In general, nutritious diets should contain a variety of foods while making an effort to shift from fatty foods to more carbohydrates, from simple to complex carbohydrates, from saturated to unsaturated fats and reduce total energy intakes to achieve an optimum weight. Cholesterol and salt intakes should be limted while fiber, fresh fruit and vegetable intakes should be increased. Fad diets based exclusively on one particular food or food component can have unhealthy and potentially dangerous consequences. Consult with your doctor before entering into any diet program that strays from a balanced approach to nutrition.
The human body requires about 40 nutrients be supplied in the diet for health. A healthy diet must provide energy substrate, essential amino acids, necessary polyunsaturated fat, vitamins, minerals, and undigestible fiber.
The energy necessary to power body functions varies with age, sex, activity level, and environmental temperature. Energy supplied by the diet in excess of that required to power bodily functions is simply stored. On a weight basis, dietary fat supplies the most energy (9 Kcal/g), followed by alcohol (7Kcal/g), and protein and carbohydrate (4 Kcal/g). Dietary excesses are associated with diseases such as obesity, Type 2 diabetes, atherosclerosis, cancer and hypertension.
Recommended Daily Allowances (RDA) are government recommendations for nutrient intake that are sufficient to meet nutritional needs. A balanced diet consisting of 2-3 servings of milk, yogurt and cheese, 2-3 servings of meat, poulty, beans, eggs and nuts, 2-4 servings of fruit, 3-5 servings of vegetables and 6-11 servings of bread, cereal, rice, or pasta each day will provide all the necessary nutrients for good health. The classic representation of a balanced diet is the Food Pyramid shown below
Protein must be supplied in the diet to replace that which is lost in the urine, feces, saliva, sloughed skin, hair and nails. Protein is required in even greater amounts in growth, pregnancy, lactation, infection, and in recovery from burns, injury or surgery. The average male looses 24 g of protein per day and the recommended intake is 56 g/d for men and 45 g/d for women. Protein and energy needs are closely related such that diets deficient in energy will necessitate greater intakes of protein to maintain nitrogen balance because some dietary protein will be used to make glucose.
Proteins vary in quality with high quality proteins providing essential amino acids. The essential amino acids are histidine, tryptophan, threonine, valine, phenylalanine, leucine, methionine, lysine, and isoleusine. Highest quality proteins are generally from animal sources (egg, meat). Plant proteins are usually deficient in one or more of the essential amino acids. Amino acids not used to make proteins are not stored within the body.
There is no actual requirement for carbohydrates, but in their natural state complex carbohydrates such as starches provide vitamins, minerals and fiber. The averge American diet contains 45% carbohydrate and the recommendation is that the level rise to 55-60%. A minimum daily intake of about 100g is recommended to prevent muscle wasting and ketosis (accumulation of the breakdown products of fats in the body causing a metabolic acidosis).
Fiber is undigestable plant material like cellulose, pectins, or lignin. High fiber diets are recommended because of an association with decreased cardiovascular and gastrointestinal disease. Fiber ads bulk to the stool and diets high in fiber have been shown to decrease cholesterol levels and blood sugar.
Fats an diet
Dietary fats are a vehicle for fat soluble vitamins, a concentrated source of energy, and the souce of the essential fatty acid, linoleic acid. Deficiency of linoleic acid leads to hair loss, dermatitis and poor wound healing. Linoleic acid is a precursor to arachadonic acid which is a precursor to prostaglandins. Fats also improve the taste and satisfaction of foods. However, diets high in fat, particularly saturated fats, are associated with obesity, coronary heart disease and cancers of the colon and breast.
Cholesterol is not essential in the diet as it is made in the liver. However, cholesterol is associated with fats from animal sources and intakes should be limited to 300 mg or less per day. Similarly, dietary fat intakes should be limited to 30% or less of total calories.
Vitmains & Minerals
Vitamins are essential nutrients that must be supplied in the diet and can be placed into two classes. Water soluble vitamins include those of the vitamin B complex and Vitamin C. Fat soluble vitamins include vitamins A, D, E, and K. Minerals required in the diet are calcium, magnesium, phosphorous, sodium, potassium, chlorine, iron, zinc, copper, manganese, molybdenum, fluorine, iodine, cobalt, chromium, and selenium. Deficiencies of these essential nutrients are associated with specific or general symptoms and disease depending on the particular vitamin or mineral.
Obesity is an excess of adipose tissue and is a common disorder that is difficult to treat. Body mass index (BMI), a measurement based on height and weight, is used to classify the level of obesity. Class I has a BMI or 30-34.9, class II 35-39.9 and class III or extreme obesity has a BMI >40. Normal BMI is defined by the National Institutes of Health at 18.5-24.9. While total weight is important, the distribution of fat is also of interest. Lower body fat presents less of a health hazard than upper body fat. 20-25% of Americans are obese and the poor are more likely to be obese.
Hypertension, type II diabetes, coronary heart disease, some cancers (colon, prostate, breast), gastrointestinal disease, and skin diseases are more common in obese individuals. Weight is a risk factor for many other disorders, especially in young and middle-aged adults.
The causation of obesity is thought to be a combination of genetics, lifestyle and diet. Sedentary lifestyle and consistently eating too much are often the chief culprits, but a hereditary component cannot be ruled out for many cases. Sometimes obesity may be the result of hypothyroidism or Cushing’s syndrome, but this is rare.
Weight loss can be achieved in motivated people by changing behavior and diet. Long-term changes in eating behavior and lifestyle are necessary to maintian weight loss. Behavior modification, education, social support, and exercise are integral to successful weight loss programs.
Medications that act at the central nervous system, such as amphetamines, appetite suppressants, and serotonin uptake inhibitors may be prescribed for obese patients by a doctor as part of a comprehensive weight loss program. Some of these drugs have considerable abuse potential, limited utility and are approved for short-term use only. A new drug that is not aimed at the central nervous system, orlistat, reduces fat absorption in the gut such that about 30% of dietary fat passes out of the body in the stool. It has the possible side-effects of diarrhea, gas and cramping. Surgery is a last resort treatment for the extremely obese.
Kwashakor & Marasmus are diseases of protein malnutrition. Kwashiorkor results when protein in the diet is insufficient but caloric intake is adequate. Patients seem to be of normal weight but may have edema. The body destroys its own nonmuscle protein in an effort to meet nutritional needs.
Marasmus occurs when protein and calories are deficient for prolonged periods. Patients appear overly thin because they loose both body fat and muscle mass. Such starvation occurs when adults are unable to eat or in anorexia nervosa and can occur in infants who are malnourished or have prolonged intestinal diseases that cause malabsorption of nutrients.
Anorexia nervosa is a psychological disorder where the patient has an altered body image, control issues regarding food intake, and a fear of getting fat. Most often occurs in females from middle- and upper-class families. Usually there is a 15% or greater loss of total body weight and a cessation of normal menstruation. Patients often are perfectionists from high-achieving families. Psychologic symptoms may also include obsessiveness, anxiety or depression. Treatment is successful in two-thirds of cases but a small percentage of patients commit suicide or die of complications of the disorder.
Bulimia nervosa is also a psychological disorder of predominately white middle- and upper-class women characterized by an excessive concern with weight. Patients secretly binge on high-calorie foods and then try to correct the excessive intake by using laxatives, fasting, excessive exercise or by vomiting. Secondary illness of the gastrointestinal system are complications of this disorder. Treatment is by psychotherapy and antidepressants may be helpful.