Food and Behaviour Research

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Fructose: it's "alcohol without the buzz"

Lustig, RH (2013) Adv Nutr 4(2) 226-35. doi: 10.3945/an.112.002998. 

Web URL: View this and related research via PubMed here. Free full text of this article is available online

Abstract:

What do the Atkins Diet and the traditional Japanese diet have in common? The Atkins Diet is low in carbohydrate and usually high in fat; the Japanese diet is high in carbohydrate and usually low in fat. Yet both work to promote weight loss.

One commonality of both diets is that they both eliminate the monosaccharide fructose. Sucrose (table sugar) and its synthetic sister high fructose corn syrup consist of 2 molecules, glucose and fructose. Glucose is the molecule that when polymerized forms starch, which has a high glycemic index, generates an insulin response, and is not particularly sweet. Fructose is found in fruit, does not generate an insulin response, and is very sweet.

Fructose consumption has increased worldwide, paralleling the obesity and chronic metabolic disease pandemic. Sugar (i.e., fructose-containing mixtures) has been vilified by nutritionists for ages as a source of "empty calories," no different from any other empty calorie. However, fructose is unlike glucose. In the hypercaloric glycogen-replete state, intermediary metabolites from fructose metabolism overwhelm hepatic mitochondrial capacity, which promotes de novo lipogenesis and leads to hepatic insulin resistance, which drives chronic metabolic disease.

Fructose also promotes reactive oxygen species formation, which leads to cellular dysfunction and aging, and promotes changes in the brain's reward system, which drives excessive consumption. Thus, fructose can exert detrimental health effects beyond its calories and in ways that mimic those of ethanol, its metabolic cousin.

Indeed, the only distinction is that because fructose is not metabolized in the central nervous system, it does not exert the acute neuronal depression experienced by those imbibing ethanol. These metabolic and hedonic analogies argue that fructose should be thought of as "alcohol without the buzz."

FAB RESEARCH COMMENT:

Dr Robert Lustig is a clinical expert in both pediatric obesity and neuroendocrinology, and has become one of the world's leading researchers on the impact of high intakes of sugar - and particularly fructose - on the development of obesity, diabetes and related metabolic conditions.

In this review, he makes clear the striking parallels between the metabolism of fructose, and of alcohol, within the body - detailing the mechanisms by which consumption of either of these in more than minimal amounts
  1. selectively disrupts sensivitiy to insulin within the liver (which equivalent glucose consumption does not)
  2. promotes the storage of excess energy as fat (rather than glycogen)
  3. leads over time to almost exactly the same patterns of chronic metabolic disease
This account provides a compelling explanation for why the dramatic increase in added sugars in human diets over recent decades has been matched by an extraordinary increase in the incidence and prevalance of 'non-alcoholic fatty liver disease' (NAFLD), as well as both obesity and Type 2 diabetes, both of which NAFLD is very strongly associated with, and typically precedes.

Even 50 years ago, 'fatty liver disease' was almost never seen in children, and was relatively rare even in adults, and almost always associated with excessive consumption of alcohol and increasing age. Now, NAFLD affect 10-15% of US children and adolescents - and around 40% of those with obesity.

With respect to their effects on the brain, he also summmarises the evidence that chronic high doses of both alcohol and fructose (unlike glucose) can override the systems that normally lead to self-regulation of their intake, albeit via different mechanisms with respect to their effects on mood and behaviour.  And while alcohol is classically 'addictive', human studies remain inconclusive on this point with respect to fructose - although they do clearly show that it is habit-forming.