Fat on its own does not stimulate insulin very much. Fat plus carbohydrate stimulates insulin more than carbohydrate alone. Fat plus protein stimulates insulin more than protein, but the effect is blunted by glucagon.I'm going to look at the effect of fat on insulin, I had no idea it had a stimulatory effect. I, like prohet, was under the assumption that it simply slowed down gastric emptying and reducing the GI og given carbs. Thanks!
The bad boy here is insuline... not glucose... the goal here is to keep insuline low (and glucose on normal range).
EFFECTS OF A COMBINATION OF MACRONUTRIENTS ON THE GI
People do not generally eat single foods, they eat meals or snacks made up of ≥2 macronutrients. Several studies have investigated the effects of combinations of macronutrients on the GI and have shown 2 things: 1) the higher the proportion of carbohydrate in a specific food, as opposed to protein and fat, the higher the GI; and 2) a mixed meal of carbohydrate, protein, and fat will have a different and variable glucose response depending on the proportions of each nutrient. Thus, the glucose responses of a food eaten alone or in combination with other foods differ (33–35). Proponents of the GI have denied this (13, 36), but I have provided some examples below.
Protein, fat, and carbohydrate
Protein-rich foods are known to increase insulin secretion without augmenting glucose concentrations (37–39). Thus, whereas the glucose response does not change much or actually decreases, the insulin response increases. Therefore, as more protein is taken in conjunction with carbohydrate, the insulin response will increase, whereas postprandial glucose will not change much. Similarly, adding fat to a carbohydrate meal also enhances insulin secretion even though the plasma glucose response actually decreases (12, 40, 41). Also, all 3 macronutrients stimulate the release of several gut peptides, but to different degrees. Protein and fat are particularly efficacious in stimulating gut peptide release despite a small glucose effect (42). Thus, the insulin response to a carbohydrate food varies with the amount of fat, protein, or both, with which it is ingested.
There are many foods that do not contain carbohydrates only, but are mixed with other macronutrients. Thus, there may be foods that have a lower GI but would not be recommended for other reasons. For example, chocolate and cashews have low GIs but contain large amounts of fat. Other foods may have high GIs but be nutritionally more attractive because they are less energy dense and more nutritionally rich with micronutrients. An example is carrots.
Fiber
The extent to which the fiber in a particular food is responsible for its GI is a subject of much debate. Wolever (43) studied this relation in 25 foods and found that total dietary fiber was related to the GI (r = 0.461, P < 0.05), although weakly. Breaking it down, he found no significant relation between soluble fiber and GI, but found the strongest relation between insoluble fiber and GI (r = 0.584, P < 0.001); he attributed the effect to the uronic acids in insoluble fiber. However, he could only explain 50% of the variability by fiber differences. In contrast with the above findings, other studies in which fiber was added to a carbohydrate meal suggested that only soluble fiber has an effect on postprandial glucose concentrations and not the insoluble component (44). However, does the presence of naturally occurring fiber in foods affect the glucose response? It seems to have very little relation (3, 45). Comparisons between brown and white rice, brown and white spaghetti, and whole-wheat and white bread showed small differences in the GI, although the fiber contents were quite different. Jenkins et al (3), in testing several foods, found no relation at all between the GI and the fiber content of the food. Holt et al (46) found no relation between the postprandial insulin response to and the fiber content of a food. In persons with type 2 diabetes, no effect of fiber on glucose concentrations was found (44, 47). Long-term studies have not been done in nondiabetic subjects.
Sugar
In the past, diabetic patients were prohibited from eating dietary sucrose because it was thought to raise blood glucose concentrations inordinately. We now know that the GI of sucrose (using white bread as a standard) is relatively low at 65. The GI of glucose is 97, whereas those of fructose and lactose are 23 and 46, respectively (15). One would expect that adding sugar to a meal would lower the GI; however, Jenkins et al (3) found no relation between the sugar content in foods and the GI in 62 commonly eaten foods, nor did Brand-Miller (13). These findings remain unexplained, but they certainly complicate the entire GI issue.
Pasta also produces different GIs depending on its type. The GIs of macaroni, star pastina, and spaghetti are 68, 54, and 45, respectively... Bread is at 100.
Acidity
An increase in the acidity of a meal can greatly lower its GI. Increasing the amount of vinegar in a meal, for instance, will affect the glucose response. The addition of sourdough bread to a meal can result in different GIs, depending on its content of organic acids (48). These foods apparently affect the glucose response, at least partially, by slowing gastric emptying. So, should we alert consumers to check how much vinegar they put on their food and how much acid is in their bread?
http://www.ajcn.org/.../76/1/290S.full
Edited by brunotto, 30 April 2012 - 03:20 PM.
