Curb Your Appetite and Lose Weight
Protein is a critical component of a nutritionally sound diet. The amino acid constituents of your dietary proteins are used in various ways to maintain your body's functional integrity. The effects of proteins and amino acids can range from maintaining the structural integrity of your body to regulating your body's metabolic activity. For example, amino acid-rich foods can help curb your appetite. This appetite-suppressant effect can occur by a variety of mechanisms. Most of these mechanisms involve their effects to raise or lower the activities of some hormones that play important roles in controlling your appetite and energy metabolism. Some hormones affected by these amino acids include cholecystokinin, serotonin and insulin. The five amino acids that help to curb your appetite are: phenylalanine, l-carnitine, tryptophan, tyrosine and 5-hydroxytryptophan (5-HTP).
The effects of these amino acids on hormones that regulate metabolism have significant and profound implications for body weight control and good health. Knowing the specific amino acids that influence certain hormones enables you to make food choices that can simplify and accelerate weight loss. Maintaining good health would also become simplified.
Amino Acids and Proteins
Proteins and amino acids can curb your appetite by keeping the plasma glucose level stable at normal levels (90 to 100 mg per dl). You feel hungry when your plasma glucose (blood sugar) falls below normal levels. If the plasma glucose level rises above normal then your body would release insulin to bring it down to normal levels. Insulin lowers your blood glucose level by causing blood sugar to go into the muscles and other tissues. Insulin also facilitates the conversion of excess blood sugar to body fat.
Foods, such as refined carbohydrates, that cause rapid increases in blood glucose will cause big spikes in the plasma insulin levels. These plasma glucose-spiking foods are called high glycemic index foods. Because your body wants to bring the glucose level down to normal levels very quickly, too much insulin is often released. Your blood glucose would then decline very sharply. The lowered level of plasma glucose would make you hungry and you may over-eat. This insulin spike and over-eating is avoided if plasma glucose is maintained at a stable steady state level by eating foods that do not stimulate the release of insulin (foods with low glycemic index values). Proteins and amino acids are examples of nutrients that do not cause notable increases in insulin release.
Phenylalanine curbs the appetite by stimulating the release of the appetite-suppressing hormone, cholecystokinin (CCK). CCK is released from the duodenal mucosa (the first segment of the small intestine) when foods, particularly amino acid and phenylalanine-rich foods are consumed. CCK signals the brain that you are satiated by stimulating the CCK receptors in the brain. It takes about 20 minutes for this satiation signal from CCK to reach the brain, so if you are a fast eater you may over-eat before the brain gets the message. Phenylalanine is found in a wide variety of foods, ranging from pumpkin seeds to sesame seeds and from almond to corn.
Tyrosine is an amino acid that can keep you energized while suppressing your appetite. Tyrosine is well-known for its effect of keeping you alert, energized and mentally focused. It is not as well-known for its appetite-suppressant effect which occurs by the activation of CCK release. This is not surprising, however, because tyrosine is a weak activator of CCK release compared to phenylalanine.
Tryptophan and 5-hydroxy tryptophan
Like phenylalanine, tryptophan is a potent activator of CCK release. Tryptophan has a dual physiological effects of promoting sleep and relaxation, and curbing the appetite. Besides curbing your appetite by releasing CCK, tryptophan also curbs your appetite and carbohydrate craving by its role as a precursor in the production serotonin in the brain. Serotonin curbs your appetite by inhibiting craving of foods, particularly carbohydrates. Like tryptophan, 5-Hydroxytryptophan (5-HTP) is a metabolite in the biochemical pathway for serotonin production. Tryptopha is the precursor for 5-HTP. Consequently, 5-HTP and tryptophan curb your appetite by the same mechanism. They both produce serotonin.
L-carnitine is an appetite suppressant that facilitates the burning of fat in your body. L-carnitine is a non-essential amino acid which is produced in the liver and kidneys from the precursor amino acids, lysine and methionine. L-carnitine from your diet, however, contributes significantly to the l-carnitine content of your body. Most of the l-carnitine (about 90 percent) is stored in the muscles.
L-carnitine transports the long chain fatty acids into the mitochondria, the site for substrate oxidation to provide energy to the body. The activity of l-carnitine suggests a preferential utilization of fat over glucose for energy metabolism. The mechanism by which l-carnitine suppresses appetite is not fully explained, but it may involve glucose and insulin. The action of l-carnitine would stabilize plasma levels of insulin and glucose at normal or near-normal levels, an effect that would prevent hunger.