Solutions Manual For Power Generation Operation Control 2e By Allen J. Wood.rar
Lutero Chaloux
The role of lipids and lipoproteins as risk factors for cardiovascular disease (CVD) is well established. Although CVD remains as the leading cause of mortality in adults, there is a decreasing trend in overall CVD mortality rate over the last two to three decades. This reduction in CVD mortality is largely driven by decreases in coronary heart disease mortality rate. Lifestyle changes remain the cornerstone of management of lipid and lipoprotein disorders and obesity, and are warranted in primary as well as secondary prevention settings. Lifestyle changes recommended for those with high cholesterol levels include adopting a diet low in saturated and trans fatty acids, incorporating functional foods rich in bioactive substances such as fiber, antioxidants, plant sterols and stanols, exercising regularly, and maintaining a healthy weight. Based on a large body of evidence, current dietary guidelines uniformly recommend reducing intakes of saturated and trans fatty acids with replacement by increasing intake of mono- and polyunsaturated fatty acids. Precision medicine options such as personal preferences regarding food choices and long-term dietary strategies are needed to improve the overall lipid profile. Given the complexity of the individual lifestyle choices, it is not surprising that a substantial heterogeneity regarding outcomes has been observed across studies, underscoring the challenge of accurately assessing effects of lifestyle changes, including diet- or physical activity-based interventions, on the lipid profile and cardiovascular risk. Many factors likely contribute to the variability in observations, including presence of substantial heterogeneity in study settings and designs, publication biases, issues related to self-reported measures of dietary intakes as well as adherence measurements to study diet. Further, there are a limited number of studies focused on certain types of diet or dietary composition including functional foods or exercise modality. Thus, while existing data offers some insights into fruitful interventions, there is a need to undertake well-designed, controlled, adequately powered, large-scale studies to bring more insights into the role of individual components of lifestyle changes in modifying cardiovascular risk factors and mortality. For complete coverage of all areas of Endocrinology, please visit our on-line FREE web-text, WWW.ENDOTEXT.ORG.
Solutions Manual For Power Generation Operation Control 2e By Allen J. Wood.rar
Over the years, numerous epidemiological observational and interventional nutritional studies have been conducted, and many meta-analyses and comprehensive reviews have evaluated the overall effects of dietary fats and interventions to reduce saturated fat intake on blood lipid profile as well as risk for CHD. On the basis of these study findings dietary guidelines have universally recommended reducing the intake of saturated fat to lower low-density lipoprotein cholesterol (LDL-C) levels and reduce CHD risk. These recommendations have been central to promote public awareness on healthy eating to improve overall cardiovascular health at a population as well as at an individual level. However, over the years, there have been shift in recommendations with regard to what macronutrients should be used to replace energy lost from lowering of saturated fat. Early Dietary Guidelines for Americans recommended to decrease total and saturated fat intake and to increase accordingly dietary carbohydrates intake, leading to a low or lower fat diet. The current dietary recommendations, however, are to reduce saturated fat intake and increase intakes of dietary MUFA and PUFA, resulting in a moderate fat diet. Other notable shifts include an emphasis on added sugar intake and/or a lessened concern about dietary cholesterol intake.
For adults who would benefit from lowering of LDL-C, the recent 2013 American Heart Association (AHA)/American College of Cardiology Guideline on Lifestyle Management to Reduce Cardiovascular Risk (19) recommends reducing saturated fat intake to 5 to 6% of total calories and reducing the percentage of calories from trans fats; and for healthy Americans (>2 years of age), the 2006 AHA Nutrition Committee Scientific Statement advises eating 25 to 35% of daily calories as fats from foods like fish, nuts, and vegetable oils, limiting the amount of saturated fats to 7% of daily calories, limiting the amount of trans fats to
The latest 2015 to 2020 edition of Dietary Guidelines for Americans emphasizes healthy eating patterns and no longer recommends limiting consumption of dietary cholesterol (28) as in previous editions. This shift, however, does not advocate for a lesser importance of dietary cholesterol in building healthy eating patterns and individuals should consume as little dietary cholesterol as possible. Another noteworthy update is on sugar consumption with a specific limit of
Research over the last a few decades, however, has produced significant amount of data supporting a minimal or no effect of dietary cholesterol on blood cholesterol level or CHD risk. The 2013 AHA/ACC Guideline on Lifestyle Management to Reduce Cardiovascular Risk concluded that there is insufficient evidence to determine whether lowering dietary cholesterol reduces LDL-C levels (19). The recent 2015 to 2020 edition of Dietary Guidelines for Americans contains no recommendation for dietary cholesterol intake (28).
The strategy of reducing dietary saturated fat intake raises a critical question about what kinds of nutrients should be used to replace saturated fat, and several major macronutrients, such as carbohydrates and cis-unsaturated fatty acids, including PUFA and MUFA, have been tested in many investigations. It is now increasingly appreciated that the effects on lipid profile and CVD risk of replacing SFA is highly dependent on whether it is being replaced with PUFA, MUFA, or carbohydrates (complex whole grain-rich vs. simple sugar-rich).
Replacement of energy from saturated fat with PUFA has been shown to decrease TC and LDL-C, with a concomitant decrease in HDL-C (83). Meta-analyses of short-term controlled dietary trials have shown a favorable influence of PUFA on the ratio of atherogenic vs. atheroprotective lipoproteins. The HDL-C/LDL-C ratio was increased due to a larger decrease in LDL-C than HDL-C (84), and the TC/HDL-C ratio was decreased (38). Interestingly, it has been noted that the availability and/or content of PUFA may modulate the effects of saturated fat on plasma lipids and lipoproteins, such that saturated fat may only increase LDL-C if the PUFA intake, specifically linoleic acid, falls below a threshold level of approximately 5% of energy (85,86). Thus, TC, LDL-C and apoB levels were not different between women who consumed diets high and low in saturated fat, but with similar ratios of polyunsaturated to saturated fat (87). Among Japanese subjects, the ratio of polyunsaturated to saturated fat was inversely associated with TC and LDL-C, but not with HDL-C, TG, and hemoglobin A1c (HbA1c) (88). A reduced LDL-C synthesis rate (89,90) and/or increased clearance rate (91) may underlie observed reductions in LDL-C when PUFA is substituted for saturated fat. In addition, in nonhuman primates, replacement of dietary saturated fat with PUFA (92) but not with MUFA (93) was shown to reduce coronary artery atherosclerosis. It was projected that the replacement of saturated fat with PUFA, through its favorable effects on TC, LDL-C, and TC/HDL-C ratio, can provide about 10% decrease in coronary risk for each 5% energy substitution (37,94). However, it could be postulated that the actual effects on overall CHD risk may be greater, considering that PUFA reduces inflammation and improves insulin resistance (95). Furthermore, the amount of cholesterol consumed in the diet modulates the effects of saturated fat, as the increase in LDL-C at lower intakes of cholesterol was minimal compared to the substantial increase of LDL-C at higher intakes of cholesterol (73).
In a meta-analysis of short-term controlled dietary trials, replacement of saturated fat with MUFA was associated with decreases in TC and LDL-C (84). Although these effects may be of a lesser magnitude than those associated with PUFA, they were of a similar magnitude to those associated with carbohydrates (84,101,102). Comparing the effects of replacement of 7% energy from saturated fat in the average American diet (AAD, 36% energy from fat) with either MUFA or carbohydrates (primarily complex), Berglund at el., showed that both diets were able to reduce TC, LDL-C, HDL-C, ApoB, and ApoA-1 concentrations (103). In this 7-wk randomized, double-blind, cross-over study among subjects with metabolic risk factors, both regimens reduced LDL-C equivalent to 6 to 7%, consistent with previous observations (104,105). Triglycerides were significantly elevated with the carbohydrate diet, but tended to be lower with the MUFA diet. Reductions in HDL-C or ApoA-1 were of a lesser magnitude with the MUFA diet vs. the carbohydrate diet. In addition, plasma lipoprotein(a), Lp(a), concentrations were elevated with both diets, with a slightly larger increase observed for the carbohydrate diet (103). Studying exclusively the effects of dietary interventions on Lp(a) concentration, a recent randomized feeding study reported that diets rich in unsaturated fat (MUFA 21% and PUFA 10% of energy) increased Lp(a) levels less than diets rich in carbohydrate or protein, with greater changes in African-Americans than Caucasians (106). Overall, these findings suggest that replacement of saturated fat with MUFA is a preferable regimen when compared to strategies using carbohydrate (or protein) as a replacement.
The findings related to replacement of energy from saturated fat with carbohydrates have been much more complex. Carbohydrate foods differ substantially in their quantitative and qualitative features with regard to micronutrients, phytochemicals, fibers, and other bioactive substances, which could in turn have differential effects on plasma lipids and CHD risk.
b1e95dc632