Diet and Nutrition- Information regarding lipids and their importance in your diet
StructureLipids are a group of compounds that include triglycerides (fats and oils), phospholipids and sterols. Of the lipids contained in food, 95 percent are fats and oils. In the body, 99 percent of the stored lipids are triglycerides (TG). Structurally, TG are three fatty acids attached to a glycerol backbone.
These fatty acids may be saturated or unsaturated. Unsaturated fatty acids may be further classified according to their degree of unsaturation. If the fatty acid has one double bond in its carbon chain, it is called a mono-unsaturated fatty acid. If there is more than one point of unsaturation, it is classified as a polyunsaturated fatty acid (PUFA).
PUFAs provide important essential fatty acids, or fats that cannot be manufactured by the body but are essential for proper health and functioning. The saturated fatty acids in your diet have been implicated as a risk factor for heart disease by raising bad cholesterol levels (LDL), while unsaturated fats are associated with increases in good cholesterol (HDL) and decreased risk of heart disease.
Mono-unsaturated fatty acids (found in olive and canola oils) and PUFA such as Omega-3 fatty acids (found in cold-water fish like salmon) are considered to have favorable effects on blood-lipid profiles and may play a role in the treatment and prevention of heart disease, hypertension, arthritis and cancer.
Another prevalent fatty acid in today’s food supply is trans-fatty acids, the result of hydrogenation or the process of adding hydrogen to unsaturated fatty acids to make them harder at room temperature and increase food shelf life. Trans-fatty acids have been shown to increase LDL cholesterol and decrease HDL cholesterol, much like saturated fats.
Function
Lipids (i.e., fats) are the most concentrated source of energy in the diet. One gram of fat yields approximately nine calories when oxidized furnishing more than twice the calories per gram of carbohydrates or proteins. In addition to providing energy, fats act as carriers for the fat-soluble vitamins A, D, E and K. Vitamin D aids in the absorption of calcium, making it available to body tissues, particularly to the bones and teeth. Fats are also an important part of your diet for the conversion of carotene to vitamin A.
Fats are involved in the following:
Digestion, Absorption and Utilization
Digestion of dietary fat starts in the mouth, moves to the stomach and is completed in the small intestine. In the intestine, the fat interacts with bile to become emulsified, when pancreatic enzymes can break the triglycerides down into two fatty acids and a monoglyceride. Absorption of these constituents occurs through the intestinal wall into the blood. In the intestinal wall, they are reassembled into triglycerides that are then released into the lymph in the form of a lipoprotein, called the chylomicron. Chylomicrons from the lymph move to the blood. The triglyceride content of the chylomicron is removed by the action of the enzyme lipoprotein lipase (LPL) and the released fatty acids are taken up by the tissues. Throughout the day, triglycerides are constantly cycled in and out of tissues, including muscles, organs and adipose.
Recommendations
If your diet doesn’t leave you feeling satiated by the amount of calories necessary to allow fat loss or energy balance you will eventually overeat. Our goal is to keep your diet within the guidelines for health. If the goal is fat loss, a diet containing less than 30 percent, possibly closer to 20 percent, of calories from fat is a good place to start. Higher fat diets are not conducive to successful weight loss or maintenance and appear to increase the ease with which the body converts ingested calories to body fat.
Fat has a lower thermic effect than other macronutrients. The thermic effect of a food (TEF) is the rise in metabolic rate that occurs after the food is ingested. Typically, TEF amounts to 10 percent of ingested calories. As fat percentage in the diet increases, the amount of heat given off (TEF) decreases. Conversely, as carbohydrate percentage in the diet increases, so does the TEF. It is metabolically inexpensive to convert dietary fat to body-fat stores. Only three percent of the calories in fat are required to store it as fat. In contrast, it takes 23 percent of the calories in carbohydrates to convert it to body fat.
Fat and Satiety
Dietary fats stimulate the release of CCK, a hormone that signals satiety. Additionally, fats slow the digestion of foods (and thus the nutrient content in the bloodstream), assisting in blood-sugar stabilization. Reducing blood sugar fluctuations can contribute to satiety.
Insulin Resistance and Obesity
Proponents of high-protein/low-carbohydrate diets have profited from the erroneous assertion that carbohydrates are to blame for the increasing prevalence of metabolic syndrome (MS or Syndrome X) and therefore lead to weight gain. Metabolic syndrome is a cluster of symptoms characterized by obesity, insulin resistance, hypertension and dyslipidemia, leading to an increased risk of cardiovascular disease. Syndrome X is usually associated with obesity (especially abdominal), a high-fat diet and a lifestyle lacking fitness and exercise.
A common denominator associated with these factors is high levels of circulating free fatty acids (FFA). In the presence of high FFA concentrations, the body will favor their use as energy, decreasing glucose oxidation, glycogen synthesis, and inhibiting glucose transport. The result of this is hyperglycemia. When blood-sugar levels are chronically high, insulin will also be elevated, leading to the conversion of the excess blood sugar to other products such as sugar proteins and fatty acids.
These facts alone seem to bolster the idea that a high carbohydrate diet leads to health problems. The truth is that a healthy person would need to eat an extremely high percentage of simple carbohydrates (such as sucrose) and fat, maintain constant energy excess, or be overweight in order to have chronically elevated blood sugar. Although there is some evidence that there may be a genetic component that contributes to insulin resistance (IR), the condition itself will not allow for weight gain without a diet that takes in calories in excess of expenditure. In fact, obesity itself is a risk factor for development of IR, not the other way around.