T Nation

Fructose/Fruits


#1

Hi,

How much per day do You think we can eat fruits/fructose per day without worried about stored it as fat? You know, fructose is stored in the first place in liver as glycogen. When liver is full than it is going stored as fat. I'm saying about bulking time ( eating above maintenance ).

What's Your daily intake? :wink:


#2

In many cases individuals can eat very large amounts without getting fat.

However, while muscles can burn glucose (including glucose resulting from having eaten a starch) they cannot burn fructose.

Fructose intake can act towards increasing instinctive drive to eat more, whereas glucose intake is correctly recognized as needed calories having been taken in, thus reducing later caloric intake. (This has to do with how fructose is metabolized in the hypothalamus.)

High fructose intake is also strongly correlated with incidences of metabolic disorder, diabetes, and obesity, and there are known mechanisms of how high frucose intake affects gene expression in these directions.

There is no good reason to, on purpose, have high fructose intake, including from sucrose, corn syrup, high fructose corn syrup, or high caloric intake of sweet juices.

25 g/day is fine.

To bulk in terms of muscle gain, protein, glucose, including by starches or cyclic dextrins, and fats are all far superior choices.


#3

My standard for net fructose is 25 g a day, plus possibly up to 1/3 of exercise related carb needs.

Fructose maintains and rebuilds liver glycogen. 25 grams a day will basically do that, plus if you get say 50 grams of carbs post workout, up to about 1/3 of that can be from fructose.

Once liver glycogen needs are met, fructose gets turned into triglycerides (bad). This is probably one of the TRUE causes of the onset of heart disease.

Fruit by the way nets only about as much fructose per gram of sugar as table sugar. Most fruit will have a fructose fraction, a glucose fraction and a sucrose fraction and on balance fruits will be between 40-60% net fructose just like table sugar.

There is evidence that after hard high volume training, the liver can take in some extra fructose, and that does not require insulin so there IS one small advantage in taking in some fructose in that it will not tend to contribute to peripheral insulin resistance or hyperglycemic damage. You can load up the liver without having to use as much insulin and stress the pancrease, and possibly reduce overall insulin sensitivity.

Muscles use mostly fatty acids though. If you can actually use your metabolic respiratory quotient to estimate how much glycogen you have used versus fat in a workout, there is evidence that 1/3 of that can be rebuilt with fructose. You would probably have to burn somewhere around 500 calories in an hour to need 50 grams of carbs (as the first 200 or so would come from fatty acids, and some would come from protein).


#4

For me, a heavy fruit day totals about 25-26 grams of whole fruit sugars but more commonly I keep to the 18 gram range based on taste alone.

Another facet to a fruit sugar/fat storage conversation is the choice of fruit based on glycemic index. If you want slowly released carbs (low on the glycemic index) choose oranges, blueberries, bananas, apples, peaches, pears, strawberries, green and red grapes. I prefer these as I have always gotten hypoglycemic reactions easily due to an overactive pancreas.

For rapidly released fruit sugars choose: watermelon, apricots, mangoes, black grapes, and to a lesser degree: Cantaloupe, & Pineapple