasting and 150 mg/100 ml 2 hours after breakfast are considered normal. Though there are slight variations in diabetic assessment technique essentially all of them highlight the ability of the body cells to assimilate free glucose from the blood for hundreds of biological functions. While high levels of blood glucose are supposed to cause hyperglycemic conditions considered dangerous, especially it it continues for long time, low levels of glucose cause hypoglycemic symptoms such as giddiness and over all weakness. Though these values are more or less accepted universally, monitoring blood glucose levels frequently, especially in the home environment is fraught with some logistical problems. Estimating glucose in a pathological laboratory may take at least a couple of hours but there are home gadgets based on mild pricking and drawing a tiny drop of blood on to a glucose oxidase enzyme strip that provides digital readings of glucose levels in a matter of a few seconds. Many people buy these gadgets for testing of glucose as and when they feel symptoms of hyper or hypo glycemia. A non-invasive system without the necessity of puncturing the skin is still in the realm of development and may take some time before becoming a common tool.

What is GI? Using a standard material like sugar for testing glucose transfer to blood from the food ingested is measured as a percentage of the time taken for the sugar to manifest in the blood, GI is expressed usually as a definitive number. Easily assimilable and fast appearance of glucose from the ingested sugar sources usually have high GI numbers while those foods which do not release glucose easily  have low GI values. Generally whole grains and pulses are slow glucose releasers and hence have low GI values. Most food products based on sugar and refined cereal flours have high GI values indicating that they cause glucose spikes in blood considered highly undesirable. Similarly processed foods containing high levels of retrograded starch and uncooked foods also have relatively lower GI values. Since a diabetic wants to avoid rapid rise in blood sugar levels, his choice is always foods with low GI numbers. Food industry also strives to evolve food products with less and less GI numbers to attract diabetes affected consumers and incidentally such tailor made foods also command higher prices.

It is almost a decade and a half since GI became a standard parameter for assessing suitability of different foods for consumption by diabetic affected people and no one has so far contested the relevance or reliability of GI to assess the glucose release and absorption by the blood. Of course from time to time there were informed criticism regarding the reliability of GI concept, in the absence of a better alternative, GI was still widely adopted by nutritionists and medical community as a practical tool. Though GI is widely used by physicians and dietitians for advising their clients regarding the best foods they must consume to control diabetes, periodic checking of fasting sugar and postprandial sugar levels still gives an idea about the extent of control of the food regimen by a diabetic patient.  Of course this traditional practice of glucose monitoring in the morning can at best give a picture about the glucose dynamics in the blood during pre-lunch period.  What about the situation in the post lunch period? Though many diabetics use home gadgets to monitor the blood glucose level as many times as they wish, it is not practical to do this often due to the physical discomfort involved in skin puncturing. The concept of glycosylated haemoglobin (HbA1c) measurement in the blood once in 2-3 months provides a reliable means of knowing about the history of food eating during that period. While a value of less than 6 is considered normal, any value beyond that can be an indicator of onset of diabetes. Values beyond 7 must be taken seriously to exercise better control of the diet by including more and more of low GI foods in their diet. 
One can realize how far the world has gone in adopting GI as a useful tool to manage diets. It is this edifice which is sought to be destroyed by the findings of a group of scientists in the US who claim that GI is not as dependable as it is thought to be, because of inconsistent values of GI noted for the same food in different people. While minor variations up to 5% can be ignored because of experimental error that may creep in in different laboratories, variations as big as 20% cannot be attributed to lab error. If their results are true the commonly consumed white bread can show GI values ranging from 47 to 77! This means white bread can be a low GI food for some, medium GI food for some body else and a high GI food for some others. How ludicrous it is? But if the results of the American scientists are validated, it is going to open a Pandora's Box with unimaginable consequences. Low GI foods have values 35-55, medium ones 57-67 and high GI category with GI 70-103. More shocking is that same food with a certain standard GI value gave widely different values in the same person when determined on different occasions according to these scientists! What can one make out of these observations and what impact it will have on various stakeholders of the diabetic disease?.

It is unfortunate that the new studies have come at a time when some consensus is emerging about the need for the food industry to include in the label information regarding the GI value of the contents within the packet. Will this be the pretext for the manufacturers to resist pressure from the consumer community to publish GI data on the label? That should not be allowed to happen at any cost unless more studies are organized to validate the new findings. Even if GI values show variations under different conditions, by and large they seem to remain same most of the time. Similarly it does not matter that GI response varies from person to person since most data applied to day is based on majority response. Till a new and better alternative energies, it may be fool hardy to ignore it for the time being. Diabetics are better advised to base their diet on low GI foods and best way to manage diabetes could be to adopt diets based on foods undergoing minimum processing.

The million dollar question is whether hundreds of scientist working on GI of foods have gone wrong some where? What can be the scientific explanation for this shocking anomaly? A larger question is if there are such wide metabolic and physiological variations amongst human beings, what relevance studies using humans as subjects can have in generalizing the results of such studies to be applicable to entire humanity? This question assumes more significance when human studies are undertaken while testing drugs for various ailments and diseases. It is urgent that the questions raised by the Tuft university scientists are further examined by a few independent groups under international collaboration to arrive at a consensus. If Gi tool is to be thrown out of the window what other alternatives we have to assess appropriateness and soundness of foods for consumption by diabetic population? No body disagrees with the universal consensus that fruits, vegetables, whole cereals, pulses and foods rich in retrograded starch must constitute the core part of any diet but to make them palatable appropriate products have to be evolved acceptable to the targeted consumers.  .     


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