Gluconeogenesis is the endogenous production of glucose in the body, especially in the liver primarily from lactic acid, glycerol, and the amino acids alanine and glutamine. When glucose availability drops further, the endogenous production of glucose is not able to keep up with the needs of the body and ketogenesis begins in order to provide an alternate source of energy in the form of ketone bodies. Ketone bodies replace glucose as a primary source of energy. During ketogenesis due to low blood glucose feedback, stimulus for insulin secretion is also low, which sharply reduces the stimulus for fat and glucose storage. Other hormonal changes may contribute to the increased breakdown of fats that result in fatty acids. Fatty acids are metabolized to acetoacetate which is later converted to beta-hydroxybutyrate and acetone. These are the basic ketone bodies that accumulate in the body as a ketogenic diet is sustained. This metabolic state is referred to as "nutritional ketosis." As long as the body is deprived of carbohydrates, metabolism remains in the ketotic state. The nutritional ketosis state is considered quite safe, as ketone bodies are produced in small concentrations without any alterations in blood pH. It greatly differs from ketoacidosis, a life-threatening condition where ketone bodies are produced in extremely larger concentrations, altering blood ph to acidotic a state.
Keto flu symptoms and side effects can include feeling tired, having difficulty sleeping, digestive issues like constipation, weakness during workouts, being moody, losing libido and having bad breath. Fortunately, these side effects don’t affect everyone and often only last for 1–2 weeks. (And yes, you CAN build muscle on keto.) Overall, symptoms go away as your body adjusts to being in ketosis.
It’s not always about how much you eat, but the nutritional balance of carbohydrates, fats, and protein in what you’re eating. Endurance athletes need extra carbs to fuel their rides, fat to feel satiated, and protein to repair your muscles post-workout. It usually isn’t necessary to make radical adjustments to achieve this balance—small changes work best. For instance, don’t eat a whole bowl of chili with meat. Instead, fill half the bowl with brown rice, then ladle a small amount of chili on top. You can also try substituting fat-free yogurt for sour cream and fruit for sweets.
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