The physiological effects of fats and carbohydrates and their role in weight loss have been debated for decades. The key to weight loss is to consume fewer calories than you burn, but certain foods might govern our appetite, the efficacy of our metabolism and the chance that extra calories are stored away as fat. Therefore, the type of diet also matters, and new research is beginning to find it is better to restrict carbohydrates than fats.
Significance
The main task of carbohydrates is to provide energy for the body. They are broken down easily by the liver into units called glucose, which is the main "input molecule" in the process of cellular respiration. A low-carbohydrate diet is therefore predicated upon the fact that low amounts of carbohydrate energy in the diet will force the body to turn instead to stored fat tissue, which can be broken down to be used as a source of energy.
Study
A 2008 study published in "The New England Journal of Medicine" compared the effectiveness of low-carbohydrate, Mediterranean and low-fat diets. Researchers found individuals on the low-carbohydrate diet lost the most weight: an average of 4.7 kg, or 10.3 lbs., over two years. These results go up to 5.5 kg for people who actually completed the diet. In addition, the low-carbohydrate diet also had a positive impact upon cholesterol levels. The low-fat group, on the other hand, only lost 2.9 kg, or 6.4 lbs., on average.
Considerations
Individuals in the low-carbohydrate group ate the highest amount of fat, protein and cholesterol; therefore, these nutrients aren't necessarily an impediment and, in the cases of protein and fat, are actually beneficial in large amounts. However, any serious diet must also be high in dietary fiber, which slows the absorption of nutrients into the blood and has a positive impact on digestion. The Mediterranean diet had the highest amount of fiber and resulted in a comparable amount of weight loss --- 4.4 kg, or 9.7 lbs., on average and 4.6 kg for people who completed the diet.
Features of Diet
In the context of the study, the low-carbohydrate diet was modeled closely after the Atkins diet. Calories were not restricted, but it did aim to provide 20 g of carbohydrates per day for the two-month induction phase and immediately after religious holidays, followed by a gradual increase to 120 g per day to maintain weight loss. Based on a 2,000-calorie-a-day diet, carbohydrates would represent a quarter of total calories at most. Protein and fat intake was not limited, but individuals were instructed to choose vegetarian sources and to avoid trans fats.
Warning
Too often, people who embark on a low-fat diet end up restricting too many of the unsaturated fats that are beneficial to the functions of the body. For example, fats play an important role in maintaining healthy skin and hair, insulating body organs, maintaining body temperature, proper immune function and brain development. According to Medline Plus, they also are important for the absorption of vitamins A, D, E and K. The mistake of restricting fats is often made because dietary fat is associated with body fat, but one is not necessarily the direct cause of the other.
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