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Fructose and Gluconeogenesis

Today I’m thinking about the relationship between fructose and gluconeogenesis. In particular, in the article entitled The Carbohydrate Roundtable, it is mentioned that fructose will help restore the liver’s glycogen supply.

What I’m wondering is…

Is there a strategy involving fructose consumption that will help us with respect to either fat loss or promotion of anabolic activity? I know it was hinted at somewhere on the site before.

However, Googling on this topic I’m getting a lot of interesting information but nothing representing a answer:

-Blood sugar concentrations are controlled by three hormones: insulin, glucagon, and epinephrine. If the concentration of glucose in the blood is too high, insulin is secreted by the pancreas. Insulin stimulates the transfer of glucose into the cells, especially in the liver and muscles, although other organs are also able to metabolize glucose.

-In the liver and muscles, most of the glucose is changed into glycogen by the process of glycogenesis. Glycogen is stored in the liver and muscles until needed at some later time when glucose levels are low. If blood glucose levels are low, then eqinephrine and glucogon hormones are secreted to stimulate the conversion of glycogen to glucose. This process is called glycogenolysis.

-If glucose is needed immediately upon entering the cells to supply energy, it begins the metabolic process called glycoysis. The end products of glycolysis are pyruvic acid and ATP.

-Gluconeogenesis occurs mainly in the liver with a small amount also occurring in the cortex of the kidney. Very little gluconeogenesis occurs in the brain, skeletal muscles, heart muscles or other body tissue. In fact, these organs have a high demand for glucose. Therefore, gluconeogenesis is constantly occurring in the liver to maintain the glucose level in the blood to meet these demands.

-Gluconeogenesis is the process of synthesizing glucose from non-carbohydrate sources. The starting point of gluconeogenesis is pyruvic acid, although oxaloacetic acid and dihydroxyacetone phosphate also provide entry points. Lactic acid, some amino acids from protein and glycerol from fat can be converted into glucose.

-Body carbohydrate pools:
? blood glucose ~ 30 g
? liver glycogen ~ 90 g
? muscle glycogen ~ 350 g

-It is liver glycogen that is the first line of defense when blood glucose concentration falls. That large glycogen reserve in our muscles cannot be released to the circulation. Hepatic gluconeogenesis takes over after some hours, using lactate and amino acids to form glucose. It should be emphasized that the level of blood glucose will be maintained within narrow limits as long as a source of amino acids is available. The only real question is “will these come from me or my food”? The body’s proteins are its largest “glucose reserve”.

-We do not need to eat carbohydrates at all; we can produce all the glucose we need from dietary proteins. The catch is that we can only get something like 1000-1500 kilocalories daily from glucose made from amino acids.

-At rest following an overnight fast the plasma FFA concentration is about 0.4 millimoles per litre (mmol/l). This is commonly observed to fall during the first hour of moderate intensity exercise, followed by a progressive increase corresponding with the breakdown of fat (lipolysis), which is stimulated by the actions of hormones including adrenaline, glucagon and cortisol. During very prolonged exercise, the plasma FFA concentration can reach 1.5-2.0 mmol/l and muscle uptake of blood-borne FFA is proportional to the plasma FFA concentration.

-The glycerol released from adipose tissue cannot be used directly by muscle. However, glycerol (together with alanine and lactate) is taken up by the liver and used to form glucose in a process called gluconeogenesis. This helps to maintain liver glucose output as liver glycogen levels decline. The utilisation of blood glucose is greater at higher workrates, increases with exercise duration during prolonged submaximal exercise and peaks after about 90 minutes. The decline in blood glucose uptake after this time is attributable to the increasing availability of plasma FFA as fuel and the depletion of liver glycogen stores.

So, if we eat fruit with a protein meal will it reduce the likelihood of converting aminos to sugars and enhance the amount of amino acids delivered to muscles? Or alternately, does the liver generally have plenty of glycogen stored such that this will make no difference?

It seems possible if fructose specifically replenishes liver glycogen supplies and if these are in fact preferentially used as a glucose source over gluconeogenesis. Is the size of any possible effect going to be significant?

On the other hand, if we are eating dietary protein, is it a better strategy in general to promote gluconeogenesis as it can also use fats as a fuel source?

Anyone care to voice an opinion or point to some useful studies?

I think if your carb intake is sufficient, regardless of the type (fructose, sucrose, glucose, etc.), then there isn’t too much to worry about.

In my opinion, the prime time for gluconeogensis to occur is after you sleep and post-workout. That’s what I always try to explaing to people who tell me they just take protein after they workout. They don’t realize that when your glycogen stores are that low, the body is gonna get it one way or the other. If you only take protein and no carbs that kicks up glucagon and your body starts gluconeogensis.

I agree with what you said but how’s this for a twist:
JB says that PWO glucagon takes over insulin and hence, even though insulin levels are high (in the presence of P+C), fat breakdown will occur.

This always seemed contradictory to me but I thought I’d point it out. Correct me if I’m wrong.

Gary

[quote]super saiyan wrote:
I think if your carb intake is sufficient, regardless of the type (fructose, sucrose, glucose, etc.), then there isn’t too much to worry about.

In my opinion, the prime time for gluconeogensis to occur is after you sleep and post-workout. That’s what I always try to explaing to people who tell me they just take protein after they workout. They don’t realize that when your glycogen stores are that low, the body is gonna get it one way or the other. If you only take protein and no carbs that kicks up glucagon and your body starts gluconeogensis.[/quote]