Food and Health Rethought

Too much fructose leads to weight gain & diabetes. Don't gorge on fruit.

fructose is “isocaloric but not isometabolic.” This means you can have the identical amount of calories from fructose or glucose, fructose and protein, or fructose and fat, but the metabolic effect will be entirely different.

fructose consumption leads to decreased signaling to the central nervous system from two hormones, leptin and insulin, both of which play key roles in hunger and satiety, as well as weight control.

Here’s a linked paper which gives a bit more science

Because fructose does not stimulate insulin secretion from pancreatic ß cells, the consumption of foods and beverages containing fructose produces smaller postprandial insulin excursions than does consumption of glucose-containing carbohydrate. Because leptin production is regulated by insulin responses to meals, fructose consumption also reduces circulating leptin concentrations. The combined effects of lowered circulating leptin and insulin in individuals who consume diets that are high in dietary fructose could therefore increase the likelihood of weight gain and its associated metabolic sequelae. In addition, fructose, compared with glucose, is preferentially metabolized to lipid in the liver. Fructose consumption induces insulin resistance, impaired glucose tolerance, hyperinsulinemia, hypertriacylglycerolemia, and hypertension in animal models.

high-carbohydrate meals stimulate leptin production in humans relative to high-fat meals

Diets high in fructose induce insulin resistance in rodents (87–89) and in dogs (90). For example, Thorburn et al (91) fed rats a diet containing 35% of energy as fructose for 4 wk and found reduced insulin sensitivity associated with impaired hepatic insulin action and whole-body glucose disposal. 

There are numerous studies in which dietary fructose has been shown to induce hyperlipidemia in rodents (104, 107–109). Herman et al (107) reported that rats fed a high-fructose diet had sustained elevations in serum triacylglycerol. Circulating triacylglycerol concentrations rose and remained elevated during the entire time fructose was fed (100 d) and fell promptly when a standard chow diet was instituted. The same investigators also concluded that there was a greater capacity of human liver to metabolize fructose to lipid compared with glucose because high-sucrose diets led to elevated serum triacylglycerol concentrations in humans, whereas the same amount of glucose resulted in lower concentrations of serum triacylglycerol 

Similar to insulin resistance and hyperlipidemia, many published experiments have shown that high-fructose diets induce hypertension in animals, including rodents (125–128) and dogs (90).

To put it in simpler terms…when you eat fructose alone, your blood sugar levels remain elevated. Not only that, but your liver tends to convert the fructose into fat, so the amount of in your blood gets elevated.  Not only that, but you don’t get the same feeling of fullness, so you just tend to eat more. If your there is too much fat in your bloodstream, you eventually get diabetes.

Here is an article that talks about that

a defect in insulin-stimulated glucose transport in skeletal muscle is the primary metabolic abnormality in insulin-resistant type 2 diabetics. Fatty acids appear to cause this defect in glucose transport by inhibiting insulin-stimulated tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and IRS-1 associated phosphatidylinositol 3-kinase activity.

Here is a table, listing the amount of fructose present in various foods

Fruit Serving Size Grams of Fructose

Limes 1 medium 0

Lemons 1 medium 0.6

Cranberries 1 cup 0.7

Passion fruit 1 medium 0.9

Prune 1 medium 1.2

Apricot 1 medium 1.3

Guava 2 medium 2.2

Date (Deglet Noor style) 1 medium 2.6

Cantaloupe 1/8 of med. melon 2.8

Raspberries 1 cup 3.0

Clementine 1 medium 3.4

Kiwifruit 1 medium 3.4

Blackberries 1 cup 3.5

Star fruit 1 medium 3.6

Cherries, sweet 10 3.8

Strawberries 1 cup 3.8

Cherries, sour 1 cup 4.0

Pineapple 1 slice

(3.5” x .75”) 4.0

Grapefruit, pink or red 1/2 medium 4.3

Boysenberries 1 cup 4.6

Tangerine/mandarin orange 1 medium 4.8

Nectarine 1 medium 5.4

Peach 1 medium 5.9

Orange (navel) 1 medium 6.1

Papaya 1/2 medium 6.3

Honeydew 1/8 of med. melon 6.7

Banana 1 medium 7.1

Blueberries 1 cup 7.4

Date (Medjool) 1 medium 7.7

Apple (composite) 1 medium 9.5

Persimmon 1 medium 10.6

Watermelon 1/16 med. melon 11.3

Pear 1 medium 11.8

Raisins 1/4 cup 12.3

Grapes, seedless (green or red) 1 cup 12.4

Mango 1/2 medium 16.2

Apricots, dried 1 cup 16.4

Figs, dried 1 cup 23.0

It’s worth noting that this table is somewhat skewed. 1/16 of a water melon is 286 grams, where as a medium orange is less than half that. Who’s to say you won’t eat 1/32 of a watermelon etc.

This site, listing fructose amounts per 100g is also useful.

Agave / Agave nectar - Has a high fructose-to-glucose ratio

Aparagus  - Contains significant amounts of fructans

Apples - 6g fructose per 100g

Artichoke  - Contains significant amounts of fructans

Banana - 4.85g fructose per 100g

Blackberries - 2.4g fructose per 100g

Blueberries - 5.0g fructose per 100g

Cherries - 5.3g fructose per 100g

Currants - 3.5g fructose per 100g

Grapes - 8g fructose per 100g

Honeydew Melon - 2.9g fructose per 100g

Inulin  - Source of fructans; sometimes added to foods such as yoghurt

Kiwi fruit - 4.3g fructose per 100g

Lemon Lime soda/softdrink - 5.8g fructose per 100g

Mango - 5.5g fructose per 100g

Onion  - Contains significant amounts of fructans

Orange juice - 2.7g fructose per 100g

Oranges - 2.2g fructose per 100g

Pears - 6.2g fructose per 100g

Pineapple - 7.2g fructose per 100g

Plum - 3.0g fructose per 100g

Raisins - 30g fructose per 100g

Raspberries - 2.3g fructose per 100g

Strawberries - 2.4g fructose per 100g

Tangerines - 2.4g fructose per 100g

Watermelon - 3.35g fructose per 100g

Note that agave syrup is blamed because of its high fructose to glucose ratio, which is ironic because it’s claimed as a healthy alternative, and arguably healthier choices could be found.

Fructans is mentioned above

A fructan is a polymer of fructose molecules. They occur in foods such as agave, artichokes, asparagus, green beans, leeks, onions (including spring onions), yacon, jícama, and wheat.

Some people have trouble digesting fructose, and for those with intestinal difficulties, it is recommended that they avoid fructans.

Here’s some more about fructose malabsorption syndrome

Even in healthy persons, however, only about 25-50g of fructose per sitting can be properly absorbed. Persons with fructose malabsorption may absorb less than 25g per sitting.

This is yet another reason not to have too much fructose at once.

The article also has this table, which is interesting

Food Fructose (grams / 100 grams) Glucose (grams / 100 grams)

Sucrose (for reference) 50 50

Apples 5.9 2.4

Pears 6.2 2.8

Fruit juice e.g. Apples, Pears 5 to 7 2 to 3

Watermelon 3.4 1.6

Raisins 29.8 27.8

Honey 40.9 35.7

High fructose corn syrup 42 to 55 45 to 58

It’s not that the ratio is particularly worse in high fructose corn syrup - it’s that the quantity of sugar consumed is typically much larger than that that would be consumed when eating fruit.

If you eat small enough portions, less sugar enters your system and therefore less insulin is needed to control a blood sugar rise, and therefore less damage is done.

Let’s look at how many calories are actually burned from eating and sitting around.

A person who weighs 150 lbs. burns about 64 calories per hour while sleeping; someone who weighs 200 lbs. burns approximately 86 calories per hour while sleeping, according to Fit Watch.

Eating burns about 140 calories per hour; watching TV or reading burns around 75; and doing homework, or anything that requires heavy concentration or brain activity, burns around 110.

Let’s be generous and assume 100 calories per hour are burned. That’s 25 grams of carbohydrate. So if you were taking small nibbles or a few pieces of fruit here and there, that’s about 1.5 pieces oranges per hour, about 200 grams of orange. The calculations are similar for standard serving sizes of other fruits. Assuming there is some glucose in the fruit, for which there will be an insulin response, the amount you can eat rises somewhat.

How to make sense of the data on fructose? As I see it, each food has a functional purpose. Protein sources like steak are effective at building muscles. On the other hand if early man came upon an orchard full of fruit in the early summer, he might well gorge and it might be an evolutionary advantage for him to get fatter to take advantage of all the fruit in front of him. Now, as fruit is available in huge quantities everywhere, the possibility of getting fat from gorging on fruit is real. 

What’s the upshot? If you want to lose weight and attain better health, pay attention to the amount of fructose you consume.

If you want to improve your insulin response, consider combining fruit with protein, as protein causes insulin levels to rise, without affecting your blood sugar.

Pure protein — protein sources that do not contain any carbohydrates — do not affect your blood glucose levels

Insulin does many things at once. It causes amino acids to be taken in to cells and causes blood sugar to be lowered via a number of different mechanisms.

So, as I see it the takeaways are:

1) Avoid sugary drinks and any drinks with high fructose corn syrups (includes most sodas).

2) If you are eating a fruit that contains fructose, don’t eat too much, so as not to raise the blood sugar too high, as insulin won’t help enough. Don’t gorge on fruit. 

3) Consider eating fruit with a meal in which you have some protein.

4) Be careful with respect to the total amount of fructose you consume in any given day. The less fructose you consume the better it is for your blood sugar & the more it prevents obesity, but fruit is good for other reasons, so try to find the compromise that’s right for you.