Nutrition
Men lose weight more easily than women. One reason for this could be that men release more stress hormones, such as norepinehrine, in response to training and emotional stress. These hormones stimulate lipolysis - the breakdown of fat into fatty acids. It works by triggering hormone-responsive lipases (HSL), an enzyme that causes the release of fat from fat cells. HSL activity determines your ability to lose weight. The higher your nervous system is set to release stress hormones, the more calories you metabolize each day. Scientists at the University of Colorado (J Clin Endocrinol Metab, 86:4440-4444,2001) found that these nerve signals are lower in some people, especially those over 30 who don't exercise. Those trying to lose weight should try to boost their metabolism by exercising intensely and eating foods that accelerate metabolic performance.
Thermogenic foods, such as green tea, capsaicin, thyrosine and calcium can rev up your metabolism. Danish scientists found that taking a supplement containing one of these nutrients increased metabolism by almost 2% per 24 hours. Many weight loss products contain these substances. This study showed that these products could promote weight loss. (Eur J Clin Nutr, 59: 733-741, 2005)
The body uses carbohydrates as its main fuel during exercise when the intensity exceeds 65% of maximum effort. Carbohydrates come from food (blood sugar), muscle and liver glycogen and gluconeogenesis. Gluconeogenesis, which occurs in the liver and to a lesser extent in the kidneys, converts amino acids (building blocks of proteins), lactates and pyruvates into new blood sugar. This process gradually becomes more and more important as the muscles and liver use stored glycogen and carbohydrates from the last meal. Glutamine is the main amino acid during and after exercise as it contributes significantly to immune, nervous, gastrointestinal and metabolic function. Researchers at the University of Iowa found that glutamine supplements improved carbohydrate metabolism in dogs during and after exercise. Glutamine supplements promoted blood glucose production and utilization during and after exercise. Glutamine had a significant effect on carbohydrate metabolism, which may justify its use as a training supplement. Some studies showed improvements in immune system function and prevention of over-exercise. (J Appl Physiol,99:1858-1865,2005).
Training causes wear and tear on the body, which needs to be repaired during the recovery period. Protein-carbohydrate drinkstaken after exercise replenish muscle and liver glycogen stores and provide amino acids needed to repair damaged tissue. Insulin is an important hormone that helps the body recover from exercise. It accelerates the transport of amino acids into the cells that are needed to make new protein to repair damaged tissue from exercise. Insulin also accelerates the transport of glucose into cells, which provides energy for future training sessions. Scientists at the Georgia Institute of Technology in Atlanta found that administering sports drinks rich in carbohydrates and protein reduced muscle soreness after exercise. Several studies have found beneficial effects in the administration of post-workout supplements. (Int J Sports Nut, 15:610-624, 2005)
Carnosine is a dipeptide consisting of the amino acids alanine and histidine and is found in muscle and nerve cells. It helps regulate the energy management and contraction of muscle cells by acting as an acid buffer, regulating calcium (which triggers muscle contraction) in the muscles and coordinating both energy supply and muscle contraction. Muscle carnosine levels are particularly high in animals that perform great physical feats. Theoretically, an increase in muscle carnosine levels should increase physical performance. British researchers have found that supplementation with 3 or 6 grams of beta-alanine over a period of 15 days can increase muscle carnosine levels by 45 to 65%. Even though the researchers did not provide any information on a change in physical performance, it can be assumed that the increase in carnosine levels observed should increase performance. (Amino Acids, published on the Internet on March 24, 2006)
Conventional wisdom suggests that meals high in simple sugars first lead to a rapid rise and then an abrupt drop in blood sugar levels, which in turn leads to renewed hunger more quickly than eating a protein-rich meal. Australian scientists were able to show that a protein-rich meal does indeed suppress hunger better than a carbohydrate-rich meal, although the difference could be attributed to hormonal reactions rather than blood sugar levels. The test subjects were each given a 300-calorie meal consisting of whey protein (52g protein), casein (52g protein), glucose (7g protein) or lactose (7g protein). Three hours later, the test subjects were able to help themselves to an all-you-can-eat buffet. This showed that the snacks with a high protein content satisfied hunger best, whereas the subjects who had received the glucose meal ate the most from the buffet. Blood glucose and insulin levels rose fastest and most strongly in the glucose group, but after 2 hours blood glucose and insulin levels were the same again in all subjects. The composition of the snack influenced hormones that control appetite and are responsible for a feeling of satiety. Protein-rich meals increased the release of the hormone cholecystokinin (CCK), which suppresses hunger, whereas carbohydrate-rich meals increased the release of the hormone ghrelin, which triggers a feeling of hunger. Protein-rich meals suppress hunger by increasing CCK secretion while preventing an increase in ghrelin secretion. (Journal Clinical Endocrinology Metabolism, 91: 1477-1483, 2006)
