The Role of Lipids, Triglycerides, Phospholipids, and Cholesterol in the Diet
Lipid is a collective term for biomolecules that are commonly referred to as fats. They consist of different molecules that share the common feature of being insoluble in water. There are three main categories of lipids with nutritional value: triglycerides, phospholipids, and cholesterol (Lichtenstein et al., 2006). The main function of lipids is to provide energy to power metabolic reactions. It is estimated that 1 gram of fat liberates 9 kilocalories of energy. Lipids also supply the body with essential fatty acids and promote the intestinal uptake of fat-soluble vitamins such as vitamins A, D, E, and K. Lipids play a structural role in the cell membranes of all tissues. In addition, certain polyunsaturated fatty acids from the N3 and N6 categories serve as precursors in the biosynthesis of compounds that play regulatory roles in the body. Lipids also determine the structure of blood lipids.
Triglycerides are chemical compounds formed by the esterification of glycerol and three fatty acid molecules. The specific characteristics of the fatty acids making up the triglycerides determine the physical and chemical properties of triglycerides. Fatty acids are grouped based on the length of their chains (number of carbon atoms) as well as the availability, position, and number of double bonds. Consequently, three main groups of fatty acids: saturated fatty acids (without any double bond), monounsaturated (have one double bond), and polyunsaturated fatty acids (with two or more double bonds) (Bailey, 2012). The physical state and melting points of fats are determined by the presence or absence of unsaturated fatty acids. Fats, which contain saturated fatty acids in large quantities, exist as solids at temperatures of between 22 and 25oC while oils exist as liquids at these temperatures due to the predominance of unsaturated fatty acids. Fatty acids can also be grouped based on their biological importance. For example, polyunsaturated fatty acids such as linoleic and alpha-linolenic acids are considered essential fatty acids because they must be supplied in the diet. They are transformed into other polyunsaturated fatty acids that serve as precursors in the biosynthesis of a group of molecules known as eicosanoids. Examples of eicosanoids include prostacyclins, prostaglandins, leukotrienes, and thromboxanes (Bailey, 2012). They facilitate crucial biological actions such as the tightening of smooth muscle, clustering of platelets, and responses to foreign bodies in the body.
Phospholipids are compounds formed by the esterification of a glycerol molecule, fatty acids, and phosphoric acid. The fatty acids attach to the glycerol molecule at positions 1 and 2 while the phosphoric acid attaches at the third position and is also linked to low molecular weight amine bases. Phospholipids are crucial constituents of cell membranes and lipid-protein multiplexes that transport lipids.
Cholesterol is alcohol with an intricate and particular structure. Cholesterol is obtained from the ingestion of animal products. However, it is also synthesized by liver enzymes. An inverse relationship exists between the nutritional intake of cholesterol and its hepatic synthesis, which influences the quantities of cholesterol in the blood. Cholesterol serves structural roles in the cell membrane. It is also used in the biosynthesis of substances with the steroidal structure, for instance, adrenal hormones, bile acids, progesterone, estrogen, and androgens. It is also a precursor for vitamin D, which is a fat-soluble vitamin. The amounts of cholesterol in the blood are also influenced by the quantities of saturated and unsaturated fatty acids. For example, consuming large quantities of saturated fatty acids elevates blood cholesterol levels while ingesting monounsaturated and polyunsaturated fatty acids reduces blood cholesterol levels. Diet fiber lowers blood cholesterol levels as well as the absorption of bile acids and cholesterol by changing the bacterial flora.
Though fats should be included in the diet, health specialists endorse a diet with average total fats and low concentrations of saturated fat, trans fat, and cholesterol. It is also advisable to substitute saturated fats with monounsaturated and polyunsaturated fats, especially omega-3 fatty acids, which are abundant in foods such as fish.
Low-density lipoprotein is referred to as ‘bad’ cholesterol because its circulation in the blood causes it to accumulate in the internal walls of the arteries leading to the formation of a thick, hard deposit that constricts the arteries and diminishes their flexibility in a disorder that is called atherosclerosis (American Heart Association, 2016). Clots can also form broken plaques leading to the obstruction of arteries thus leading to heart attack or stroke. The amounts of LDL in the blood are grouped into five main categories: optimal, above optimal, borderline high, high, and very high. The corresponding concentrations for each category are <100 mg/dL, 100 to 129 mg/dL, 130 to 159 mg/dL, 160 to 189 mg/dL and ≥190 mg/dL.
HDL cholesterol is referred to as ‘good cholesterol.’ It moves through the bloodstream and gets rid of harmful cholesterol thus reducing the chances of heart disease. The amount of high-density lipoproteins (HDL cholesterol) is inversely linked with the chance of developing cardiovascular diseases. This relationship is attributed to a collection of occurrences jointly known as reverse cholesterol transport, which is the conveyance of cholesterol from outlying tissues to the liver for consequent metabolism or elimination. HDL protects against the occurrence of atherosclerosis. The exact quantities of HDL that should be present in the blood are not specified. However, levels below 50 mg/dL in women and less than 40 mg/dL in men are used to classify metabolic syndrome. Similarly, there are no triglyceride goals. However, levels greater than 150 mg/dL are indicators of metabolic disorders (Grundy et al., 2005).
Case Study 1
LDL, HDL, and Triglycerides
The HDL level in subject 1 is 30 mg/dL, which is less than the minimum recommended level of more than 40 mg/dL in men. The level of LDL cholesterol is 160 mg/dL, which is considered high. The concentration of triglycerides is 300 mg/dL, which is higher than the maximum recommended level of 150 mg/dL.
Their Impact on Overall Cardiovascular Health
The low levels of HDL and high levels of LDL and triglycerides predispose the subject to cardiovascular diseases (Fletcher et al., 2005).
Appropriate Levels
The required levels of HDL, LDL, and triglycerides for subject 1 should be more than 50 mg/dL, less than 100 mg/dl, and 150 mg/dL or less respectively.
The Risk of Heart Disease
The subject is at risk of heart disease due to the low levels of HDL, which are reported to protect against atherosclerosis and cardiovascular disease. However, his risk is not very high because he does not have existing health conditions.
Recommendations to Monitor Blood Lipids and Lower the Risks
Subject 1 can monitor his blood lipid levels by increasing his intake of foods with unsaturated fatty acids, for example, fish that is rich in omega 3 fatty acids. Increasing the concentrations of unsaturated fatty acids will boost his HDL levels and lead to a reduction in LDL levels. Though the subject is moderately active and his weight is within the normal range, he should increase his level of physical activity to burn more fats and reduce the concentrations of triglycerides.
Case Study 2
LDL, HDL, and Triglycerides
Subject 2’s HDL level is 40 mg/dL, which is lower than the minimum recommended level of 50 mg/dL in females (Lichtenstein et al., 2006). The LDL is 140 mg/dL, which is classified as borderline high. The triglyceride level is 250 mg/dL, which is higher than the maximum allowable limit of 150 mg/dL.
Their Impact on Overall Cardiovascular Health
The subject already has a history of elevated blood pressure, which is worsened by low HDL levels, high triglycerides, and elevated LDL cholesterol levels. Therefore, keeping up with the current lipid profile is likely to aggravate the subject’s cardiovascular health.
Appropriate Levels
The recommended levels of HDL are a minimum of 50 mg/dL, whereas the LDL and triglyceride levels should be 100 mg/dl or less and a maximum of 150 mg/dL respectively.
The Risk of Heart Disease
The subject’s body mass index is 29.2, which makes her overweight. Excessive body weight has adverse consequences on the risk factors of CVD risk factors by increasing LDL cholesterol levels, triglyceride levels, and blood pressure. It also reduces HDL cholesterol levels. An additional effect is an increase in blood glucose levels, which further predisposes the patient to type 2 diabetes. These values increase the risk of having coronary heart disease, heart breakdown, stroke, and cardiac arrhythmias.
Recommendations to Monitor Blood Lipids and Lower the Risks
The subject needs to stop living a sedentary lifestyle and engage in regular physical activity. She also needs to cut down on her intake of saturated fats and increase her consumption of unsaturated fatty acids to augment her HDL levels and reduce LDL levels. Her diet should cut down on salt, increase potassium, entail caloric insufficiency to stimulate weight loss, and follow the recommendations of the DASH (Dietary Approaches to Stop Hypertension) diet (Bluementhal et al., 2010).
Case Study 3
LDL, HDL, and Triglycerides
The LDL cholesterol is 240 mg/dL, which is very high. The HDL cholesterol is 25 mg/dL, which is less than the minimum required of 40 g/dl in men. Subject 1’s triglycerides level is 115 mg/dL, which is within the recommended range because the maximum triglyceride limit is 150 mg/dL.
Their Impact on Overall Cardiovascular Health
High LDL and triglycerides increase the risk of CVD.
Appropriate Levels
The subject should increase his LDL levels to less than 100 mg/dl and increase the HDL levels to a minimum of 40 mg/dL. The triglyceride levels are within the recommended levels. Therefore, the subject should strive to maintain the triglycerides within this range.
The Risk of Heart Disease
The subject has a body mass index of 34, which classifies him as obese. His weight is responsible for the high levels of LDL cholesterol and low HDL. Therefore, his risk for heart disease is very high. In addition, his age increases his risk of cardiovascular disease. It is reported that the risk of CVD increases with advancing age and is higher in people aged 50 and above (Lloyd-Jones et al., 2005). His sedentary lifestyle does not allow him to burn calories to reduce his fat levels.
Recommendations to Monitor Blood Lipids and Lower the Risks
The subject should reduce his intake of fats and improve his physical activity to bring down his body mass index to normal.
References
American Heart Association. (2016). Heart encyclopedia. Web.
Bailey, J. (Ed.). (2012). Prostaglandins, leukotrienes, and lipoxins: biochemistry, mechanism of action, and clinical applications. New York, USA: Springer Science & Business Media.
Blumenthal, J. A., Babyak, M. A., Hinderliter, A., Watkins, L. L., Craighead, L., Lin, P. H.,… Sherwood, A. (2010). Effects of the DASH diet alone and in combination with exercise and weight loss on blood pressure and cardiovascular biomarkers in men and women with high blood pressure: The ENCORE study. Archives of Internal Medicine, 170(2), 126-135.
Fletcher, B., Berra, K., Ades, P., Braun, L. T., Burke, L. E., Durstine, J. L.,… Hiatt, W. R. (2005). Managing abnormal blood lipids a collaborative approach: Cosponsored by the Councils on Cardiovascular Nursing; Arteriosclerosis, Thrombosis, and Vascular Biology; Basic Cardiovascular Sciences; Cardiovascular Disease in the Young; Clinical Cardiology; Epidemiology and Prevention; Nutrition, Physical Activity, and Metabolism; and Stroke; and the Preventive Cardiovascular Nurses Association. Circulation, 112(20), 3184-3209.
Grundy, S. M., Cleeman, J. I., Daniels, S. R., Donato, K. A., Eckel, R. H., Franklin, B. A.,… Spertus, J. A. (2005). Diagnosis and management of the metabolic syndrome an American Heart Association/National Heart, Lung, and Blood Institute scientific statement. Circulation, 112(17), 2735-2752.
Lichtenstein, A. H., Appel, L. J., Brands, M., Carnethon, M., Daniels, S., Franch, H. A.,… Karanja, N. (2006). Diet and lifestyle recommendations revision 2006 A scientific statement from the American Heart Association nutrition committee. Circulation, 114(1), 82-96.
Lloyd-Jones, D. M., Leip, E. P., Larson, M. G., d’Agostino, R. B., Beiser, A., Wilson, P. W.,… Levy, D. (2006). Prediction of lifetime risk for cardiovascular disease by risk factor burden at 50 years of age. Circulation, 113(6), 791-798.