F stands for fructose and fat Flashcards
fructose rich foods
soft drinks and processed foods
increased fructose intake has led to
obesity and metabolic syndrome epidemics
glucose and fructose have the same…
caloric value
where is fructose metabolized?
exclusively in the liver
what enzyme metabolizes fructose?
ketohexokinase (KHK) aka fructokinase
fructose 1-phosphate is diff from fructose 6-phosphate bc
F6P is in glycolysis
F1P can bypass major regulatory step in glycolysis that generates fructose 1,6-bisphosphate throgh PFK (energy sensitive enzyme)
which is more easily converted to fat: fructose or glucose?
fructose!
it is not limited by cellular controls that prevent unrestrained lipid synthesis from glucose
which is more easily converted to fat: fructose or glucose?
fructose!
it is not limited by cellular controls that prevent unrestrained lipid synthesis from glucose
why is it bad that fructose can be turned directly into fat?
could cause excess fat accumulation in liver
could also release fat into circulation
may cause metabolic syndrome
in humans, high fructose diet promotes
insulin resistance, elevated levels of lipid triglyceride, and visceral obesity
yet, high glucose overweight individuals don’t show these symptoms
Ishimoto study in…
mice
wild-type mice fed western diet
high in fat and fructose
developed fatty liver and liver inflammation
KHK-deficient mice fed western diet
protected from liver inflammation and fibrosis
only had mild fatty liver
Ishimoto study conclusion
both mice groups had same caloric intake, so mutant’s inability to process fructose shows that sugar exacerbates specific features of metabolic syndrome
Lanaspa et al.
looked at carbohydrate-rich diets devoid of fructose in KHK-deficient mice
KHK-deficient mice with high carb no fructose diet
also protected from adverse effects of excess glucose consumption
MAKES SENSE: in liver, polyol pathway converts excess glucose into fructose, stored as fat only in presence of KHK
polyol pathway
converts excess glucose into fructose, stored as fat only in presence of KHK
mice lacking polyol-pathway enzyme aldose reductase
also protected from glucose-induced fatty liver
glucose is mainly metabolized by…
glycolysis
glycolysis: ATP or citrate
redirect glycolysis towards storage as glycogen
in liver cells expressin ketohexokinase (KHK)
fructose is metabolized to fatty acids, glycerol, and triglycerides
KHK pathway regulation
NOT regulated by ATP or citrate feedback mechanisms
glucose is converted to fructose by…
polyol pathway
polyol pathway enzyme
aldose reductase (AR)
in the absence of feedback inhibition, glucose metabolites can also be used to generate…
fatty acid and triglyerides
PFK aka
phosphofructokinase
