Everything you need to know about fructose and its affects on body composition.
Are you looking for that nutritional edge to get your body composition to the next level?
Have you been eating your "five-a-day" like a good boy should, but just can't shake that last bit of icing off your jelly belly?
Well, take close note: if you reduce the fructose in your diet, you will lose that stubborn body fat!
Fructose Metabolism 101, the simplified version
Fructose is a type of simple sugar (a carbohydrate in its simplest form) that is much different than its sister sugar, namely glucose. When you eat fructose, it's absorbed more slowly in the intestine, and its absorption is slightly limited.
Some people–like those with diabetes, see fructose as a superior simple sugar because it doesn't get used as quickly or as efficiently. What they don't realize, is that fructose is normally consumed at the same time as glucose, which speeds up the absorptive process.
Once fructose passes through the intestine, it's quickly taken to the liver for processing. Here, it has two fates: it's either turned into glucose and then stored as liver glycogen; or it's used for energy by liver cells.
Unlike glucose, fructose can only be metabolized in the liver, whereas glucose can be passed to other body tissues, like your muscles.
Why fructose is a problem for dieters:
If you have a lot of fructose in your diet, it only has one place to go: your liver. If your liver glycogen levels are full, which is the case all times of the day except before you eat breakfast, then that fructose is turned into fat!
Since your liver doesn't want to store this new fat, it ships it to other parts of your body; places you don't want it, like your abdomen or lower back.
Do you now see why too much fructose in your diet can be one of the biggest reasons you can't shrink those last few fat cells?
How do I avoid eating fructose?
When people hear the word fructose, they usually think fruit. Ready for a shocker? Fruit is actually not the major source of fructose in your diet!
Yes, it does have fructose, but only certain fruits are high in it, while others are relatively low. Not all fruits are bad for your body composition; vegetables are the same way.
The major contributors of fructose in your diet, in descending order, are as follows:
- High Fructose Corn Syrup (HFCS)
- Table Sugar, which is a 50:50 combination of glucose and fructose
- Brown Sugar
- Maple Sugar
- Cane Sugar
- Concentrated Fruit Juice
Avoid the top eight in this list at all costs!
Read labels carefully, because HFCS is hiding in almost every food you eat nowadays. And, just because honey is natural, doesn't mean you should use it in abundance.
How do we really know fructose makes your fat?
You must have been living under a rock if you haven't already heard about HFCS being related to every common human disease we face today, such as diabetes, heart disease, obesity and cancer.
This relationship was first discovered in lab experiments with rodents. (1) When a high fructose diet (about 50-60% of total energy intake) is given to rats, they present symptoms of the Metabolic Syndrome, which is the precursor to full-blown diabetes and heart disease.
These animals develop high blood pressure, endothelial dysfunction, weight gain, increased abdominal fat, hyper-triglyceridemia, and insulin resistance. The weight and fat gain is thought to be due to leptin resistance; rats that eat a high fructose diet long-term have higher leptin levels than rats that don't eat a lot of this simple sugar.
Researchers then concluded that in humans, it's the fructose and not glucose that begins the cascade of Metabolic Syndrome risk markers (2); and this seems to be initiated by insulin resistance. Men forced to eat experimental high fructose diets develop insulin resistance within a week (3), compared to no insulin abnormalities in people given a high starch diet.
Sucrose, also known as "table sugar" (glucose and fructose combination), is even worse: people given a 28% sucrose diet for 10 weeks not only develop insulin resistance, but also gain weight and have increased blood pressure!
In another study, when overweight women were put on a "no-restriction" diet high in either sucrose, fat, or starch, only the high starch diet group lost weight and body fat. (4)
Today, most Americans are eating about 70-100 grams of fructose per day, and we're getting fatter by the minute. In bright contrast to today's world, this nation consumed just 15 to 40 grams of fruit & veggie-derived fructose in the 19th century, when we weren't even close to being this chubby. (5)
Why does fructose cause fat-gain?
Fructose and fructose-containing foods will usually make your meals taste better, so you end up eating much more than necessary. They also fail to make you feel satisfied after you eat them, due to inadequate stimulation of leptin and ghrelin, the two satiety hormones. (6)
There is also evidence that fructose slows your metabolism: kids who drink sodas and fruit juices (both are rich in HFCS and fructose) are fatter than those who don't drink them, but who eat the same amount of calories. (7)
So, what kinds of fruits and vegetables can I eat and not get fat?
Although fruit does contain some fructose, it's not the only sugar that it contains. Fruit is beneficial for you because it's the best natural source of antioxidants that help you fight free-radicals, a major cause of aging and muscle damage. It's also an important source of fiber.
Your best bet is to choose fruits that are low in fructose, and only eat the higher fructose fruits in the morning, when your liver glycogen levels are low. At this time, your liver can use or store the fructose without converting it to fat.
The following fruits are highest in fructose (per typical serving size)*. They contain more than 4 grams of fructose per serving.
Stay away from these outside of an occasional breakfast:
- cherries (1 Cup)
- grapes (1 Cup)
- melon (2 wedges)
- pineapple (2 rings)
- watermelon (1 large slice)
These fruits are lowest in fructose; they contain less than 4 grams of fructose per serving.
You can eat these with less restriction:
- avocado (1/3 medium; yes, it's a fruit)
- blackberries (1/2 cup)
- grapefruit (1/2 medium)
- raspberries (1/2 cup)
- strawberries (1/2 cup)
- tomato (yes, also a fruit)
* Note: these values were calculated by adding all of the fructose plus half of the sucrose per typical serving size (i.e., a typical apple weighs 120 grams).
Vegetables are much lower in fructose than fruits. The highest fructose-containing vegetables are corn and sweet potatoes, and they only have roughly 1.2 grams of fructose per serving. If you're really trying to keep this sugar low, also avoid white potatoes and green peas.
Fructose may be one of the reasons your body is not dropping the stubborn body fat you've been fighting for weeks, or even months. Before you start avoiding the produce section of the grocery store, start scanning the labels of some of your most frequently consumed foods.
Does your salad dressing contain HFCS? Do you douse your morning eggs with HFCS-laden ketchup? Or maybe you're known to eat "all-natural" products made with honey?
Once you've eliminated these major fructose-suspects, turn to your fruit intake. Don't eliminate it completely because some fruit will aid your overall health and studliness by fighting free-radical-induced aging and muscle damage. Just choose fruits lower in fructose.
Apples may keep the doctor away, but with their high fructose content, they'll keep your six-pack just as out of sight.
- Segal MS, Gollub E, Johnson RJ (2007) Is the fructose index more relevant with regards to cardiovascular disease than the glycemic index? Eur J Nutr 46:406-417
- Elliott SS, Keim NL, Stern JS, Teff K, Havel PJ (2002) Fructose, weight gain, and the insulin resistance syndrome. Am J Clin Nutr 76:911–922
- Beck-Nielsen H, Pedersen O, Lindskov HO (1980) Impaired cellular insulin binding and insulin sensitivity induced by high-fructose feeding in normal subjects. Am J Clin Nutr 33:273–278
- Raben A, Vasilaras TH, Moller AC, Astrup A (2002) Sucrose compared with artificial sweeteners: different effects on ad libitum food intake and body weight after 10 wk of supplementation in overweight subjects. Am J Clin Nutr 76:721–729
- Raben A, Macdonald I, Astrup A (1997) Replacement of dietary fat by sucrose or starch: effects on 14 d ad libitum energy intake, energy expenditure and body weight in formerly obese and never-obese subjects. Int J Obes Relat Metab Disord 21:846–859
- Teff KL, Elliott SS, Tschop M, Kieffer TJ, Rader D, Heiman M, Townsend RR, Keim NL, D'Alessio D, Havel PJ (2004) Dietary fructose reduces circulating insulin and leptin, attenuates postprandial suppression of ghrelin, and increases triglycerides in women. J Clin Endocrinol Metab 89:2963–2972
- Dennison BA, Rockwell HL, Baker SL (1997) Excess fruit juice consumption by preschool-aged children is associated with short stature and obesity. Pediatrics 99:15–22