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Showing posts with the label ketosis

Do you lose muscle if you lift weights after a 24-hour fast? Probably not if you do that regularly

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Compensatory adaptation (CA)  is an idea that is useful in the understanding of how the body reacts to inputs like dietary intake of macronutrients and exercise. CA is a complex process, because it involves feedback loops, but it leads to adaptations that are fairly general, applying to a large cross-section of the population. A joke among software developers is that the computer does exactly what you tell it to do, but not necessarily what you want it to do. Similarly, through CA your body responds exactly to the inputs you give it, but not necessarily in the way you would like it to respond. For example, a moderate caloric deficit may lead to slow body fat loss, while a very high caloric deficit may bring body fat loss to a halt. Strength training seems to lead to various adaptations, which can be understood through the lens provided by CA. One of them is a dramatic increase in the ability of the body to store glycogen, in both liver and muscle. Glycogen is the main fuel used by ...

Amino acids in skeletal muscle: Are protein supplements as good as advertised?

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When protein-rich foods, like meat, are ingested they are first broken down into peptides through digestion. As digestion continues, peptides are broken down into amino acids, which then enter circulation, becoming part of the blood plasma. They are then either incorporated into various tissues, such as skeletal muscle, or used for other purposes (e.g., oxidation and glucose generation). The table below shows the amino acid composition of blood plasma and skeletal muscle. It was taken from Brooks et al. (2005), and published originally in a classic 1974 article by Bergström and colleagues . Essential amino acids, shown at the bottom of the table, are those that have to be consumed through the diet. The human body cannot synthesize them. (Tyrosine is essential in children; in adults tryptophan is essential.) The data is from 18 young and healthy individuals (16 males and 2 females) after an overnight fast. The gradient is a measure that contrasts the concentration of an amino acid in mu...

Ketones and Ketosis: Physiological and pathological forms

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Ketones are compounds that have a specific chemical structure. The figure below (from: Wikipedia) shows the chemical structure of various types of ketones. As you can see, all ketones share a carbonyl group; that is the “O=” part of their chemical structure. A carbonyl group is an oxygen atom double-bonded to a carbon atom. Technically speaking, many substances can be classified as ketones. Not all of these are involved in the same metabolic processes in humans. For example, fructose is technically a ketone, but it is not one of the three main ketones produced by humans from dietary macronutrients (discussed below), and is not metabolized in the same way as are those three main ketones. Humans, as well as most other vertebrates, produce three main ketones (also known as ketone bodies) from dietary macronutrients. These are acetone, acetoacetate and beta-hydroxybutyrate. Low carbohydrate diets tend to promote glycogen depletion, which in turn leads to increased production of th...

Ketosis, methylglyoxal, and accelerated aging: Probably more fiction than fact

This is a follow up on this post . Just to recap, an interesting hypothesis has been around for quite some time about a possible negative effect of ketosis. This hypothesis argues that ketosis leads to the production of an organic compound called methylglyoxal, which is believed to be a powerful agent in the formation of advanced glycation endproducts (AGEs). In vitro research, and research with animals (e.g., mice and cows), indeed suggests negative short-term effects of increased ketosis-induced methylglyoxal production. These studies typically deal with what appears to be severe ketosis, not the mild type induced in healthy people by very low carbohydrate diets. However, the bulk of methylglyoxal is produced via glycolysis, a multi-step metabolic process that uses sugar to produce the body’s main energy currency – adenosine triphosphate (ATP). Ketosis is a state whereby ketones are used as a source of energy instead of glucose. (Ketones also provide an energy source that is distinct...

Ketosis, methylglyoxal, and accelerated aging: Fact or fiction?

Ketosis is a state typically associated with very low carbohydrate diets, such as the Atkins diet. In this state, the liver produces ketones based on fat (body fat or dietary fat). Unlike fats, ketones are water soluble and used by many tissues (including brain tissues) as a source of energy. Unlike glucose and lipoprotein-bound fats (in VLDL, for example), unused ketones cannot be converted back to substances that can be stored by the body. Thus excess ketones are eliminated in the urine; leading to their detection by various tests, e.g., Ketostix tests. This elimination of unused ketones in the urine is one of the reasons why very low carbohydrate diets are believed to lead to enhanced body fat loss. From an evolutionary perspective, one could argue that a ketosis state that involves the elimination of ketones in the urine is an inefficient and unnatural emergency mechanism. For our Paleolithic ancestors, dying of starvation was a much bigger problem than dying of obesity complicatio...