Skip to comments.Examining the Health Effects of Fructose
Posted on 06/07/2013 7:29:21 PM PDT by neverdem
In the 1990s, excessive fat consumption was commonly believed to be the main cause of obesity. High sugar consumption was often considered to be innocuous and possibly protective against obesity by displacing dietary fat.1 A decade later, the American Heart Association linked intake of added sugars to weight gain and recommended substantial decreases in consumption to a daily maximum of 100 kcal for women and 150 kcal for men.2 Some experts now argue that sugar comprises the single most important cause of the worldwide epidemics of obesity and diabetes, primarily through the effects of fructose at prevailing levels of consumption.3 This Viewpoint examines the physiological effects of common sugars and argues against a narrow public health focus on fructose.
Fructose, a 6-carbon sugar, is more than twice as sweet as its isomer glucose. Most caloric sweeteners contain approximately equal amounts of these 2 sugars, either linked covalently in sucrose (table sugar) or as monosaccharide mixtures in high-fructose corn syrup and honey. Pure glucose, as found in unmodified corn syrup, has relatively little sweetness, and pure fructose may cause malabsorption in some people, limiting its practical use.
Despite chemical similarities, the metabolism of these 2 sugars differs markedly, and this difference underlies recent health concerns.3 Following consumption, glucose potently stimulates insulin secretion, promoting glycogen synthesis in the liver and glucose uptake by tissues throughout the body. In contrast, fructose does not directly elicit insulin secretion and is taken up almost exclusively by the liver. Moreover, unlike glucose, the metabolism of fructose is not tightly regulated by liver cell energy state. Consequently, fructose rapidly undergoes glycolysis, fueling de novo lipogensis under some conditions. This newly synthesized lipid may accumulate locally, causing fatty liver and hepatic insulin resistance, or be exported, increasing serum triglycerides, systemic insulin resistance, and fat deposition in adipose tissue. Fructose metabolism may also up-regulate hepatic signal transduction pathways involved in inflammation and drive uric acid production, possibly contributing to hypertension and endothelial dysfunction. Consistent with these mechanisms, feeding studies have demonstrated marked metabolic aberrationsincluding insulin resistance, dyslipidemia, higher blood pressure, and increased visceral adiposityamong obese individuals consuming fructose compared with glucose.3
However, these feeding studies have been criticized for providing unrealistically high amounts of fructose, typically exceeding the 95th percentile of consumption by 50% or more.4 A recent meta-analysis found no adverse effects of isocaloric substitution of fructose and glucose at average consumption levels for body weight, lipids, blood pressure, uric acid, or insulin levels and found possible benefit for glucose tolerance and glycemic control in diabetes.5 The monosaccharide feeding studies have also been criticized because humans virtually always consume fructose together with glucose, as in sucrose, high-fructose corn syrup, or honey, not in isolation.4
Another argument against fructose having uniquely harmful effects involves the glycemic index, a measure of how food affects blood glucose in the postprandial period. Glucose and most commonly consumed starchy foods (all starches are polymers of glucose) have a high glycemic index, whereas fructose has an exceptionally low value. If the effects of fructose on health predominated, and the various forms of glucose were innocuous, then the glycemic index should have a null or inverse association with disease risk. However, systematic reviews and meta-analyses have linked a high glycemic index diet to the same adverse effects as fructose, including obesity and diabetes.6- 7
In light of these considerations, a critical scientific question is whether replacement of fructose-containing sweeteners at prevailing consumption levels with glucose (as a monosaccharide or as starch) would provide health benefits. If so, a specific public health focus on fructose may be warranted. If not, then broader measures targeting all highly processed carbohydrate foods would be indicated. However, no modern controlled feeding studies adequately address this question, but research dating back to the 1970s is informative. In 1 study, 9 men and women, aged 37 to 62 years, living in a metabolic ward consumed a high-sugar diet (containing 70% of carbohydrate as sucrose, an average of about 675 kcal/d) or a sucrose-free diet (containing wheat and potato starch), each for 4 weeks. Upon repeated measurements, fasting blood glucose was slightly higher (3 mg/dL) for the sucrose condition but no differences between diets were found in body weight, glucose tolerance, fasting and stimulated insulin, cholesterol, triglycerides, or nonesterified fatty acids.8
Fruit is the primary natural source of fructose. Most fruits have about 10 g of fructose, as monosaccharide or sucrose, per 80-kcal serving, comprising at least half the total sugar content. If fructose were toxic at high dosage, then individuals consuming large amounts of fruit might experience adverse effects. However, observational studies report inverse associations between fruit consumption and body weight or risk of obesity-associated diseases, with no evident upper threshold for protection,9 although some studies do not adequately distinguish between fruits and vegetables.
In possibly the only interventional study of its kind, 17 Bantu and white adults in South Africa, aged 20 to 64 years, consuming a Western diet were instructed to eat primarily fruit (20 servings per day for the typical participant) supplemented with nuts to satisfy basic macronutrient requirements.10 Despite the extraordinarily high fructose content of this diet, presumably about 200 g/d, the investigators reported no adverse effects (and possible benefit) for body weight, blood pressure, and insulin and lipid levels after 12 to 24 weeks. Nevertheless, findings from this study must be interpreted cautiously because of important design limitations, including lack of an active control group.
The absence of harm from high fruit consumption likely relates to the slow digestion rate of whole fruit compared for example with a sugar-sweetened beverage, producing portal fructose concentrations that do not exceed hepatic metabolic capacity. Although soluble fiber helps to reduce sugar absorption rates from the digestive tract (primarily by increasing luminal viscosity), the physical form and cellular structure of whole fruit probably have a greater effect, by sequestering sugar away from the absorptive surface of the small intestine. In addition, the high micronutrient and antioxidant content of fruit may protect against hepatic inflammation and systemic insulin resistance.
Few modern studies have compared the long-term effects of glucose, fructose, and starch under physiologically relevant condition, and such research should assume high priority. The available evidence suggests 3 key points. First, fructose in its primary natural form (whole fruit) is not associated with adverse effects up to the limits of human consumption. Second, excessive intake of refined sugar plays a significant role in the epidemics of obesity and related diseases, in part because large amounts of rapidly absorbed fructose can overwhelm hepatic biochemical pathways. Third, rapidly absorbed forms of glucosepresent in both sugar and high glycemic index starchalso contribute importantly to these diseases, especially considering their much greater caloric contribution to typical diets than fructose. Therefore, the recommendation to replace fructose with glucose lacks an evidence basis. Rather, public health efforts should focus on reducing intakes of all highly processed carbohydrates, not just refined sugar.
Published Online: June 3, 2013. doi:10.1001/jama.2013.6562
Conflict of Interest Disclosures: The author has completed and submitted the ICMJE Form for Disclosure of Potential Conflicts of Interest and reported receiving grants from the National Institutes of Health and foundations for obesity-related research, mentoring, and patient care and receiving royalties from a book about childhood obesity.
Funding/Support: Dr Ludwig is supported in part by an endowment from Boston Children's Hospital and career award K24DK082730 from the National Institute of Diabetes and Digestive and Kidney Diseases.
Role of Sponsors: The funders had no role in the preparation, review, or approval of the manuscript or in the decsion to submit the manuscript for publication.
Disclaimer: The content of this article is solely the responsibility of the author and does not necessarily represent the official views of the National Institute of Diabetes and Digestive and Kidney Diseases or the National Institutes of Health.
Additional Contributions: I thank Marion Nestle, PhD, of New York University, Dariush Mozaffarian, MD, DrPH, and Frank Sacks, MD, of Harvard School of Public Health, Bruce Bistrian, MD, PhD, of Harvard Medical School, and Cara Ebbeling, PhD, of Boston Children's Hospital for providing detailed comments on an earlier version of the manuscript. None of these individuals received compensation for their efforts.
I detest the "nanny state" and Mike Bloomberg is the worst form of despot that there is. But yes. 25 years practicing medicine has confirmed for me what I knew then. Sugar kills. It's not the government's job to tell you what to eat. Its your job to decide.
I’m with you, I now STAY CLEAR of High Fructose Corn Syrup like the plague. I just feel like an IDIOT for not figuring that out sooner.
Ping for later read.
FReepmail me if you want on or off the diabetes ping list.
Ditto! I used to drink Dr. Pepper like it was going out of style. Haven't had one in well over a year and don't miss it AT ALL. I also avoid anything with Aspertame. It wreaks havoc on your body as well. Originally invented as a pesticide.
Type of sugar consumed is not important....it’s the dose that makes the poison.
Glucose is absolutely essential for life"
Serum glucose is absolutely essential for life. Dietary glucose is not.
The body is perfectly capable of manufacturing all the glucose it needs from protein and fat.
I’m a bit suspicious of the fructose is bad, only when you drink it in a soda crowd. I don’t think that anyone has been able to show any chemical difference between fructose in soda and fructose in fruit.
I wonder if we could do any cross-cultural comparisons with countries such as Mexico which have cane sugar in their drinks. As I understand it, the key reason fo HFCS is that American sugar prices are kept unfairly high by legislation which protects cane and beet farmers.
I dont think that anyone has been able to show any chemical difference between fructose in soda and fructose in fruit.
But there's a huge difference in how fast they are absorbed.
Ever been to a BBQ and had four beers over four hours? Sat at a bar and slammed four shots in four minutes? They contain about the same amount of ethanol. The effects are very different.
There's a rate at which the body can process fructose. Eating it as a solid, bound up in fiber, as in fruit, results in an extended period of moderate levels of fructose entering the system. Drinking the same amount as a liquid results in an extremely rapid, extremely high level of fructose. It's not at all inconceivable that this would make a difference.
I dunno, without my fruit and protein I would keel over. I hit the gym and ride my bike daily. Do they ever put into the argument how much someone moves around? I’m 20% body fat in my 50’s. Fruit, vegetables and protein are an integral part of my diet.
I’ve found that my body weight increases substantially based on how much and what type sugar I’m taking in. Fruits and vegetables actually help me maintain a desirable weight. Processed sugars can cause me to gain weight. Corn syrup sugars cause me to gain weight rapidly. I know some people who can scarf down sugars of all types without consequence, but I have to watch my intake.
I figured it out over twenty years ago, and was pretty much labelled a conspiracy theorist. At least now it's gotten possible to get food that doesn't have corn syrup in it. A little bit of granulated sugar as an ingredient is fine.
I'm also avoiding added whey and added gluten (I'm okay with the normal amounts that are part of foods). They destroy the natural balance of food. And besides, when you get used to food without these three additives, it tastes much better.
” I also avoid anything with Aspertame. It wreaks havoc on your body as well. Originally invented as a pesticide.”
Yea, I heard that too. Freaky stuff. I think the key is how much ‘processing’ (i.e., chemical changes) is done, as human bodies, of which our medical community knows squat about, is not designed to handle them.
I’m with you.
Do you know of any studies that have been done on the health effect of aspertame? If so I'd appreciate a heads up
The other thing is cooked plain vegetables. At a buffet, if I can get plain boiled or steamed carrots, brocolli, cabbage, celery and some others, a dish of that as an appetizer is filling, nutritious, and very tasty when your taste buds adjust. Breads or cereals...only 100% whole grain, no added sugar. Instead of butter...a Smart Balance concoction with olive oil. Also, no sauces and no breading. No cooking in butter. The result....I'm an average weight for the first time in my life (I was born 10% overweight) and have never enjoyed food more!
And I still enjoy a good steak dinner, often.
Yes, this is true. Is a diet of only protein and fat as healthy as one that includes carobohydrates?