Dietary Fats and Health: Dietary Recommendations in the Context of Scientific Evidence

Abstract

Although early studies showed that saturated fat diets with very low levels of PUFAs increase serum cholesterol, whereas other studies showed high serum cholesterol increased the risk of coronary artery disease (CAD), the evidence of dietary saturated fats increasing CAD or causing premature death was weak. Over the years, data revealed that dietary saturated fatty acids (SFAs) are not associated with CAD and other adverse health effects or at worst are weakly associated in some analyses when other contributing factors may be overlooked. Several recent analyses indicate that SFAs, particularly in dairy products and coconut oil, can improve health. The evidence of ω6 polyunsaturated fatty acids (PUFAs) promoting inflammation and augmenting many diseases continues to grow, whereas ω3 PUFAs seem to counter these adverse effects. The replacement of saturated fats in the diet with carbohydrates, especially sugars, has resulted in increased obesity and its associated health complications. Well-established mechanisms have been proposed for the adverse health effects of some alternative or replacement nutrients, such as simple carbohydrates and PUFAs. The focus on dietary manipulation of serum cholesterol may be moot in view of numerous other factors that increase the risk of heart disease. The adverse health effects that have been associated with saturated fats in the past are most likely due to factors other than SFAs, which are discussed here. This review calls for a rational reevaluation of existing dietary recommendations that focus on minimizing dietary SFAs, for which mechanisms for adverse health effects are lacking.

Dietary PUFA and cancer

“…With regard to dietary fat, the Western diet is characterised by an increased energy intake and decreased energy expenditure, increased SFA, n-6 fatty acid (FA) and trans FA with decreased intake of n-3 FA, vegetables and fruit (5,6) . Dietary components such as vegetables,…”

Setting the Lipid Component of the Diet: A Work in Process

“…Only vegetables, nuts, fruits, and whole grains have been associated with healthy body weight (67). In addition, a low-fat, high-carbohydrate diet causes an increase in serum TGs and small, dense LDL particles; this is an atherogenic lipid profile (66).…”

“…First, although decreased intake of SFAs lowers LDL cholesterol, it also lowers HDL cholesterol (65). A recent review by Lawrence (66) highlighted the necessity for a rational reevaluation of dietary recommendations that focus on minimizing dietary SFAs, for which the mechanisms of adverse health effects are lacking (65,66). Second, excess intake of carbohydrates, such as starches, refined grains, sugar-sweetened beverages, sweets, and fruit juice are associated with weight gain.…”

Hyperinsulinemia and Insulin Resistance: Scope of the Problem

“…72 Chronic, unresolved inflammation and oxidative stress are increasingly recognised as underlying factors in atherosclerosis and other forms of heart disease. 4,73 Insulin profoundly influences sodium and fluid dynamics, and therefore may play a role in idiopathic hypertension even in the absence of other signs of MetSy. Hyperinsulinemia, compounded with hyperglycaemic glycation of the fragile renal tubules, results in overall fluid retention, manifesting as oedema.…”

“…• excessively high refined carbohydrates in the diet, resulting in a glycaemic load that overwhelms human physiological regulatory mechanisms 79,80 • biologically inappropriate amounts of polyunsaturated fatty acids (specifically, omega-6 linoleic acid, coming primarily from isolated vegetable and seed oils, such as soy, corn and cottonseed) 73,81 • insufficient dietary omega-3 fatty acids, particularly when coupled with excessive intake of omega-6 fatty acids 82,83,84,85,86,87 • disrupted circadian rhythms and an extended photoperiod, which may have an adverse influence on internal biorhythms and the pulsatile secretion of hormones, including cortisol and human growth hormone 88,89,90,91 • reduced physical activity, affecting mitochondrial biogenesis, skeletal muscle glucose uptake and insulin sensitivity 92,93,94,95,96 • increased feeding opportunities -decreased time between meals, allowing less time for a return to baseline in hormones that regulate blood glucose, appetite and fuel partitioning, such as insulin, glucagon and leptin, and reduced time for autophagy and cellular repair. 97,98,99 This is but a small selection of the host of factors purported to contribute to the development of IR.…”