The nutritional sciences are increasingly considering the quality of the overall diet, instead of assessing the effects of individual components, when estimating future disease risk. This is advantageous because it limits the possible interference from confounding variables. Further to this aim of assessing whole diets, the quality of the macronutrients included within the diet are important considerations. Various measures of the amino acid ratios in proteins are used to create a number of protein quality indices that are routinely used in dietary analysis. However, less emphasis has been placed on quantifying the quality of carbohydrate or fat. However, the glycaemic load is a useful tool in this respect for carbohydrate because high glycaemic load diets increase the risk for blood sugar disorders such as diabetes, insulin resistance, metabolic syndrome and obesity, whereas low glycaemic loads attenuate such risk. Generally, low glycaemic load diets contain predominately whole grain foods.
A low glycaemic load may be inversely associated with inflammation and oxidative stress, and the use of glycaemic load as a measure of carbohydrate quality may therefore be justified. Most of the research involving low glycaemic load diet have however been performed in diabetic subject, with weight loss as a confounding variable. There is therefore a need to clarify the benefits of high quality dietary carbohydrate characterised by a low glycaemic load on healthy individuals. To these ends, researcher1 have used a randomised, cross-over design study to administer a high or low glycaemic load diet to 80 participants with body mass indexes of between 18.5 and 24.9 kg/m2. The subjects consumed a high glycaemic diet (glycaemic load per day: 250) or a low glycaemic diet (glycaemic load per day: 125), in a random order for 28 days each. The authors used dual energy x-ray absorptiometry to measure fat mass.
Following adjustment by multivariate analysis for known confounding variables, the results showed that males and females with a body fat mass over 35 and 25 %, respectively, experienced a reduction in C-reactive protein with the low glycaemic load diet. This same group of individuals also experienced a trend for increased adiponectin, although the result was not quite statistically significant (p=0.06). However, for normal weight individuals, the glycaemic load of the diet did not significantly alter any of the measured biochemical markers of inflammation or oxidative stress. These results suggest that in overweight individuals, high quality carbohydrate, as defined by a low glycaemic load, is beneficial at lowering C-reactive protein, a marker of systemic inflammation. This may suggest that a high glycaemic load is a contributory factor in systemic inflammation and that including a higher quality dietary carbohydrate may benefit overweight individuals.
Adipose tissue functions as an endocrine organ and can secrete a number of hormones including adiponectin. Adiponectin, is a cytokine released from adipocytes and normal concentrations are around 3 to 30 µg/L. Levels fall with increasing obesity, but the exact relationship between adiponectin and fat mass is not fully understood. Low plasma levels of adiponectin are a risk factor for obesity and are associated with a number of invasive breast cancers. Adiponectin is known to improve insulin sensitivity and increase fatty acid oxidation, and is inversely associated with systemic inflammation, suggesting a role for adiponectin in preventing obesity. In this study, adiponectin levels increased in those subjects with the highest body mass indexes, after eating a low glycaemic index diet for 28 days. This might suggest that longer-term assessment of these subject may have resulted in beneficial changes to fat mass.
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