What is the role of dieting in the treatment of obesity?
The basis of dietary treatment for obesity is to reduce energy intake. The desired outcome of negative energy balance (energy intake minus energy output) is to lose body fat, spare muscle protein, normalize blood lipids (fats in blood like cholesterol and triglycerides), stabilize blood glucose, and reduce hypertension (high blood pressure).
Diets for obesity
The Low Calorie Diet (LCD) is designed to provide 500 to 1000 calories below daily energy needs. It aims to produce a weight loss of 0.5– 1.0 kg per week. In general, the LCD uses low-fat content. If the weight loss required to achieve a normal BMI (Body mass Index – an indicator of weight in relation to height of an individual) is between 5 and 10 kg, this loss can be accomplished within the confines of a 3 to 4 month program. If the excess weight is greater, a longer program is required. Health benefits become evident before optimal weight is reached. Even a modest weight loss of 5% to 10% of body weight can improve blood sugar control, blood lipid levels and reduce blood pressure. When obesity is associated with a complication like ‘obstructive sleep apnea’ (difficulty in breathing during sleep due to partial obstruction of the breathing passage), weight loss can be hastened by developing more stringent dietary plans. A medically supervised very low calorie diet (VLCD) of less than 800 calories supplies a minimal amount of energy and enough essential nutrients to avoid side effects. A VLCD reduces the time needed to reach a weight goal.
Composition of diets
These diets may use liquid formulas or high-protein foods with nutritional supplements. The modern VLCD contains adequate carbohydrate, potassium, magnesium, and other nutrients and minerals and leads to significant weight reduction. Regular evaluation of baseline and follow-up markers of nutritional status (hematocrit, red blood cell indices, liver enzymes, electrolytes) and cardiovascular (heart and blood vessels related) function like EKG or electrocardiograph of individuals receiving VLCDs are recommended. Unfortunately, the benefit of a significantly higher initial weight loss on the VLCD seems to be short term. Several studies indicate that after 1 to 5 years the weight loss with a VLCD is not significantly different from that with a LCD.
In a study comparing diet composition, it was found that increasing the proportion of protein to carbohydrate from the standard low-fat diet had positive effects on body composition, blood lipid levels, blood sugar level, and satiety during weight loss. The major controversy seems to be between low-fat and low-carbohydrate diets. Low-fat diets restrict fat intake to less than 25% to 35% of daily energy intake. Low-carbohydrate diets advocate carbohydrate intake of 20-100 grams per day. Numerous studies comparing the two types of diets show that in the long term (at least one year) low-carbohydrate diets do not induce more weight loss than low-fat diets.
Total cholesterol and low density lipoprotein levels decreased more after low-fat diet but high density lipoproteins and triglyceride values changed more after low-carbohydrate diets. There was no difference in blood pressure, lipid profile or blood glucose changes. The added value of low-carbohydrate diets is due to higher amount of proteins, which promotes satiety more than carbohydrates, on-going gluconeogenesis (glucose is made from amino acids) to compensate for the body’s carbohydrate needs which is an energy consuming process and high levels of circulating ketones which suppress appetite. Experimental data also suggest that dietary calcium plays a role in energy metabolism and weight regulation in humans. There is an inverse relationship between dietary calcium intake and body weight.