Adaptive effects of dietary carbohydrate quality and quantity on insulin and glucose levels. A randomised controlled trial of people with obesity (CARBFUNC)
Year: 2018
Type: dissertation
Abstract: Background: The obesity epidemic continues to rise despite efforts made to reverse the\nincreasing prevalence. The burden of disease associated with obesity poses large threats to\nthe public health, as well as it represents a major socioeconomic burden. Dietary\nmodifications remain key to successful weight loss, and thus a reduction in the burden of\ndisease. The primary dietary strategy to prevent obesity and development of metabolic\nabnormalities, such as glucose intolerance and type 2 diabetes, has been to reduce energy\nintake by cutting dietary fat. However, the consumption of processed carbohydrate-rich foods\nhas increased during the recent decades, coinciding with the increasing prevalence of obesity\nand metabolic diseases. It has been hypothesised that postprandial insulin surges and\nperpetual hyperinsulinemia confer a metabolic disadvantage of refined carbohydrate-dense\nfoods via the fat storing effects of insulin (the Carbohydrate-Insulin-Model of obesity).\nHowever, we lack controlled prospective studies that assess whether the quality as well as\nquantity of dietary carbohydrates alters insulin and glucose levels in an adaptive manner, and\nhow this may relate to reduction of adiposity.\nObjective: To determine whether quality and quantity of dietary carbohydrates, given equal\nintake of energy and protein in normocaloric diets, cause differential hormonal and metabolic\nadaptations with respect to insulin levels and glucose metabolism in people with obesity, and\nfurther how the dietary effects on insulin and glucose levels relate to changes in adiposity.\nMethods: We developed a novel index of carbohydrate quality based on the degree of\ndisruption of the cellular structures. “Acellular” carbohydrates were presumed to promote\nhigher insulin release throughout the intervention period compared to diets with cellular or\nlow carbohydrate content. 52 healthy women and men with obesity (body mass index >30\nkg/m2 and/or waist circumference >88/102 cm for women and men, respectively), a subgroup\nof the randomised controlled CARBFUNC study, were included in the current thesis.\nParticipants were randomly allocated to one of three normocaloric diets differing in quality\nand quantity of dietary carbohydrates; 1) a moderate-carbohydrate diet based on acellular\n(refined) carbohydrates (45 energy percent (E%) carbohydrate, 38 E% fat), 2) a moderatecarbohydrate diet based on cellular (minimally refined) carbohydrates (45 E% carbohydrate,\n38 E% fat), and 3) a low-carbohydrate high-fat diet (LCHF, 8 E% carbohydrates, 75 E% fat). \nV\nAnthropometric measures and blood samples were obtained at baseline and after 3 months.\nThe participants consumed a mixed meal test (56 g carbohydrate, 47 g fat, 9 g protein) at the\nstudy visits for measurement of postprandial insulin and glucose responses. Dietary intake\nwas recorded repeatedly throughout the intervention period. Study outcomes were analysed\nby linear mixed-effects models. Spearman´s rank-order correlation analysis was used to\ndetermine associations between variables. All tests were two-tailed with a nominal alpha level\nof 0.05.\nResults: 52 randomised participants were included in the final analyses (acellular\ncarbohydrate (AC) diet n = 15, cellular carbohydrate (CC) diet n = 18, LCHF diet n = 19). The AC\ndiet achieved significant reductions in fasting levels of insulin (P = 0.026), fasting levels of\nglucose (P = 0.006) and insulin resistance (measured as HOMA2-IR, P = 0.017). However, these\nchanges did not remain significant when adjusting for changes in adiposity during the\nintervention period. The CC diet did not achieve any significant changes in the glycaemic\noutcomes after three months, whereas the LCHF diet significantly increased the postprandial\nglycaemic response, measured as area under the curve for 4-hour postprandial glucose\nresponse (4-hour AUCGLUCOSE) after a mixed-meal (P < 0.001). There were no statistically\nsignificant group-differences in reduction of body weight after three months (4.3%, 4.7% and\n6.3% on the AC, CC and LCFH diets, respectively). Statistically significant differences were\nobserved between the AC diet and the LCHF diet after 3 months, where the AC diet achieved\nsignificantly greater reductions in fasting levels of glucose (P = 0.03) and 4-hour AUCGLUCOSE (P\n= 0.028) compared to the LCHF diet. However, these differences did not remain significant\nwhen adjusting for changes in adiposity. There were no statistically significant differences\nbetween the AC diet and the CC diet in any of the glycaemic outcome measures after three\nmonths. Finally, insulin secretion at baseline, measured as 30-minute postprandial insulin\nconcentration, was not found to predict the effects of quality or quantity of dietary\ncarbohydrate on weight loss in healthy subjects with obesity after 3 months.\nConclusion: In the present subset of the CARBFUNC study, there were no statistically\ndifferences in fasting or postprandial insulin levels on the acellular, cellular or lowcarbohydrate high-fat diets, suggesting that insulin levels did not adapt according to the diets´\ncarbohydrate quality or quantity. The acellular carbohydrate diet achieved significantly \nVI\ngreater reductions in fasting and postprandial levels of glucose compared to the lowcarbohydrate high-fat diet, despite not differentially affecting measures of adiposity.\nHowever, these differences did not remain significant when controlling for changes in\nadiposity. The data suggest that a diet based on acellular carbohydrate sources may enhance\nglucose metabolism to a greater degree than cellular carbohydrate- and low-carbohydrate\nhigh-fat diets in healthy subjects with obesity after three months, although reductions in\nadiposity may partly explain some of the changes seen in insulin resistance and glucose\nmetabolism.
Author: Revheim, Ingrid
Language: English
Subfield: Endocrinology, Diabetes and Metabolism
Field: Medicine
Domain: Health Sciences
Open Access status: green
OpenAlex ID: W2906204744