6.5: Conditions Related to Deficient and Excessive Lipid Intake

Deficient Lipid Intake: Essential Fatty Acid Deficiency

An essential fatty acid (EFA) is a fatty acid that is necessary for human function but a substance we cannot produce in adequate amounts; therefore, it is required that we obtain some essential fatty acids in the diet. Linoleic acid and linolenic acid are the primary essential fatty acids in humans. They are necessary for maintaining cell membranes and keeping the skin intact. In addition, substances synthesized from essential fatty acids are important for the brain and retina. EFA deficiency, characterized by a dry scaly rash, can result in decreased growth in infants and children, poor wound healing, and increased risk of infection. EFA deficiency in humans is rare but can occur. Babies fed an inferior baby formula can develop EFA deficiency, as can a patient who receives long-term parental nutrition (nutrition given by IV) without appropriate additions of fatty acids in the nutrition formula. Diseases and conditions in which fat malabsorption occurs (cystic fibrosis and some gastric surgeries, for example) or conditions of high metabolic needs (patients with severe burns, for example) can also increase the risk of EFA deficiency.¹ In anorexia nervosa (a psychological disorder that results in severe weight loss), an increased risk of EFA deficiency may be linked to the associated malnutrition, extreme lack of fat intake, and altered fat metabolism.^2,3

Excessive Lipid Intake and Chronic Diseases

Cardiovascular (heart and blood vessel) disease, stroke, diabetes, and cancer are among the leading causes of death in the United States. These conditions are considered chronic diseases, defined as "conditions that last one year or more and require ongoing medical attention or limit activities of daily living or both." There are risk factors associated with these diseases. A health risk factor is defined as anything that can increase the chance of getting a disease or condition. It is critical to address dietary and lifestyle choices that will ultimately decrease risk factors for disease. According to the Centers for Disease Control and Prevention (CDC), the following are risk factors that we can control: being overweight, and obesity, diabetes, high blood cholesterol, poor diet, physical inactivity, high blood pressure, excess alcohol intake, and nicotine use.⁴ One or many of these risk factors may be present at the same time and often overlap in how they impact disease. A more detailed review of overweight and obesity risk factors common to multiple health conditions is available in Chapter 10. In this section, we will introduce how the amount of fat and the type of fat in a person's food pattern can impact health.

Excess Fat Intake and Cancer

Cancer is defined as "a disease in which some of the body’s cells grow uncontrollably and spread to other parts of the body."⁵ A review of evidence-based research on dietary fat and cancer resulted in several observations related to cancer development. The general theme was that lipids alter the microbiome, which can impact chronic inflammation. The microbiome consists of trillions of microorganisms (microbes or microbiota) that live in and on our bodies. Some microbiota are helpful, while others are potentially harmful and promote disease. Certain illness, eating patterns, and medication use can offset the balance within the microbiome, making us more susceptible to disease, including certain cancers, cardiovascular disease, intestinal diseases, kidney disease, and type 2 diabetes.⁶

Total Fat: Total fat alone was not associated with cancer risk unless the excess fat intake contributed to obesity. Obesity is associated with an increased risk of many chronic diseases, including cancer. Obesity is defined as a body mass index of 30 or higher.

Fatty Acids: Diets higher in saturated fatty acids may have a negative impact on cancer risk, whereas omega-3 rich diets may have beneficial effects against cancer. However, the research reports that even different chain lengths of saturated fatty acids can have differing effects. Given that foods contain variations in fatty acid content, it is difficult to identify any one particular fatty acid as a link to cancer. There is evidence that red meat and processed meats may increase colon, lung, prostate, and pancreatic cancer risk, but this link is due to factors other than saturated fat content. The Mediterranean diet, reviewed in section 2.6, was associated with a lower risk of cancer death, including cancers of the colon, breast, stomach, liver, head and neck, and prostate. The Mediterranean Diet emphasizes monounsaturated fatty acids from olive oil, as well as an abundance of vegetables, fruits, whole grains, legumes, nuts, and fish. The many components of this pattern of eating may jointly be responsible for the positive news regarding cancer rather than one single nutrient.

Excess Fat Intake and Diabetes

Diabetes, reviewed in a prior chapter, is a group of metabolic disorders characterized by increased blood glucose concentration. A high-fat diet has been associated with higher Hemoglobin A1C (three-month average blood glucose level) in children and adolescents with type 1 diabetes. In addition, it was reported that high-fat meals increased glucose levels to the point of needing to adjust insulin doses. Long-term increased risk of cardiovascular disease may also be associated with how a high-fat diet impacts the gut microbiome.⁷

Total Fat: In type 2 diabetes, a review of research concluded that a low-fat diet did not increase or decrease the risk of this condition. However, excess body weight is associated with type 2 diabetes risk, and the authors recommended a balance between Calorie intake and physical activity to maintain weight as a means of diabetes risk reduction.⁸

Fatty Acids: The type of fat has also been addressed. Study participants with diabetes who replaced saturated fatty acids with monounsaturated fatty acids and polyunsaturated fatty acids had positive benefits in cardiovascular disease risk and better long-term survival rates.⁹ Additional studies were more specific to foods rich in saturated fat, noting that higher intakes of all fatty acids from meat were "adversely associated with markers of insulin resistance and insulin secretion, whereas the fatty acids from dairy and plant sources were not."¹⁰

Excess Fat Intake and Non-Alcoholic Liver Disease

Non-alcoholic fatty liver disease (NAFLD), a chronic liver disease, is defined as the presence of fat accumulation in the liver without significant alcohol intake. NAFLD can progress to non-alcoholic steatohepatitis (NASH), liver cirrhosis, and liver cancer. It is strongly associated with obesity, especially central obesity (more fat around the midsection), type 2 diabetes, insulin resistance, hypertension, and metabolic syndrome.

Total fat: Weight loss is a primary treatment for NAFLD. A review of studies related to dietary interventions reported that both a low fat eating pattern and a low carbohydrate eating pattern could provide benefit if weight loss occurs and can be sustained.¹¹

Fatty acids: Both clinical investigation trials and observational studies support that the Mediterranean Diet, which emphasizes monounsaturated fatty acids, may prevent NAFLD through its impact on body weight, insulin sensitivity/resistance, and lipid metabolism. In a smaller observational study, an eating pattern characterized by high intakes of fruits, vegetables, nuts, olive oil, low-fat dairy, fish, and garlic was associated with lower risk of NAFLD, whereas a dietary pattern with high amounts of fast foods, soft drinks, processed meat, high-fat dairy, hydrogenated fats, mayonnaise, salty snacks, sugar-sweetened desserts, organ meats, and refined grains was linked to a greater risk of NAFLD.¹²

Excess Fat Intake and Female Reproduction

Although studies in humans are limited, a high-fat diet impairs female reproductive function, with or without obesity. However, the reproductive function was worse when obesity was in place. Reproductive function was defined as an alteration in "menstrual cycle length, changes in reproductive hormone levels, and embryo quality in assisted reproductive technology cycles."¹³

Excess Saturated Fatty Acids and Heart Disease

This section provides an overview of excess lipid intake related to heart disease. Detailed information is provided in Section 6.6 Cardiovascular Disease.

In proper amounts, cholesterol is a compound used by the body to sustain many important body functions. In excess, cholesterol is harmful if it accumulates in the structures of the body’s vast network of blood vessels. High blood LDL-cholesterol and low blood HDL-cholesterol have been stated as indicators of blood cholesterol risk, but we are learning more about LDL-cholesterol size, with not all types of LDL-cholesterol being a heart disease risk concern. The American Heart Association and the Dietary Guidelines for Americans promote that the largest influence on blood cholesterol levels rests in the saturated fatty acid (SFA) content in the diet. In the United States and other developed countries, populations acquire their saturated fat content mostly from meat, seafood, poultry (with skin consumed), and whole-milk dairy products (cheese, milk, and ice cream). Some plant foods are also high in saturated fats, including coconut oil, palm oil, and palm kernel oil. Yet the question remains: is it the excess of saturated fat that is associated with heart risk, or is it the foods we lack (fresh vegetables, fruits, and fibers), or the primary Calories we take in from processed foods? The American College of Cardiology states, "The current information suggests that genetic predisposition modulates the association between saturated fat intake and cardiovascular risk. It is this segment of the population (the SFA-sensitive) in which the reduction in SFA intake may be beneficial and could therefore be recommended."¹⁴ This supports the concept that not one food or one nutrient can be tied to disease risk, but rather we need to look at the synergy of moderating all nutrients within a balance between the variety of food groups.

Excess Dietary Cholesterol and Heart Disease

Dietary cholesterol does have a small impact on overall blood cholesterol levels, but not as much as some people once thought. The average American female consumes 237 milligrams of dietary cholesterol per day, and for males, the figure is slightly higher—about 358 milligrams. The USDA Dietary Guidelines suggest a daily limit intake of cholesterol not to exceed 300 milligrams for healthy people and 200 milligrams for those who may be suffering from high cholesterol. Most people display little response to normal dietary cholesterol intake as the body responds by halting its own synthesis of the substance in favor of using the cholesterol obtained through food. Genetic factors may also influence the way a person’s body modifies cholesterol. Therefore, more emphasis is being placed on the balance of the entire pattern of eating rather than a single nutrient.

Attributions:

Zimmerman, "An Introduction to Nutrition (Zimmerman)," CC BY-NC-SA 3.0. Text and references added.

References

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