Response to letter to editor: On glycemic status and energy expenditure

During the initial hours of fasting, the body uses up its glycogen stores as an energy source. Once these glycogen reserves are depleted, the body begins breaking down stored triglycerides and structural proteins. During this stage, glycerol becomes a key substrate for gluconeogenesis, while free fatty acids undergo beta-oxidation to provide energy for tissues, such as skeletal muscle. In the fasting state, the body spares protein breakdown as much as possible to conserve muscle and structural...

Carbohydrates consumed through foods are converted into glucose, a crucial energy source for the body. In the prandial state, high blood glucose levels stimulate the secretion of insulin from the pancreas. Insulin inhibits hepatic glucose production and stimulates glucose uptake and metabolism by muscle and adipose tissue. The excess glucose is converted into glycogen and stored in the liver and muscles.
During fasting, when blood glucose levels are low, the pancreas secretes glucagon. it...

Without prolonged fasting, healthy individuals maintain blood glucose levels above 3.5 mM due to a well-adapted neuroendocrine counterregulatory system that effectively prevents acute hypoglycemia, a potentially life-threatening condition. The primary clinical scenarios for hypoglycemia encompass diabetes treatment, inappropriate production of endogenous insulin or insulin-like substances by tumors, and the use of glucose-lowering agents in non-diabetic individuals. Notably, hypoglycemia in the...

The postabsorptive state usually starts about four hours after a meal and lasts until the next meal is eaten. During this time, the digestive system stops absorbing nutrients, and the body uses stored energy reserves to maintain stable blood glucose levels.
Initially, glycogen stored in the liver is broken down to release glucose into the bloodstream, while glycogen in the muscles is broken down to supply glucose for energy directly within the muscle cells. As glycogen stores diminish,...

Carbohydrate metabolism is a fundamental biochemical process that ensures a constant supply of energy to living cells. The most important carbohydrate is glucose, which can be broken down via glycolysis to enter into the Krebs cycle and eventually lead to the production of ATP through oxidative phosphorylation.
Glucose transport into cells is facilitated by a family of transport proteins called GLUT (Glucose Transporters). GLUT4 is the primary glucose transporter for insulin-stimulated glucose...

Carbohydrates are polymers composed of molecules containing atoms of carbon, hydrogen and oxygen. One gram of carbohydrate can provide four kilo-calories of energy, which makes it the most efficient instant energy source.
Starch accounts for approximately 60% of the carbohydrates consumed by humans. Since amylase enzymes cannot function in the stomach's acidic environment, starch can only be digested in the mouth and small intestine. Simple sugars are found naturally in milk and fruits in...