Benefit of Low-Fat Over Low-Carbohydrate Diet on Endothelial Health in Obesity

Abstract

Abstract-Obesity is associated with impaired endothelial-dependent flow-mediated dilation, a precursor to hypertension and atherosclerosis. Although dieting generally improves cardiovascular risk factors, the direct effect of different dietary strategies on vascular endothelial function is not known. The purpose of this study was to test the hypothesis that a low-fat (LF) diet improves endothelial function compared with an isocaloric low-carbohydrate (LC) diet. Obese (nϭ20; body mass index: 29 to 39; mean systolic blood pressure: 107 to 125 mm Hg) and otherwise healthy volunteers were randomly assigned to either the American Heart Association modeled LF (30% fat calories) diet or an isocaloric LC Atkins' style diet (20 g of carbohydrates) for 6 weeks (4-week weight loss and 2-week maintenance phase). Brachial flow-mediated dilation and dilation to nitroglycerin were measured with ultrasound using automated edge detection technology (baseline, week 2, and week 6). Blood pressure, weight loss, and cholesterol profiles were measured throughout the study. Key Words: diet Ⅲ weight loss Ⅲ endothelium Ⅲ obesity Ⅲ blood pressure O besity is a risk factor for atherosclerosis, a major cause of morbidity and mortality throughout the world. In the United States, the incidence of obesity has risen dramatically in the past decade. Public awareness of the "obesity epidemic" has resulted in various dietary weight loss strategies, and it is estimated that 45% of American women and 30% of American men diet to lose weight. 1 However, the nutrientspecific effects of these diets on cardiovascular health are largely unknown.Mounting evidence suggests that the integrity of the vascular endothelium is critical in the prevention of atherosclerosis, likely through release of endothelial-derived factors such as NO, which confer antiproliferative, antiinflammatory, and antithrombotic properties, in addition to vasodilation. 2,3 Abnormal endothelial function marked by reduced dilation to an increase in flow (endotheliumdependent flow-mediated dilation [FMD]) is an early hallmark of cardiovascular disease and a strong prognostic factor for future cardiovascular events. 4 -9 Most risk factors for coronary artery disease are associated with reduced FMD. 10 Weight loss through conventional low-fat (LF) diets improve endothelial function 11,12 ; however, some currently popular diets emphasize low-carbohydrate (LC) intake supplemented by high dietary fat and protein. Initial reports show sustained weight loss while on LC diets without detrimental effects on serum lipid levels. 13,14 Further benefit may be derived from the reduction in arterial pressure from either LF or LC diets. However, it is unclear whether these cardiovascular benefits of weight loss on a LC diet are negated by the known detrimental effects on endothelial function of even a single high-fat meal. [15][16][17] Weight loss is similar on LC and LF diets, but effects on cardiovascular health, a major anticipated benefit of most weight-loss regimens, may diverge. Therefore, the pur...

Combined effects of resistance training and carbohydrate-restrictive or conventional diets on weight loss, blood variables and endothelium function

“…On the contrary, Seshadri et al 10 observed that reductions in high sensitivity C-reactive protein were directly associated with body mass loss. Results similar to the present study were reported by Phillips et al 5 and Keogh et al 7 , who found that significant body mass reductions were independent of modifications in high sensitivity C-reactive protein levels in subjects submitted to six to twelve weeks of a CRD or conventional diet without exercise.…”

“…Very few studies have examined the effects of CRD on FMD. Some of them have observed significant reductions after very short intervention periods 5,6 , while others observed no significant changes after short-or long-term adherence to a CRD 7,8 .…”

Endothelial Dysfunction in Diabetes: Pathogenesis, Significance, and Treatment

“…In type 2 diabetic patients, a reduction in insulin resistance and fat mass following prolonged aerobic exercise resulted in improvements in lipoprotein metabolism [84]. Dietary restriction, weight loss, and increased physical activity have been shown to improve conduit and resistance artery ED in overweight and obese non-diabetic subjects with and without CAD [85][86][87][88]. In obese, but otherwise healthy subjects, brachial artery FMD improved with a 6-week lowfat diet but was blunted with a low-carbohydrate diet despite similar degrees of weight loss, suggesting that greater vascular benefit is conferred by a low-fat diet [85].…”

“…Dietary restriction, weight loss, and increased physical activity have been shown to improve conduit and resistance artery ED in overweight and obese non-diabetic subjects with and without CAD [85][86][87][88]. In obese, but otherwise healthy subjects, brachial artery FMD improved with a 6-week lowfat diet but was blunted with a low-carbohydrate diet despite similar degrees of weight loss, suggesting that greater vascular benefit is conferred by a low-fat diet [85]. In obese non-diabetic subjects, improvement in brachial artery FMD following a 6-week low-fat weight loss diet, but not a high-fat weight loss diet, was associated with decreased visceral fat mass and an improved adipokine profile, specifically increased adiponectin and decreased leptin and resistin [89].…”

Macronutrients and type 1 diabetes (revision number 6)

“…Three randomised controlled trials were identified that presented evidence on diets differing in the proportion of carbohydrate in relation to flow mediated dilatation, all of which were included in a meta-analysis (Keogh et al, 2007;Keogh et al, 2008;Phillips et al, 2008). One trial was subsequently identified in the update search (Wycherley et al, 2010) et al, 2008) duplicated the results of the study by Howard et al, (2006); three trials (Wolever & Mehling, 2002;O'Brien et al, 2005;Noakes et al, 2006) did not provide sufficient information and one trial was excluded because the differences in carbohydrate intake were less than 5% energy between groups (Dale et al, 2009) (Cardio-metabolic review, incident hypertension and blood pressure chapter p 47-57).…”