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the protein supply consumed during a KD “preserves,” as demonstrated, lean body mass

The importance of glycerol as a glucose source increases progressively during ketosis; in fact, glycerol passes from supplying 16% of total glucose to an average of 60% after many days (>7 d) of complete fasting (from 38% in lean individual to 79% in the obese).

The possible reasons for the effectiveness of KD for weight loss may be listed as follows, in order of evidence, strongest first: Figure 3Image Tools 1. Appetite reduction: protein satiety, effects on appetite-related hormones such as ghrelin, and possibly a sort of direct appetite-blocking effect of KB 2. Reduced lipogenesis and increased fat oxidation 3. A reduction in respiratory quotient may indicate a greater metabolic efficiency in fat oxidation 4. A thermic effect of proteins and increased energy usage by gluconeogenesis

all data regarding biochemical and molecular mechanisms suggest that it is very difficult to increase muscle mass during a KD; use of which really should be limited to the few days immediately before competition in bodybuilding.

a long-term KD can interfere with some muscle hypertrophy mechanisms and this could be counterproductive if the aim of the athlete is to gain muscle mass

complex functional interactions between diet, gut microbiota, and host health.

Gut bacteria in the cecum and large intestine produce SCFAs mainly from nondigestible carbohydrates that pass the small intestine unaffected

plant cell-wall polysaccharides, oligosaccharides, and resistant starches

inulin shifted the relative production of SCFAs from acetate to propionate and butyrate

age of approximately 3–4 years, when it becomes mature

SCFAs affect lipid, glucose, and cholesterol metabolism

colonocytes, the first host cells that take up SCFAs and which depend largely on butyrate for their energy supply

the microbiota educate the immune system and increase the tolerance to microbial immunodeterminants

the microbiota act as a metabolic organ that can break down otherwise indigestible food components, degrade potentially toxic food compounds like oxalate, and synthesize certain vitamins and amino acids

a large part of the SCFAs is used as a source of energy

The general idea is that colonocytes prefer butyrate to acetate and propionate, and oxidize it to ketone bodies and CO2

Exogenous acetate formed by colonic bacterial fermentation enters the blood compartment and is mixed with endogenous acetate released by tissues and organs (103, 104). Up to 70% of the acetate is taken up by the liver (105), where it is not only used as an energy source, but is also used as a substrate for the synthesis of cholesterol and long-chain fatty acids and as a cosubstrate for glutamine and glutamate synthesis

SCFAs regulate the balance between fatty acid synthesis, fatty acid oxidation, and lipolysis in the body.

Fatty acid oxidation is activated by SCFAs, while de novo synthesis and lipolysis are inhibited

obese animals in this study showed a 50% reduction in relative abundance of the Bacteroidetes (i.e., acetate and propionate producers), whereas the Firmicutes (i.e., butyrate producers) were proportionally increased compared with the lean counterparts.

increase in total fecal SCFA concentrations in obese humans.

In humans the distinct relation between the Firmicutes:Bacteroidetes ratio and obesity is less clear.

There is evidence that among weight cycling, people those who switch between dieting and binge-eating more frequently gain more weight