Fructose makes you lazy and fat

If you consume large amounts of sugar you’ll not only get fatter, you’ll also get fatter faster than if you consume large amounts of glucose. That’s because fructose – one of the components of sugar – makes you lazy, which means you move less. Nutritionists at the University of Illinois at Urbana-Champaign discovered this when they studied the effect of a high-fructose diet on mice.

Glucose, fructose and sugar
You probably know already, but we’ll repeat it just in case. Thanks to the food industry we consume too much refined carbohydrates. These are not healthy for us and the unhealthiest of all refined carbohydrates are sucrose and fructose.

Fructose is a component of sucrose, ordinary sugar, but an increasing number of foods also contain fructose alone. Fructose is a component, for example, of High Fructose Corn Syrup (HFCS).


Researchers like Robert Lustig have been warning for years about the consequences of a high fructose intake. Fructose doesn’t convert easily into glucose. It’s glucose that stimulates the production of insulin, the hormone that induces cells to absorb glucose.

With fructose the process doesn’t go so smoothly, so fructose tends to hang around more in the bloodstream. As a result, a diet that contains a lot of fructose is more likely to lead to diabetes, cardiovascular disease and overweight than a diet that contains a lot of glucose.

The animal study done at the University of Illinois at Urbana-Champaign, which was recently published in Scientific Reports, confirms the dangers of our current intake levels of fructose.

The researchers gave mice food that contained 180g fructose per kg for 11 weeks. The food was an imitation of the diet of heavy consumers of fructose. A control group was given food that contained 180 g glucose per kg.

The mice in both groups put on weight, but the fructose mice became fatter than the mice in the glucose group.


The researchers used cameras to monitor how much the mice moved around in their cages at night [mice are nocturnal animals]. They observed that the mice in both groups started to move less when the experiment began. But the decrease in movement was bigger in the fructose group than in the glucose group.


“In support of our observations, a recent study reported that ingestion of fructose (25% energy intake, 10 weeks) in human volunteers also resulted in reduced energy expenditure in relation to a diet with the same glucose dose”, the researchers wrote. [Eur J Clin Nutr. 2012 Feb;66(2):201-8.]

“Such changes in energy expenditure are likely to have important implications in regard to regulation of body weight and energy balance in long-term consumption of fructose. It is realistic to consider an increase in physical activity as a way to ablate the potential negative impact of fructose consumption in body weight.”

Fructose decreases physical activity and increases body fat without affecting hippocampal neurogenesis and learning relative to an isocaloric glucose diet


Recent evidence suggests that fructose consumption is associated with weight gain, fat deposition and impaired cognitive function. However it is unclear whether the detrimental effects are caused by fructose itself or by the concurrent increase in overall energy intake. In the present study we examine the impact of a fructose diet relative to an isocaloric glucose diet in the absence of overfeeding, using a mouse model that mimics fructose intake in the top percentile of the USA population (18% energy). Following 77 days of supplementation, changes in body weight (BW), body fat, physical activity, cognitive performance and adult hippocampal neurogenesis were assessed. Despite the fact that no differences in calorie intake were observed between groups, the fructose animals displayed significantly increased BW, liver mass and fat mass in comparison to the glucose group. This was further accompanied by a significant reduction in physical activity in the fructose animals. Conversely, no differences were detected in hippocampal neurogenesis and cognitive/motor performance as measured by object recognition, fear conditioning and rotorod tasks. The present study suggests that fructose per se, in the absence of excess energy intake, increases fat deposition and BW potentially by reducing physical activity, without impacting hippocampal neurogenesis or cognitive function.