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Watermelon has a high glycemic index, but a low glycemic load for the quantity typically consumed. A dictionary of food and nutrition 3rd ed. Jarvis , and Robert O. What did the study find? The glycemic index only indicates the impact on glucose level two hours after eating the food.
It claims to work by separating food into three groups: Hay's use of these terms does not completely conform to the scientific use, i. Acid foods are not combined with the alkaline ones. Acidic foods are protein rich, such as meat, fish, dairy, etc. Alkaline foods are carbohydrate rich, such as rice, grains and potatoes. It is also known as the food combining diet. A similar theory, called nutripathy, was developed by Gary A.
Martin in the s. Jarvis , and Robert O. In , Hay seems to have had an episode of acute heart failure following running for a train. Hay started looking for ways to improve his condition. He first turned to a vegetarian diet and restricted his eating to once a day in the evening. Then he gave up coffee and a few months later he quit smoking tobacco. His theories went on to encompass food-combining; stating that incorrect combinations of foods would cause even alkaline foods to leave a less desirable acidic digestion end-product.
Neither should these be combined with a protein of concentrated sort as these protein foods will excite too much hydrochloric acid during their stomach digestion. The Hay System promoted eating three meals per day with meal one being what the diet considers to be alkaline foods only, meal two composed of what the diet considers to be protein foods with salads, vegetables and fruit, and meal three composed of what the diet considers to be starchy foods with salads, vegetables and sweet fruit; with an interval of 4.
The Hay diet was popular in the s and many restaurants offered 'Hay-friendly' menus; followers of his dietary advice, included Henry Ford  and Man Ray.
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. Jenkins and colleagues  in — 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 can 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 can 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 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 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 by definition.
This has the advantages of being universal and producing maximum GI values of approximately 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, because there is no universal standard for the carbohydrate content of white bread. GI values can be interpreted intuitively as percentages on an absolute scale and are commonly interpreted as follows:.
A low-GI food will cause blood glucose levels to increase 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 level 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.
In general, coarse, grainy breads with higher amounts of fiber have a lower GI value than white breads. 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.
Carrots were originally and incorrectly reported as having a high GI. 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. Dietary replacement of saturated fats by carbohydrates with a low glycemic index may be beneficial for weight control , whereas substitution with refined, high glycemic index carbohydrates is not.
Several lines of recent  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.
Postprandial hyperglycemia is a risk factor associated with diabetes. A study 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.
A study from the University of Sydney in Australia suggests that having a breakfast of white bread and sugar-rich cereals, over time, can make a person susceptible to diabetes, heart disease, and even cancer. 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 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 can also provide greater benefits to overweight and obese women. 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.
Depending on quantities, the number of grams of carbohydrate in a food can have a bigger impact on blood sugar levels than the glycemic index does. Consuming less dietary energy, losing weight, and carbohydrate counting can be better for lowering the blood sugar level. Consuming carbohydrates with a low glycemic index and calculating carbohydrate intake would produce the most stable blood sugar levels.
While the glycemic index of foods is used as a guide to the rise in blood glucose that should follow meals containing those foods, actual increases in blood glucose show considerable variability from person to person, even after consumption of identical meals. 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.